The impact of the laser on the body. Laser radiation and its impact on humans. Laser eye lesions

The biological effect of laser radiation depends on a number of factors: radiation power, wavelength, pulse nature, pulse repetition rate, irradiation duration, the size of the irradiated surface, etc. Thermal and non-thermal, local and general action radiation.

The thermal effect for CW lasers has much in common with conventional heating. Under the influence of lasers operating in a pulsed mode in irradiated tissues, there is a rapid heating and instantaneous boiling of liquid media, which ultimately leads to mechanical damage to tissues. The non-thermal effect is mainly due to the processes resulting from the selective absorption of electromagnetic energy by tissues, as well as electrical and photochemical effects.

In the nature of the action of laser radiation on the human body, two effects can be distinguished: primary and secondary.

Primary effects occur in the form of organic changes in the exposed tissues (eye, skin). Getting into the eye, the laser energy is absorbed by the pigment elements and within a very short time raises the temperature in it to high levels, causing thermocoagulation of adjacent tissues - chorioretinal burn.

Thermal disorders are accompanied by damage to the retina of the eye. Damage to the fovea of ​​the retina is especially dangerous as it is more functionally important. Damage to this area can lead to profound and permanent impairment of central vision.

Laser radiation can cause skin damage. The degree of exposure is determined both by the parameters of the laser radiation, and by skin pigmentation, the state of blood circulation. Skin lesions resemble a thermal burn, which has clear boundaries surrounded by a small area of ​​redness.

Secondary effects - non-specific changes that occur in the body as a reaction to radiation. In this case, functional disorders of the central nervous and cardiovascular systems, neuroses of the asthenic type, pathology of the vegetative-vascular system in the form of vegetative-vascular dysfunctions and astheno-vegetative syndromes are possible.

Cardiovascular disorders can be manifested by vascular dystonia of the hypotonic or hypertonic type, impaired cerebral circulation. In the peripheral blood picture, a slight decrease in hemoglobin, an increase in the number of erythrocytes, reticulocytes, and a decrease in the number of platelets are revealed. Changes in lipid, carbohydrate and protein metabolism, etc. are possible.

To ensure the safety of work on laser systems, it is necessary to comply with the requirements for technological processes, equipment placement and organization of workplaces:

1. Remote control must be provided when servicing installations with class IV lasers.

2. In technological processes, as a rule, laser systems of a closed type should be used in order to exclude personnel exposure.

3. It is necessary to limit the laser-dangerous zone or shield the radiation beam. With flame retardant light absorbing material.

4. The design of laser installations provides for the protection of workers from electromagnetic waves, radio frequencies and ^ ionizing radiation.

5. Lasers are marked with a laser hazard symbol in accordance with the current standard.

For the safe operation of lasers, it is important that the premises in which they are placed meet the hygienic requirements:

1. Class IV lasers must be placed in separate rooms, the device of which and their interior decoration must meet the requirements of sanitary standards and rules for the design and operation of lasers.

2. The doors of rooms for lasers of classes III - IV must be equipped with internal locks, a sign "Entrance prohibited by strangers" and a laser hazard sign.

3. Natural and artificial lighting must match current regulations. The air of the working area, the production area of ​​the premises where lasers are operated, must comply with

hygiene requirements. If the operation of the laser is accompanied by the formation of harmful gases, vapors, aerosols, then exhaust ventilation is installed at the workplace, which localizes and removes harmful products from the place of their formation.

4. In open areas where lasers are located, a zone of increased radiation energy density is designated, and screens are installed to prevent the spread of laser radiation outside the area.

5. To prevent damage by a direct or specularly reflected laser beam, barriers are provided to prevent the beam from leaving the closed installation and the possibility of a person entering the beam passage area. Locks or closures are used to protect the eyes of a person working on an installation in which the observation system is combined with the optical system. Protective goggles are used.

6. To protect the worker from injury electric shock various remote controls, interlocks, automatic contactors, mechanical earthing switches, alarms and protective equipment. All elements of the laser installations under voltage are protected, and the metal casings of the installations are grounded. Methods for protecting personnel from electromagnetic fields and noise, as well as permissible sanitary standards, the timing of control measurements, instruments and methods for these measurements are indicated in the relevant sections of a special reference book.

7. Persons who have reached the age of 18 are allowed to work with the laser. Personnel operating laser systems must undergo periodic and preliminary medical examinations, mandatory instruction on safe methods of working with lasers, etc.

8. Personnel are prohibited from carrying out observation without personal eye protection during the operation of lasers of II-IV hazard classes and placing objects in the laser beam zone that cause specular reflection of radiation, if it is not associated with a technological need. Protective glasses with light filters are used as personal protective equipment, and when working with hazard class IV lasers, protective masks are used. For protection against laser radiation and during sleep operation of laser systems, only those means of protection are used for which there is regulatory and technical documentation approved in the prescribed manner.

Lecture 8

"Laser" is an abbreviation formed from initial letters English phrase Light amplification by stimulated emission of radiation - light amplification due to the creation of stimulated emission.

Laser (optical quantum generator) - generator electromagnetic radiation optical range, based on the use of stimulated (stimulated) radiation.

laser radiation is the electromagnetic radiation that is formed in ( lasers ) with a wavelength of 0.2-1000 μm: 0.2 ... 0.4 μm - ultraviolet, 0.4 ... 0.75 μm - visible light, near infrared 0.75 ... 1.4 μm, infrared 1.4 ... 10 2 µm.

distinctive peculiarity laser radiation is: monochrome radiation ( exactly the same wavelength) radiation coherence (all radiation sources emit electromagnetic waves in one phase); sharp beam direction (small discrepancy).

Laser radiation is distinguished by type of radiation on

- direct(contained in a limited solid angle)

- scattered(scattered from a substance that is part of the medium through which the laser beam passes)

- mirror-reflected ( reflected from the surface at an angle equal to the angle of incidence of radiation)

- diffusely reflected(reflected from the surface in all possible directions)

As a technical device, a laser consists of three main elements:

- active environment

- resonator

- pumping systems.

Depending on the nature active environment lasers are divided into the following types: solid-state (on crystals or glasses); gas (He-Ne, Ar, Kr, Xe, Ne, He-Cd, CO 2, etc.); liquid; semiconductor, etc.

As resonator Usually, parallel mirrors with a high reflection coefficient are used, between which the active medium is placed.

Pumping, i.e. the transfer of atoms of the active medium to the upper level is provided either by a powerful light source or by an electric discharge.

There are continuous and pulsed lasers.

The classification of lasers can be represented as follows (Fig.):

According to the degree of danger of the generated radiation, lasers are classified according to GOST 12.1.041-83 (1996):

Class 1 ( safe)- the output radiation does not pose a danger to the eyes and skin;

Class II ( low-dangerous) - output radiation is dangerous when the eyes are exposed to direct or specularly reflected radiation;

Class III ( moderately hazardous) - direct, specular, as well as diffusely reflected radiation is dangerous for the eyes;

Class IV ( highly dangerous) - diffusely reflected radiation is dangerous for the skin at a distance of 10 cm from the reflected surface.

The classification of lasers according to the degree of danger is carried out on the basis of temporal, energy and geometric (point or extended source) characteristics of the radiation source and the maximum allowable levels of laser radiation.

Specifications laser : wavelength, µm; emission line width; radiation intensity (determined by the energy or power of the output beam and expressed in J or W); pulse duration, s; pulse repetition frequency, Hz.

Lasers have been widely used in scientific purposes, in practical medicine, as well as in various fields of technology. The fields of application of the laser are determined by the energy of the laser radiation used:

The biological effect of laser radiation depends on the radiation energy E, impulse energy E and, power density (energy) W p( W e), exposure time t, wavelength l, pulse duration t, pulse repetition frequency f, radiation flux F, surface radiation density E e, radiation intensity I.

Under the influence of laser radiation, the vital activity of both individual organs and the organism as a whole is disrupted. At present, a specific effect of laser radiation on biological objects has been established, which differs from the effect of other hazardous industrial physical and chemical factors. Under the influence of laser radiation on a continuous biological structure (for example, on the human body), three stages are distinguished: physical, physicochemical and chemical.

At the first stage ( physical) interactions of radiation with matter occur, the nature of which depends on the anatomical, optical-physical and functional features tissues, as well as on the energy and spatial characteristics of the radiation and, above all, on the wavelength and intensity of the radiation. At this stage, the substance is heated, the energy of electromagnetic radiation is converted into mechanical vibrations, the ionization of atoms and molecules, the excitation and transition of electrons from valence levels to the conduction band, the recombination of excited atoms, etc. When exposed to continuous laser radiation, the thermal mechanism of action predominates, in which results in protein coagulation, and at high power - the evaporation of biological tissue. In pulsed mode (with pulse duration<10 -2 с) механизм взаимодействия становится более сплошным и приводит к переходу энергии излучения в энергию механических колебаний среды, в частности ударной волны. При мощности излучения свыше 10 7 Вт и высокой степени фокусировки лазерного луча возможно возникновение ионизирующих излучений.

At the second stage ( physical and chemical ) from ions and excited molecules, free radicals are formed, which have a high ability to chemical reactions.

At the third stage ( chemical ) free radicals react with the molecules of the substances that make up the living tissue, and in this case, molecular damage occurs, which further determine the overall picture of the impact of laser radiation on the irradiated tissue and the body as a whole. Schematically, the main factors that determine the biological effect of laser radiation can be represented as follows:

Laser radiation poses a danger mainly to tissues that directly absorb radiation, therefore, from the standpoint of the potential hazard of exposure and the possibility of protection from laser radiation, mainly eyes and skin are considered.

The cornea and lens of the eye are highly sensitive to electromagnetic radiation, and the optical system of the eye is capable of increasing the energy density of the visible and near infrared range in the fundus relative to the cornea by several orders of magnitude.

Prolonged action of laser radiation in the visible range (not much less than the burn threshold) on the retina of the eye can cause irreversible changes in it, and in the near infrared range it can lead to clouding of the lens. Retinal cells do not regenerate after damage.

The action of laser radiation on the skin, depending on the initial absorbed energy, leads to various lesions: from mild erythema (redness) to superficial charring and, ultimately, the formation of deep skin defects.

Distinguish 6 types of LI effects on a living organism :

1) thermal (thermal) action. When focusing laser radiation, a significant amount of heat is released in a small volume in a short period of time;

2) energy action. Determined by the large gradient of the electric field due to the high power density. This action can cause polarization of molecules, resonant and other effects.;

3) photochemical action. Manifested in the fading of a number of dyes;

4) mechanical action. It manifests itself in the occurrence of ultrasonic vibrations in the irradiated organism.

5) electrostriction - deformation of molecules in the electric field of laser radiation;

6) formation within the cell of microwave electro magnetic field.

Energy exposures are accepted as maximum permissible levels (MPL) of exposure. For remote control of continuous laser radiation, choose the energy exposure of the smallest value that does not cause primary and secondary biological effects (taking into account the wavelength and duration of exposure). For repetitively pulsed radiation, the exposure limit is calculated taking into account the repetition rate and the effect of a series of pulses.

When operating lasers, in addition to laser radiation, other types of hazards arise. These are the release of harmful chemicals, noise, vibration, electromagnetic fields, ionizing radiation, etc.

The influence of laser radiation on the human body has not been fully studied at the moment, but many are confident in its negative impact on all living things. Laser radiation originates according to the principle of creating light and involves the use of atoms, but with a different set of physical processes. It is for this reason that the effect of an external electromagnetic field can be traced with laser radiation.

Scope of application

Laser radiation is a narrowly directed forced energy flow of a continuous or pulsed type. In the first case, there is an energy flow of one power, and in the second, the power level periodically reaches certain peak values. The formation of such energy is assisted by a quantum generator, represented by a laser. The energy flows in this case are electromagnetic waves that propagate relative to each other only in parallel. Thanks to this feature, a minimum angle of light scattering and a certain precise directionality are created.

Sources of laser radiation based on its properties are widely used in various areas of human life, including:

• science - research and experiments, experiments and discoveries;
• military defense industry;
• space navigation;
• production area;
• technical area;
• local heat treatment - welding and soldering, cutting and engraving;
• domestic use in the form of laser barcode readers, CD readers, and pointers;
• laser deposition, which significantly increases the wear resistance of metals;
• creation of modern holograms;
• improvement of various optical devices;
• chemical industry - analysis and start of reactions.

Especially important is the use of devices of this type in the field of modern medical technology.

Laser in medicine

From the point of view of modern medicine, laser radiation is a unique and very timely breakthrough in the treatment of patients who need surgical intervention. The laser is actively used in the production of high-quality surgical instruments.

The indisputable advantages of surgical treatment include the use of a high-precision laser scalpel, which makes it possible to perform bloodless incisions in soft tissues. This result is ensured by almost instant adhesion of capillaries and small vessels. During the use of a laser instrument, the surgeon is able to fully see the surgical field. Tissues are dissected by laser energy flow at a certain distance, while there is no contact of the instrument with blood vessels and internal organs.

An important priority in the use of modern surgical instruments is represented by ensuring absolute maximum sterility. Due to the strict direction of the beams, all operations occur with minimal traumatization, while the standard rehabilitation period of the patients who underwent the operation becomes much shorter and full-fledged working capacity returns much faster.

A distinctive feature of the use of a laser scalpel during surgery today is painlessness in the postoperative period. The very rapid development of modern laser technology has contributed to a significant expansion of its application possibilities. Relatively recently, the properties of laser radiation were discovered and scientifically proven to have a positive effect on the condition of the skin, due to which devices of this type began to be actively used in dermatology and cosmetology.

Areas of medical application

Medicine is by far not the only, but very promising area of ​​application of modern laser equipment:

• the process of epilation with the destruction of hair follicles and effective hair removal;
• treatment of severe acne;
• effective removal of birthmarks and age spots;
• skin resurfacing;
• therapy of bacterial lesions of the epidermis with disinfection and destruction of pathogenic microflora;
• prevention of the spread of infection of various origins.

The very first industry in which laser equipment and its radiation began to be actively used is ophthalmology. The areas of eye microsurgery in which laser technology is widely used are:

• laser coagulation in the form of the use of thermal properties in the treatment of vascular eye diseases, accompanied by damage to the vessels of the retina and cornea;
• photodestruction in the form of tissue dissection at the peak power of laser equipment in the treatment and dissection of secondary cataracts;
• photoevaporation in the form of prolonged thermal exposure in the presence of inflammatory processes of the optic nerve, as well as in conjunctivitis;
• photoablation in the form of a gradual removal of tissues in the treatment of dystrophic changes in the eye cornea, the elimination of its opacity, in the surgical treatment of glaucoma;
• laser stimulation with anti-inflammatory and resolving effects, which significantly improves eye trophism, as well as in the treatment of scleritis, exudation inside the eye chamber and hemophthalmos.

Laser irradiation is widely used in the treatment of skin cancer. Modern laser equipment shows the greatest efficiency in the removal of melanoblastoma. This method can also be used in the treatment of cancer of the esophagus or tumors of the rectum in stages 1-2. It should be noted that in conditions of too deep location of the tumor and multiple metastases, the laser is practically not at all effective.

Danger of laser radiation

At the moment, the negative impact of laser radiation on living organisms is relatively well studied. Irradiation can be scattered, direct and reflected. Negative impact causes the ability of laser devices to emit light and heat fluxes. The degree of damage directly depends on several factors at once, including:

• electromagnetic wave length;
• site of localization of negative impact;
• tissue absorption capacity.

The eyes are most susceptible to the negative effects of laser energy. It is the retina of the eye that is extremely sensitive and can receive burns of varying severity.

The consequences of this influence are the partial loss of vision by the patient, as well as complete and irreversible blindness. Sources of negative radiation are most often represented by various infrared devices emitting visible light.

Symptoms of damage to the retina, iris, lens and cornea with a laser:

• soreness and spasms in the eyes;
• severe swelling of the eyelids;
• hemorrhages of varying degrees;
• clouding of the eye lens.

Irradiation of moderate intensity can cause thermal burns of the skin. At the point of contact between the laser equipment and the skin, in this case, a sharp increase in temperature is noticeable, accompanied by boiling and evaporation of the interstitial and intracellular fluid. In this case, the skin acquires a characteristic red coloration. Under the action of pressure, ruptures of tissue structures occur and edema appears, which can be supplemented by intradermal hemorrhages. Subsequently, necrotic areas are observed at the burn sites, and in the most severe cases, noticeable charring of the skin occurs.

Signs of negative impact

A hallmark of a laser burn are clear boundaries on the affected areas of the skin with bubbles that form directly in the layers of the epidermis, and not under it. Diffuse skin lesions are characterized by an almost instantaneous loss of sensation, and erythema appears several days after exposure to radiation.

The main features are presented:

• changes in blood pressure;
• slow heartbeat;
• increased sweating;
• unexplained general fatigue;
• excessive irritability.

A feature of the laser radiation of the infrared spectrum is the penetration deep inside, through tissues, with damage to internal organs. A characteristic difference of a deep burn is represented by the alternation of healthy and damaged tissues. Initially, when exposed to radiation, people do not experience tangible pain, and the liver is one of the most vulnerable organs. In general, the impact of laser radiation on the human body provokes functional disorders in the central nervous system and cardiovascular activity.

Protection against negative impact and precautions

The greatest risk of exposure occurs in people whose activities are directly related to the use of quantum generators. According to the basic sanitary standards adopted today, radiation classes 2, 3 and 4 are dangerous for humans.

Technical protective methods are presented:

• competent planning of industrial premises;
• correct interior decoration without mirror reflection;
• appropriate placement of laser systems;
• fencing zones of possible exposure;
• compliance with the requirements for the maintenance and operation of laser equipment.

Personal protection includes special goggles and overalls, safety screens and housings, as well as prisms and lenses to reflect rays. Employees of such enterprises should be regularly sent for preventive medical examinations.

At home, you must be careful and be sure to adhere to certain rules of operation:

• do not direct radiation sources at reflective surfaces;
• do not direct laser light into the eyes;
• Keep laser gadgets out of the reach of small children.

The most dangerous for the human body are lasers that have direct radiation, high intensity, narrow and limited beam directivity, as well as too high radiation density.

Currently, lasers are firmly entrenched in all spheres of human life. They are used in medicine, chemistry, physics, biology and many other areas of modern science. It is difficult to overestimate the contribution of this phenomenon to the progress of mankind. However, careless use of this technology can lead to detrimental effects on human health. Blinding, burns, electrical injuries - this is not a complete list of injuries that can be obtained when interacting with a laser. High-power unshielded laser radiation is a serious danger if it is treated lightly and basic safety rules are not followed.

This article will help you understand the nuances of this phenomenon and give you an idea of ​​the threats that laser radiation poses to human health. You will also get an idea about the basics of safe laser work and learn how modern lasers are divided into classes according to the level of threat to human health. Here you can also find a small historical background about lasers.

Laser as a phenomenon

LASER - Light Amplification by Stimulated Emission of Radiation. As you can see, this word hides an abbreviation in English. In Russian, this can be translated as "amplification of light by induced radiation." Amplification of energy to a state of increased intensity leads to the appearance of laser radiation. As a result of multiple reflections in a system of mirrors, radiation is amplified, and as a result, we can observe a phenomenon that is absolutely unique in its physical properties. The laser beam is much narrower than the light beam of a conventional lamp, but their differences do not end there. Laser radiation projects a wave of one wavelength and one pure color, in addition, the light waves completely coincide in time with each other. What distinguishes laser beams from ordinary light is their organization (coherence, in scientific terms).

In 1916, the first steps were taken towards the study of the laser. After lengthy research, the notorious Albert Einstein put forward his theory of the interaction of radiation with matter, thus making possible the development of quantum amplifiers capable of projecting electromagnetic waves. The next significant breakthrough came in 1928, when Landenburg conducted his series of experiments. The result of painstaking work was the formulation of the condition for finding induced emission as its predominance over absorption. And only more than a quarter of a century later, in 1955, the Soviet physicists Basov and Prokhorov designed a quantum generator with ammonia as an active medium. Since then, a huge number of scientists have become participants in the race to design laser systems, which does not stop today.
This technology has made an invaluable contribution to the development of medicine.

Many tasks that seemed unsolvable before, with the improvement of lasers, have become a thing of the past. His miraculous rays restored health to many thousands of people. What is worth only laser vision correction, which in just 10 minutes allows you to return perfect vision to any patient. The efficiency of this operation reaches 100%. Cosmetologists have also found application for this technology in their activities. Radiation of a medical laser makes it possible to selectively act on hair roots, age spots and other skin defects. Today it is possible to quickly and almost painlessly remove a mole, as well as a boring tattoo.

At one time, an outstanding French scientist, Louis de Broglie, uttered a prophetic phrase: “A grandiose future is destined for the laser. It is difficult to predict exactly how it will be used, but I believe that there is an entire technical era behind the laser.” And we really live in an era when there are almost no areas of activity in which, in one way or another, technologies based on laser beams are not used. Modern measuring instruments cannot be imagined without the use of laser beams in their design. The laser made it possible to measure the distance from the Earth to the Moon, the accuracy of these measurements was several hundred meters. The use of laser beams in the field of radar has made it possible to greatly increase the accuracy of the data obtained. There is no doubt that this technology will play its role in further scientific and technological progress.

How do laser beams affect the human body?

One of the characteristics of laser beams is an extremely high level of energy concentration. A beam of light produced by a laser is capable of raising the temperature of the surface it is directed at. With the help of directional irradiation, it is possible to achieve deformation of almost any surface in a short period of time. The concentration of a colossal energy flow in a small area allows you to reach a temperature of more than a million degrees. Due to this property, lasers are widely used in surgery and material processing, it also makes them a threat to human skin when exposed to excessive radiation. Damage to the skin with a laser beam is similar to a thermal burn. Also, a significant danger lies in the laser radiation produced by the photochemical effect. However, modern devices reduce this risk to a minimum.

It is worth noting that the lightning speed of exposure to laser beams makes it possible to avoid pain. Due to this property, the laser is widely used in surgery. Short-term laser surgeries do not require any anesthesia. Few major surgeries can be performed without anesthesia. At the same time, the time spent on such operations is much lower than with traditional surgery with a scalpel.

Often, the operation of laser systems is accompanied by noise, which can reach a level of up to 120 dB. Prolonged exposure to such equipment may cause hearing problems. Also, the chemical reaction of a powerful laser beam and air is accompanied by an abundant release of ozone. People who have been involved in working with lasers for a long time can be diagnosed with dysfunctions of the vestibular apparatus. The frequency of these violations depends on the professional experience. Laser radiation can cause irreversible changes in the human body, disorders of the organs of vision, the central nervous system and the autonomic system.

Take care of your eyes

Eye- one of the most fragile elements of our body. Unlike other organs, it has no protection from the environment. When an invisible infrared laser hits the eye, a person will not feel anything, because the brain will not perceive it as a source of light and there will be no defensive reaction. Absorption of ultraviolet radiation by the cornea of ​​the eye can lead to epithelial edema and erosion. In especially severe cases, clouding of the anterior chamber is possible. The retina of the eye is much more at risk. After the laser radiation reaches the retina, it spreads further to the entire optical system of the organ of vision.

If a direct laser beam enters the eye when looking into the distance, the consequences can be very deplorable. The concentration of the spectrum of the collimated beam on the retina at this moment can reach 100,000 times. In the fundus of the eye with such damage, a burn and swelling of the retina, hemorrhage with the further appearance of a scar and a decrease in visual acuity are found. Such a powerful effect can even lead to blindness. From this it follows that the probability of loss of vision as a result of strong radiation is quite high.

Classification of lasers

The vast majority of laser equipment manufactured around the world is manufactured and certified according to international standards agreed by the American association CDRH (Center for Devices and Radiological Health). Depending on the level of threat that various laser systems pose to the human body, they are divided into four main classes:

Class I (safe)- low-power laser systems that do not emit a level of radiation harmful to humans. Such lasers cannot cause damage to the eye. This class also includes devices equipped with a housing that does not emit a laser beam to the outside. In this case, the beam may be more powerful than the norm allowed for the first class.

Class II (low hazard)- These lasers are already capable of causing damage to the human eye, with eye contact for more than 0.25 seconds. They do not include devices that produce radiation with an invisible wave.

Class III (medium hazard)- even a short visual contact with the beam of such a laser installation can lead to damage to the organ of vision. It is impossible to work with such devices without special protective glasses in any case. Scattered radiation does not pose a danger at a visual contact distance of more than 13 centimeters and a time of less than 10 seconds. There is a significant risk of ignition if the beam comes into contact with flammable materials. The output power is about 500 mW.

Class IV (highly hazardous)- powerful lasers that pose a health hazard. They are able to cause significant damage to the retina of the eye with a short radiation of a direct beam. In the practice of using such devices, there were situations when the beam was accidentally reflected into the eye from an ordinary screwdriver or a button on the sleeve. Exposure to these lasers is highly likely to cause severe burns to the skin, as well as ignite combustible and other flammable materials. Danger creates and increased ultraviolet radiation of flash lamps. Recently, the governments of many countries have been actively working on adapting such lasers for military purposes. Companies presenting their developments at exhibitions receive funding from the state.

Precautionary measures

In the wrong hands, a powerful laser is no less dangerous than a firearm. Only certified personnel are allowed to work with such devices. The best prevention of laser radiation is to follow the rules of operation and protection. The use of laser systems of II-III levels involves fencing the area of ​​work with the laser and shielding the radiation. Level IV lasers must be completely isolated from the rest of the production, work with them is carried out remotely. Surfaces in such rooms are painted in colors with a low reflectivity. If the level of illumination is insufficient, work with lasers is unacceptable. Observation windows must be equipped with protective glass. If it is necessary to repair the device, it is strictly forbidden to use parts and consumables that are not approved by the manufacturer.

Protective equipment against laser radiation must ensure that the harmful effects of radiation are prevented or its magnitude is reduced to a level that does not exceed safety. The equipment of workers interacting with the laser should include shields, masks, technological coats and special goggles. Once a year, they need to undergo a complete medical examination. This precaution is more than justified. Most of the researchers studying the health of laser attendants have established a predisposition to asthenic and vegetative-vascular disorders in them. Access to production areas where laser work takes place must be strictly limited. The laser system must be securely secured against unauthorized use by a key-operated switch or other similar mechanism.

1. The passage of monochromatic light through a transparent medium.

2. Creation of an inverse population. Pumping methods.

3. The principle of operation of the laser. Types of lasers.

4. Features of laser radiation.

5. Characteristics of laser radiation used in medicine.

6. Changes in tissue properties and its temperature under the action of continuous high-power laser radiation.

7. Use of laser radiation in medicine.

8. Basic concepts and formulas.

9. Tasks.

We know that light is emitted in separate portions - photons, each of which arises as a result of the radiative transition of an atom, molecule or ion. Natural light is a collection of a huge number of such photons, differing in frequency and phase, emitted at random times in random directions. Obtaining powerful beams of monochromatic light using natural sources is a practically insoluble task. At the same time, the need for such beams was felt by both physicists and specialists in many applied sciences. The creation of a laser made it possible to solve this problem.

Laser- a device that generates coherent electromagnetic waves due to the stimulated emission of microparticles of the medium in which a high degree of excitation of one of the energy levels is created.

Laser (LASER Light Amplification by Stimulated of Emission Radiation) - light amplification by stimulated emission.

The intensity of laser radiation (LI) is many times greater than the intensity of natural light sources, and the divergence of the laser beam is less than one arc minute (10 -4 rad).

31.1. The passage of monochromatic light through a transparent medium

In Lecture 27, we found out that the passage of light through matter is accompanied by both photon excitation its particles, and acts stimulated emission. Let us consider the dynamics of these processes. Let it spread in the environment monochromatic light, the frequency of which (ν) corresponds to the transition of the particles of this medium from the ground level (E 1) to the excited level (E 2):

Photons hitting particles in the ground state will be absorbed and the particles themselves will pass into the excited state E 2 (see Fig. 27.4). Photons that hit the excited particles initiate stimulated emission (see Fig. 27.5). In this case, the doubling of photons occurs.

In a state of thermal equilibrium, the ratio between the number of excited (N 2) and unexcited (N 1) particles obeys the Boltzmann distribution:

where k is the Boltzmann constant, T is the absolute temperature.

In this case, N 1 >N 2 and absorption dominates over doubling. Consequently, the intensity of the outgoing light I will be less than the intensity of the incident light I 0 (Fig. 31.1).

Rice. 31.1. Attenuation of light passing through a medium in which the degree of excitation is less than 50% (N 1 > N 2)

As light is absorbed, the degree of excitation will increase. When it reaches 50% (N 1 = N 2), between takeover And doubling equilibrium will be established, since the probabilities of photons hitting the excited and unexcited particles will become the same. If the illumination of the medium stops, then after some time the medium will return to the initial state corresponding to the Boltzmann distribution (N 1 > N 2). Let's make a preliminary conclusion:

When the medium is illuminated with monochromatic light (31.1) impossible to achieve such a state of the medium in which the degree of excitation exceeds 50%. And yet, let's consider the question of the passage of light through a medium in which the state N 2 > N 1 has been reached in some way. This state is called the state of population inversion(from lat. inversion- flip).

population inversion- such a state of the medium in which the number of particles at one of the upper levels is greater than at the lower one.

In a medium with an inverse population, the probability of a photon hitting an excited particle is greater than that of an unexcited one. Therefore, the doubling process dominates the absorption process and takes place gain light (Fig. 31.2).

As light passes through a medium with an inverse population, the degree of excitation will decrease. When it reaches 50%

Rice. 31.2. Amplification of light passing through a medium with population inversion (N 2 > N 1)

(N 1 \u003d N 2), between takeover And doubling equilibrium will be established and the light amplification effect will disappear. If the illumination of the medium stops, then after some time the medium will return to the state corresponding to the Boltzmann distribution (N 1 > N 2).

If all this energy is released in radiative transitions, then we will receive a light pulse of enormous power. True, it will not yet have the required coherence and directivity, but it will be highly monochromatic (hv = E 2 - E 1). This is not a laser yet, but already something close.

31.2. Creation of an inverse population. Pumping methods

So is it possible to achieve an inverse population? It turns out that you can, if you use three energy levels with the following configuration (Fig. 31.3).

Let the environment light up powerful flash Sveta. Part of the radiation spectrum will be absorbed in the transition from the main level E 1 to the broad level E 3 . Recall that wide is the energy level with a short relaxation time. Therefore, most of the particles that have fallen into the E 3 excitation level nonradiatively pass to the narrow metastable E 2 level, where they accumulate. Due to the narrowness of this level, only a small fraction of the flare photons

Rice. 31.3. Creation of inverse population at the metastable level

capable of causing a forced transition E 2 → E 1. This provides the conditions for creating an inverse population.

The process of creating a population inversion is called pumped. Modern lasers use different kinds pumping.

Optical pumping of transparent active media uses light pulses from external source.

Electric discharge pumping of gaseous active media uses an electric discharge.

Injection pumping of semiconductor active media uses electric current.

Chemical pumping of the active medium from a mixture of gases uses energy chemical reaction between the components of the mixture.

31.3. The principle of operation of the laser. Types of lasers

The functional diagram of the laser is shown in fig. 31.4. The working body (active medium) is a long narrow cylinder, the ends of which are covered with two mirrors. One of the mirrors (1) is translucent. Such a system is called an optical resonator.

The pumping system transfers particles from the ground level Е 1 to the absorption level Е 3 , from where they nonradiatively pass to the metastable level Е 2 , creating its inverse population. After that, spontaneous radiative transitions E 2 → E 1 begin with the emission of monochromatic photons:

Rice. 31.4. Schematic device of the laser

Photons of spontaneous emission emitted at an angle to the resonator axis exit through side surface and are not involved in the generation process. Their flow is quickly drying up.

Photons, which, after spontaneous emission, move along the resonator axis, repeatedly pass through the working body, being reflected from the mirrors. At the same time, they interact with excited particles, initiating stimulated emission. Due to this, an "avalanche-like" growth of induced photons, moving in the same direction, takes place. The multiply amplified stream of photons exits through a semitransparent mirror, creating a powerful beam of almost parallel coherent beams. In fact, laser radiation is generated first a spontaneous photon that moves along the resonator axis. This ensures the coherence of the radiation.

Thus, the laser converts the energy of the pump source into the energy of monochromatic coherent light. The efficiency of such a transformation, i.e. The efficiency depends on the type of laser and ranges from fractions of a percent to several tens of percent. Most lasers have an efficiency of 0.1-1%.

Types of lasers

The first created laser (1960) used a ruby ​​and an optical pumping system as a working medium. Ruby is a crystalline aluminum oxide A1 2 O 3 containing about 0.05% chromium atoms (it is chromium that gives the ruby ​​its pink color). Chromium atoms embedded in the crystal lattice are the active medium

with the configuration of energy levels shown in Fig. 31.3. The radiation wavelength of a ruby ​​laser is λ = 694.3 nm. Then came lasers using other active media.

Depending on the type of working fluid, lasers are divided into gas, solid-state, liquid, semiconductor. In solid-state lasers, the active element is usually made in the form of a cylinder, the length of which is much greater than its diameter. Gaseous and liquid active media are placed in a cylindrical cuvette.

Depending on the pumping method, continuous and pulsed generation of laser radiation can be obtained. With a continuous pumping system, the population inversion is maintained for a long time due to an external energy source. For example, continuous excitation by an electric discharge in a gaseous medium. With a pulsed pumping system, the population inversion is created in the pulsed mode. Pulse repetition rate from 10 -3

Hz to 10 3 Hz.

31.4. Features of laser radiation

Laser radiation in its properties is significantly different from the radiation of conventional light sources. We note its characteristic features.

1. Coherence. Radiation is highly coherent which is due to the properties of stimulated emission. In this case, not only temporal, but also spatial coherence takes place: the phase difference at two points of the plane perpendicular to the direction of propagation remains constant (Fig. 31.5, a).

2. Collimation. Laser radiation is collimated those. all rays in the beam are almost parallel to each other (Fig. 31.5, b). At a large distance, the laser beam only slightly increases in diameter. Since the angle of divergence φ is small, then the intensity of the laser beam decreases slightly with distance. This makes it possible to transmit signals over great distances with little attenuation of their intensity.

3. Monochromatic. Laser radiation is in highly monochromatic, those. contains waves of almost the same frequency (the width of the spectral line is Δλ ≈0.01 nm). On

Figure 31.5c shows a schematic comparison of the linewidth of a laser beam and an ordinary light beam.

Rice. 31.5. Coherence (a), collimation (b), monochromaticity (c) of laser radiation

Before the advent of lasers, radiation with a certain degree of monochromaticity could be obtained using devices - monochromators, which single out narrow spectral intervals from the continuous spectrum (narrow bands wavelengths), but the power of light in such bands is low.

4. High power. With the help of a laser, it is possible to provide a very high power of monochromatic radiation - up to 10 5 W in continuous mode. The power of pulsed lasers is several orders of magnitude higher. Thus, a neodymium laser generates a pulse with an energy of E = 75 J, the duration of which is t = 3x10 -12 s. The power in the pulse is P = E / t = 2.5x10 13 W (for comparison: the power of the hydroelectric power station is P ~ 10 9 W).

5. High intensity. In pulsed lasers, the intensity of laser radiation is very high and can reach I = 10 14 -10 16 W/cm 2 (cf. intensity sunlight near the earth's surface I \u003d 0.1 W / cm 2).

6. High brightness. For lasers operating in the visible range, brightness laser radiation (light intensity per unit surface) is very high. Even the weakest lasers have a brightness of 10 15 cd/m 2 (for comparison: the brightness of the Sun is L ~ 10 9 cd/m 2).

7. Pressure. When a laser beam falls on the surface of a body, a pressure(D). With the complete absorption of laser radiation incident perpendicular to the surface, pressure D = I / c is created, where I is the radiation intensity, c is the speed of light in vacuum. With total reflection, the pressure is twice as high. For intensity I \u003d 10 14 W / cm 2 \u003d 10 18 W / m 2; D \u003d 3.3x10 9 Pa \u003d 33,000 atm.

8. Polarization. Laser light is completely polarized.

31.5. Characteristics of laser radiation used in medicine

Radiation wavelength

The radiation wavelengths (λ) of medical lasers lie in the range of 0.2 -10 µm, i.e. from ultraviolet to far infrared.

Radiation power

The radiation power (P) of medical lasers varies over a wide range, determined by the purpose of the application. For lasers with continuous pumping, P = 0.01-100 W. Pulsed lasers are characterized by pulse power P and pulse duration τ and

For surgical lasers P u = 10 3 -10 8 W, and the pulse duration t u = 10 -9 -10 -3 s.

Energy in a radiation pulse

The energy of one pulse of laser radiation (E u) is determined by the relation E u = P u -m u, where t u is the duration of the radiation pulse (usually t u = 10 -9 -10 -3 s). For surgical lasers E and = 0.1-10 J.

Pulse frequency

This characteristic (f) of pulsed lasers indicates the number of radiation pulses generated by the laser in 1 s. For therapeutic lasers f = 10-3000 Hz, for surgical lasers f = 1-100 Hz.

Average radiation power

This characteristic (P cf) of repetitively pulsed lasers shows how much energy the laser emits in 1 s, and is determined by the following relationship:

Intensity (power density)

This characteristic (I) is defined as the ratio of the laser radiation power to the beam cross-sectional area. For cw lasers I = P/S. In the case of pulsed lasers, a distinction is made pulse intensity I and = P and /S and the average intensity I cf = P cf /S.

The intensity of surgical lasers and the pressure created by their radiation have the following meanings:

for cw lasers I ~ 10 3 W/cm 2 , D = 0.033 Pa;

for pulsed lasers I and ~ 10 5 -10 11 W / cm 2, D \u003d 3.3 - 3.3x10 6 Pa.

Energy density in a pulse

This value (W) characterizes the energy per unit area of ​​the irradiated surface per pulse and is determined by the relation W = E and /S, where S (cm 2) is the area of ​​the light spot (i.e., the cross section of the laser beam) on the surface biotissue. For lasers used in surgery, W ≈ 100 J/cm2.

The parameter W can be considered as the radiation dose D per 1 pulse.

31.6. Changes in tissue properties and its temperature under the action of continuous high-power laser radiation

Change in temperature and tissue properties

under the action of continuous laser radiation

The absorption of high-power laser radiation by biological tissue is accompanied by the release of heat. To calculate the released heat, a special value is used - bulk density of heat(q).

The release of heat is accompanied by an increase in temperature and the following processes occur in the tissues:

at 40-60°C, there is an activation of enzymes, the formation of edema, a change and, depending on the time of action, cell death, protein denaturation, the onset of coagulation and necrosis;

at 60-80°C - collagen denaturation, membrane defects; at 100°C - dehydration, evaporation of tissue water; over 150°C - charring;

over 300 ° C - tissue evaporation, gas formation. The dynamics of these processes is shown in fig. 31.6.

Rice. 31.6. Dynamics of changes in tissue temperature under the influence of continuous laser radiation

1 phase. First, the tissue temperature rises from 37 to 100 °C. In this temperature range, the thermodynamic properties of the fabric remain practically unchanged, and the temperature rises linearly with time (α = const and I = const).

2 phase. At a temperature of 100 °C, evaporation of tissue water begins, and until the end of this process, the temperature remains constant.

3 phase. After the water evaporates, the temperature begins to rise again, but more slowly than in section 1, since the dehydrated tissue absorbs energy weaker than normal.

4 phase. Upon reaching the temperature T ≈ 150 °C, the process of charring and, consequently, “blackening” of the biological tissue begins. In this case, the absorption coefficient α increases. Therefore, a non-linear, accelerating temperature increase with time is observed.

5 phase. Upon reaching the temperature T ≈ 300 °C, the process of evaporation of the dehydrated charred biological tissue begins and the temperature rise stops again. It is at this moment that the laser beam cuts (removes) the tissue, i.e. becomes a scalpel.

The degree of temperature increase depends on the depth of the tissue (Fig. 31.7).

Rice. 31.7. Processes occurring in irradiated tissues at different depths: A- in the surface layer, the fabric is heated up to several hundred degrees and evaporates; b- the radiation power attenuated by the top layer is insufficient to evaporate the tissue. Tissue coagulation occurs (sometimes together with charring - a black thick line); V- heating of the tissue occurs due to the transfer of heat from the zone (b)

The lengths of individual zones are determined both by the characteristics of the laser radiation and by the properties of the tissue itself (primarily by the coefficients of absorption and thermal conductivity).

The impact of a powerful focused beam of laser radiation is also accompanied by the appearance shock waves, which can cause mechanical damage to adjacent tissues.

Ablation of tissue under the influence of high-power pulsed laser radiation

When the tissue is exposed to short pulses of laser radiation with a high energy density, another mechanism of dissection and removal of biological tissue is realized. In this case, there is a very rapid heating of the tissue fluid to a temperature T > T boiling. In this case, the tissue fluid is in a metastable overheated state. Then there is an "explosive" boiling of tissue fluid, which is accompanied by the removal of tissue without charring. This phenomenon is called ablation. Ablation is accompanied by the generation of mechanical shock waves that can cause mechanical damage to tissues in the vicinity of the laser impact zone. This fact must be taken into account when choosing the parameters of pulsed laser radiation, for example, when polishing the skin, drilling teeth, or laser correction of visual acuity.

31.7. The use of laser radiation in medicine

The processes characterizing the interaction of laser radiation (LR) with biological objects can be divided into 3 groups:

non-disturbing action(not having a noticeable effect on the biological object);

photochemical action(a particle excited by a laser either itself takes part in the corresponding chemical reactions, or transfers its excitation to another particle participating in a chemical reaction);

photodestruction(due to the release of heat or shock waves).

Laser diagnostics

Laser diagnostics is a non-perturbing effect on a biological object, using coherence laser radiation. We list the main diagnostic methods.

Interferometry. When laser radiation is reflected from a rough surface, secondary waves arise that interfere with each other. As a result, a pattern of dark and light spots (speckles) is formed, the location of which provides information about the surface of the biological object (speckle interferometry method).

Holography. With the help of laser radiation, a 3-dimensional image of the object is obtained. In medicine, this method allows obtaining three-dimensional images of the internal cavities of the stomach, eyes, etc.

Scattering of light. When a highly directed laser beam passes through a transparent object, light is scattered. Registration of the angular dependence of the scattered light intensity (nephelometry method) makes it possible to determine the size of the medium particles (from 0.02 to 300 μm) and the degree of their deformation.

During scattering, the polarization of light can change, which is also used in diagnostics (the method of polarization nephelometry).

Doppler effect. This method is based on measuring the Doppler shift of the LR frequency, which occurs when light is reflected even from slowly moving particles (anenometry method). In this way, the speed of blood flow in the vessels, the mobility of bacteria, etc. are measured.

Quasi-elastic scattering. With such scattering, an insignificant change in the wavelength of the probing LR occurs. The reason for this is a change in the scattering properties (configuration, particle conformation) during the measurement process. Temporal changes in the parameters of the scattering surface are manifested in a change in the scattering spectrum in comparison with the spectrum of the input radiation (the scattering spectrum is either broadened or additional maxima appear in it). This method makes it possible to obtain information about the changing characteristics of scatterers: diffusion coefficient, directional transport velocity, and dimensions. This is how protein macromolecules are diagnosed.

Laser mass spectroscopy. This method is used to study chemical composition object. Powerful beams of laser radiation evaporate the substance from the surface of the biological object. Pairs are subjected to mass spectral analysis, the results of which are used to judge the composition of the substance.

Laser blood test. A laser beam passed through a narrow quartz capillary, through which specially treated blood is pumped, causes its cells to fluoresce. The fluorescent light is then captured by a sensitive sensor. This glow is specific for each type of cells passing singly through the section of the laser beam. The total number of cells in a given volume of blood is counted. Precise quantitative indicators are determined for each cell type.

photodestruction method. It is used to study the surface composition object. Powerful LR beams make it possible to take microsamples from the surface of biological objects by evaporation of a substance and subsequent mass-spectral analysis of this vapor.

The use of laser radiation in therapy

The therapy uses low-intensity lasers (intensity 0.1-10 W/cm2). Low-intensity radiation does not cause a noticeable destructive effect on tissues directly during irradiation. In the visible and ultraviolet regions of the spectrum, the effects of irradiation are due to photochemical reactions and do not differ from the effects caused by monochromatic light obtained from conventional incoherent sources. In these cases, lasers are simply convenient monochromatic light sources that provide

Rice. 31.8. Scheme of using a laser source for intravascular blood irradiation

determining the exact localization and dosage of exposure. As an example, in fig. 31.8 shows a diagram of the use of a laser radiation source for intravascular blood irradiation in patients with heart failure.

Below are the most common methods of laser therapy.

Therapy with red light. He-Ne laser radiation with a wavelength of 632.8 nm is used for anti-inflammatory purposes for the treatment of wounds, ulcers, coronary heart disease. The therapeutic effect is associated with the influence of light of this wavelength on the proliferative activity of the cell. Light acts as a regulator of cellular metabolism.

Therapy with blue light. Laser radiation with a wavelength in the blue region of visible light is used, for example, to treat neonatal jaundice. This disease is a consequence of a sharp increase in the concentration of bilirubin in the body, which has a maximum absorption in the blue region. If children are irradiated with laser radiation of this range, then bilirubin breaks down, forming water-soluble products.

Laser physiotherapy - the use of laser radiation in combination with various methods of electrophysiotherapy. Some lasers have magnetic nozzles for the combined action of laser radiation and a magnetic field - magnetic laser therapy. These include the magnetic-infrared laser therapeutic apparatus "Milta".

The effectiveness of laser therapy increases with combined exposure to medicinal substances previously applied to the irradiated area (laserophoresis).

Photodynamic therapy of tumors. Photodynamic therapy (PDT) is used to remove tumors that are exposed to light. PDT is based on the use of photosensitizers localized in tumors that increase the sensitivity of tissues during their

subsequent irradiation with visible light. The destruction of tumors during PDT is based on three effects: 1) direct photochemical destruction of tumor cells; 2) damage to the blood vessels of the tumor, leading to ischemia and death of the tumor; 3) the occurrence of an inflammatory reaction that mobilizes the antitumor immune defense of body tissues.

To irradiate tumors containing photosensitizers, laser radiation with a wavelength of 600-850 nm is used. In this region of the spectrum, the depth of light penetration into biological tissues is maximum.

Photodynamic therapy is used in the treatment of tumors of the skin, internal organs: lungs, esophagus (at the same time, laser radiation is delivered to the internal organs using light guides).

The use of laser radiation in surgery

In surgery, high-intensity lasers are used to cut tissues, remove pathological areas, stop bleeding, and weld biological tissues. By properly choosing the wavelength of radiation, its intensity and duration of exposure, various surgical effects can be obtained. So, for cutting biological tissues, a focused beam of a continuous CO 2 laser is used, having a wavelength λ = 10.6 μm, a power of 2x10 3 W/cm 2 .

The use of a laser beam in surgery provides a selective and controlled effect. Laser surgery has a number of advantages:

Non-contact, giving absolute sterility;

Selectivity, which allows the choice of the radiation wavelength to destroy pathological tissues in a dosed way, without affecting the surrounding healthy tissues;

Bloodlessness (due to protein coagulation);

Possibility of microsurgical effects due to the high degree of beam focusing.

Let us indicate some areas of surgical application of lasers.

Laser welding of fabrics. The connection of dissected tissues is a necessary step in many operations. Figure 31.9 shows how the welding of one of the trunks of a large nerve is carried out in contact mode using solder, which

Rice. 31.9. Nerve welding with a laser beam

drops from a pipette is applied at the place of lasering.

Destruction of pigmented areas. Pulsed lasers are used to destroy pigmented areas. This method (photothermolysis) used to treat angiomas, tattoos, sclerotic plaques in blood vessels, etc.

laser endoscopy. The introduction of endoscopy has revolutionized operative medicine. To avoid large open operations, laser radiation is delivered to the site of exposure using fiber optic light guides, which allow laser radiation to be delivered to the biological tissues of the internal hollow organs. This significantly reduces the risk of infection and postoperative complications.

laser test. Short-pulse lasers in combination with light guides are used to remove plaques in blood vessels, stones in the gallbladder and kidneys.

Lasers in ophthalmology. The use of lasers in ophthalmology makes it possible to perform bloodless surgical interventions without violating the integrity of the eyeball. These are operations on the vitreous body; welding of the exfoliated retina; treatment of glaucoma by "piercing" holes (diameter 50÷100 microns) with a laser beam for the outflow of intraocular fluid. Layer-by-layer ablation of corneal tissues is used for vision correction.

31.8. Basic concepts and formulas

End of table

31.9. Tasks

1. In the phenylalanine molecule, the energy difference in the ground and excited states is ΔE = 0.1 eV. Find the relation between the populations of these levels at T = 300 K.

Answer: n \u003d 3.5 * 10 18.