Reflected laser radiation. What is laser radiation

The use of laser devices is associated with a certain danger to humans. In this work, we will consider only the features practical application laser devices and methods of protection associated with the possibility of damage to the eyes and skin of a person. At the same time, the fundamental regulatory documents are: the 825th publication of the International Technical Commission (IEC) entitled "Radiation safety of laser products, equipment classification, requirements and guidelines for consumers" as the most competent world-class recommendation; the newest domestic development SNiP; GOS

Laser radiation of any wavelength directly affects a person; however, due to the spectral features of organ damage and significantly different maximum permissible doses of radiation, the effects on the eyes and skin of a person are usually distinguished.

There are two areas of application of lasers and industry. The first direction is associated with a targeted effect on the processed substance (microwelding, heat treatment, cutting brittle and hard materials, adjusting the parameters of microcircuits, etc.), the second direction - medicine - is increasingly developing.

The wavelength range emitted by lasers covers the visible spectrum and extends into the infrared and ultraviolet regions. For each mode of laser operation and spectral range, the corresponding maximum permissible levels (MPL) are recommended for the energy (W) and power (P) of radiation that has passed the limiting aperture d = 7 mm. For the visible range or d = 1.1 mm, for the rest, the energy exposure (H) and irradiance (E), averaged over the limiting aperture: H = W / Sa, E = P / Sa, where Sa is the limiting aperture.

Chronic MPUs are 5 - 10 times lower than the MPLs of a single exposure. Under the simultaneous action of LRs of different ranges, their action is summed up and multiplied by the corresponding energy input.

Laser radiation is characterized by some features:

1 - wide spectral (& = 0.2..1 µm) and dynamic (120..200 dB);

2 - short pulse duration (up to 0.1 ns.);

3 - high power density (up to 1e + 9 W / cm ^ 2) energy;

4 - Measurement of energy parameters and characteristics of laser radiation

Types of action of laser radiation

The most dangerous is laser radiation with a wavelength:

380¸1400 nm - for the retina,
180-380 nm and over 1400 nm - for the anterior media of the eye,
180¸105 nm (i.e. in the entire considered range) - for skin.

The main hazard during laser operation is direct laser radiation.

The degree of potential hazard of laser radiation depends on the power of the source, wavelength, pulse duration and purity of its following, environmental conditions, reflection and scattering of radiation.

Biological effects arising from exposure to laser radiation on the human body are divided into two groups:

The primary effects are organic changes that occur directly in the irradiated tissues;
Secondary effects are non-specific changes that appear in the body in response to radiation.
Most susceptible to laser radiation damage to the human eye. The laser beam focused on the retina by the lens of the eye will have the form of a small spot with an even denser concentration of energy than the radiation incident on the eye. Therefore, the hit of laser radiation in the eye is dangerous and can cause damage to the mesh and choroid with impaired vision. At low energy densities, hemorrhage occurs, and at high densities, a burn, rupture of the retina, the appearance of eye bubbles in the vitreous body.
Laser radiation can also damage the skin and internal organs of a person. Laser damage to the skin is similar to a thermal burn. The degree of damage is influenced by both the input characteristics of the lasers and the color and degree of skin pigmentation. The intensity of the radiation that causes damage to the skin is much higher than the intensity that causes damage to the eye.

Ensuring laser safety

Methods and means of protection against exposure to laser radiation can be divided into organizational, engineering and technical and personal protective equipment. Reliable protection against accidental contact with a person is the shielding of the beam with a light guide along the entire path of its action. As personal protective equipment, special protective glasses are used, glasses in which are selected in accordance with GOST 9411-81E; technological gowns and gloves made of light green or blue cotton fabric.

The presentation for the work presents indicators of permissible levels of laser radiation, as well as illustrative material on the types of negative effects of laser radiation on the human body and methods of protection.

The word "laser" itself is an abbreviation of the English "Light Amplification by Stimulated Emission of Radiation", which means "amplification of light using induced radiation."

The era of laser medicine began more than half a century ago, when, in 1960, Theodore Mayman first used a ruby laser in a clinic.

The ruby was followed by other lasers: 1961 - a neodymium yttrium-aluminum garnet (Nd: YAG) laser; 1962 - argon; 1964 - carbon dioxide (CO 2) laser.

In 1965, Leon Goldman reported on the use of the ruby laser to remove tattoos. Later, up to 1983, various attempts were made to use neodymium and argon lasers to treat vascular skin pathologies. But their use has been limited by the high risk of scarring.

In 1983, Rox Anderson and John Parrish published their concept of selective photothermolysis (SFT) in Science, revolutionizing laser medicine and dermatology. This concept made it possible to better understand the processes of interaction of laser radiation with tissue. This, in turn, facilitated the development and manufacture of lasers for medical applications.

Features of laser radiation

Three inherent properties of laser radiation make it unique:

Coherence. The peaks and troughs of the waves are located in parallel and coincide in phase in time and space.
Monochrome. The light waves emitted by the laser are of the same length, exactly that provided by the medium used in the laser.
Collimation. The waves in the light beam remain parallel, do not diverge, and the beam transfers energy practically without loss.

How laser radiation interacts with skin

Laser surgery methods are used to manipulate the skin much more often than any other tissue. This is explained, firstly, by the exceptional variety and prevalence of skin pathology and various cosmetic defects, and secondly, by the relative ease of performing laser procedures, which is associated with the superficial location of objects requiring treatment. The interaction of laser light with tissues is based on the optical properties of tissues and physical properties laser radiation. The distribution of light hitting the skin can be divided into four interrelated processes.

Reflection. About 5-7% of the light is reflected at the level of the stratum corneum.

Absorption (absorption). It is described by the Bouguer-Lambert-Beer law. The absorption of light passing through tissue depends on its initial intensity, the thickness of the layer of matter through which the light passes, the wavelength of the absorbed light, and the absorption coefficient. If the light is not absorbed, no effect on the tissue occurs. When a photon is absorbed by a target molecule (chromophore), all of its energy is transferred to that molecule. The most important endogenous chromophores are melanin, hemoglobin, water and collagen. Exogenous chromophores include tattoo dyes and trauma-impregnated dirt particles.

Diffusion. This process is mainly due to collagen in the dermis. The importance of the scattering phenomenon is that it rapidly reduces the energy flux density available for absorption by the target chromophore, and, consequently, the clinical effect on tissues. Scattering decreases with increasing wavelength, making more long waves ideal for delivering energy to deep dermal structures.

Penetration. The depth of light penetration into the subcutaneous structures, as well as the scattering intensity, depends on the wavelength. Short waves (300-400 nm) are intensely scattered and do not penetrate deeper than 100 microns . And waves of longer length penetrate deeper, since they are scattered less .

The main physical parameters of a laser that determine the effect of quantum energy on a particular biological target are the generated wavelength and energy flux density and exposure time.

Generated wavelength. The laser wavelength is comparable to the absorption spectrum of the most important tissue chromophores (Fig. 2). When choosing this parameter, it is imperative to take into account the depth of the target structure (chromophore), since light scattering in the dermis depends significantly on the wavelength (Fig. 3). This means that long waves are absorbed weaker than short ones; accordingly, their penetration into tissues is deeper. It is also necessary to take into account the inhomogeneity of the spectral absorption of tissue chromophores:

Melanin normally found in the epidermis and hair follicles. Its absorption spectrum lies in the ultraviolet (up to 400 nm) and visible (400 - 760 nm) spectral ranges. The absorption of laser radiation by melanin gradually decreases as the wavelength of light increases. Weakening of absorption occurs in the near infrared region of the spectrum from 900 nm.
Hemoglobin contained in erythrocytes. It has many different absorption peaks. The maxima of the absorption spectrum of hemoglobin lie in the UV-A (320-400 nm), violet (400 nm), green (541 nm) and yellow (577 nm) ranges.
Collagen forms the basis of the dermis. The absorption spectrum of collagen is in the visible range from 400 nm to 760 nm and the near infrared range from 760 to 2500 nm.
Water makes up 70% of the dermis. The absorption spectrum of water lies in the middle (2500 - 5000 nm) and far (5000 - 10064 nm) infrared regions of the spectrum.

Energy flux density. If the wavelength of light affects the depth at which it is absorbed by one or another chromophore, then for direct damage to the target structure, the value of the laser radiation energy and the power that determines the rate of receipt of this energy are important. Energy is measured in joules (J), power is in watts (W, or J / s). In practice, these radiation parameters are usually used in terms of per unit area - energy flux density (J / cm 2) and energy flux rate (W / cm 2), or power density.

Types of laser interventions in dermatology

All types of laser interventions in dermatology can be conditionally subdivided into two types:

I type. Operations during which an area of the affected skin, including the epidermis, is ablated.
II type. Operations aimed at selective removal of pathological structures without compromising the integrity of the epidermis.

Type I. Ablation.
This phenomenon is one of the fundamental, intensively studied, although not yet fully resolved problems of modern physics.
The term "ablation" is translated into Russian as removal or amputation. In non-medical vocabulary, this word means erosion or melting. In laser surgery, ablation is understood as the elimination of an area of living tissue directly under the action of photons of laser radiation on it. This refers to the effect that manifests itself precisely during the irradiation procedure itself, in contrast to the situation (for example, during photodynamic therapy) when the irradiated tissue site remains in place after the laser exposure stops, and its gradual elimination occurs later as a result of a series of local biological reactions developing in the irradiation zone.

The energy characteristics and performance of ablation are determined by the properties of the irradiated object, the characteristics of the radiation and parameters that inextricably link the properties of the object and the laser beam - the coefficients of reflection, absorption and scattering of a given type of radiation in a given type of tissue or its individual components. The properties of the irradiated object include: the ratio of liquid and dense components, their chemical and physical properties, the nature of intra- and intermolecular bonds, thermal sensitivity of cells and macromolecules, tissue blood supply, etc. pulse), power, pulse energy, total absorbed energy, etc.

The ablation mechanism has been studied in most detail using a CO2 laser (l = 10.6 μm). Its radiation at a power density of ³ 50 kW / cm 2 is intensively absorbed by tissue water molecules. Under such conditions, the water quickly heats up, and from it the non-aqueous components of the tissue. The consequence of this is the rapid (explosive) evaporation of tissue water (vaporization effect) and the eruption of water vapor together with fragments of cellular and tissue structures outside the tissue with the formation of an ablation crater. Together with the overheated material, most of the heat energy is removed from the fabric. A narrow strip of heated melt remains along the walls of the crater, from which heat is transferred to the surrounding intact tissues (Fig. 4). At a low energy density (Fig. 5, A), the emission of ablation products is relatively small; therefore, a significant part of the heat from the massive melt layer is transferred to the tissue. At a higher density (Fig. 5, B), the opposite picture is observed. In this case, minor thermal injuries are accompanied by mechanical trauma to the tissue due to the shock wave. Part of the heated material in the form of a melt remains along the walls of the ablation crater, and it is this layer that is the reservoir of heat transferred to the tissue outside the crater. The thickness of this layer is the same along the entire contour of the crater. With an increase in the power density, it decreases, and with a decrease, it increases, which is accompanied, respectively, by a decrease or an increase in the zone of thermal damage. Thus, by increasing the radiation power, we achieve an increase in the rate of tissue removal, while reducing the depth of thermal damage.

The field of application of the CO 2 laser is very wide. In focused mode, it is used for tissue excision while simultaneously coagulating blood vessels. In the defocused mode, by reducing the power density, layer-by-layer removal (vaporization) of pathological tissue is performed. It is in this way that superficial malignant and potentially malignant tumors are eliminated (basal cell carcinoma, actinic cheilitis, Keir's erythroplasia), a number of benign skin neoplasms (angiofibroma, trichlemmoma, syringoma, trichoepithelioma, etc.), large post-inflammatory scabs, inflammatory skin diseases(granulomas, nodular chondrodermatitis of the auricle), cysts, infectious skin lesions (warts, recurrent condylomas, deep mycoses), vascular lesions (pyogenic granuloma, angiokeratoma, annular lymphangioma), formations that cause cosmetic defects (rhinophyma, deep post-acne scarring spots, lentigo, xanthelasma), etc.

A defocused CO 2 laser beam is also used in a purely cosmetic procedure - the so-called laser dermabrasion, that is, layer-by-layer removal of the surface layers of the skin in order to rejuvenate the patient's appearance. In a pulsed mode with a pulse duration of less than 1 ms, 25-50 microns of tissue is selectively vaporized in one pass; in this case, a thin zone of residual thermal necrosis is formed in the range of 40-120 microns. The size of this zone is sufficient to temporarily isolate the dermal blood and lymph vessels, which in turn reduces the risk of scar formation.

Skin renewal after laser dermabrasion is due to several reasons. Ablation reduces the severity of wrinkles and textural abnormalities through surface evaporation of tissue, thermal coagulation of cells in the dermis, and denaturation of extracellular matrix proteins. During the procedure, there is an instant visible contraction of the skin in the range of 20-25% as a result of tissue shrinkage (compression) due to dehydration and compression of collagen fibers. The onset of a delayed, but more prolonged result of skin renewal is achieved through processes associated with the reaction of tissues to trauma. After exposure to the laser, aseptic inflammation develops in the area of the formed wound. This stimulates the post-traumatic release of growth factors and fibroblast infiltration. The upcoming reaction is automatically accompanied by a burst of activity, which inevitably leads to the fact that fibroblasts begin to produce more collagen and elastin. As a result of vaporization, the renewal processes and the kinetics of proliferation of epidermal cells are activated. In the dermis, the processes of collagen and elastin regeneration are triggered, followed by their arrangement in a parallel configuration.

Similar events occur when using pulsed lasers emitting in the near and middle infrared region of the spectrum (1.54-2.94 microns): diode-pumped erbium (l = 1.54 microns), thulium (l = 1.927 microns), Ho: YSSG (l = 2.09 μm), Er: YSSG (l = 2.79 μm), Er: YAG (l = 2.94 μm). These lasers are characterized by very high absorption coefficients in water. For example, Er: YAG laser radiation is absorbed by water-containing tissues 12-18 times more actively than CO 2 laser radiation. As in the case of a CO 2 laser, a melt layer is formed along the walls of the ablation crater in the tissue irradiated with the Er: YAG laser. It should be borne in mind that when working on biological tissues with this laser, the energy characteristic of the pulse, primarily its peak power, is of significant importance for the nature of tissue changes. This means that even with a minimum radiation power, but with a longer pulse, the depth of thermonecrosis sharply increases. Under such conditions, the mass of the removed superheated ablation products is relatively less than the mass of the remaining ones. This causes deep thermal damage around the ablation crater. At the same time, with a powerful pulse, the situation is different - minimal thermal damage around the crater during highly efficient ablation. True, in this case, a positive effect is achieved at the cost of extensive mechanical damage to the tissue by the shock wave. In one pass with an erbium laser, tissue is ablated to a depth of 25-50 microns with minimal residual thermal damage. As a result, the process of re-epithelialization of the skin is much shorter than after exposure to a CO 2 laser.

II type. Selective impact.
Operations of this type include procedures during which laser damage to certain intradermal and subcutaneous formations is achieved without violating the integrity of the skin. This goal is achieved by selecting the characteristics of the laser: wavelength and irradiation mode. They must ensure that the laser light is absorbed by the chromophore (colored target structure), which will lead to its destruction or discoloration due to the conversion of radiation energy into thermal energy (photothermolysis), and in some cases into mechanical energy. The target of laser exposure can be: hemoglobin of erythrocytes located in numerous dilated dermal vessels with port wine stains (PWS); pigment melanin of various skin formations; coal, as well as other, differently colored foreign particles introduced under the epidermis during tattooing or getting there as a result of other influences.

An ideal selective action can be considered such an action in which the laser beams are absorbed only by the structures of the target, and there is no absorption outside of it. To achieve this result, a specialist who has chosen a laser with an appropriate wavelength would only have to establish the radiation energy density and the duration of exposures (or pulses), as well as the intervals between them. These parameters are determined taking into account (HTE) for a given target - the time interval during which the target temperature, which has increased at the moment of impulse delivery, drops by half of its increase in relation to the initial one. Exceeding the pulse duration over the VTP value will cause unwanted overheating of the tissue around the target. A decrease in the interval between pulses will lead to the same effect. In principle, all these conditions can be simulated mathematically before the operation, however, the very composition of the skin does not allow taking full advantage of the calculated data. The fact is that in the basal layer of the epidermis there are melanocytes and individual cratinocytes, which contain melanin. Since this pigment intensively absorbs light in the visible, as well as near ultraviolet and infrared regions of the spectrum (the "optical window" of melanin is in the range from 500 to 1100 nm), any laser radiation in this range will be absorbed by melanin. This can lead to thermal damage and cell death. Moreover, radiation in the visible part of the spectrum is also absorbed by cytochromes and flavin enzymes (flavoproteins) of both melanin-containing cells and all other types of cells of the epidermis and dermis. It follows from this that with laser irradiation of a target located under the skin surface, some damage to epidermal cells becomes inevitable. Therefore, the real clinical problem is reduced to a compromise search for such modes of laser irradiation, in which it would be possible to achieve maximum target damage with the least damage to the epidermis (with the expectation of its subsequent regeneration, mainly due to neighboring non-irradiated skin areas).

Compliance with all these conditions in relation to a specific target will lead to its maximum damage (heating or decay) with minimal overheating or mechanical injury to adjacent structures.

So, for irradiation of pathological vessels of the port wine stain (PWS), the most rational is to use the laser with the longest wavelength corresponding to the peaks of light absorption of hemoglobin (l = 540, 577, 585 and 595 nm), with a pulse duration of the order of milliseconds, since the absorption of radiation melanin will be insignificant (position 1 of the theory of selective photothermolysis). A relatively long wavelength will effectively provide deep tissue heating (position 2), and a relatively long pulse will correspond to a very large target size (vessels with erythrocytes; position 3).

If the purpose of the procedure is to eliminate tattoo particles, then in addition to selecting the radiation wavelength corresponding to the color of these particles, it will be necessary to set the pulse duration, which is much shorter than in the case of wine stains, in order to achieve mechanical destruction of the particles with minimal thermal damage to other structures (position 4 ).

Of course, compliance with all these conditions does not provide absolute protection of the epidermis, however, it excludes too gross damage to it, which would subsequently lead to a persistent cosmetic defect due to excessive scarring.

Tissue reactions to laser exposure

When laser light interacts with tissue, the following reactions occur.

Photostimulation. Low-intensity therapeutic lasers are used for photostimulation. In terms of energy parameters, a therapeutic laser has an effect that does not damage the biosystem, but at the same time, this energy is sufficient to activate the body's vital processes, for example, to accelerate wound healing.

Photodynamic reaction. The principle is based on the effect of light of a certain wavelength on a photosensitizer (natural or artificially introduced), which provides a cytotoxic effect on pathological tissue. In dermatology, photodynamic exposure is used to treat acne vulgaris, psoriasis, lichen planus, vitiligo, urticaria pigmentosa, etc.

Photothermolysis and photomechanical reactions when radiation is absorbed, the energy of the laser beam is converted into heat in the area of the skin that contains the chromophore. With sufficient power of the laser beam, this leads to thermal destruction of the target . Selective photothermolysis can be used to remove malformations of superficial vessels, some pigmented formations of the skin, hair, and tattoos.

Literature

Laser and light therapy. Douver J.C. Moscow. Reed Elsiver 2010, pp. 5-7
Nevorotin A.I. Introduction to laser surgery. Tutorial. - SPb .: SpetsLit, 2000.
Nevorotin A.I. Laser wound in theoretical and applied aspects. // Laser biology and laser medicine: practice. Mat. report rep. school-seminar. Part 2. - Tartu-Pyhäjärve: Publishing house of the Tartu University of the Estonian SSR, 1991, p. 3-12.
Anderson R. R., Parish J. A. The optics of human skin. J Invest Dermatol 1981; 77: 13-19.
Anderson R. R., Parrish J. A. Selective photothermolysis: precise microsurgery by selective absorption of pulsed radiation. Science 1983; 220: 524-527.
Goldman L., Blaney D. J., Kindel D. J. et al. Effect of the laser beam on the skin: preliminary report. J Invest Dermatol 1963; 40: 121-122.
Kaminer M. S., Arndt K. A., Dover J. S. et al. Atlas of cosmetic surgery. 2nd ed. - Saunders-Elsevier 2009.
Margolis R. J., Dover J. S., Polla L. L. et al. Visible action spectrum for melanin-specific selective photothermolysis. Lasers Surg Med 1989; 9: 389-397.

Laser radiation is a special type of electromagnetic radiation generated in the wavelength range of 0.1 ... 1000 microns. Lasers are widely used in various fields of human activity due to such unique properties, as a high degree of coherence and monochromaticity of radiation, low beam divergence, sharp focusing of radiation and the possibility of obtaining a huge radiation power density.

In addition to wide scientific, technical and industrial use, laser systems have various applications in medicine, biology, biotechnology, genetic engineering, etc.

By type, laser radiation is subdivided into direct; scattered; mirror-reflected; diffuse.

Properties of laser radiation. Radiation intensity. Unlike all known optical sources, laser radiation has an extremely high intensity. The power of a solid-state optical quantum generator (laser) can reach 10 12 W. When focusing, this radiation can be concentrated in a small spot. The power density of laser radiation can reach high values - of the order of 10 17 W cm -2 and more. When a substance is exposed to such radiation, high temperatures of the order of 10 6 K and higher develop. Naturally, no refractory material can withstand such a radiation density. The exposure time of such densities in the case of impulse action is much shorter than the settling time stationary process, in this case, the interaction of intense radiation with matter in the local volume occurs, i.e. in the irradiated area without affecting neighboring areas.

Emission line width and coherence. A monochromatic wave has a strictly defined vibration frequency:

Е = E 0 cos [(ωt - kх) + φ], (5.29)

where E 0 is the amplitude of the vector of the electric field strength; k is the wavenumber; x is the coordinate of the wave propagation axis; φ - phase (E 0, ω, k, φ - do not depend on t).

When two waves of the same frequency propagate in space, but with different phases (φ 1, φ 2), at any time, the phase difference Δφ = (φ 1 -φ 2) will remain constant. Two waves are coherent if the amplitude, frequency, phase, polarization and direction of propagation of these waves remain constant or change according to a certain law. Ideal monochromatic vibrations do not exist in nature, since each energy level has a finite width associated with the lifetime of the level. From the uncertainty relation (Heisenberg relation) it follows that the uncertainty of the value of the upper level Δε during radiation is associated with the uncertainty of the lifetime of this level Δt by the relation

The duration of the radiation process τ and the natural width of the radiation line Δω = 2πΔν are related by the expression

(5.31)

Taking into account that the laser has an optical resonator in which there are natural frequencies (vibration modes with width Δν ρ), a high degree of monochromaticity can be obtained by appropriately choosing the dimensions of the resonator and operating conditions of the laser. In gas lasers, it is relatively easy to obtain Δν ρ / ν 0 = 10 -10 (where v 0 is the resonant transition frequency) and even less. This is done if in the interval Δν l at the resonant frequency ν 0 there is one mode Δν m of resonator oscillation (single-mode mode). Monochromaticity of solid-state lasers is worse than the monochromaticity of gas lasers. The high degree of monochromaticity of laser sources makes it easier to obtain a smaller spot r s when focusing. In this case, the chromatic aberration of optical lenses practically does not play a role. This property of laser sources contributes to the production of significant intensities.

Laser radiation has high degree temporal and spatial coherence. This property of laser radiation contributes to obtaining large values of W s, since the small divergence of the laser beam contributes to obtaining smaller values of r s. The concept of coherence plays great importance when using laser radiation in optical location.

Electric field strength. Laser radiation, having an extremely high intensity, makes it possible to obtain high values of the electrical intensity in the flow. These values are comparable to intra-atomic fields. The maximum value of the electromagnetic bond of an electron with a hydrogen proton H is determined by the expression

where e is the electron charge; r 0 is the radius of the electron orbit.

When go = 10 -8 cm, the value of E n, = 10 9 V / cm. For other substances, this value is 107 ... 108 V / cm.

As is known, the field intensity (power density) is related to the electric field strength E by the ratio

where ε 0 is the dielectric constant of the vacuum; c is the speed of light.

At intensities, for example, 10 14 W · cm -2, the value of E is about 10 8 V cm -1.

Laser radiation makes it possible to relatively simply vary the power of the beam flux, change the direction of its propagation using focusing lenses, external collimators, reflecting mirrors or special devices.

Brightness. The properties of lasers make it possible to obtain an unusually high brightness of the radiation. Table 5.10 shows the comparative values of the brightness of some optical sources, from which it can be seen that the brightness of the laser source is many orders of magnitude higher than the brightness of the Sun and the power of artificial sources of spontaneous optical radiation.

Table 5.10. Luminance values of some sources

Beam divergence angle. One of the important characteristics of laser radiation is the directivity (collimation) of the radiation. The importance of collimation lies in the fact that the energy carried by the laser beam can be collected (focused) over a small area.

The limitation on the angle of divergence of the laser beam is imposed by diffraction:

where θ is the angle of divergence; K is a numerical coefficient of the order of unity (for a homogeneous beam K = 1.22); λ is the wavelength; d is the diameter of the outlet aperture.

Classification of lasers. The main source of laser radiation is an optical quantum generator (laser). Lasers are generators of electromagnetic waves in the optical range, in which stimulated electromagnetic radiation of molecules is used active substance driven into an excited state by a pump source. The types of lasers differ in the type of active substance and the method of pumping.

Solid-state lasers use ruby crystals, yttrium-aluminum garnet (YAG) or glass doped with neodymium (Nd) or erbium as an active substance. Pulsed xenon lamps are used to excite the active substance. In the free-running mode, solid-state lasers generate pulses with a duration of 0.1-1 ms, with an energy of tens of joules and a pulse power of tens or hundreds of kilowatts (10 9 ... 10 10 W). The beam divergence angle in solid-state lasers is 20 ... 30 °.

In gas lasers, the active substance is a gas or a mixture of gases, which are brought to an excited state by a gas discharge. Gas lasers are characterized by a small beam divergence angle - only 1 ... 3 °. The most widespread are lasers based on a mixture of helium (He) and neon (Ne) with a generation wavelength of 0.63 μm and lasers based on carbon dioxide(CO 2) with a wavelength of 10.6 microns. The power of helium-neon lasers is low and amounts to tens or hundreds of milliwatts. Carbon dioxide lasers are characterized by high power - hundreds of watts in continuous mode and high efficiency - 20 ... 30%.

In semiconductor lasers, the active substance is a semiconductor crystal. The laser is excited by an electric current passing through the crystal. The maximum power is about 100 watts in pulsed mode and several watts in continuous mode. Has a beam divergence angle of several degrees.

In liquid lasers, organic dyes are usually used as active substances. Excitation of the active substance is carried out either by coherent radiation of another laser, or by incoherent radiation of flash lamps. In liquid lasers, with an appropriate choice of active substance, coherent radiation with wavelengths from 0.34 to 11.75 μm can be obtained. The radiation energy per pulse is up to 10 J.

The impact of laser radiation on humans, living organisms, living cells is many-sided and contradictory.

Currently, laser radiation is used both as a surgical knife for the removal of malignant tumors and other formations, and as a delicate instrument in eye microsurgery, and as a healing beam for the treatment of a wide variety of diseases of the heart, liver, vegetative-vascular system, digestive tract, etc. ...

On the other hand, laser radiation poses a certain danger if it is used carelessly and ineptly. Even work with a low-power laser is dangerous, especially for the eyes.

The biological effect of laser radiation depends on the wavelength and intensity of radiation, therefore the entire wavelength range is divided into areas: ultraviolet (0.2 ... 0.4 microns); visible (0.4 ... 0.5 μm); infrared - near (0.75 ... 1) and far (over 1.0).

According to the degree of danger of laser radiation for the human body, all laser installations are divided into four classes. Class I includes lasers, the radiation of which does not pose a danger to the skin and eyes of a person, to class II - the radiation of which is dangerous to the eyes or skin when irradiated with direct or specularly reflected radiation.

Radiation from class III lasers poses an eye and skin hazard when exposed to direct or specularly reflected radiation and an eye hazard when exposed to diffusely reflected radiation at a distance of 10 cm from a reflective surface.

Class IV includes lasers whose radiation is hazardous to the skin and eyes when irradiated by diffusely reflected radiation at a distance of 10 cm from the reflecting surface.

Dividing lasers into classes allows you to define safety measures when working with different types of lasers.

A. Einstein's brilliant foresight, made by him back in 1917, about the possibility of induced emission of light by atoms, was brilliantly confirmed almost half a century later when Soviet physicists N.G.Basov and A.M. Prokhorov created quantum generators. According to the English abbreviation, this device is also called a laser, and the radiation generated by them is called a laser.

Where do we meet at Everyday life with laser radiation? Nowadays, lasers are widely used - these are different areas technology and medicine, as well as lighting effects in stage performances and shows. The beauty of the sparkling and dancing laser beams has made them very attractive to home experimenters and laser gadget manufacturers. But how does laser radiation affect human health?

To deal with these issues, it is necessary to remind what laser radiation is. To do this, "fast forward" to a physics lesson in grade 10 and talk about quanta of light.

What is laser radiation

Ordinary light is born in atoms. Laser radiation is the same. However, with other physical processes and as a result of exposure to an external electromagnetic field. Therefore, the laser radiation is stimulated (stimulated).

Laser radiation is electromagnetic waves that travel almost parallel to each other. Therefore, the laser beam has a sharp directivity, an extremely small scattering angle and a very significant intensity of impact on the irradiated surface.

What is the difference between laser radiation and, for example, radiation from an incandescent lamp? An incandescent lamp is a man-made light source that emits electromagnetic waves, as opposed to laser radiation, in a wide spectral range with a propagation angle of about 360 degrees.

Influence of laser radiation on the human body

The possibility of an extremely diverse application of quantum generators prompted specialists in various fields of medicine to come to grips with the effect of laser radiation on the human body. It was found that this type of radiation has the following properties:

The sequence of damage during the biological action of laser radiation is as follows:

a sharp increase in temperature, accompanied by a burn;
this is followed by boiling of interstitial, as well as cellular fluid;
the resulting steam creates tremendous pressure, resulting in an explosion and a shock wave that destroys the surrounding tissue.

At low and medium radiation intensities, the skin is especially affected. With stronger exposure, damage to the skin takes the form of edema, hemorrhage and dead areas. But the internal tissues undergo significant changes. Moreover, the greatest danger comes from direct and specularly reflected radiation. It also causes pathological changes in the work of the most important systems of the body.

Let us dwell in particular on the effect of laser radiation on the organs of vision.

The short pulses of radiation generated by the laser cause severe damage to the retina, cornea, iris and lens of the eye.

There are 3 reasons for this.

Typical symptoms of eye damage are cramps and swelling of the eyelids, pain in the eyes, and retinal opacity and hemorrhage. Retinal cells are not restored after damage.

The radiation intensity that causes damage to the eyes is at a lower level than the radiation that causes damage to the skin. Any infrared lasers, as well as devices emitting radiation of the visible spectrum with a power of more than 5 mW, can pose a danger.

Dependence of the influence of laser radiation on a person on its spectrum

laser radiation in medicine

Remarkable scientists different countries, who worked on the creation of a quantum generator, could not even predict what wide application their brainchild would find in various spheres of life. But each of these areas will require specific, specific wavelengths.

What does the wavelength of laser radiation depend on? It is determined by the nature, more precisely, by the electronic structure of the working fluid (the environment where this radiation is generated). There are various solid state and gas lasers. These miracle rays can belong to the ultraviolet, visible (more often red) and infrared regions of the spectrum. Their range is in the range of 180 nm. and up to 30 microns.

The nature of the effect of laser radiation on the human body largely depends on the wavelength. Our eyesight is about 30 times more sensitive to green than to red. Therefore, we will react to the green laser faster. In this sense, it is safer than red.

Protection against laser radiation in production

There is a huge category of people whose professional activity is directly or indirectly related to quantum generators. They are subject to strict regulations and standards for the protection against laser radiation. They include measures of general and individual protection, depending on the degree of danger that this laser device poses to all structures of the human body.

use of laser in production

In total, there are 4 hazard classes that the manufacturer must indicate. The danger to the human body is represented by lasers 2,3 and 4 classes.

Collective means of protection against laser radiation, these are protective screens and housings, light guides, television and telemetric tracking methods, alarm and blocking systems, as well as fencing an area with radiation exceeding the maximum permissible level.

Individual protection of employees is provided with a special set of clothing. To protect your eyes, wearing glasses with a special coating is a compulsory rule.

The best prevention of laser radiation is compliance with the rules of operation and protection, as well as a timely medical examination.

Laser protection for laser gadget users

The uncontrolled use of homemade lasers, lamps, light pointers, laser flashlights in everyday life is a serious danger to others. To avoid tragic consequences, you should remember:

Quantum generators and any laser gadgets pose a potential threat to their owners and those around them. And only careful observance of security measures will allow you to enjoy these achievements without harm to yourself and your friends.

The laser is considered one of Albert Einstein's most ideal foresight. He actively insisted that atoms can emit light. This theory was confirmed half a century later, when Prokhorov and Basov invented a quantum generator. The laser is capable of emitting special radiation. IN modern world they are widely used in medicine, in different areas techniques, in shows and performances on the stage. Despite the crazy popularity, it is important to understand what effect is carried out on the human body.

Specificity of radiation

Laser radiation is born in atoms, just like simple light. However, this requires special physical processes, due to which, the necessary influence of the external field - the electromagnetic one - occurs. That is why radiation is considered to be stimulated, forced. To measure its power, a special device is used - a meter for this is used in many ways.

In simple words, laser radiation is electromagnetic waves that propagate parallel to each other. That is why the laser beam has a sharp directivity, a very small scattering angle, as well as an increased intensity of influence on the surface that is exposed to irradiation.

What is the difference between laser radiation and that which is obtained from a lamp? It should be noted that the accumulation paw is considered to be a man-made source of illumination, which gives electromagnetic waves, which is different from a laser one. The angle of propagation in the spectral range is three hundred and sixty degrees.

The impact of the laser on the human body

Because of various uses quantum generator, many scientists and physicians decided to study laser radiation, as well as its effect on the human body. Thanks to numerous experiences, scientific work, it became known that laser radiation has the following properties:

in the process of interaction with a source of such radiation, the installation and reflected rays can act as a damaging factor;
the severity of the lesion is directly related to the parameters of the localization of radiation, electromagnetic waves;
the energy that is absorbed by such tissues causes a list of negative, harmful effects, namely, light, heat and others.

At the moment of the biological effect of such radiation, the defeat occurs in a certain sequence:

The body temperature rises sharply, which is accompanied by burns.
Then the interstitial, cellular fluid boils.
The steam that is formed as a result of such a process exerts incredible pressure, so everything ends in an explosion, a kind of shock wave that destroys tissue.

Low, medium intensity of radiation has a damaging effect on the skin. If more serious radiation occurs, then the damage is manifested by edema on the skin, necrosis of parts of the body, and hemorrhage. As for the internal tissues, they are highly transformed. The main hazard comes from specularly reflected, direct radiation. This process becomes the cause of serious changes in the work of all internal systems, bodies.

The organs of vision are most affected - the eyes, which is why when working with a laser, you must wear special protective glasses.

The laser generates short pulses of radiation that cause severe damage to the cornea and retina, lens, and iris of the eye.

There are three main reasons for these phenomena:

In a short period of time, during which the laser radiation is triggered, the blinking reflex does not have time to work in time.
The cornea and membrane are considered the most vulnerable.
Harmful impact provoked optical system eye, which focuses radiation to the bottom of the eye. The laser point hits the retinal vessels, blocking it. Given that there are no pain receptors, damage to the retina is almost invisible. If the burned-out part of the eye becomes large, the images of objects falling on it simply evaporate.

Typical signs of damage to the organs of vision:

there is a hemorrhage in the tissue;
swelling of the eyelids;
painful sensations in the eyes;
blurred, blurry image;
spasms of the eyelids.

As a result of such damage, it is impossible to restore retinal cells! The amount of radiation that causes damage to the eyes is at a lower level than the amount of radiation that damages the skin. All infrared lasers are the main hazard. In addition, all devices that emit visible spectrum radiation with a power size of more than 5 mW are extremely dangerous for humans!

The main methods of protection in production

Most people will immediately think that they need only laser goggles, but they will not be enough. Considering the fact that many people work in enterprises with quantum generators, it is important to know the main prescriptions and standards regarding protection from such radiation. They consist of individual, general protection, since everything depends on the degree of danger posed by the laser installation.

There are four groups of danger that the manufacturer should warn about. For the human body, those lasers that are included in the second, third, fourth groups are dangerous. Collective means of protection include casings, protective screens and light guides, blocking and alarms, telemetric tracking methods, fencing a place with radiation that exceeds the permissible norm.

As for the personal protection of workers, they must be provided with special clothing. As for the eyes, you will need protective goggles with a special coating. Glasses can help you reduce the level of negative impact, maintain vision and eye health. The ideal prevention of such exposure is a modern visit to a doctor, compliance with all safety rules.

It is important to always wear protective glasses, overalls, so you can protect yourself and your health from problems.

Protection Measures Against Laser Gadgets

There are more cases when people use lamps, homemade lasers, laser flashlights and light pointers in everyday life without much control, without understanding what danger they pose. Even when using them, protective goggles must be worn. To prevent unfortunate consequences, it is important to always remember:

wear safety glasses;
those rays that are reflected from buckles, glass, objects are especially dangerous;
protective goggles must be suitable for the wavelength of all radiation from the laser;
You can “play” with the laser where there are no people;
if a beam of low intensity enters the eyes of an athlete, pilot or driver, tragedy can occur;
keeping such gadgets out of the reach of children and adolescents;
do not look into the lens, which is a source of radiation.

It is worth remembering that laser gadgets, quantum generators, can pose a huge threat to others, as well as their owners. Careful observance of safety rules will allow you to protect yourself. Safety glasses are not an accessory, but reliable and effective protection.

Benefits of Low Intensity Radiation

Low-intensity laser radiation is especially popular in modern dermatology and cosmetology. In the process of exposure to such radiation on the human body, positive transformations can be observed:

all inflammatory processes in the body are eliminated;
aging of cells and tissues slows down;
general, local immunity is strengthened;
antibacterial effect occurs;
the elasticity of the skin increases;
the epidermal layer thickens;
the dermis is reconstructed;
the number of sebaceous, sweat glands increases, due to the normalization of their full activity;
accumulation of fat is fixed, muscle mass increases, thanks to improved metabolic processes;
due to good nutrition of tissues and cells, increased blood circulation, active hair growth is observed.

A similar positive effect is possible due to long-term, systematic treatment. The first result is noticeable after three sessions, but generally at least 10-30 therapies are required. To consolidate the result, prevention is carried out three times a year for 10 sessions.

Radiation power measurement

As for the energy and power of radiation, they are completely different, but the quantities are related to each other, they are called energy parameters. Measurement of energy, power, is made in different ways, as well as those that are used in the microwave range. You will need a special meter.

The power meter is as follows:

Photoelectric power meter for laser radiation. Almost every photodetector that has an output signal proportional to the incident flux will allow measurement of the power from continuous emissions. For this purpose, you will need a semiconductor photodetector.
High power meter. This will require crystal effects. For example, a ferroelectric power meter. When the rays fall on it, then on a special crystal or resistor, you can see a voltage that can be measured. The role of a ferroelectric can be barium or lead titanate. Such a meter is very efficient.
Power meter with reverse electro-optical effect. When monochromatic radiation hits the crystal, polarization occurs. When such a crystal is placed in a special capacitor, it is powerful to measure the power, which is associated with a special voltage.

The meter will help determine the strength of the laser radiation. It is important to remember that when working with lasers, especially in large production, all possible safety measures must be observed. Remember to wear special glasses and clothing.