CN104048944A - System and method for differential interferometric imaging - Google Patents
System and method for differential interferometric imaging Download PDFInfo
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- CN104048944A CN104048944A CN201410096015.2A CN201410096015A CN104048944A CN 104048944 A CN104048944 A CN 104048944A CN 201410096015 A CN201410096015 A CN 201410096015A CN 104048944 A CN104048944 A CN 104048944A
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Abstract
The invention discloses a system and a method for differential interferometric imaging. The system comprises a light source for outputting an optical signal, a first focusing lens, a slit aperture, a first collimating lens, a flow field observation zone, a second focusing lens, a first Wollaston prism, an analyzer, a second collimating lens, a digital microarray reflector, a convergent lens, a single-point photoelectric detector and a compression algorithm module electrically connected to the single-point photoelectric detector, wherein the first focusing lens, the slit aperture, the first collimating lens, the flow field observation zone, the second focusing lens, the first Wollaston prism, the analyzer, the second collimating lens, the digital microarray reflector, the convergent lens and the single-point photoelectric detector are orderly connected along a light source output optical-signal path. Light deflects by a nonuniform-density air flow field, then is focused by the lenses and then is subjected to differential interference by the Wollaston prism and the analyzer, then a differential interference image is reconstructed by a compressed sensing method, flow field layered density gradient is calculated according to parameters such as image interference fringe intervals, and the novel differential interferometric method is realized based on compressed sensing.
Description
Technical field
The present invention relates to schlieren measure imaging field, relate in particular to a kind of differential interferometry based on compressed sensing and measure imaging system and method.
Background technology
In last century, the optical meanss such as shade, schlieren and interference are being used widely aspect the measurement of current density variation.Along with the progress of the Researches on Fluids work such as atmosphere, ocean, stratified flow research becomes important subject gradually.1967, Mowbray measures shade and stration technique for the Density Distribution of stratified flow interface, 1983, McEwan is the measurement for continuously stratified fluid bulk properties by colour schlieren method, 1977, Debler and Vest measure holographic interference technique for the velocity field of stratified fluid, nineteen eighty-two, Laws etc. adopt six mirror interferometers to measure fluid layering feature measurement.Along with further developing of fluid measurement technology, U.S. NASA, European ESA and Japanese JAXA are in the Lewis structural change that tower, Japanese Microgravity Falling well, freely falling body etc. adopt the methods such as schlieren method, differential interferometry, shadowing method, rainbow schlieren to measure fluid in microgravity environment in short-term that falls.The research work that China recent years has also been carried out schlieren method and measured flame structure, mechanics institute of the Chinese Academy of Sciences and scientist in Poland cooperation development correlative study, the normal interferometric method acquisition flow field density that adopts in wind tunnel test.Interferometric method is a kind of strict quantitative measurment technology, index distribution that can strict computational flow by flow field interferogram, and then by lattice Lars logical-Dell's constant formula can extrapolate flow field density and the gentle kinetic parameters of other fluid mechanics.Aspect shock tunnel and ballistic range test, the technology such as Mach interference, holographic interference and schlieren interference are applied, and have all utilized schlieren light path in these methods, and light path using this light path as object beam.Obtain test interferogram by these methods, and obtained the density quantitative values in flow field.
Differential interferometry, shadowing method, schlieren, rainbow schlieren measure technology are used widely in fluid fields such as burnings.Diagnostic techniques in microgravity combustion experiment, requires temperature, flow field, gas ingredients and concentration, solid particle composition and the concentration etc. that realize combustion process to carry out qualitative or quantitative measurment, and by data processing, combustion phenomena is analyzed.In the time that differential interferometry, shadowing method, schlieren, rainbow schlieren measure method acquired results are carried out to data processing, can obtain about fluid physics parameters such as symmetrical flow field, asymmetric flow field, supersonic flow field, gas mixing flow field, the astable flow field of bidimensional, three-dimensional flow field measurements by the analysis that light field is changed.In addition, can realize imaging and location to invisbile plane, its principle is mainly utilized in invisbile plane flight course, produce the violent disturbance of air-flow, the eddy current that formation scope is huge, the retention time is grown, by measuring the air trajectory of invisbile plane disturbance, measures invisbile plane indirectly.
Compressed sensing is to be proposed in 2004 by researchists such as E.J.Candes, J.Romberg, T.Tao and D.L.Donoho, as far back as last century, French mathematician Prony proposes sparse signal restoration methods, and this method is to estimate the non-zero magnitude of sparse trigonometric polynomial and corresponding frequency by separating eigenvalue problem; B.Logan proposes the sparse constraint method based on L1 Norm minimum the earliest.The compressive sensing theory developing is subsequently that L1 Norm minimum sparse constraint is combined with stochastic matrix, obtain the optimum of sparse signal reconstruction performance, the compressibility of compressed sensing based on signal, realizes the perception of high dimensional signal by lower dimensional space, low resolution, the irrelevant observation of owing Nyquist sampled data.Be widely used in the ambits such as information theory, image processing, geoscience, optics/microwave imaging, pattern-recognition, radio communication, atmospheric science, geoscience, physical astronomy, high-accuracy optical measurement.
Compressive sensing theory is that sampling and compression are carried out simultaneously, the priori of having utilized well natural sign to represent under certain sparse base, can realize the sub-sampling far below Nyquist/Shannon sampling limit, and can almost Perfect ground reconstruction signal information.It is applied is the most widely single pixel camera technology, it can use a point probe instead of planar array detector just can complete all detection missions, if this technology is applied in optics schlieren measure field, will reduce detection dimension, avoid optical noise and the electrical noise brought by planar array detector, and employing Digital Micromirror Device DMD, this is a passive optical component, can not bring any noise to signal, detector aspect also no longer needs prime amplifier, this external system can also be accomplished the high-speed sampling of 23kHz, this is that traditional planar array detector cannot be reached, the outer reconstruction algorithm of robust in addition, will cause how potential application.
Summary of the invention
The object of the invention is to compressive sensing theory to be applied to fluid schlieren measure field, thereby provide a kind of differential interferometry based on compressed sensing to measure imaging system and method.
To achieve these goals, the invention provides a kind of differential interferometry and measure imaging system, it comprises:
Light source, for output optical signal; And the first condenser lens, slit diaphragm, the first collimation lens, the second condenser lens, the first wollaston prism, analyzer, the second collimation lens, digital microarray catoptron, plus lens and the single-point photodetector that set gradually along described light source output optical signal path, flow observation region is between the first collimation lens and the second condenser lens; Compression algorithm module, it is connected with single-point photodetector electric signal, for reconstructed image, according to parameters such as the interference fringe spacing of image, calculates the density gradient of flow field layering.
Further, along described light source output optical signal path, between described slit diaphragm and described the first collimation lens, be provided with the 3rd condenser lens, the polarizer and the second wollaston prism.。
Further, also comprise mirror unit, it comprises the first catoptron and the second catoptron, and described the first catoptron is located between described the first collimation lens and described flow observation region, for the emergent light of the first collimation lens is reflected into into observation area, flow field; Described the second catoptron is located between described flow observation region and described the second condenser lens, for the emergent light in described flow observation region is reflexed to the second condenser lens.
Further, the catoptron in described mirror unit is broadband deielectric-coating catoptron, metal film catoptron, dielectric laser line reflection mirror or cold and hot catoptron.
Further, carving between angle and described the second condenser lens focal length of described the first wollaston prism meets interference condition.
Further, described light source is LASER Light Source or white light source.
Further, described LASER Light Source is pulsed laser light source or continuous laser source, and wavelength is at the visible-range of 400-800nm, and laser output wavelength is 405nm, 445nm, 473nm, 488nm, 515nm, 640nm or 660nm.
Further, described white light source is continuous spectrum light source, it is xenon source, Halogen lamp LED, deuterium lamp, Laser Driven white light source or the super continuum source based on ultrafast Fiber laser technology, the spectral range of described white light source is that the spectral range of 400nm-800nm or described white light source is that the spectral range of 170nm-2100nm or described white light source is 400nm-2400nm, and power bracket is 30mW-100W.
Further, described digital microarray catoptron adopts reflective and transmission-type LCD space light modulator.
Further, described single-point photodetector is visible ray photodetector or single-photon detector.
Further, described single-photon detector is avalanche photodide, solid-state photomultiplier or superconducting single-photon detector.
Further, between described digital microarray catoptron and described single-point photodetector, synchronize, the every upset of micro mirror array in described digital microarray catoptron once, described single-point photodetector adds up to survey all light intensity of arrival in interval in this flip-flop transition, realize photoelectric signal collection conversion, then by extremely described compression algorithm module of electric signal transmission.
In order to address the above problem, the present invention also provides a kind of differential interferometry to measure formation method, and it comprises:
Step 1, light source output optical signal, after the first condenser lens focuses on, by the spuious bias light of slit diaphragm filtering;
Step 2, after the first collimation lens beam-expanding collimation, incides flow observation region;
Step 3 after the second condenser lens converges, forms interference fringe by the light beam of described flow observation region outgoing after the first wollaston prism and analyzer;
Step 4 incides digital microarray catoptron after place collimation lens collimation, and light field is carried out to Stochastic Modulation;
Step 5 incides single-point photodetector after plus lens converges, and the electric signal being converted to is delivered to compression algorithm module by described single-point photodetector;
Step 6, through compression algorithm Restructuring Module image, according to the interference fringe spacing parameter of image, can calculate the density gradient of flow field layering, and the differential interferometry of realizing based on compressed sensing is measured.
Further, in described step 2, before the first collimation lens beam-expanding collimation, first after the 3rd condenser lens converges again by the light of slit diaphragm, then rise partially through the polarizer, then after the second wollaston prism light splitting.
Further, in described step 2, the light beam after the first collimation lens beam-expanding collimation incides flow observation region after the first catoptron reflection.
Further, in implementation step 3, reflex to described the second condenser lens by the light beam of described flow observation region outgoing through the second catoptron and converge.
The present invention combines compressive sensing theory with differential interferometry measurement, the sparse differential interferometry measuring method of creationary proposition, there is the feature of high flux, high s/n ratio, fast and flexible, being suitable for conventional light intensity, the low light level, faint light, the ultra micro low light level and single photon differential interferometry metering system, is a kind of sparse differential interferometry measuring method of great dynamic range.
Adopt compressed sensing to combine with differential interferometry measurement and can realize the measurement of high flux differential interferometry, classical differential interferometry measuring technique signal to noise ratio (S/N ratio) in the aspect measuring processes such as flame, wind-tunnel, air-flow is lower, especially in high speed, hypervelocity flow field measurement, environmental background disturbs larger, utilize this high flux feature, can improve the signal to noise ratio (S/N ratio) of schlieren measure.
By the inventive method, adopt single-photon detector and sparsely owe the combination of sampling, realize quantum differential interferometry measuring method, can realize the physical features in remote flow field is obtained.
Sparse differential interferometry measurement is an important development direction in high-accuracy optical measurement field, in the other field that this technology is also can widespread use relevant to flow field simultaneously, especially stratified fluid high-acruracy survey, in the practical problems such as atmosphere, ocean, can realize the sparse differential interferometry measurement of high precision that density gradient distributes.
Brief description of the drawings
Fig. 1 is that the present invention real first executes differential interferometry measurement imaging system structural representation in example.
Fig. 2 is that the present invention real second executes differential interferometry measurement imaging system structural representation in example.
Wherein: light source 1; The first condenser lens 2; Slit diaphragm 3; The 3rd condenser lens 4; The polarizer 5; The second wollaston prism 6; The first collimation lens 7; The first catoptron 8; Smooth observation area 9; The second catoptron 10; The second condenser lens 11; The first wollaston prism 12; Analyzer 13; The second collimation lens 14; Numeral microarray catoptron 15; Plus lens 16; Single-point photodetector 17; Compression algorithm module 18.
Embodiment
Hereinafter in connection with accompanying drawing, embodiments of the invention are elaborated.It should be noted that, in the situation that not conflicting, the combination in any mutually of the feature in embodiment and embodiment in the application.
Density measure for linear and non-linear stratification fluid calculates, and adopts differential interferometry measuring method to obtain higher measuring accuracy.Differential interferometry mainly comprises the methods such as single wollaston prism, two wollaston prism, holographic interference.Belong to for stratified fluid under the condition of linear distribution, obtain one group of equally spaced parallel stripes by differential interferometry, can calculate according to following formula the Density Distribution of stratified fluid,
In formula, K is Gladston-Dale constant; For LASER Light Source, l is optical source wavelength, and for white light source, l is average wavelength of light source; L is the thickness of the parallel incident light direction in flow field; D is difference distance, equals condenser lens angle and wollaston prism and carves the product at angle; S is the fringe spacing in even density district; DS is the stripe shift amount that density non-uniform Distribution produces.The gradient that can calculate thus density distributes.In the practical problems such as atmosphere, ocean, according to the definite precision of lattice size, take out a continually varying curve, measure stripe shift amount dS, the gradient that just can calculate density according to above formula distributes.
The present invention combines compressive sensing theory with differential interferometry measurement, the sparse differential interferometry measuring method of creationary proposition, there is the feature of high flux, high s/n ratio, fast and flexible, being suitable for conventional light intensity, the low light level, faint light, the ultra micro low light level and single photon differential interferometry metering system, is a kind of sparse differential interferometry measuring method of great dynamic range.
Differential interferometry based on compressed sensing of the present invention is measured imaging system and method has adopted compressed sensing (Compressive Sensing, be called for short CS) principle, can be in the mode of stochastic sampling, ideally recover original signal by data sampling number (far below the limit of Nyquist/Shannon's sampling theorem) still less.First utilize priori, choose suitable sparse base Ψ, it is the most sparse making point spread function x obtain x ' after Ψ conversion; Under the condition of known measurements vector y, measurement matrix A and sparse base Ψ, set up mathematical model y=A Ψ x'+e, carry out protruding optimization by compressed sensing algorithm, obtain after x ', then by
be finally inversed by x.Compressive sensing theory is combined with the differential interferometry measurement differential interferometry measuring method based on compressed sensing proposing, structurally comprise single wollaston prism and two two kinds of different structures of wollaston prism, but principle is identical.Wherein, adopt the differential interferometry of the compressed sensing of single wollaston prism to measure imaging arrangement principle as shown in Figure 2, adopt the differential interferometry of the compressed sensing of two wollaston prisms to measure imaging arrangement principle as shown in Figure 1.
Be more than the explanation to compressive sensing theory algorithm, specifically describe differential interferometry measuring system of the present invention below with reference to compressed sensing principle.
Differential interferometry is measured imaging system the first embodiment
Shown in figure 1, the differential interferometry of the present embodiment is measured the first condenser lens 2, slit diaphragm 3, the first collimation lens 7, the second condenser lens 11, the first wollaston prism 12, analyzer 13, the second collimation lens 14, digital microarray catoptron 15, plus lens 16 and the single-point photodetector 17 that imaging system comprises light source 1 and sets gradually along light source 1 output optical signal path.Smooth observation area 9 is between the first collimation lens 7 and the second condenser lens 11.Compression algorithm module 18 is connected with single-point photodetector 17 electric signal, for reconstructed image, according to parameters such as the interference fringe spacing of image, calculates the density gradient of flow field layering.
Shown in Fig. 1, for regulating the path of light source 1 output optical signal, in the present embodiment, also comprise mirror unit, mirror unit comprises the first catoptron 8 and the second catoptron 10, the first catoptron 8 is located between the first collimation lens 7 and flow observation region 9, for the emergent light of the first collimation lens 7 is reflected into into observation area, flow field 9; The second catoptron 10 is located between flow observation region 9 and the second condenser lens 11, for the emergent light in flow observation region 9 being reflexed to the second condenser lens 11.
By light source 1 output optical signal, after the first condenser lens 2 focuses on, by the spuious bias light of slit diaphragm 3 filtering, then by after the first collimation lens 7 beam-expanding collimations, after the first catoptron 8 reflections, incide flow observation region 9, then after being input to the second condenser lens 11 and converging via the second catoptron 10 reflection, after the first wollaston prism 12 and analyzer 13, form interference fringe, then after the second collimation lens 14 collimations, incide digital microarray catoptron 15, light field is carried out after Stochastic Modulation, after converging, plus lens 16 incides single-point photodetector 17, pass through again compression algorithm module 18 reconstructed images, according to parameters such as the interference fringe spacing of image, can calculate the density gradient of flow field layering, finally realize the differential interferometry new method of measuring based on compressed sensing.
In the present embodiment, light source 1 is LASER Light Source or white light source composition, after the first condenser lens 2 focuses on, be irradiated to again on slit diaphragm 3, wherein LASER Light Source can be pulsed laser light source and continuous laser source, wavelength is at the visible-range of 400-800nm, laser output wavelength can be 405nm, 445nm, 473nm, 488nm, 515nm, 640nm, 660nm etc., and what form by LASER Light Source is laser interferencefringes; White light source is made up of continuous spectrum light source, be applicable to differential interferometry measurement and have xenon source, Halogen lamp LED, deuterium lamp, Laser Driven white light source etc., super continuum source based on ultrafast Fiber laser technology, white-light spectrum scope comprises 400nm-800nm, 170nm-2100nm, 400nm-2400nm, and power bracket comprises 30mW-100W.
Slit diaphragm 3 is realized differential interferometry and is measured needed pointolite, eliminates background stray light simultaneously, improves the signal to noise ratio (S/N ratio) of light path system; Slit diaphragm 3 comprises slit and pinhole diaphragm, diaphragm can be by the diaphragm parts of manual or motorized adjustment or replacing, also can be standard form diaphragm of fixed measure etc., the size that is applicable to differential interferometry measuring method is the smaller the better, but ensure enough incident intensities, representative width is 50um left and right simultaneously.
The first catoptron 8 and the second catoptron 10, the light source after expanding, by the first catoptron 8, enters flow observation region 9, then is input on the second condenser lens 11 by the second catoptron 10; The catoptron adopting comprises broadband deielectric-coating catoptron, metal film catoptron, dielectric laser line reflection mirror, cold and hot catoptron etc., also comprise ultrafast, polished backside, circle and square, D shape, spill, cylinder concave surface, off axis paraboloid mirror, elliptical reflector etc., in addition, also comprise the passive or active optical component of beam splitter, prism etc. for reflecting.
Flow observation region 9 is the interactional regions in light and flow field, can be for researchs such as microgravity flame combustion flow field survey, Flow Field in Wind Tunnel measurement, the tower Combustion Flow Field that falls measurement, the measurement of rocket Combustion Flow Field, liquid flow field measurement, vane cyclone measurement, gas jet measurements, concrete application comprises symmetrical flow field, asymmetric flow field, supersonic flow field, gas mixing flow field, the astable flow field of bidimensional, three-dimensional flow field measurement etc.
The second condenser lens 11, the first wollaston prism 12 and analyzer 13 form differential interferometry unit; Focus on the first wollaston prism 12 through the light field of flow observation region 9 deviations through the second condenser lens 11 and form interference fringe, then by analyzer 13, the differential interferometry stripe pattern that forms flow field change is incided to collimation lens 14; The first wollaston prism 12 wavelength coverage 350-2300nm, carving between angle and the second condenser lens 11 focal lengths of the first wollaston prism 12 will meet interference condition.
Illumination after the second collimation lens 14 collimations is mapped on digital microarray catoptron 15, then differential interferometry stripe pattern is carried out after stochastic space optical modulation, to the coded image imaging after Stochastic Modulation, be then input to single-point photodetector 17 by plus lens 16; Wherein digital microarray catoptron 15 also can adopt other adjustable spatial light modulators such as reflective and transmission-type LCD space light modulator.
Plus lens 16 converges to the image after the random optical modulation of digital microarray catoptron 15 a bit, then incide corresponding single-point photodetector 17, realize high flux imaging by plus lens 16, can be applied to the low light level, superweak smooth single photon differential interferometry measurement imaging aspect.
Differential interferometry light field signal after single-point photodetector 17 receives plus lens 16 and converges, then be input to compression algorithm module 18, reconstruct DInSAR interferogram, wherein said single-point photodetector 17 can adopt visible ray photodetector or single-photon detector; Wherein single-photon detector can be visible ray avalanche diode, solid-state photomultiplier, superconducting single-photon detector etc.
Compression algorithm module 18 adopts following any one algorithm to realize compressed sensing: greedy reconstruction algorithm, coupling track algorithm MP, orthogonal coupling track algorithm OMP, base track algorithm BP, LASSO, LARS, GPSR, Bayesian Estimation algorithm, magic, IST, TV, StOMP, CoSaMP, LBI, SP, l1_ls, smp algorithm, SpaRSA algorithm, TwIST algorithm, l0 reconstruction algorithm, l1 reconstruction algorithm, l2 reconstruction algorithm etc., and sparse base can adopt dct basis, wavelet basis, Fourier transform base, gradient base, gabor transform-based etc.; By using above-mentioned compression algorithm Restructuring Module to go out the differential interferometry stripe pattern in observed flow field.
Between numeral microarray catoptron 15 and single-point photodetector 17, need to synchronize, the every upset of micro mirror array in numeral microarray catoptron 15 once, single-point photodetector 17 adds up to survey all light intensity of arrival in interval in this flip-flop transition, realize photoelectric signal collection conversion, then deliver to corresponding compression algorithm module 18.
Differential interferometry is measured imaging system the second embodiment
Shown in figure 2, the differential interferometry of the present embodiment is measured imaging system on the basis of the first embodiment: along described light source 1 output optical signal path, between slit diaphragm 3 and described the first collimation lens 7, be provided with the 3rd condenser lens 4, the polarizer 5 and the second wollaston prism 6.
Light signal by slit diaphragm 3, after the 3rd condenser lens 4 focuses on, forms polarized light by polaroid 5, is input to after the second wollaston prism 6 light splitting, then by the first collimation lens 7 beam-expanding collimations; Wherein, polaroid 5 Main Functions form polarized light to incident white light source or laser light light source, and polaroid 5 comprises linear thin film polarizer, wire grating polarizer, holographic line lattice polarizer, two-phase look film polarizer, polarization beam splitting cube, circular polarisers, laser polarization prism, kalzit polarizer, Glan-Taylor polarizer etc.
Differential interferometry is measured formation method embodiment
The present embodiment differential interferometry is measured formation method and is comprised:
Step 1, light source output optical signal, after the first condenser lens focuses on, by the spuious bias light of slit diaphragm filtering;
Step 2, after the first collimation lens beam-expanding collimation, incides flow observation region;
Step 3 after the second condenser lens converges, forms interference fringe by the light beam of described flow observation region outgoing after the first wollaston prism and analyzer;
Step 4 incides digital microarray catoptron after place collimation lens collimation, and light field is carried out to Stochastic Modulation;
Step 5 incides single-point photodetector after plus lens converges, and the electric signal being converted to is delivered to compression algorithm module by described single-point photodetector;
Step 6, through compression algorithm Restructuring Module image, according to the interference fringe spacing parameter of image, can calculate the density gradient of flow field layering, and the differential interferometry of realizing based on compressed sensing is measured.
In above-mentioned steps 2: before the first collimation lens 7 beam-expanding collimations, first after the 3rd condenser lens 4 converges again by the light of slit diaphragm 3, more inclined to one side through 5 of the polarizers, then after the second wollaston prism 6 light splitting; Light beam after the first collimation lens 7 beam-expanding collimations incides flow observation region 9 after the first catoptron 8 reflections.
In above-mentioned steps 3, reflex to described the second condenser lens 11 by the light beam of described flow observation region 9 outgoing through the second catoptron 10 and converge.
In above-mentioned steps 4, the imaging signal of incident by serial optical transform after, be transferred on digital microarray catoptron 15, digital microarray catoptron 15 carries out intensity modulation by loading stochastic matrix A to its reflected light.
In above-mentioned steps 5, described single-point photodetector 17 is sampling simultaneously within the time interval of the each upset of corresponding digital microarray catoptron 15, and numerical value after single-point photodetector 17 is changed is as final measured value y;
In above-mentioned steps 6, step 4 and random measurement matrix A measured value y in step 5 with together with as the input of compression algorithm module 18, choose suitable sparse base imaging x can be represented by minimum coefficient, carry out the light distribution image after signal reconstruction deviation by compressed sensing algorithm.
In technique scheme, differential interferometry based on compressed sensing is measured imaging system and method, the data processing method that differential interferometry is measured flame temperature is: for rotational symmetry flame temperature field, solve refractive index by coordinate transform, coordinate transform mathematical notation is.
Wherein, m is interference fringe level order, and r is light coordinate, y is the distance of x-z plane, and λ is lambda1-wavelength, and n is gas refracting index, d is the required distance that in field experiment, two coherent light beams must be satisfied, and the prism that its value is W-prism is carved the product of angle ε and lens L2 focal length.
After the refractive index at known r=r0 place, the above-mentioned coordinate transform Mathematical representation of direct integral can obtain the index distribution along radial direction.In computation process, utilize the method for curve, and in conjunction with the symmetry of fringe order order, adopt least square method that fringe order order is fitted to an even polynomial expression.Region to be measured is radially divided into centered by axis of symmetry to the concentric annular band unit of k spacing as Δ r, and approximate thinks that each ring-type element has uniform refractive index gradient along radial direction, can build a triangular matrix like this.When calculating, first determine the corresponding refractive index gradient of outmost turns fringe order order, then from outer ring successively to center calculation, the refractive index gradient that just can obtain each ring-type unit region distributes.
When outmost turns refractive index is while being known, can calculate the refractive index that each circle is corresponding by following formula, Difference Calculation formula table is shown:
The Gladstone-Dale formula that utilizes the refractive index shown in following formula and Media density relation, expression is as follows:
n
i-1=Kr
i
Wherein, ρ i is Media density, and K is Gladstone-Dale constant, in conjunction with the equation of gas state, can utilize following formula to calculate the gas temperature of radius for ri place, and gas temperature calculation expression formula is:
Wherein, the mean molecular weight that M is gas, p is environment atmospheric pressure, R is ideal gas constant.
Be more than the description of the differential interferometry based on compressed sensing of the present invention being measured to the general structure of imaging system, below the specific implementation of all parts be wherein further described.
Described digital microarray mirror unit can load on information on the optical data field of one dimension or bidimensional, it is the Primary Component in the contemporary optics fields such as real-time optical information processing, adaptive optics and photometry calculation, this class device can be under the control of time dependent electric drive signal or other signals, change photodistributed amplitude or intensity, phase place, polarization state and wavelength on space, or incoherent light is changed into coherent light.Its kind has a variety of, mainly contains Digital Micromirror Device (Digital Micro-mirror Device is called for short DMD), frosted glass, liquid crystal light valve etc., the intensity modulation being modulated to including Modulation and Amplitude Modulation used here.
The DMD adopting in the present embodiment includes the thousands of arrays that are arranged on the micro mirror on hinge (DMD of main flow is made up of 1024 × 768 array, maximum can be to 2048 × 1152), each eyeglass is of a size of 14 μ m × 14 μ m(or 16 μ m × 16 μ m) and light that can a pixel of break-make, these micro mirrors are all suspending, carry out electronic addressing by the storage unit under each eyeglass with scale-of-two planed signal, just can allow each eyeglass 10～12 ° of left and right (getting in the present embodiment+12 ° and-12 °) that tilt to both sides with electrostatic means, this two states is designated as to 1 and 0, respectively corresponding " opening " and " pass ", in the time that eyeglass is not worked, they are in " berthing " state of 0 °.
Professional should further recognize, unit and the algorithm steps of each example of describing in conjunction with embodiment disclosed herein, can realize with electronic hardware, computer software or the combination of the two, for the interchangeability of hardware and software is clearly described, composition and the step of each example described according to function in the above description in general manner.These functions are carried out with hardware or software mode actually, depend on application-specific and the design constraint of technical scheme.Professional and technical personnel can realize described function with distinct methods to each specifically should being used for, but this realization should not thought and exceeds scope of the present invention.
The software module that the method for describing in conjunction with embodiment disclosed herein or the step of algorithm can use hardware, processor to carry out, or the combination of the two is implemented.Software module can be placed in the storage medium of any other form known in random access memory (RAM), internal memory, ROM (read-only memory) (ROM), electrically programmable ROM, electrically erasable ROM, register, hard disk, moveable magnetic disc, CD-ROM or technical field.
The foregoing is only the preferred embodiments of the present invention, be not limited to the present invention, for a person skilled in the art, the present invention can have various modifications and variations.Within the spirit and principles in the present invention all, any amendment of doing, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.
Claims (16)
1. differential interferometry is measured an imaging system, it is characterized in that, comprising:
Light source, for output optical signal; And the first condenser lens, slit diaphragm, the first collimation lens, the second condenser lens, the first wollaston prism, analyzer, the second collimation lens, digital microarray catoptron, plus lens and the single-point photodetector that set gradually along described light source output optical signal path, flow observation region is between the first collimation lens and the second condenser lens;
Compression algorithm module, it is connected with single-point photodetector electric signal, for reconstructed image, according to parameters such as the interference fringe spacing of image, calculates the density gradient of flow field layering.
2. differential interferometry as claimed in claim 1 is measured imaging system, it is characterized in that, along described light source output optical signal path, between described slit diaphragm and described the first collimation lens, is provided with the 3rd condenser lens, the polarizer and the second wollaston prism.
3. differential interferometry as claimed in claim 1 is measured imaging system, it is characterized in that, also comprise mirror unit, it comprises the first catoptron and the second catoptron, described the first catoptron is located between described the first collimation lens and described flow observation region, for the emergent light of the first collimation lens is reflected into into observation area, flow field; Described the second catoptron is located between described flow observation region and described the second condenser lens, for the emergent light in described flow observation region is reflexed to the second condenser lens.
4. differential interferometry as claimed in claim 3 is measured imaging system, it is characterized in that, the catoptron in described mirror unit is broadband deielectric-coating catoptron, metal film catoptron, dielectric laser line reflection mirror or cold and hot catoptron.
5. differential interferometry as claimed in claim 1 is measured imaging system, it is characterized in that, carving between angle and described the second condenser lens focal length of described the first wollaston prism meets interference condition.
6. differential interferometry as claimed in claim 1 is measured imaging system, it is characterized in that, described light source is LASER Light Source or white light source.
7. differential interferometry as claimed in claim 6 is measured imaging system, it is characterized in that, described LASER Light Source is pulsed laser light source or continuous laser source, wavelength is at the visible-range of 400-800nm, and laser output wavelength is 405nm, 445nm, 473nm, 488nm, 515nm, 640nm or 660nm.
8. differential interferometry as claimed in claim 6 is measured imaging system, it is characterized in that, described white light source is continuous spectrum light source, it is xenon source, Halogen lamp LED, deuterium lamp, Laser Driven white light source or the super continuum source based on ultrafast Fiber laser technology, the spectral range of described white light source is that the spectral range of 400nm-800nm or described white light source is that the spectral range of 170nm-2100nm or described white light source is 400nm-2400nm, and power bracket is 30mW-100W.
9. differential interferometry as claimed in claim 1 is measured imaging system, it is characterized in that, described digital microarray catoptron adopts reflective and transmission-type LCD space light modulator.
10. differential interferometry as claimed in claim 1 is measured imaging system, it is characterized in that, described single-point photodetector is visible ray photodetector or single-photon detector.
11. differential interferometries as claimed in claim 10 are measured imaging system, it is characterized in that, described single-photon detector is avalanche photodide, solid-state photomultiplier or superconducting single-photon detector.
12. differential interferometries as claimed in claim 1 are measured imaging system, it is characterized in that, between described digital microarray catoptron and described single-point photodetector, synchronize, the every upset of micro mirror array in described digital microarray catoptron once, described single-point photodetector adds up to survey all light intensity of arrival in interval in this flip-flop transition, realize photoelectric signal collection conversion, then by extremely described compression algorithm module of electric signal transmission.
13. 1 kinds of differential interferometries are measured formation method, it is characterized in that, described method comprises:
Step 1, light source output optical signal, after the first condenser lens focuses on, by the spuious bias light of slit diaphragm filtering;
Step 2, after the first collimation lens beam-expanding collimation, incides flow observation region;
Step 3 after the second condenser lens converges, forms interference fringe by the light beam of described flow observation region outgoing after the first wollaston prism and analyzer;
Step 4 incides digital microarray catoptron after place collimation lens collimation, and light field is carried out to Stochastic Modulation;
Step 5 incides single-point photodetector after plus lens converges, and the electric signal being converted to is delivered to compression algorithm module by described single-point photodetector;
Step 6, through compression algorithm Restructuring Module image, according to the interference fringe spacing parameter of image, can calculate the density gradient of flow field layering, and the differential interferometry of realizing based on compressed sensing is measured.
14. differential interferometries as claimed in claim 13 are measured formation method, it is characterized in that, in described step 2, before the first collimation lens beam-expanding collimation, light by slit diaphragm is first after the 3rd condenser lens converges again, rise partially through the polarizer again, then after the second wollaston prism light splitting.
15. differential interferometries as claimed in claim 13 are measured formation method, it is characterized in that, in described step 2, the light beam after the first collimation lens beam-expanding collimation incides flow observation region after the first catoptron reflection.
16. differential interferometries as claimed in claim 13 are measured formation method, it is characterized in that, in implementation step 3, reflex to described the second condenser lens converge by the light beam of described flow observation region outgoing through the second catoptron.
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