RU2101744C1 - Color visualizer of fields of optical density - Google Patents

Abstract

FIELD: color visualization of gradient of two-dimensional distribution of refractive index in gas and condensed media in real time. SUBSTANCE: color visualizer of field of optical density has forming objective with dichromatic slit source in front Fourier plane Fourier-coupled to forming receiving objective in which rear Fourier plane biquad Faucault-Gilbert filter matched with slit source is positioned, videocamera with image processing system and videoregister arranged in series. It is supplemented with second dichromatic slit source orthogonal to first one and optically coupled to biquad Faucault-Gilbert filter, commutator of dichromatic slit sources and synchronizer which output is connected to controlling inputs of commutator of dichromatic slit sources, videoregister and image processing system. EFFECT: enhanced accuracy and stability of color visualizer. 1 dwg

Description

 The invention is intended for real-time color visualization of optical density fields and can be used in scientific research and in industrial technologies related to the need for contactless monitoring of the structure of gas and condensed media.

 Known devices for this purpose. In [1], a system is described, which is a standard black-and-white shadow tube in which pseudo-coloring of shadowgrams is carried out by means of electronic computer technology. The disadvantage is the limited performance associated with the sequential processing mode of the data array corresponding to the image of the shadow diagrams and the loss of information about the sign of the gradient of the optical density field.

 Another device described in [2] is a device that contains a slit white light source and a Foucault bichromatic knife coupled to it. The disadvantage of this device is its low sensitivity due to technological problems in the formation of the visualizing edge and narrow-band color filters of the Foucault bichromatic knife.

 The closest analogue of the invention is the color visualizer described in [3]. It is a shadow device in which a dichromatic narrow-band gap source is optically coupled to a Foucault-Hilbert filter and the output signal is recorded by a color video camera. This configuration successfully solves the problem of real-time color visualization of the projection of the gradient of the optical density field in the direction perpendicular to the gap. In this case, chromatic coding of the sign of the visualized projection of the gradient of the refractive index is performed. The main disadvantage of this device is the impossibility of obtaining information about the two-dimensional spatial distribution.

 The basis of the invention is the task of creating a visualizer that allows you to visualize the gradient of a two-dimensional optical density field. The problem is solved in that in a color visualizer of optical density fields containing a sequentially located forming lens with a bichromatic slit source in the front Fourier plane, Fourier-conjugate to the forming receiving lens, in the rear Fourier plane of which is placed a Foucault-Hilbert biquadrant filter, consistent with a slit source, a video camera with an image processing system and a video recorder connected to it, according to the invention, additionally introduced: a second bichromatic A slit source, orthogonal to the first and optically coupled to a Foucault-Hilbert biquadrant filter, a switch for bichromatic slot sources and a synchronizer, the output of which is connected to the control inputs of the switch for bichromatic slot sources, a video recorder, and an image processing system.

 The drawing shows a diagram of the proposed visualizer.

 The visualizer contains a bichromatic cross-shaped source, in which light emitters 1 and 2, matching lenses 3 and 4, optical fibers 5 and 6 are sequentially placed, the output channels of which form gap sources 7 and 8 with orthogonally oriented in space with bichromatic filters, the recombination element 9 in the form for example, a cube with a recombining diagonal plane, a lens 10 projecting images of the slot sources 7 and 8 onto a cross-shaped slot mask 11 located in the front Fourier plane of the forming about the lens 12. The receiving lens 13 is Fourier-conjugated to the forming lens 12. In the rear Fourier plane of the receiving lens 13 is mounted a Foucault-Hilbert filter 14, optically coupled to a bichromatic cross-shaped source. A color video camera 15 is installed sequentially behind the Foucault-Hilbert bi-quadrant filter. The output of the synchronizer 16 is connected to the control inputs of the light emitter switch, the image processing system 18 and the video recorder 19, the signal inputs of which are connected to the output of the video camera.

 In this device, a light source is a superposition of two orthogonally oriented and sequentially switched slot-type sources. One of them is formed by a light emitter 1, a matching lens 3, a light guide 5 having a light configuration of the output end with a bichromatic filter 7, a recombination element 9, a lens 10 and a corresponding slot mask 11. Another slot source is formed by elements 2, 4, 6, 8, 10 and a second slit component in a cross mask. The color components of each of the bichromatic sources are selected in the separated spectral regions of the radiation (for example, in red and green).

Здесь λ₁ и λ₂ длины волн излучения, 2b длина щелевого источника, 2а его ширина, a/b <<1. Оптические неоднородности, присутствующие в исследуемой среде, вызывают фазовую модуляцию волнового фронта световой волны, описываемой фурье-трансформантой функции бихроматического щелевого источника. Приемный объектив 13 выполняет обратное фурье-преобразование оптического сигнала, представляющего произведение фурье-образа функции источника и функции, описывающей фазовые свойства исследуемой среды. Поэтому в пространственно-частотной плоскости объектива 13 оптическое поле определяется сверткой функции щелевого источника и фурье-образа фазовой функции среды. В фурье-плоскости объектива 13 помещен фильтр Фуко-Гильберта, выполняющий преобразование

частота. Поскольку световой источник сформирован в виде бихроматической щели, оптически сопряженной с фильтром, поле непосредственно за фильтром является суперпозицией двух хроматически окрашенных световых сигналов, возникающих из-за преломления световой волны на фазовых неоднородностях в среде. Для источника S₁, ориентированного вдоль оси y₀, сопряженной с осью пространственных частот ω_y, световой сигнал на длине волны λ₁ соответствует пространственным частотам ω_x, а сигнал на длине волны λ₂ - отрицательным пространственным частотам (-ω_x). Соответственно для бихроматического щелевого источника S₂, ориентированного по оси x₀, оптически сопряженной с осью пространственных частот ω_x, световой сигнал на длине волны λ₁ соответствует положительным пространственным частотам (-ω_y), а сигнал на длине волны λ₂ отрицательным пространственным частотам ω_y. Оптическая система видеокамеры выполняет обратное фурье-преобразование сигнала, сформированного на выходе фильтра Фуко-Гильберта. Гильберт-преобразование в фурье-плоскости сводится к умножению спектра исследуемого сигнала на функцию [4]
H(ω) = jsgn(ω) (3).The visualizer operates as follows. The lens 12 performs the Fourier transform of the functions S ₁ and S ₂ describing the bichromatic gap sources:

Here, λ ₁ and λ _{2 are} the radiation wavelengths, 2b is the length of the gap source, 2a is its width, a / b << 1. The optical inhomogeneities present in the medium under study cause phase modulation of the wavefront of the light wave described by the Fourier transform of the function of the bichromatic gap source. The receiving lens 13 performs the inverse Fourier transform of the optical signal representing the product of the Fourier image of the source function and the function that describes the phase properties of the medium under study. Therefore, in the spatial frequency plane of the lens 13, the optical field is determined by the convolution of the function of the gap source and the Fourier image of the phase function of the medium. In the Fourier plane of the lens 13 is placed the Foucault-Hilbert filter that performs the conversion

frequency. Since the light source is formed in the form of a bichromatic gap optically coupled to the filter, the field immediately after the filter is a superposition of two chromatically colored light signals arising from the refraction of the light wave by phase inhomogeneities in the medium. For the source S ₁ oriented along the y ₀ axis conjugated with the spatial frequency axis ω _y , the light signal at wavelength λ ₁ corresponds to spatial frequencies ω _x , and the signal at wavelength λ ₂ corresponds to negative spatial frequencies (-ω _x ). Accordingly, for a bichromatic slot source S ₂ oriented along the x ₀ axis optically conjugated to the spatial frequency axis ω _x , the light signal at wavelength λ ₁ corresponds to positive spatial frequencies (-ω _y ), and the signal at wavelength λ _{2 to} negative spatial frequencies ω _y . The optical system of the video camera performs the inverse Fourier transform of the signal generated at the output of the Foucault-Hilbert filter. The Hilbert transform in the Fourier plane reduces to multiplying the spectrum of the signal under study by a function [4]
H (ω) = jsgn (ω) (3).

Аналогично для ортогонального бихроматического щелевого источника S₂ получаем выходной сигнал:

где A₁ и B₁ квазипостоянные величины, характеризующие аддитивный и мультипликативный фон, несущественный для результатов анализа выходного сигнала;
i индекс, соответствующий длине волны λ_i в излучении бихроматического источника;
φ функция, описывающая распределение слабых фазовых неоднородностей в исследуемой среде;
H_x(φ) и H_y(φ) соответственно x и y компоненты гильберт-преобразования поля оптической плотности φ;
(-1)¹ sgn(H_x,y) знаковая функция гильберт-трансформанты S_1F;
S_2F фурье-образы функций источников S₁ и S₂.Therefore, the output signal after the inverse transformation contains a Hilbert transform of the phase function φ characterizing the distribution of optical density in the medium under study [3] For the output signal corresponding to the bichromatic gap source S ₁ , we have:

Similarly, for the orthogonal bichromatic slit source S ₂ we get the output signal:

where A ₁ and B ₁ quasi-constant values characterizing the additive and multiplicative background, insignificant for the results of the analysis of the output signal;
i is the index corresponding to the wavelength λ _i in the radiation of the bichromatic source;
φ is a function describing the distribution of weak phase inhomogeneities in the medium under study;
H _x (φ) and H _y (φ), respectively, x and y are the components of the Hilbert transform of the optical density field φ;
(-1) ¹ sgn (H _{x, y} ) sign function of the Hilbert transform S _1F ;
S _2F Fourier transforms of source functions S ₁ and S ₂ .

 From (4) and (5) it is seen that the intensity of the output signal is a superposition of the Hilbert transform of the optical density of the studied medium and background. In this case, the color coding of the sign of the Hilbert image is carried out.

 The operation of the Hilbert transform, as is known [4], has some similarities with spatial differentiation. Therefore, the hilbert image of the output optical signal reflects the gradient properties of the spatial distribution of the refractive index in the medium under study. Optical inhomogeneities are visualized, the gradient projection of which is directed orthogonally to the larger side of the slit of the slot source.

, где f_к частота коммутирования каналов. Это соотношение удовлетворяет известной теореме отсчетов Котельникова, согласно которой частота регулярной выборки должна вдвое превышать наивысшую частоту в спектре исследуемого процесса. Например, при частоте коммутации f 40 Гц осуществляется цветная визуализация двумерного поля оптической плотности в полосе частот 10 гЦ.The switching of gap sources S ₁ and S _{2 is} synchronized with the switching of channels of the image processing system 18 and the video recording device 19. The system allows you to visualize the gradient of the two-dimensional distribution of the optical density field in the medium under study. In this case, the dynamics of changes in two-dimensional density fields in the spectral band is recorded, the upper boundary of which

where f _{to the} frequency of switching channels. This relation satisfies the well-known Kotelnikov counting theorem, according to which the frequency of a regular sample should be twice as high as the highest frequency in the spectrum of the process under study. For example, at a switching frequency of f 40 Hz, color visualization of a two-dimensional field of optical density in the frequency band of 10 Hz is carried out.

 Thus, the proposed device allows real-time color visualization of the gradient of two-dimensional fields of optical density with chromatic coding of the sign of the gradient.

 The proposed device is implemented in the form of a laboratory operating layout.

Sources of information
1. Arbuzov V.A., Poleshchuk A.G. Fedorov V.A. Laser color diagnostics of optical media // Abstracts dokl. All-Union Conference "Computer-based Automation of Scientific Research". Novosibirsk, September 14-18, 1974.

 2. Vasiliev L.A. Shadow methods. M. Science. 1986. 400 c.

 3. V.A. Arbuzov, Yu.N. Dubnistchev. Real-time colored visualization of phase flows by the schliren method // Optics and Laser Technology. 1991. V.23, N 2, p. 118-120.

 4. Forty. Hilbert optics. M. Science. 1981.-S. 160.

Claims (1)

 A color visualizer of the optical density fields of gas and condensed matter containing a sequentially located forming lens with a bichromatic target source in the front Fourier plane, a Fourier conjugate to the forming receiving lens, in the rear Fourier plane of which is placed a Foucault-Hilbert biquad filter, matched with the slot source , a video camera with an image processing system and a video device connected to it, characterized in that the second is further introduced bichromatically the first slit source, orthogonal to the first and optically conjugated Foucault-Hilbert biquadratic filter, a switch for bichromatic slot sources and a synchronizer, the output of which is connected to the control inputs of the switch for bichromatic slot sources, a video recorder and an image processing system.