RU2463632C1 - Anti-laser protective light filter - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: anti-laser protective light filter has a radiation-absorbing component made from coloured optical glass and a reflecting multi-layer dielectric coating on said glass. According to the invention, the wavelength of the maximum of the spectral reflection coefficient of the dielectric coating is shifted towards the long-wave region of the spectrum with respect to the wavelength of the active laser radiation by a value d=0.2-0.3 times the half-width of the spectral reflection band of the dielectric coating.

EFFECT: high degree of protection with increase in angle of incidence of laser radiation.

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Description

The invention relates to the field of ophthalmology and optical instrumentation and can be used in the manufacture of anti-laser glasses, sights, telescopes, sights and other visual observation devices as a means of individual eye protection from direct, reflected or scattered laser radiation.

The widespread introduction of laser technology in numerous areas of modern industrial and scientific activities (from medicine to heavy engineering and mining) puts forward a very urgent and quite complex technical task of reliable protection of the eyes of service personnel from the harmful effects of laser radiation in the spectral range of transparency of the optical environment of the eye λ = 380 -1400 nm.

So, the operators servicing laser technological installations should be equipped with personal protective equipment (glasses) that reliably protect the eyes not only from direct (frontal) radiation, but also from inclined (side) rays in the range of incidence angles θ = ± (0-30 °) (GOST R 12.4.254 - 2010), specularly reflected by the treated surface and / or scattered on the irregularities of the equipment of the working area.

Reliable protection against oblique radiation beams is also required for personnel not directly involved in laser technological operations, but located in the premises where such operations are performed. In this case, the danger is radiation reaching the eye at large angles of incidence θ due to scattering by the surfaces of the premises and the equipment inside them.

Protection against oblique laser radiation flows is required not only for the naked eye, but also for visual observation armed with telescopic devices (telescopes, binoculars, sights) with an extended field of view. In this case, an additional and unconditional requirement for the absence of a noticeable distortion of the wavefront of the radiation entering the device from the observed object is presented to the anti-laser protective filters. Fulfillment of this condition requires the use of materials of high categories in optical parameters (uniformity, weakness, bubbling) and high quality surface manufacturing [1]:

- deviation from flatness N≤ (1-5) interference fringes,

- local error ΔN≤ (0.1-0.5) of the interference band,

- allowable wedge shape Δφ≤ (30 ”-3 ').

Therefore, for the protection of eyes armed with an observing device, it is unacceptable to use filters made of transparent plastics (polycarbonate, polymethyl methacrylate, etc.), which, unlike optical glasses, do not meet the high requirements for the parameters of the optical quality of the material and cannot process the necessary requirements for processing values of N, ΔN and Δφ.

Due to the high power of modern laser technology systems (pulsed radiation energy of up to tens of joules, continuous radiation power of hundreds of watts), anti-laser filters used in personal protective equipment must comply with high degrees of protection L3-L8. The optical density of the light filters, providing the required degree of protection, in accordance with GOST R 12.4.254 - 2010 should be at laser wavelengths D _λ = (3.0-8.0) B (spectral transmittance τ _λ = 10 ^-3 -10 ^-8 ), and the visual transmittance of the filters, which guarantees a sufficiently high efficiency of visual work, should be at least τ _v = 20% (clause 4.2.1 GOST R 12.4.254 - 2010). In addition, the filters used in anti-laser goggles should have the smallest dimensions and weight.

The conflicting requirements listed above are partially satisfied by protective filters made of colored optical glasses (GOST 9411-91), which have a sufficiently high absorption coefficient k _λ at laser wavelengths. The angular characteristic of such filters, i.e. the dependence of their optical density D _λ on the angle of incidence of the radiation θ - D _λ (θ) has a slightly pronounced increasing character. This is due to an increase with an oblique drop in the length of the optical path traveled by the radiation and an increase with increasing θ Fresnel losses of the radiation flux at the air-optical medium interface.

Thus, for protection from laser radiation in the near-infrared (λ = 780-1400 nm _IR) may use blue-green glasses group - 21 BES, BES-22, BES-26, which, however, provide the required degree of protection L3 -L8 only for thicknesses t> 5-6 mm. To protect against laser radiation in the visible region of the spectrum (λ _in = 380-780 nm), filters from these glasses should have a thickness exceeding 10-12 mm, because their optical density in the spectral range λ _in at an acceptable thickness t = 6 mm does not exceed the value of D _λ ≈ 2.0 B, which is completely insufficient for high degrees of protection L3-L8.

Reducing the thickness of anti-laser filters without deteriorating their protective characteristics (degree of protection L) can be achieved by using two-component systems consisting of an absorbing filter made of colored optical glass and a reflective multilayer dielectric coating deposited on an absorbing filter or on a separate part - substrate. The wavelength of the maximum of the spectral reflection coefficient - λ _{m of the} dielectric coating is chosen equal to the wavelength of the laser radiation λ, for protection against which the anti-laser filter is intended. The gain achieved in this case in the thickness (and hence in weight) of the filter is explained by the calculation below.

If the optical density of the two-component filter providing the required degree of protection L is D _λ , and the optical density of the absorbing component of the filter is D _1λ , and the optical density by transmittance of the dielectric coating is D _2λ , then the obvious equality D _λ = _1λ + D _2λ . Then the optical density of the absorbing component is found as D _1λ = D _λ -D _2λ .

Denote by k _λ the absorption coefficient of the material of the absorbing component, then its thickness, and therefore the thickness of the anti-laser filter itself (the thickness of the dielectric coating is negligible) will be t ₁ = D _1λ / _Kλ = (D _λ -D _2λ ) / k _λ .

If, as an anti-laser protective filter, a one-component system is used, containing only an absorbing filter of the same material as in the previous case, then to ensure the necessary optical density D _{λ, the} thickness of the filter should be equal to t ₂ = D _λ / k _λ .

Therefore, the use of a combined two-component system consisting of an absorbing light filter and a dielectric reflective coating reduces the thickness of the anti-laser protective light filter by

Δt = t ₂ -t ₁ = D _{λ /} k _λ - (D _λ -D _2λ ) / k _λ = D _2λ / k _λ .

Modern dielectric reflective coatings have insignificant (less than 1%) absorption of radiation outside the spectral reflection band [2, 3]. In addition, due to the small width of the reflection band (10-50 nm) compared with the spectral range of the visible radiation of 380-780 nm, dielectric coatings designed to operate in the visible region slightly weaken the integral light flux entering the eye during visual observation. Therefore, the use of a dielectric coating along with a decrease in the thickness of the absorbing component increases the visual transmittance τ _{v of the} protective filter, which, in turn, significantly increases the visual performance of an observer equipped with personal protective equipment with such a filter.

However, the positive effect of the use of reflective dielectric coatings is accompanied by a deterioration in the angular characteristic D _λ (θ) of the protective filters, since the transmittance D _{λ of the} multilayer dielectric coatings (and hence the degree of protection L) at a wavelength λ _m decreases significantly with increasing angle of incidence of radiation θ [2]. Therefore, the anti-laser light filter, consisting of an absorbing component and a dielectric coating and providing proper eye protection under normal radiation incidence (θ = 0 °), is unsuitable in the field of laser radiation formed by inclined beams (θ> 0).

Thus, the satisfaction of all of the above requirements for anti-laser protective light filters is a rather complicated technical task that has not yet found an adequate solution.

Thus, in particular, a T26 type anti-laser protective light filter, manufactured by LASERVISION from absorbing glass without reflective dielectric coating, is known. The T26 light filter is used for the eyewear manufactured by the company, models ECO-7, ALL STAR and PROTECTOR, which differ only in the type of frame. The filter is designed to protect the eyes from laser radiation in the near infrared region of the spectrum in the wavelength range λ = 900-1400 nm, where it provides a degree of protection L3-L8. The visual transmittance of the filter is τ _v ≈35%.

The disadvantage of the T26 filter is its large thickness t = 7 mm and the resulting significant weight. Therefore, to facilitate wearing glasses with this filter, the ALL STAR frame model provides the possibility of using an additional head mount equipped with an elastic strap.

To protect against laser radiation in the extended spectral range (visible and near infrared), LASERVISION manufactures an S3102 brand anti-laser filter from absorbing glass. This one-component filter without reflective coating has a low visual transmittance τ _v ≈6%. Its thickness is very significant - t = 11-12 mm, and therefore, the S3102 filter is not considered as an analogue of the claimed device.

Also known anti-laser two-component protective light filter type T37, manufactured by LASERVISION (Germany) from absorbing glass coated with a dielectric coating. The T37 filter has a thickness of t = 9 mm and is designed to protect against laser radiation with a wavelength of λ = 532 nm. The manufacturer uses the T37 filter in goggles of the ALL STAR, ECO-7, PROTECTOR models, which differ in the type of frame. The reflecting dielectric coating of the T37 filter has a maximum spectral reflection coefficient at a wavelength of λ = 532 nm, which coincides with the wavelength of laser radiation, for which the filter is intended to be protected. The T37 filter has a visual transmittance τ _v ≈14% and provides a degree of protection equal to L7 at a wavelength of λ = 532 nm.

According to the technical nature of the filter E37 company LASERVISION is a prototype of the invention.

The disadvantages of the T37 filter are:

- the use of a reflective multilayer dielectric coating with a wavelength maximum of the spectral reflection coefficient, which coincides with the wavelength of the laser radiation, which the filter is intended to protect against. As a result, when exposed to inclined radiation beams incident on the filter at angles θ> 0 °, the optical density of the filter (and therefore the degree of protection L provided by it) significantly decreases compared with the required values that the filter has at θ = 0 °,

- the large thickness and weight of the filter, making it difficult to use, since for long-term wearing of goggles with T37 filters, the use of a special frame with an additional head mount is required,

- low value of the visual transmittance τ _v ≈14%, which significantly reduces the efficiency of the visual work of an observer using a filter in the twilight time of the day [4].

The aim of the invention is to eliminate a significant drawback of anti-laser light filters containing a multilayer reflective dielectric coating with a maximum spectral reflectance that matches the radiation wavelength, which the filter is intended to protect against. The disadvantage of such filters is a quick and systematic decrease in their optical density (and hence the degree of protection) with increasing angle of incidence of radiation.

The object of the invention is achieved by the fact that in the anti-laser protective filter for protecting the eyes from laser radiation in the spectral region of 380-1400 nm, including the radiation absorbing component and a reflective multilayer dielectric coating, the wavelength of the maximum spectral reflectance of the coating is shifted to the long-wavelength region of the spectrum relative to the wavelength laser radiation by an amount equal to δ = 0.2-0.3 from the half-width of the spectral reflection band of the dielectric coating.

The essence of the proposed technical solution is illustrated in Fig. 1, on the left side of which (see curves I and II) two versions of typical spectral characteristics R (λ) of reflective multilayer dielectric coatings are shown at normal (θ = 0 °) radiation incidence.

Both coatings are designed for protective filters from laser radiation with a wavelength of λ = 539 nm, have the same half-width of the spectral reflection band Δλ / 2 = 50 nm and differ only in the wavelength of the maximum spectral reflection coefficient λ _m . In the first coating (curve I), the value of λ _m1 = 545 nm is shifted relative to the wavelength of laser radiation in the long-wavelength region of the spectrum by δ = 9.3 (Δλ / 2) = 15 nm. For the second coating (curve II), λ _m2 = 530 nm coincides with the wavelength of the laser radiation.

The relative values of the spectral reflection coefficients R _{λ are} plotted along the ordinate axis of Fig. 1, and the maximum values of R _{λ of} both coatings are taken as unity. On the abscissa axis of the right-hand side of Fig. 1, where the angular characteristics R (θ) of coatings I and II are plotted, the angles of incidence of radiation θ are plotted, and on the abscissa on the left-hand side in the upper row of values are the values of δλ, which shift the maximum reflection coefficient of coatings with a change in the angle of incidence θ.

With a normal incidence of radiation (θ = 0 °) on the surface of dielectric coating 1, the relative value of its reflection coefficient at a wavelength of λ = 539 nm corresponds to the ordinate of point 1 of the curve R (λ). The coordinates of point 1 'of the function R (θ) at normal incidence are determined in Fig. 1 from the condition:

- the ordinate of point 1 'is equal to the ordinate of point 1,

- the abscissa of point 1 'is θ = 0 °.

Suppose that the angle of incidence of radiation increased compared to the normal incidence by δθ = 5 ° and amounted to θ = 5 °. Then the spectral band R (λ) of coating 1 and the maximum of its reflection coefficient shift to the short-wavelength region of the spectrum [2] (to the left in Fig. 1) by δλ, and the reflection coefficient of this coating at λ = 539 nm - R (λ = 539 ) will correspond to the ordinate of point 2 of curve I. We find the point 2 'of the function R (θ) at the intersection of the ordinate of point 2 and the abscissas θ = 5 °.

If the angle of incidence of radiation increases by another δθ = 5 ° and amounts to θ = 10 °, then the curve R (λ) of coating 1, shifted to the short-wavelength region by δλ relative to the previous value, will occupy the position at which R (λ = 530) will be correspond to point 3 of curve I. Point 3 'of the angular dependence R (θ) is found at the intersection of the ordinate of point 3 and the abscissas θ = 10 °.

Similarly, the coordinates of the remaining pairs of points 4-4 'are determined; 5-5 ';...; 9-9 ', and in the range of incidence angles θ = 0 ° -40 ° there is (see curve I' Fig. 1) a function of the angular dependence R (θ) of the dielectric coating, the wavelength of the maximum spectral reflection coefficient of which λ _m1 = 545 nm shifted to the long-wavelength region relative to the wavelength of the acting radiation λ = 530 nm.

If we apply the described procedure to the spectral characteristic R (λ) of coating II (points 1a – 6a), we obtain the angular dependence R (θ) (curve II ') of the dielectric coating, the wavelength of the maximum spectral reflection coefficient of which λ _m2 ≈530 nm coincides with wavelength of laser radiation.

Thus, the described theoretical consideration convincingly shows that an increase in the angle of incidence of radiation θ on a type 1 dielectric coating does not lead to a rapid and systematic decrease in its reflection coefficient R _λ , as is the case [2] for type II coatings with a wavelength of maximum reflection coefficient coinciding with the working wavelength λ of the protective filter.

Modern multilayer dielectric coatings are weakly absorbing and practically non-scattering radiation media [2, 3]. Therefore, between their spectral reflection coefficients R _λ and transmittance τ _λ there is an approximate equality: R _λ ≈1-τ _λ . Then τ _λ = 1-R _λ , and the optical density of the coating D _λ , which determines its degree of protection L, is D _λ = -lg (1-R _λ ). Consequently, an increase in the angle of incidence of radiation, which does not cause, as shown above, a decrease in R _λ , does not lead to a similar decrease in the optical density D _{λ of the} dielectric coating, the maximum of the spectral reflection coefficient of which is shifted to the long wavelength region relative to the working wavelength (in the case under consideration, with respect to λ = 530 nm).

A similar relationship between the spectral R (λ) and angular R (θ) characteristics occurs in dielectric coatings designed to protect against laser radiation not only at a wavelength of λ = 530 nm, but also at any other in the range λ = 380-1400 nm if the geometry of the spectral characteristics of these coatings R (λ) is similar to that shown in Fig. 1. The possibility of the practical manufacture of such coatings is illustrated in Fig. 2, which is discussed in detail below.

For experimental verification of the proposed technical solution, two multilayer dielectric coatings of type (5ВН) ⁸ 5В were made from alternating layers of zinc sulfide (ZnS-В) and yttrium fluoride (YF ₃ -Н), deposited on a plane-parallel substrate from K-8 glass. Figure 2 shows the spectral characteristic R (λ) of the coating, measured on a Lambda-9 precision spectrophotometer (manufactured by Perkin Elmer, USA). It can be seen from the figure that for this coating, the wavelengths of the maxima λ _{m of} the reflection coefficients are shifted to the long wavelength region relative to the laser wavelengths λ = 530, 693 and 1060 nm by a value of δ equal to 12, 10 and 18 nm, respectively. With respect to the half-width Δλ / 2 of the corresponding reflection bands, such a shift will be:

for λ = 530 nm-12 nm / 40 nm = 0.3 (Δλ / 2),

for λ = 693 nm-10 nm / 52 nm = 0.19 (Δλ / 2),

for λ = 1060 nm-18 nm / 66 nm = 0.27 (Δλ / 2).

The second coating was of the same type as in Fig. 2, but the centers of its reflection bands coincided with the laser wavelengths.

The angular characteristics D _λ (θ) of both coatings were measured experimentally on a photometric setup containing a goniometric table for changing and accurately measuring the angles of incidence of laser radiation in the range θ = 0-45 °. Solid-state lasers operating on ruby (λ = 693 nm) and neodymium-activated glass (λ = 1060 nm) served as radiation sources. To generate radiation at a wavelength of λ = 530 nm, a frequency doubler of the radiation of a neodymium KDP crystal laser was used.

The results of experimental studies are shown in Fig. 3, where the solid curves are the dependence D _λ (θ) of the dielectric coating, the values of λ _{m of} which are shifted to the long-wavelength region relative to the wavelength of the laser radiation λ (see Fig. 2); the dashed curves are the characteristics of the coating for which λ _m = λ.

Comparison of the angular characteristics shown in Fig. 3 convincingly shows that the dielectric coating of the anti-laser protective filter made in accordance with the claimed technical solution has a significant advantage compared to the dielectric coating of the prototype device, in which the wavelength of the maximum spectral reflection coefficient λ _m coincides with the wavelength of the laser radiation λ = 530 nm. In the first case (solid curves in Fig. 3), there is no significant and systematic decrease in the values of D _λ when the angle of incidence θ changes from 0 to 30 °. In the second case (dashed curves), a sharp and systematic decrease in the optical density D _λ has a pronounced character.

Thus, the proposed technical solution has a significant advantage over the prototype device, since the inventive anti-laser protective filter, equipped with the described reflective dielectric coating, can reliably protect the eyes of observers not only from direct (frontal) irradiation, but also from inclined (side) rays when angles of incidence θ = ± (0-30 °), i.e. within the angular field of view 2θ = 60 °.

In the practical implementation of the claimed device for the manufacture of its absorbing component, the following colored optical glasses of domestic production (GOST 9411-91) or their foreign analogues can be used:

- in the spectral region λ = 380-580 nm, glass of yellow or orange groups of grades ZhS-3, 4, 10-12, 16-18; OS-5, 11-14, 23 and purple glass of the PS-7 brand;

- in the spectral region λ = 580-640 nm, glass is a blue-green group of grades SZS-3, 8, 9, 20 and red glasses are grades KS-10, 11, 13;

- in the spectral region λ = 640-1400 nm, glass is a blue-green group of grades SZS-3, 8, 9, 21, 22, 25, 26.

Three prototypes of anti-laser protective light filters manufactured in accordance with the proposed technical solution were tested. The absorbing components in these filters were plane-parallel wafer substrates made of colored glasses OS-23 (λ = 530 nm), SZS-21 (λ = 693 nm) and SZS-26 (λ = 1060 nm). As a dielectric coating, a multilayer (5BH) ⁸ 5B system was used, the electrovacuum deposition technology of which ensured accurate reproduction of the spectral characteristics of Fig. 2 by the spectral width of the reflection bands and the mutual arrangement of the parameters λ and λ _m .

The test results of the prototypes are shown in the table, which compares the parameters of the proposed protivolazernogo protective light filter and filter prototype T37 company LASERVISION.

Thus, the test results of the prototype filters and the experimental results of the study of the dielectric coating, which is part of the filters, show that in relation to the prototype of the claimed technical solution "Anti-laser protective filter" has significant advantages and novelty, which are as follows.

Table Test results of prototypes of “Anti-laser protective light filter”. Filter parameters Prototype filter T37 Claimed device Sample Number one 2 3 Working wavelength, λ, nm 532 530 693 1060 Optical density, D _λ , Bel 7.3 8.1 7.8 9.2 Degree of protection, L L7 L8 L7-L8 L9 Visual transmittance, τ _v ,% fourteen 34 41 65 The thickness of the absorbing component, t, mm 9.0 4.9 4.9 4.3 Glass brand of the absorbent component - OS-23 SZS-21 SZS-26

1. The claimed filter does not have a sharp and systematic decrease in optical density D _λ with increasing angles of incidence of radiation within θ = ± (0-30 °), i.e. the proposed filter provides the necessary degree of protection in the angular field of view 2θ = 60 °. The noted advantage is achieved through the use of a dielectric coating, the maximum spectral reflection coefficient of which λ _{m is} shifted to the long wavelength region relative to the wavelength of the acting radiation λ by an amount equal to (0.2-0.3) from the half width of the spectral reflection band.

2. The claimed filter has a significantly smaller (almost 2 times) thickness, and hence the weight, in comparison with the prototype T37 filter. Due to this, the use of the claimed filter in anti-laser glasses does not require a specialized frame with an additional head mount.

3. The claimed filter has a significantly higher visual transmittance (τ _v > 30%) than the prototype T37 filter (τ _v = 14%). Due to this, the effectiveness of the visual work of an observer using the claimed filter at dusk will be almost the same as in the daytime [4].

As a material for the manufacture of the claimed “Anti-laser protective light filter”, colored glasses are proposed, the high optical parameters of which are guaranteed by GOST 9411-91. This, as well as a sufficient thickness of the filters t> 4 mm, allows them to be manufactured in accordance with the requirements of the minimum permissible distortion of the wavefront of the radiation passing through the filter when working with visual observation devices.

LITERATURE

1. M.D. Maltsev. Calculation of tolerances for optical parts. M., "Engineering", 1974, 68 S.

2. T.N. Krylova. Interference coatings. L., "Mechanical Engineering", 1973, 224 pp.

3. L.B. Katsnelson, Sh.A. Furman. WMD, No. 12, 1973, p.19.

4. N.P. Travnikova. The effectiveness of visual search. M., "Engineering", 1985, 128 S.

Claims (1)

Anti-laser protective light filter to protect the eyes from laser radiation in the spectral region of 380-1400 nm, including an absorbing component of colored optical glass and a reflective multilayer dielectric coating, characterized in that the wavelength of the maximum spectral reflectance of the coating is shifted to the long-wavelength region of the spectrum relative to the wavelength the effect of radiation by an amount equal to δ = 0.2-0.3 from the half-width of the spectral reflection band of the dielectric coating.

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