CN111595559B - First-order wavefront error measuring system of non-continuous mirror telescope - Google Patents
First-order wavefront error measuring system of non-continuous mirror telescope Download PDFInfo
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Abstract
The invention relates to a first-order wavefront error measuring system of a discontinuous mirror telescope, which comprises a mask, an electric control rotary filter wheel, a polarization grating, a diffraction element, a micro-displacement actuator, a first lens, a spatial filter, a second lens, a pixel displacement polarization measuring device and a data acquisition and processing computer, wherein the data acquisition and processing computer is respectively connected with the electric control rotary filter wheel, the micro-displacement actuator and the pixel displacement polarization measuring device; the pixel shift polarization measurement device comprises a photoelectric detector array, a micro polarizer array and a lens array which are sequentially arranged; the pixel shift polarization measurement device sends the acquired light intensity signal to the data acquisition and processing computer, and the data acquisition and processing computer processes the light intensity signal to obtain a first-order wavefront error between the two discontinuous mirror surfaces. The invention realizes multi-wavelength measurement by automatically replacing the optical filter by the filter wheel, and can simultaneously realize dynamic measurement of large measurement range and high measurement precision of first-order wavefront errors among spliced sub-mirrors or sparse sub-mirror arrays.
Description
Technical Field
The invention relates to the technical field of optical detection, in particular to a first-order wavefront error measuring system of a non-continuous mirror telescope.
Background
With the rapid development of modern astronomy technology, astronomers extend the observation range to a deeper position in the universe, and the observed target is darker and weaker and approaches the resolution limit of the existing telescope. In order to improve the resolution and contrast of the observation, it is necessary to make more powerful visible/infrared astronomical telescopes, which require telescopes of larger calibers. However, due to the restriction of a series of practical factors such as the manufacturing of mirror blanks, optical processing, structural design, transportation, installation and adjustment, technical risk, development cost and the like, the development capability of the aperture of the single-piece main mirror telescope is currently 8m grade, which is in contradiction with the appeal of a telescope with a larger aperture required for astronomical observation. To solve this conflict, a tiled mirror technique and a sparse aperture technique have been proposed, both of which use non-continuous mirrors to produce the same or similar optical performance as a single mirror.
The splicing sub-mirrors in the splicing mirror technology are various in shapes, and typically comprise hexagons and sectors, and telescopes based on the hexagonal splicing sub-mirrors comprise Keck telescopes (Keck I and II), thirty-meter telescopes (TMT), European very large telescopes (E-ELT), South African Large Telescopes (SALT), Hobby-Eberley telescopes (HET), James Weber telescopes (JWST), large-day area multi-target optical fiber spectrum telescopes (LAMOST) and the like. The telescope based on the fan-shaped splicing sub-mirror comprises a 3.8m new technology telescope 'Seimei' of Kyoto university and the like. The sparse aperture telescope is represented by a Giant Mecho Telescope (GMT) and the like. The problem that the mirror surface of a visible/infrared telescope cannot be increased all the time is solved through sub-mirror splicing and a sparse aperture technology, but a new problem is introduced along with the problem, namely the problem of confocal common phase of the spliced mirror surface and the sparse aperture.
The confocal and common phase of the spliced sub-mirror or the sparse sub-mirror is required to be kept in order to achieve the same or close optical performance with the same aperture single mirror surface. In the confocal mode, the image points of the spliced sub-mirror or the sparse sub-mirror on the focal plane are stacked together to form a minimum bright spot, and the phase of the mirror surfaces of the spliced sub-mirror or the sparse sub-mirror is required to be consistent in the common phase, so that a sharp light spot is generated on the image plane, and the optical performance which is the same as or close to that of a single mirror surface with the same aperture is achieved or approximate.
The phases of the reflecting surfaces of the sub-mirrors are kept consistent after the spliced sub-mirror or the sparse sub-mirror is calibrated through a confocal common-phase technology, and the confocal common-phase keeping is realized through an active optical technology. The active optical technology monitors the relative spatial position and posture between the splicing sub-mirrors in real time through displacement sensors positioned at the edges of the splicing sub-mirrors, then the compensation amount of a displacement actuator positioned below each sub-mirror is calculated through an active optical control system, and the splicing sub-mirrors or the sparse sub-mirrors are readjusted to be in a confocal and common-phase state through displacement compensation until the confocal and common-phase optical measurement calibration is carried out next time.
The confocal detection of the splicing sub-mirror or the sparse sub-mirror is realized by a Shack-Hartmann wavefront detection technology, the Shack-Hartmann wavefront detection technology is sensitive to wavefront inclination, the inclined wavefront error can be accurately measured, and the confocal adjustment is easily realized by matching with an active optical technology. After confocal adjustment, a certain piston error and a tip/tilt error with extremely small residual exist between the spliced sub-mirror and the sparse sub-mirror. The traditional Shack-Hartmann wavefront detection technology is insensitive to the pixel error and cannot measure. The method for measuring the piston error mainly comprises a chromatic dispersion fringe technology, a wave front curvature technology, a pyramid sensor technology, a phase difference and phase recovery technology, a Shack-Hartmann narrow-band technology, a broadband technology and the like. The piston error and tip/tilt error are collectively referred to as first order wavefront error.
The phase difference and phase recovery technology needs a large amount of iterative operation and is easily influenced by atmospheric disturbance, the method is only suitable for space telescopes without atmospheric disturbance, and the phase measurement range is small and is +/-lambda/2. The curvature sensing technology reconstructs wavefront and phase measurement by using light intensity distribution on conjugate planes which are equidistant from the front and back of a focal plane, but is essentially an improved phase difference technology, so that the phase measurement range is small, and high spatial resolution and phase resolution cannot be simultaneously obtained. The dispersion fringe sensor utilizes Fraunhofer double-hole diffraction dispersion of polychromatic light, the pixel error modulates the maximum displacement of the energy of diffraction spots with different wavelengths, the dispersion effect of a dispersion element such as a prism grating enables diffraction patterns to be dispersed along the dispersion direction, and the pixel error is calculated through processing fringes. The wide-band method of Shack-Hartmann has a large measuring range but low precision, and the narrow-band method of Shack-Hartmann has high measuring precision but small measuring range of +/-lambda/2. The technologies are difficult to realize large measurement range and high measurement precision simultaneously.
In the existing splicing lens confocal and common-phase detection technology, the Tip/tilt error is mainly measured by a Shack-Hartmann wavefront measurement technology, the technical principle of the Shack-Hartmann wavefront measurement technology is that the centroid operation is calculated on an image surface through a micro lens array to calculate the wavefront slope, and the TIp/tilt error with extremely small residue can not be measured due to the influence of factors such as installation error and measurement noise of the micro lens array.
Disclosure of Invention
Therefore, the first-order wavefront error measuring system of the non-continuous mirror telescope is necessary to solve the problems that the existing splicing lens confocal and common-phase detection technology cannot realize large measuring range and high-precision measurement of a piston error in a first-order wavefront error and cannot accurately measure a tip/tilt error.
In order to solve the problems, the invention adopts the following technical scheme:
a first-order wavefront error measuring system of a discontinuous mirror telescope comprises a mask, an electric control rotary filter wheel, a polarization grating, a diffraction element, a micro-displacement actuator, a first lens, a spatial filter, a second lens, a pixel shift polarization measuring device and a data acquisition processing computer;
the mask, the electric control rotary filter wheel, the polarization grating, the diffraction element, the first lens, the spatial filter, the second lens and the pixel shift polarization measurement device are sequentially and coaxially arranged, the micro-displacement actuator is arranged on the diffraction element, and the data acquisition processing computer is respectively connected with the electric control rotary filter wheel, the micro-displacement actuator and the pixel shift polarization measurement device;
emergent light of an optical system of the non-continuous mirror telescope is incident to a conjugate surface of an image surface of a first-order wavefront error measuring system, the mask positioned on the conjugate surface is used for sampling reflected light rays of different sub-mirror areas in an equal circular area mode, two light beams after being sampled by the mask pass through an optical filter on the electric control rotary filter wheel to become monochromatic light, the two monochromatic light beams pass through the polarization grating, the polarization grating is used for selectively splitting light according to the polarization state of the monochromatic light to form + 1-order diffracted light and-1-order diffracted light, the + 1-order diffracted light is left-handed circularly polarized light, the-1-order diffracted light is right-handed circularly polarized light, the diffraction element is moved to an overlapping area of the + 1-order diffracted light and the-1-order diffracted light under the control of the data acquisition and processing computer and is used for synthesizing the +1, the combined light sequentially passes through the first lens, the spatial filter and the second lens to form collimated light beams, and the collimated light beams enter the pixel shift polarization measurement device;
the pixel shift polarization measurement device comprises a photoelectric detector array, a micro polarizer array and a lens array which are sequentially arranged, wherein the micro polarizer array comprises a plurality of polarizer units, each polarizer unit corresponds to one pixel unit of the photoelectric detector array and one lens unit of the lens array, and each polarizer unit comprises four wire grid polarizing plates with different polarization angles;
the pixel shift polarization measurement device collects light intensity signals recorded by four wire grid polarizer classified pixels by using the photoelectric detector array, sends the light intensity signals to the data acquisition and processing computer, the data acquisition and processing computer processes the light intensity signals to obtain four phase shift interferograms, and phase unwrapping is carried out on the four phase shift interferograms to obtain a first-order wavefront error between two discontinuous mirror surfaces.
Compared with the prior art, the invention has the following beneficial effects:
(1) compared with a monochromatic light-based first-order wavefront error measurement technology, the method has the advantages that the filter wheel is used for automatically replacing the optical filter to realize multi-wavelength measurement, the technical problem of 2 pi ambiguity which cannot be solved by the monochromatic light-based first-order wavefront error measurement technology is effectively solved, and a larger measurement range can be obtained;
(2) the telescope pitch axis and azimuth axis rotate and can cause the vibration of discontinuous mirror system and the vibration of confocal looks measurement system altogether when tracking the target, receive the influence of factors such as time sequence change wind pressure disturbance that is used in the telescope structure moreover and also can cause measurement system's vibration, this is extremely unfavorable to precision measurement, and prior art all can't avoid the influence that the structural vibration caused in principle. In particular, the related art based on Shack-Hartmann test requires that the sampling circle of the microlens on the conjugate plane of the image plane exactly cross the side seam of the splicing mirror, otherwise the change of the far field diffraction pattern can be caused to introduce the measurement error. The manufacturing precision requirement of the rectangular pyramid which is a key element of the pyramid wavefront sensing technology is extremely strict, and the requirement on the position of the cone tip of the rectangular pyramid with the cutting wavefront is also strict during testing. The application defect of the splicing mirror common-phase error detection technology based on the micro-lens element and the rectangular pyramid sensor in the common-phase measurement of a large-scale splicing mirror system is more and more obvious. The invention utilizes polarized light measurement and pixel shift technology, utilizes an integrated lens array, a micro polarizer array and a high-resolution photoelectric detector array, can simultaneously obtain four phase shift interferograms, and can obtain transient measurement wavefront through the calculation of a data acquisition processing computer;
(3) the sampling position of the invention is in the corresponding area on the image surface conjugate plane of the splicing sub-mirror or the sparse sub-mirror, and the sampling sub-aperture does not need to be accurately spanned on the splicing seam of the splicing mirror, thereby reducing the installation tolerance of a test system and being easier to install, debug and maintain.
(4) The test object of the invention has no special requirements on the composition form of the non-continuous mirror surface, and the target to be tested can be a spliced mirror surface in the form of a spliced sub-mirror such as a hexagon or a fan or a sparse aperture mirror surface;
(5) compared with the most advanced measurement technology at present, the device used by the invention has smaller shape and size and higher space utilization rate, and saves the precious space of the imaging end of the telescope;
(6) the core element used in the invention has smaller size and is easy to be made into an integrated detection system;
(7) compared with the prior art that the prior art can only measure the piston, tip and tilt errors between two adjacent spliced sub-mirrors or sparse sub-mirrors at the same time, the method can measure the piston, tip and tilt errors between a plurality of spliced sub-mirrors or sparse sub-mirror arrays at the same time, thereby greatly improving the measurement efficiency;
(8) the core elements used in the invention are mature commodity elements, so the interchangeability is good, and the replacement and the maintenance are easy;
(9) the invention can simultaneously realize the dynamic measurement of large measurement range and high measurement precision of the errors of the piston, tip and tilt between the spliced sub-mirrors or the sparse sub-mirror arrays, which are not possessed by other measurement technologies at present.
Drawings
FIG. 1 is a schematic diagram of a first-order wavefront error measurement system of a non-continuous mirror telescope according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of an electrically controlled rotary filter wheel;
fig. 3 is a schematic structural diagram of a pixel shift polarization measurement apparatus.
Detailed Description
The invention provides a first-order wavefront error (pixel _ tip _ tilt) measuring system of a non-continuous mirror telescope, which aims at the defect that the prior art can not realize a large measuring range and high measuring precision for a pixel error between spliced sub-mirrors or sparse sub-mirrors, utilizes a polychromatic light measuring technology and a pixel shifting technology to respectively inhibit the influence of 2 pi fuzzy in a monochromatic light measuring technology to realize a large measuring range and realize high-precision interference measuring wavefront so as to realize high measuring precision, and makes up the problem that the tiny tip/tilt error can not be detected in the traditional Shack-Hartmann technology and generates a measuring blind area of residual tip/tilt error. The invention is suitable for the first-order wavefront error measurement of spliced mirror surfaces in the form of fan-shaped or hexagonal spliced sub-mirrors and discontinuous mirror surfaces in sparse aperture and the like in the field of discontinuous mirror surface visible/infrared telescopes. The technical solution of the present invention will be described in detail with reference to the accompanying drawings and preferred embodiments.
FIG. 1 is a schematic diagram of a first-order wavefront error measurement system of a non-continuous mirror telescope according to an embodiment of the present invention. As shown in fig. 1, the present invention provides a first-order wavefront error measuring system of a non-continuous mirror telescope, the system comprises a mask 2, an electric control rotary filter wheel 3, a polarization grating 4, a diffraction element 5, a micro-displacement actuator 6, a first lens 7, a spatial filter 8, a second lens 9, a pixel shift polarization measuring device 10 and a data acquisition and processing computer 11, wherein the mask 2, the electric control rotary filter wheel 3, the polarization grating 4, the diffraction element 5, the first lens 7, the spatial filter 8, the second lens 9 and the pixel shift polarization measuring device 10 are coaxially arranged in sequence, the micro-displacement actuator 6 is arranged on the diffraction element 5, for example, the data acquisition and processing computer 11 is arranged on the back of the diffraction element 5 to adjust the position of the diffraction element 5 on the optical axis, and is respectively connected with the electrically controlled rotary filter wheel 3, the micro-displacement actuator 6 and the pixel shift polarization measurement device 10.
When the non-continuous mirror telescope carries out confocal and co-phase detection, a bright star is observed firstly, star light from the bright star is incident on the non-continuous mirror reflector 1 of the telescope, and reflected light rays sequentially pass through all optical elements in an optical system of the telescope and then reach a conjugate surface of an image surface of the first-order wavefront error measuring system. The first-order wavefront error measuring system of the discontinuous mirror telescope provided by the invention is suitable for splicing mirror telescopes or sparse aperture telescopes.
Emergent light of an optical system of the non-continuous mirror telescope is incident to a conjugate surface of an image surface of the first-order wavefront error measuring system, the mask 2 positioned on the conjugate surface performs equal-circle-domain sampling on reflected light of different sub-mirror regions, and due to the fact that the technology that the mask 2 positioned on the image surface conjugate surface samples in the non-continuous mirror surface is adopted, sampling requirements are expanded, and error requirements of element alignment are reduced. Two beams of light sampled by the mask 2 pass through a long-wave optical filter on the electric control rotary filter wheel 3 to be changed into monochromatic light, the two beams of monochromatic light pass through the polarization grating 4, the polarization grating 4 selectively splits the light according to the polarization state of the monochromatic light to form + 1-order diffraction light and-1-order diffraction light, the + 1-order diffraction light is left circularly polarized light, and the-1-order diffraction light is right circularly polarized light. The polarization grating 4 can realize selective light splitting based on the polarization state of incident light, the diffraction angle depends on the line number of the grating, the polarization grating can regulate and control the energy distribution between a positive order and a negative order by controlling the polarization state of the incident light, and when the polarization states of the incident light beams are different, the polarization grating 4 has different diffraction characteristics. When the incident light is unpolarized light or linearly polarized light, the polarization grating 4 has positive and negative first-order diffracted light, the + 1-order diffracted light is left-handed circularly polarized light, and the-1-order diffracted light is right-handed circularly polarized light. The reflected unpolarized light from the two splicing mirrors I and II passes through the electrically-controlled rotary filter wheel 3 and then enters the polarization grating 4, the polarization grating 4 divides the two beams of unpolarized light into + 1-order diffracted light and-1-order diffracted light respectively, the + 1-order diffracted light is left-handed circularly polarized light, and the 1-order diffracted light is right-handed circularly polarized light. As shown in fig. 2, which is a schematic structural diagram of the electrically controlled rotary filter wheel 3, the electrically controlled rotary filter wheel 3 is installed with filters with different wavelengths matching with the working wavelength range of the polarization grating 4, and optionally, the wavelength range of the polarization grating 4 in this embodiment is 450 to 650 nm. Fig. 2 is only illustrated by taking an example that the electrically controlled rotary filter wheel 3 includes four filters which are uniformly distributed circumferentially and have different wavelength ranges, the arrow direction in the figure represents the rotation direction of the electrically controlled rotary filter wheel, the wavelength ranges of the four filters match with the working wavelength range of the polarization grating 4, and in the actual measurement process, the number of the filters and the wavelength of the filters mounted on the electrically controlled rotary filter wheel 3 can be selected according to actual needs, which is not limited herein.
The-1 st order diffracted light (right circularly polarized light) of the splicing mirror I and the +1 st order diffracted light (left circularly polarized light) of the splicing mirror II are overlapped at proper positions, a micro-displacement actuator 6 is arranged on the diffraction element 5 to realize the movement of the diffraction element 5 along the optical axis direction, therefore, the diffraction element 5 is always located in the overlapping area of the-1 st order diffraction light and the +1 st order diffraction light, the diffraction element 5 moves to the overlapping area of the +1 st order diffraction light and the-1 st order diffraction light under the control of the data acquisition processing computer 11 and combines the +1 st order diffraction light and the-1 st order diffraction light, the combined light generates convergent light after passing through the first lens 7, the convergent light reaches the second lens 9 after passing through the spatial filter 8, the second lens 9 changes the divergent light into a collimated light beam, and the collimated light beam enters the pixel shift polarization measurement device 10. The first lens 7, the spatial filter 8 and the second lens 9 constitute a light beam adjusting and filtering device, and the light beam adjusting and filtering device is used for adjusting and filtering the size of the light beam combined by the diffraction element 5 so as to ensure the final measurement precision.
As shown in fig. 3, the pixel shift polarization measurement device 10 includes a photodetector array 10-1, a micro polarizer array 10-2, and a lens array 10-3, which are sequentially arranged, the micro polarizer array 10-2 includes a plurality of polarizer units, each of which corresponds to one pixel unit of the photodetector array 10-1 and one lens unit of the lens array 10-3, respectively, and the polarizer units include four wire grid polarizers with different polarization angles. Specifically, FIG. 3(a) is a side view of the pixel-shifted polarization measurement device 10, with the photodetector array 10-1, the micro-polarizer array 10-2, and the lens array 10-3 arranged in sequence from the bottom layer to the top layer; FIG. 3(b) is a top view of the micro polarizer array 10-2, the micro polarizer array 10-2 includes several polarizer units, and each polarizer unit corresponds to one pixel unit in the photodetector array 10-1 and one lens unit in the lens array 10-3; fig. 3(c) is a schematic diagram of a polarization unit, each polarization unit includes four wire grid polarizers with different polarization angles, optionally, the polarization angles of the four wire grid polarizers are 0 °, 45 °, 90 °, and 135 °, and fig. 3(c) illustrates the polarization unit by only taking an example that the four wire grid polarizers are distributed in a manner that the polarization angles are 0 °, 45 °, 90 °, and 135 ° in sequence from the lower right corner in the counterclockwise direction, and the distribution manner of the four wire grid polarizers is not limited in the present invention. Still referring to fig. 3(a), after the 0 ° polarized light enters the wire grid polarizer with the polarization angle of 0 °, the 0 ° polarized light enters the pixel unit corresponding to the photodetector array 10-1, and after the 0 ° polarized light enters the wire grid polarizer with the polarization angle of 90 °, the 0 ° polarized light is reflected and cannot enter the photodetector array 10-1, so that the combined left-handed circularly polarized light and right-handed circularly polarized light pass through the lens array 10-3 and the micro polarizer array 10-2 and then enter the photodetector array 10-1, and the two-dimensional lattice holes of the array correspond to the pixel points of the detector. Each wire grid polarizer can have different rotation amount of unit pixel, different phase difference of two reference arms is selected, and different phase shift of the unit pixel can be formed, by this way, four-frame high-resolution transient interference pattern can be recorded by classifying pixels along the rotation direction of the analyzer of 0 degree, 45 degree, 90 degree and 135 degree, namely, the pixel shift polarization measurement device 10 uses the photoelectric detector array 10-1 to collect the light intensity signals (interference fringes) recorded by the classified pixels of the four wire grid polarizers and sends the light intensity signals to the data acquisition processing computer 11, then the data acquisition processing computer 11 processes the light intensity signals recorded by the classified pixels of the wire grid polarizers with the polarization angles of 0 degree, 45 degree, 90 degree and 135 degree respectively to obtain four phase shift interference patterns, and the high-precision first-order wavefront error between two non-continuous mirrors can be obtained by performing phase unwrapping processing on the four phase shift interference patterns, and obtaining high-precision information of the piston, the tip and the tilt, wherein the two discontinuous mirror surfaces can be two adjacent mirror surfaces or two non-adjacent mirror surfaces. By combining the light rays with different wavelengths which can be generated by the plurality of optical filters of the electric control rotary filter wheel 3 shown in fig. 3, the data acquisition and processing computer 11 controls the electric control rotary filter wheel 3 to rotate and switch the optical filters, thereby realizing the switching of the polychromatic light, realizing the first-order wavefront error measurement of the polychromatic light, effectively avoiding the influence of the ubiquitous 2 pi fuzzy effect in the existing monochromatic light piston error detection, and greatly improving the measurement range of the piston error.
The invention provides a first-order wavefront error measuring system of a non-continuous mirror telescope, which utilizes the principle of polarized light interference measurement and utilizes a pixel shifting polarization measuring device to simultaneously generate 4 interference patterns, thereby realizing high-precision transient wavefront measurement and avoiding the influence of vibration; meanwhile, the invention realizes the switching of the polychromatic light by utilizing the electric control rotary filter wheel, realizes the measurement of the polychromatic light, can effectively avoid the influence of the ubiquitous 2 pi fuzzy effect in the existing monochromatic light piston error detection, and greatly improves the measurement range of the piston error.
In order to further improve the measurement efficiency and the measurement precision of the first-order wavefront error, the data acquisition and processing computer 11 firstly controls the electric control rotary filter wheel 3 to rotate to the optical filter with longer wavelength, then the pixel shift polarization measurement device utilizes the photoelectric detector array 10-1 to acquire light intensity signals recorded by the classified pixels of the four wire grid polaroids and sends the light intensity signals to the data acquisition and processing computer 11, the data acquisition and processing computer 11 obtains four phase shift interference graphs according to the light intensity signal processing, a preliminary first-order wavefront error between two discontinuous mirror surfaces is obtained by carrying out phase unwrapping processing on the four phase shift interference graphs, then the data acquisition and processing computer determines a corresponding preset error range according to the preliminary first-order wavefront error, wherein the preset error range is a first-order wavefront error empirical value obtained according to parameters such as the type of a non-continuous mirror telescope, the wavelength of the optical filter, the wavelength of the polarization grating and the like, then the data acquisition processing computer 11 controls the rotation of the electric control rotary filter wheel 3 according to a preset error range, replaces the current long-wave filter with a short-wave filter corresponding to the preset error range, the pixel shift polarization measurement device 10 acquires light intensity signals again and sends the acquired light intensity signals to the data acquisition processing computer 11, the data acquisition processing computer 11 obtains four phase-shift interferograms according to the light intensity signal processing, and the high-precision first-order wavefront error between the two discontinuous mirror surfaces is obtained by performing phase unwrapping processing on the four phase-shift interferograms. According to the embodiment, the electric control rotary filter wheel 3 is firstly rotated to the optical filter with longer wavelength, the data acquisition processing computer 11 calculates to obtain the preliminary first-order wavefront error, then the electric control rotary filter wheel is controlled to rotate according to the preliminary first-order wavefront error, the long-wavelength optical filter is switched to the short-wavelength optical filter, the high-precision first-order wavefront error between the two discontinuous mirror surfaces is finally obtained, and the efficiency of measuring the first-order wavefront error is greatly improved. When the polychromatic light measurement technology is used for eliminating the 2 pi fuzzy effect, the piston error within one wavelength is remained, at the moment, the electrically controlled rotary filter wheel is rotated to be switched from the long-wavelength filter to the short-wavelength filter, and finally, the interference wavefront measurement under the measurement of the shortest filter wavelength is realized, and the high measurement precision is realized. Simulation results show that the first-order wavefront error measuring system of the discontinuous mirror telescope provided by the invention is practical and effective.
Optionally, the micro-displacement actuator 6 is a piezoelectric ceramic (PZT) micro-displacement actuator, and has the characteristics of high micro-displacement resolution, high stability and capability of bearing a certain tensile force.
Optionally, the photodetector array 10-1 is a CCD sensor or a CMOS sensor.
Alternatively, the pixel-shifting polarization measurement device 10 may be implemented using an IMX250MZR sensor from Sony corporation.
The invention has the following beneficial effects:
(1) compared with a monochromatic light-based first-order wavefront error measurement technology, the method has the advantages that the filter wheel is used for automatically replacing the optical filter to realize multi-wavelength measurement, the technical problem of 2 pi ambiguity which cannot be solved by the monochromatic light-based first-order wavefront error measurement technology is effectively solved, and a larger measurement range can be obtained;
(2) the telescope pitch axis and azimuth axis rotate and can cause the vibration of discontinuous mirror system and the vibration of confocal looks measurement system altogether when tracking the target, receive the influence of factors such as time sequence change wind pressure disturbance that is used in the telescope structure moreover and also can cause measurement system's vibration, this is extremely unfavorable to precision measurement, and prior art all can't avoid the influence that the structural vibration caused in principle. In particular, the related art based on Shack-Hartmann test requires that the sampling circle of the microlens on the conjugate plane of the image plane exactly cross the side seam of the splicing mirror, otherwise the change of the far field diffraction pattern can be caused to introduce the measurement error. The manufacturing precision requirement of the rectangular pyramid which is a key element of the pyramid wavefront sensing technology is extremely strict, and the requirement on the position of the cone tip of the rectangular pyramid with the cutting wavefront is also strict during testing. The application defect of the splicing mirror common-phase error detection technology based on the micro-lens element and the rectangular pyramid sensor in the common-phase measurement of a large-scale splicing mirror system is more and more obvious. The invention utilizes polarized light measurement and pixel shift technology, utilizes an integrated lens array, a micro polarizer array and a high-resolution photoelectric detector array, can simultaneously obtain four phase shift interferograms, and can obtain transient measurement wavefront through the calculation of a data acquisition processing computer;
(3) the sampling position of the invention is in the corresponding area on the image surface conjugate plane of the splicing sub-mirror or the sparse sub-mirror, and the sampling sub-aperture does not need to be accurately spanned on the splicing seam of the splicing mirror, thereby reducing the installation tolerance of a test system and being easier to install, debug and maintain.
(4) The test object of the invention has no special requirements on the composition form of the non-continuous mirror surface, and the target to be tested can be a spliced mirror surface in the form of a spliced sub-mirror such as a hexagon or a fan or a sparse aperture mirror surface;
(5) compared with the most advanced measurement technology at present, the device used by the invention has smaller shape and size and higher space utilization rate, and saves the precious space of the imaging end of the telescope;
(6) the core element used in the invention has smaller size and is easy to be made into an integrated detection system;
(7) compared with the prior art that the prior art can only measure the piston, tip and tilt errors between two adjacent spliced sub-mirrors or sparse sub-mirrors at the same time, the method can measure the piston, tip and tilt errors between a plurality of spliced sub-mirrors or sparse sub-mirror arrays at the same time, thereby greatly improving the measurement efficiency;
(8) the core elements used in the invention are mature commodity elements, so the interchangeability is good, and the replacement and the maintenance are easy;
(9) the invention can simultaneously realize the dynamic measurement of large measurement range and high measurement precision of the errors of the piston, tip and tilt between the spliced sub-mirrors or the sparse sub-mirror arrays, which are not possessed by other measurement technologies at present.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (9)
1. A first-order wavefront error measurement system of a non-continuous mirror telescope is characterized by comprising a mask (2), an electric control rotary filter wheel (3), a polarization grating (4), a diffraction element (5), a micro-displacement actuator (6), a first lens (7), a spatial filter (8), a second lens (9), a pixel displacement polarization measurement device (10) and a data acquisition processing computer (11);
the mask (2), the electric control rotary filter wheel (3), the polarization grating (4), the diffraction element (5), the first lens (7), the spatial filter (8), the second lens (9) and the pixel shift polarization measurement device (10) are sequentially and coaxially arranged, the micro-displacement actuator (6) is arranged on the diffraction element (5), and the data acquisition and processing computer (11) is respectively connected with the electric control rotary filter wheel (3), the micro-displacement actuator (6) and the pixel shift polarization measurement device (10);
emergent light of an optical system of the non-continuous mirror telescope is incident to a conjugate surface of an image surface of a first-order wavefront error measuring system, the mask (2) positioned on the conjugate surface is used for sampling reflected light rays in different sub-mirror areas in an equal circular area, two light beams sampled by the mask (2) pass through an optical filter on the electric control rotary filter wheel (3) to be changed into monochromatic light, the two monochromatic light beams pass through the polarization grating (4), the polarization grating (4) is used for selectively splitting light according to the polarization state of the monochromatic light to form + 1-order diffracted light and-1-order diffracted light, the + 1-order diffracted light is left-handed circular polarized light, the-1-order diffracted light is right-handed circular polarized light, the diffraction element (5) is moved to an overlapping area of the + 1-order diffracted light and the-1-order diffracted light under the control of the data acquisition processing computer (11) and is used for the + 1-order diffracted, the combined light sequentially passes through the first lens (7), the spatial filter (8) and the second lens (9) to form a collimated light beam, and the collimated light beam enters the pixel shift polarization measurement device (10);
the pixel shift polarization measurement device (10) comprises a photoelectric detector array (10-1), a micro polarizer array (10-2) and a lens array (10-3) which are sequentially arranged, wherein the micro polarizer array (10-2) comprises a plurality of polarizer units, each polarizer unit corresponds to one pixel unit of the photoelectric detector array (10-1) and one lens unit of the lens array (10-3), and the polarizer units comprise four wire grid polarizing plates with different polarization angles;
the pixel shift polarization measurement device (10) collects light intensity signals recorded by four wire grid polarizer classified pixels by utilizing the photoelectric detector array (10-1), and sends the light intensity signals to the data acquisition processing computer (11), the data acquisition processing computer (11) obtains four phase shift interferograms according to the light intensity signal processing, and the first-order wavefront error between two discontinuous mirror surfaces is obtained by carrying out phase unwrapping processing on the four phase shift interferograms.
2. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1,
the polarization angles of the four wire grid polarizers are 0 °, 45 °, 90 ° and 135 °, respectively.
3. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1 or 2,
the data acquisition processing computer (11) determines a corresponding preset error range according to the first-order wavefront error, controls the electric control rotary filter wheel (3) to rotate according to the preset error range, replaces the current optical filter with the optical filter corresponding to the preset error range, the pixel shift polarization measurement device (10) acquires light intensity signals again and sends the acquired light intensity signals to the data acquisition processing computer (11), the data acquisition processing computer (11) processes the light intensity signals to obtain four phase shift interferograms, and the four phase shift interferograms are subjected to phase unwrapping processing to obtain the high-precision first-order wavefront error between the two discontinuous mirror surfaces.
4. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1 or 2,
the non-continuous mirror telescope is a spliced mirror telescope or a sparse aperture telescope.
5. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1 or 2,
the micro-displacement actuator (6) is a piezoelectric ceramic micro-displacement actuator.
6. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1 or 2,
the electric control rotary filter wheel (3) comprises four optical filters which are uniformly distributed on the circumference and have different wavelength ranges, and the wavelength ranges of the four optical filters are matched with the working wavelength range of the polarization grating (4).
7. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1 or 2,
the wavelength range of the polarization grating (4) is 450-650 nm.
8. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1 or 2,
the photoelectric detector array (10-1) is a CCD sensor or a CMOS sensor.
9. The first-order wavefront error measuring system of the non-continuous mirror telescope of claim 1 or 2,
the pixel-shifting polarization measurement apparatus (10) employs an IMX250MZR sensor.
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| CN113834639A (en) * | 2021-09-29 | 2021-12-24 | 中国科学院长春光学精密机械与物理研究所 | Distortion eliminating ultramicro-nano optical system based on pixel-level polaroid |
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