RU2425337C2 - Method of recording optical wave front and system to this end - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: monochromatic acoustic wave is excited in optical-acoustic cell made from optically anisotropic crystal that allows Bragg's optical-acoustic diffraction with dissipation of light radiation at simultaneous to diffraction peaks of +1-th and -1-th orders. Then, spatially-modulated coherent light wave that carry analysed image is passed through said cell. At the same time light wave is dissipated through two Braggs' peaks of +1-th and -1-th orders. Images formed in said diffraction peaks are separately recorded by means of two matrix photo cells and their output signals are analysed in electronic unit. Two electric signals with separated data on amplitude and phase structure of analysed image are generated to display visible images of amplitude and phase structure on monitor.

EFFECT: simultaneous analysis of amplitude and phase structure of optical field.

10 cl, 5 dwg

Description

Technical field

The invention relates to the field of laser physics, adaptive optics and holography, in particular to visualization of the wavefront.

State of the art

It is known from the prior art that a light wave, passing through an object or reflected from it, experiences in the general case amplitude and phase spatial modulation. However, the eye or any other photosensitive device records only the amplitude distribution (more precisely, the light intensity). Thus, all information about the object contained in phase modulation is completely lost, although this information can be very important, and sometimes (in the case of the so-called phase objects) the only information about the object. Phase objects include, in particular, optical elements (lenses, prisms, mirrors, etc.), gas, liquid, and crystalline media that distort the optical wavefront due to internal inhomogeneity, and various biological structures characterized by a very low coefficient of light absorption (cells, bacteria) ) etc. The problem of visualizing phase objects or, in other words, visualizing an optical wavefront has become especially urgent after the advent of lasers and in connection with their widespread use in non-destructive measurements, not only in physics and technology, but also in chemistry, biology, medicine and ecology. In a more general setting, this problem, formulated as recording the optical wavefront, is key for adaptive optics systems.

преобразуется в модуляцию интенсивности, пропорциональную квадрату фазы:

. В методе фазового контраста центральная компонента сдвигается по фазе на

, вследствие чего получается линейный закон преобразования фазы в интенсивность:

. В интерференционном (голографическом) методе оптический волновой фронт регистрируется в виде интерференционной структуры, возникающей при пространственном совмещении на поверхности фоточувствительного материала сигнальной и опорной световых волн (J. Goodman, Introduction to Fourier optics, - McGraw-Hill Book Comp., N.Y., 1968).Currently, several methods for visualizing phase objects are known (see, for example, M. Born, E. Wolf, Principles of optics, - Pergamon Press, Oxford, 1964). In the dark field method, the central component is removed from the spatial spectrum of the optical signal. As a result of this, phase modulation of the light field

converted to intensity modulation proportional to the square of the phase:

. In the phase contrast method, the central component is phase shifted by

as a result of which the linear law of phase to intensity conversion is obtained:

. In the interference (holographic) method, the optical wavefront is recorded as an interference structure arising from the spatial combination of the signal and reference light waves on the surface of the photosensitive material (J. Goodman, Introduction to Fourier optics, - McGraw-Hill Book Comp., NY, 1968) .

The acousto-optical method for detecting the phase structure of a light field based on light diffraction by a short acoustic pulse propagating in a transparent medium — an acousto-optic cell (VIBalakshy, Application of acousto-optic interaction for holographic conversion of light fields, Optics & Laser Techn ., 1996, v. 28, No. 2, p. 109-117). This method can be considered as the closest analogue of the invention. In this method, the phase image is projected onto the plane of the cell. When an acoustic pulse propagates in a cell, different portions of the image are successively diffracted on it. Diffracted radiation is detected by a photodetector. In fact, the acoustic impulse plays the role of a moving window through which the phase structure of the light field is sequentially viewed. The output signal of the photodetector is a scan signal of a separate line of the light field. To register two-dimensional images, a deflector is located in front of the cell, deflecting the light beam with a frame frequency in the direction orthogonal to the propagation of the acoustic pulse.

преобразуется по тому или иному закону в интенсивность

. Поэтому если исходное световое поле промодулировано не только по фазе, но также и по амплитуде (что имеет место в большинстве случаев), то в выходном сигнале амплитудная информация накладывается на фазовую. Разделение амплитудной и фазовой информации возможно лишь при одновременной регистрации в двух разных установках анализируемого оптического поля: суммарного распределения интенсивности фазочувствительным методом и распределения интенсивности нечувствительным к фазе методом с последующей компьютерной обработкой полученных электрических сигналов. Такой подход приводит к сложной оптической схеме системы регистрации, трудностям ее юстировки, значительным ошибкам и неоднозначной интерпретации получаемых результатов.The main difficulty in implementing the described methods for visualizing the optical wavefront known from the prior art arises from the fact that the local value of the phase of the light field

converted according to one law or another into intensity

. Therefore, if the initial light field is modulated not only in phase, but also in amplitude (which occurs in most cases), then in the output signal the amplitude information is superimposed on the phase. Separation of amplitude and phase information is possible only if the analyzed optical field is simultaneously recorded in two different settings: the total intensity distribution by the phase-sensitive method and the intensity distribution by the phase-insensitive method, followed by computer processing of the received electrical signals. Such an approach leads to a complex optical design of the registration system, difficulties in its adjustment, significant errors and ambiguous interpretation of the results.

A special place is occupied by the holographic method in which phase information, when recording a hologram, is converted into amplitude information by frequency modulation of the spatial carrier, while the amplitude information is presented in the form of amplitude modulation of this carrier. However, the separation of the amplitude and phase information in this case, although theoretically possible, is currently problematic due to the insufficient resolution of the transmitting television cameras.

Another important drawback of the methods known from the prior art is the unambiguous certainty of the law of phase to intensity conversion and the impossibility of reconfiguring the system to another law that is more optimal in a particular situation.

-ю часть светового потока, где N - число элементов разложения изображения. В существующем телевизионном стандарте N=500000. Поэтому известный акустооптический метод пригоден для обработки только световых сигналов большой мощности.The main disadvantage of the acousto-optical method (VIBalakshy, Application of acousto-optic interaction for holographic conversion of light fields, Optics & Laser Techn., 1996, v.28, No. 2, p.109-117), is selected as the closest analogue sensitivity of the photodetector system. This system uses a single-element photodetector that records only

-th part of the light flux, where N is the number of elements of image decomposition. In the existing television standard, N = 500000. Therefore, the known acousto-optical method is suitable for processing only high-power light signals.

The claimed method for registering an optical wavefront and its implementation system eliminate the disadvantages of the methods known from the prior art and, unlike the above known methods, allow simultaneous analysis of both the amplitude and phase structure of the optical field. The system that implements this method according to the invention generates two television-type electrical signals at the output, which can be used both for separate visualization of the amplitude and phase structure of images, and for measuring local values of the amplitude and phase of the light field. Moreover, the system uses a small set of optical elements; The optical scheme of the device is quite simple, which ensures stable and reliable operation, high measurement accuracy. The use of matrix photodetectors in the system ensures operation in the “charge accumulation” mode and increases the sensitivity by several orders of magnitude (compared to the prototype). By electrically changing the parameters of the control signal, a quick (in real time) restructuring of the system is possible, providing a transition from one law of visualization of the phase structure to another.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a method for recording an optical wavefront, comprising:

a) the excitation of a monochromatic acoustic wave in an acousto-optical cell made of a special section optical-anisotropic crystal;

b) transmitting a spatially modulated coherent light wave carrying the analyzed image through an acousto-optical cell;

c) ensuring simultaneous scattering of the light wave into two Bragg diffraction maxima of the 1st and 1st orders by appropriate selection of the frequency of the acoustic wave and the geometry of the acousto-optical interaction;

d) independent registration of images formed at these diffraction maxima using two matrix photodetectors that convert optical images into television-type electrical signals;

d) joint processing of the output signals of the photodetectors in the electronic unit, as a result of which two electrical signals are generated that carry separate information about the amplitude and phase structure of the analyzed image;

f) forming from these signals visible images of the amplitude and phase structure on the monitor screen.

In addition, in the method according to the first aspect of the invention, the processing of photodetector signals includes adding and subtracting these signals, as well as dividing the difference signal by the total.

According to a second aspect of the invention, there is provided an optical wavefront registration system, including:

a) an acousto-optic cell made of a special-section optical-anisotropic crystal, which provides the Bragg regime of acousto-optical diffraction with scattering of light radiation simultaneously into two diffraction maxima of the 1st and 1st orders;

b) a high-frequency electric generator that serves to excite a monochromatic acoustic wave in an acousto-optic cell and allows the amplitude and frequency of the acoustic wave to be tuned;

c) a source of coherent optical radiation to illuminate the object under study;

d) a lens forming an amplitude-phase image in the central plane of an acousto-optical cell;

e) an optical unit consisting of one or several lenses that transfers two images formed at diffraction maxima of the 1st and 1st orders to the photodetection plane;

f) two matrix photodetectors simultaneously registering two images in the + 1st and -1th diffraction orders and generating two television-type electrical signals;

g) an electronic signal processing unit, providing joint processing of photodetector signals, as a result of which two electrical signals are generated that carry separate information about the amplitude and phase structure of the analyzed light field;

h) a video block electrically connected to the electronic signal processing unit, which forms visible images of the amplitude and phase structure of the studied light field.

In addition, in the optical wavefront registration system according to the second aspect of the invention, the electronic signal processing unit includes:

a) the adder-subtractor, which converts the signals of the photodetectors into differential and total signals;

b) a divider, electrically connected with the adder-subtractor, which generates, by dividing the total signal by a difference signal, a signal that carries information only about the phase structure of the studied light field.

In the inventive optical wavefront registration system, the optical anisotropic crystal used to make the acousto-optic cell is a uniaxial crystal, while the uniaxial acousto-optic cell is a paratellurite (TeO ₂ ) crystal.

).In addition, paratellurite is cut out so that the plane of acousto-optical interaction coincides with the crystallographic plane (

)

] относительно кристаллографических осей кристалла парателлурита.Moreover, in the claimed registration system of the optical wavefront, the optical wavefront excited in the acousto-optical cell is a slow shear acoustic mode polarized in the direction [

] relative to the crystallographic axes of the paratellurite crystal.

In addition, in the indicated claimed system, two matrix photodetectors are television cameras or CCD arrays, and the video unit includes two monitors or one monitor on which two images are independently formed, reflecting the spatial distribution of amplitude and phase in the analyzed light field.

The essence of the claimed method and the operation of the proposed optical wavefront registration system are based on the properties of light diffraction by a phase diffraction grating and on the subsequent processing of images obtained in two diffracted beams. An effective implementation of the method is possible due to the found specific properties of the diffraction of optical radiation by a bulk phase diffraction grating induced in an optically anisotropic medium.

It is proposed to use an acousto-optical lattice induced by an acoustic wave in a birefringent crystal as a bulk phase grating. The acousto-optic interaction in such an acousto-optic cell is realized in the form of Bragg diffraction, which is ensured by a sufficiently large width of the acoustic beam and a high frequency of ultrasound. It is proposed to use a special geometry of the Bragg interaction of light with ultrasound in the crystal, which allows one to observe two diffracted optical beams carrying information about the amplitude and phase of the original image. In the subsequent joint processing of the detected optical signals, it is possible to obtain information about the amplitude and phase of the original optical image.

List of drawings

Figure 1 - the conversion of the phase modulation of the light wave to the modulation of the intensity when Bragg diffraction of light.

(a) the usual geometry of Bragg light scattering;

(b) - Bragg scattering geometry simultaneously at two lateral maxima.

Figure 2 is a vector diagram of the Bragg acousto-optic interaction.

(a) the usual geometry of Bragg light scattering;

(b) - Bragg scattering geometry simultaneously at two lateral maxima.

Figure 3 is a block diagram of a registration system for an optical wavefront.

Description of preferred embodiments of the invention

The proposed method for recording an optical wavefront and a system for its implementation allow simultaneously registering the amplitude and phase structure of a spatially coherent optical field. The claimed method is based on the angular selectivity of the Bragg acousto-optic interaction, i.e. on the dependence of acousto-optic diffraction efficiency on the angle of incidence of a light beam on a cell (V.I. Balakshy, V.N. Parygin, L.E. Chirkov. "Physical fundamentals of acousto-optics". M., Radio and communications, 1985).

(здесь для упрощения предлагается одномерный фазовый объект), направление волновой нормали меняется от точки к точке вдоль волнового фронта по закону

, где

- длина волны света,

- фазовый градиент. При прохождении такой волны через акустооптическую ячейку разные участки волны, вследствие различия в углах падения

, дифрагируют с разной эффективностью. В результате дифрагированная волна оказывается промодулированной по интенсивности пропорционально локальным значениям фазового градиента. Таким образом, можно сказать, что акустооптическая ячейка работает как фазовый дискриминатор, обеспечивающий преобразование фазово-модулированной световой волны в волну, промодулированную по интенсивности.In a phase-modulated light wave, which can be written as

(here, for simplicity, a one-dimensional phase object is proposed), the direction of the wave normal changes from point to point along the wave front according to the law

where

is the wavelength of light,

- phase gradient. When such a wave passes through an acousto-optic cell, different sections of the wave, due to differences in the angles of incidence

diffract with different efficiencies. As a result, the diffracted wave is modulated in intensity in proportion to the local values of the phase gradient. Thus, we can say that the acousto-optical cell acts as a phase discriminator, which provides the conversion of a phase-modulated light wave into a wave that is modulated in intensity.

от угла падения

. Эффективность дифракции достигает максимума при падении света под углом Брэгга

. Кривой 2 показана форма градиента фазы

в падающей волне, а кривой 3 - распределение интенсивности света в дифрагированном пучке. Конкретный закон преобразования фазы в интенсивность зависит от выбора рабочей точки

на кривой 1. Из фиг.1а ясно, что максимальная чувствительность системы к фазовому градиенту достигается, когда рабочая точка выбирается на середине склона угловой характеристики. Переход с одного склона на другой приводит к инверсии контраста в визуализированном изображении. Меняя частоту и амплитуду акустической волны, можно оперативно и в широком диапазоне варьировать положение рабочей точки и форму угловой характеристики, обеспечивая тем самым адаптацию системы к конкретной решаемой задаче.Figa illustrates the visualization process of an optical wavefront. Here curve 1 shows the angular characteristic of the Bragg diffraction - the dependence of the intensity of diffracted light

from the angle of incidence

. Diffraction efficiency reaches its maximum when light is incident at a Bragg angle

. Curve 2 shows the shape of the phase gradient

in the incident wave, and curve 3 is the distribution of light intensity in the diffracted beam. The specific law of phase to intensity conversion depends on the choice of the operating point

on curve 1. From figa it is clear that the maximum sensitivity of the system to the phase gradient is achieved when the operating point is selected in the middle of the slope of the angular characteristic. The transition from one slope to another leads to inversion of contrast in the rendered image. By changing the frequency and amplitude of the acoustic wave, it is possible to quickly and widely vary the position of the operating point and the shape of the angular characteristic, thereby ensuring the adaptation of the system to the specific task being solved.

, то эта модуляция также будет перенесена в дифрагированный пучок. Для разделения амплитудной и фазовой информации предлагается использовать особый вариант брэгговской дифракции, реализуемый только в оптически-анизотропной среде - в двулучепреломляющем кристалле. Соответствующим выбором среза кристалла, а также направления взаимодействующих световых и акустических волн и частоты ультразвука можно обеспечить брэгговский режим дифракции с рассеянием света одновременно в два дифракционных максимума +1-го и -1-го порядков. Диаграмма волновых векторов для такого варианта брэгговского взаимодействия показана на фиг.2b, а на фиг.2а для сравнения показан обычный вариант брэгговского взаимодействия. Здесь

и

- волновые векторы соответственно падающего и дифрагированного света, K - волновой вектор звука. Диаграмма фиг.2б построена для случая, когда плоскость взаимодействия перпендикулярна оптической оси одноосного кристалла. Свет падает перпендикулярно акустическому пучку и рассеивается в два симметрично расположенных дифракционных максимума +1-го и -1-го порядков. Частота ультразвука при этом определяется выражением

, где V - скорость звука,

и

- показатели преломления для падающего и дифрагированного света. Угловые характеристики обоих дифракционных максимумов

и

в этом случае совпадают. При увеличении или уменьшении частоты ультразвука характеристики

и

смещаются друг относительно друга (фиг.1b). Если рабочую точку

выбрать так, как показано на фиг., то в обоих максимумах будет происходить визуализация оптического волнового фронта. Однако распределение интенсивности света в них будет иметь инверсный характер. Можно получить, что оптимальные акустические частоты определяются формулой

, где l - ширина акустического пучка в плоскости акустооптического взаимодействия. Распределение интенсивности света в дифракционных порядках имеет вид:However, if amplitude modulation is present in the analyzed light wave

, then this modulation will also be transferred to the diffracted beam. To separate the amplitude and phase information, it is proposed to use a special version of the Bragg diffraction, realized only in an optically anisotropic medium — in a birefringent crystal. The appropriate choice of the crystal slice, as well as the direction of the interacting light and acoustic waves and the ultrasound frequency, can provide the Bragg diffraction mode with light scattering simultaneously into two diffraction maxima of the 1st and 1st orders of magnitude. A wave vector diagram for such an embodiment of the Bragg interaction is shown in FIG. 2b, and FIG. 2a shows a conventional embodiment of the Bragg interaction for comparison. Here

and

are the wave vectors of incident and diffracted light, respectively, and K is the wave vector of sound. The diagram of FIG. 2b is constructed for the case when the interaction plane is perpendicular to the optical axis of the uniaxial crystal. Light falls perpendicular to the acoustic beam and is scattered into two symmetrically located diffraction maxima of the 1st and 1st orders. The frequency of ultrasound is determined by the expression

where V is the speed of sound,

and

- refractive indices for incident and diffracted light. Angular characteristics of both diffraction maxima

and

in this case match. With increasing or decreasing ultrasound frequency characteristics

and

are displaced relative to each other (fig.1b). If the operating point

choose as shown in Fig., then at both maxima the visualization of the optical wavefront will occur. However, the distribution of light intensity in them will have an inverse character. It can be obtained that the optimal acoustic frequencies are determined by the formula

where l is the width of the acoustic beam in the plane of the acousto-optic interaction. The distribution of light intensity in diffraction orders has the form:

, имеют разные знаки в этих максимумах. Поэтому суммирование и вычитание сигналов матричных фотоприемников, регистрирующих изображения в +1-м и -1-м дифракционных порядках, позволяют получить два электрических сигнала, один из которых содержит информацию только о распределении амплитуды (

), а другой - информацию о распределении амплитуды и фазы в анализируемом световом поле (

). Поделив второй сигнал на первый, можно получить фазовую информацию в чистом виде.where A is the Raman-Nath parameter, which is proportional to the amplitude of the acoustic wave. As can be seen from this relation, the amplitude modulation of the initial light wave u ₀ (x) is transferred equally to both diffraction maxima, while the terms determined by the phase modulation

have different signs at these highs. Therefore, the summation and subtraction of the signals of matrix photodetectors registering images in the + 1st and -1th diffraction orders allow us to obtain two electrical signals, one of which contains information only about the distribution of the amplitude (

), and the other, information on the distribution of the amplitude and phase in the analyzed light field (

) By dividing the second signal into the first, you can get the phase information in pure form.

One possible implementation of the described method for recording an optical wavefront is shown in FIG. 3, in which 1 denotes a coherent radiation source (laser); position 2 - the investigated object; position 3 - the lens; position 4 — acousto-optic cell; position 5 - the generator of HF harmonic oscillations; position 6 - the optical unit (lens or lenses); position 7 is the plane of registration of optical images; 8, 9 — photodetector arrays (CCD arrays); position 10 - electronic signal processing unit; position 11 - adder-subtractor; position 12 is a divider; at 13, 14 - monitors and at 15 - video block.

The coherent radiation source 1 illuminates the object under study 2. The optical radiation generated by the object under study, i.e. Passing through the object or reflected by it, then passes through the lens 3, which creates an image of the object in the acousto-optical cell 4. In the cell, optical radiation is diffracted simultaneously in the + 1st and -1st diffraction orders. Cell 4 is controlled by a harmonic electric signal generator 5. Images formed in the + 1st and -1st orders are transferred by the optical unit 6 to the plane 7 for recording optical images. In this plane are two matrix photodetectors 8 and 9, which convert the optical images corresponding to the + 1st and -1th diffraction orders into electrical signals U ₁ and U ₂ . As photodetectors 8 and 9, television cameras or CCD arrays can be used. The electrical signals U ₁ and U ₂ are fed to an electronic signal processing unit 10, which can be a standard computer or a specialized electronic device consisting of an adder-subtractor 11 and a divider 12. The signal processing unit 10 sums and subtracts the electric signals U ₁ and U ₂ , as well as dividing the difference signal U ^(-) = U ₁ -U ₂ by the total signal U ⁽⁺⁾ = U ₁ + U ₂ . The total signal U ⁽⁺⁾ enters the monitor 13 and forms an image corresponding to the spatial distribution of the amplitude of the investigated optical field. At the same time, the signal U ^(-) / U ⁽⁺⁾ enters the second monitor 14 and forms an image corresponding to the spatial distribution of the phase of the studied optical field. Two images corresponding to the distribution of the amplitude and phase inhomogeneities of the studied object can also be displayed on one monitor.

It should be noted that the spatial distribution of the amplitude in the light wave can be easily detected and measured using conventional TV systems. However, the simultaneous registration of the amplitude and phase structure of the light field gives much more information about the object under study.

). В данной плоскости акустооптического взаимодействия реализуется наибольшая эффективность дифракции при наименьшей мощности ультразвука. При этом в качестве волны ультразвука, индуцирующей в кристалле объемную фазовую решетку, следует использовать медленную сдвиговую акустическую моду. Необходимая геометрия акустооптического взаимодействия, обеспечивающая одновременное существование двух порядков брэгговской дифракции, предусматривает следующие направления для взаимодействующих пучков света и звука. Волновой вектор K акустической волны должен быть направлен под углом 86° к оптической оси кристалла парателлурита, а волновой вектор k_i падающей на кристалл световой волны должен быть направлен внутри кристалла под углом 4,55° к оптической оси кристалла (для света с длиной волны

мкм). Для возбуждения акустической волны предпочтительно использовать пъезоэлектрический преобразователь на основе пластины, вырезанной из монокристалла ниобата лития (LiNbO₃) перпендикулярно его кристаллографической оси X. Данный срез кристалла ниобата лития обеспечивает сдвиговые колебания пъезоэлектрической пластины, в результате чего в акустооптической ячейке возбуждается нужная акустическая мода. Для рассматриваемого варианта частота

равна 77,5 МГц, а рабочие частоты f составляют 76,6 МГц и 78,4 МГц при длине акустооптического взаимодействия l=1 см.As the radiation source 1 (figure 3), it is preferable to use a laser. The acousto-optic cell 4 should be made on the basis of a birefringent crystal, in which the so-called anisotropic diffraction of light is realized with rotation of the plane of polarization. Currently, the most suitable material for this in the visible range of light is a uniaxial paratellurite single crystal (TeO ₂ ), which provides high acousto-optic diffraction efficiency at low ultrasound power. An acousto-optic cell on a paratellurite crystal should be made in such a way that the wave vector k _{i of the} axial component of the optical radiation entering the acousto-optic cell from the object under study and the wave vector of the acoustic wave K lie in the crystallographic plane of paratellurite (

) In this plane of acousto-optic interaction, the highest diffraction efficiency is realized at the lowest ultrasound power. In this case, a slow shear acoustic mode should be used as an ultrasound wave inducing a volume phase grating in the crystal. The necessary geometry of the acousto-optic interaction, which ensures the simultaneous existence of two Bragg diffraction orders, provides the following directions for interacting beams of light and sound. The wave vector K of the acoustic wave should be directed at an angle of 86 ° to the optical axis of the paratellurite crystal, and the wave vector k _{i of the} light wave incident on the crystal should be directed inside the crystal at an angle of 4.55 ° to the optical axis of the crystal (for light with a wavelength

μm). To excite an acoustic wave, it is preferable to use a piezoelectric transducer based on a plate cut from a lithium niobate single crystal (LiNbO ₃ ) perpendicular to its crystallographic axis X. This section of a lithium niobate crystal provides shear vibrations of the piezoelectric plate, as a result of which the desired acoustic mode is excited in the acousto-optical cell. For the considered option, the frequency

equal to 77.5 MHz, and the operating frequencies f are 76.6 MHz and 78.4 MHz with an acousto-optic interaction length l = 1 cm.

It should be emphasized that the described system allows not the only option for its implementation; various changes in design, parameters and details are possible, which are not deviations from the essence and scope of the present invention, as reflected in the attached claims.

Industrial applicability

The proposed method and system of the amplitude and phase structure of optical images can be reproduced on the basis of elements mastered and commercially available by industry. In particular, acousto-optical deflectors or tunable paratellurite-based acousto-optical filters that have been developed by industry and have shown high reliability, good optical characteristics, and also characterized by low power consumption can be used as an acousto-optical cell. As the video block 10 (Fig.3) can be used a standard personal computer or a specially designed portable electronic computing device.

Claims (10)

1. The method of recording an optical wavefront, which consists in
a) excitation of a monochromatic acoustic wave in an acousto-optic cell made of an optically anisotropic crystal cut out in such a way as to ensure the Bragg regime of acousto-optic diffraction with the scattering of light radiation simultaneously into two diffraction maxima of the 1st and 1st orders of magnitude;
b) transmitting a spatially modulated coherent light wave carrying the analyzed image through an acousto-optical cell;
c) ensuring simultaneous scattering of the light wave into two Bragg diffraction maxima of the 1st and 1st orders by appropriate selection of the frequency of the acoustic wave and the geometry of the acousto-optical interaction;
d) independent registration of images formed at these diffraction maxima using two matrix photodetectors that convert optical images into television-type electrical signals;
d) joint processing of the output signals of the photodetectors in the electronic unit, as a result of which two electrical signals are formed that carry separate information about the amplitude and phase structure of the analyzed image;
f) forming from these signals visible images of the amplitude and phase structure on the monitor screen. 2. The method of recording the optical wavefront according to claim 1, in which the processing of the signals of the photodetectors includes the addition and subtraction of these signals, as well as the division of the difference signal by the total signal. 3. The registration system of the optical wavefront, containing
a) an acousto-optic cell made of an optically anisotropic crystal cut out in such a way as to ensure the Bragg regime of acousto-optic diffraction with scattering of light radiation simultaneously into two diffraction maxima of the 1st and 1st orders;
b) a high-frequency electric generator that serves to excite a monochromatic acoustic wave in an acousto-optic cell and allows the amplitude and frequency of the acoustic wave to be tuned;
c) a source of coherent optical radiation to illuminate the object under study;
d) a lens forming an amplitude-phase image in the central plane of an acousto-optical cell;
e) an optical unit consisting of one or several lenses that transfers two images formed at diffraction maxima of the 1st and 1st orders to the photodetection plane;
f) two matrix photodetectors simultaneously registering two images in the + 1st and -1th diffraction orders and generating two television-type electrical signals;
g) an electronic signal processing unit, providing joint processing of photodetector signals, as a result of which two electrical signals are generated that carry separate information about the amplitude and phase structure of the analyzed light field;
h) a video block electrically connected to the electronic signal processing unit, which forms visible images of the amplitude and phase structure of the studied light field. 4. The registration system of the optical wavefront according to claim 3, in which the electronic signal processing unit includes
a) the adder-subtractor, which converts the signals of the photodetectors into differential and total signals;
b) a divider electrically connected to the adder-subtractor, which generates, by dividing the total signal by a difference signal, a signal that carries information only about the phase structure of the studied light field. 5. The registration system of the optical wavefront according to claim 3, in which the optically anisotropic crystal used to fabricate an acousto-optic cell is a uniaxial crystal. 6. The registration system of the optical wavefront according to claim 5, in which the uniaxial crystal of the acousto-optic cell is a paratellurite crystal (TeO ₂ ). 7. The registration system of the optical wavefront according to claim 6, in which the paratellurite crystal is cut so that the plane of acousto-optical interaction coincides with the crystallographic plane (

) 8. The registration system of the optical wave front according to claim 7, in which the acoustic wave excited in the acousto-optical cell is a shear slow acoustic mode polarized in the direction [

] relative to the crystallographic axes of the paratellurite crystal. 9. The registration system of the optical wavefront according to claim 3, in which two matrix photodetectors are television cameras or CCD arrays. 10. The registration system of the optical wavefront according to claim 3, in which the video unit includes two monitors or one monitor on which two images are independently formed, reflecting the spatial distribution of the amplitude and phase in the analyzed light field.

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