The stitching interferometry for the surface profile measurement of a large aperture component is studied. To analyze the
overlapping region interferogram of the adjacent subapertures with Scale Invariant Feature Transform(SIFT) algorithm,
the stitching parameters of the adjacent subapertures and then overall surface information of the tested component can be
obtained. SIFT algorithm of subaperture positioning, interferogram processing, phase unwrapping, Zernike polynomials
wavefront fitting and subaperture wavefront stitching programs are written. A principle experiment has been carried out.
Compared with the measurement results between the stitching interferometry and full caliber testing, the deviation of
RMS is less than 2nm.
A two-path adaptive phase-shifting interferometry, which is insensitive to the disturbance of constant term of phase
perturbations induced by environmental vibration and air turbulence, is proposed. The beam sent from the source is
divided into two parts by polarization beam splitter and the two parts enter a phase-shifting interference system, and then
a two-path adaptive phase-shifting interference system is formed. The beam intensity of the one path is modulated in
high frequency with an acousto-optic modulator, and phase lock-in as well as the closed loop control techniques is used
in this path. Thus, the wobble of interference fringes can be compensated, and sequentially the fringes will be locked at
arbitrarily chosen phase for phase-shifting testing. Meantime, surface profile of an optical element is measured in another
path with five-step phase-shifting interferometry algorithm. Comparing with other similar techniques, here the depth of
signal modulation is not limited by the optical path difference and the contrast of the fringe used to evaluate the surface
profile is not reduced, hence a high signal-to-noise ratio can be obtained. In order to verify the feasibility of this
interferometry, a two-path adaptive phase-shifting interference system is set up and the experiments of phase-locking and
surface profile testing have been carried out. After phase-locking being realized, the residual wobble amplitude of optical
phase difference is 2.65°RMS. Comparing with ZYGO interferometer, the result of surface profile testing is the same but
the measurement repeatability is better.
An active co-phasing imaging testbed with high accurate optical adjustment and control in nanometer scale was set up to
validate the algorithms of piston and tip-tilt error sensing and real-time adjusting. Modularization design was adopted.
The primary mirror was spherical and divided into three sub-mirrors. One of them was fixed and worked as reference
segment, the others were adjustable respectively related to the fixed segment in three freedoms (piston, tip and tilt) by
using sensitive micro-displacement actuators in the range of 15mm with a resolution of 3nm. The method of twodimension
dispersed fringe analysis was used to sense the piston error between the adjacent segments in the range of
200μm with a repeatability of 2nm. And the tip-tilt error was gained with the method of centroid sensing. Co-phasing
image could be realized by correcting the errors measured above with the sensitive micro-displacement actuators driven
by a computer. The process of co-phasing error sensing and correcting could be monitored in real time by a scrutiny
module set in this testbed. A FISBA interferometer was introduced to evaluate the co-phasing performance, and finally a
total residual surface error of about 50nm rms was achieved.
In order to achieve a spatial resolution comparable to a monolithic telescope of the same diameter, the segmented mirror
surface must be phased with an accuracy about λ/20 wavefront rms, which is comparable with the accuracy of the segment figure. During the phasing procedure, piston, tip-tilt are controlled to achieve the best image quality of the telescope. The residual rms wavefront error of whole aperture taken as the merit function reaches minimum analytically when the least-square-fit plane of tested segment meets together with that of reference mirror, which means that "phasing" is a statistical mood of the whole aperture, not to match some small areas of the segments. The impact of segment aberration on the whole aperture residual rms wavefront error is simulated using the whole segment aperture sensing and edge sensing respectively. By the analytical and numerical simulation, it is demonstrated that the whole segment aperture phase sensing can make a better image quality than the edge sensing.
The primary mirror's aperture limits the telescope's resolution. A segmented primary mirror is adopted to improve the
resolution. Since the primary mirror with large diameter is segmented, the segmented mirrors must be co-phased to
ensure the imaging quality. Optical method and electrics method can be used to test the co-phasing error between the two
adjacent segment mirrors. However the optical system of telescope will be complicated by attaching an optical cophasing
test system, and some unstable factors will be introduced. In this paper, an electrics co-phasing testing method
was discussed. Capacitance micrometer technology was used in this method, and relevant experiments have been carried
out. And the result of these experiments indicated that the method described in this paper is feasible.
A single longitudinal mode and narrow line width external cavity semiconductor laser is proposed. It is constructed with a semiconductor laser, collimator, a flame grating, and current and temperature control systems. The one facet of semiconductor laser is covered by high transmission film, and another is covered by high reflection film. The flame grating is used as light feedback element to select the mode of the semiconductor laser. The temperature of the constructed external cavity semiconductor laser is stabilized in order of 10-3°C by temperature control system. The experiments have been carried out and the results obtained ---the spectral line width of this laser is compressed to be less than 1.4MHz from its original line-width of more than 1200GHz and the output stability (including power and mode) is remarkably enhanced.
An optical diagnostic system designed for the microgravity experiments on Marangoni drop migrations has been depicted in the presented paper. One part of the optical system was used to image and record the drops tracks; the other part was an equal-thick interferential system, it has the ability to observe the fine structures of the drop migrations. Some ground-based experiments had been performed and the results were simply discussed in the present paper.
Using an actuator array to thrust load onto the back of a mirror can control the profile of the mirror or correct its residual irregularity. It is meaningful to study how to improve the control or correction capability of active mirror for practice. The closest profile of a mirror to a given Zernike element profile can be obtained through linear combination of the influence functions. The algorithm of evaluating an active mirror's capability of correction is presented. Static analysis via Finite Element Method (FEM) is studied at various conditions with different amount and distribution of actuators, as well as the fixing manner, and the optimum scheme of actuator array is yielded.
A mini adaptive optics system is developed in which a micro-machined membrane deformable mirror and the technique of cross-folded optical path are employed. The system has a volume of 30x20x10cm3, a weight of 4kg, while its bandwidth is 17Hz, and the accuracy of its wave-front sensor is ?/15 mis. The system is aimed at improving the image quality of space-based optical systems, but it is versatile. The control host is a PC computer, and various functions are realized, such as, real time display of image or wave-front, testing of the response matrix of the deformable mirror, and closed-loop control. An experimental system is also setup to test the performance ofthe AO system. The results of the experiments show that the AO system is very effective in compensation for thermal deformations and dynamic disturbances.
A novel method named radial slope testing for measuring the wave aberration of an optical imaging system with a large aperture is introduced, which is a kind of self referenced testing. A Zernike slope polynomial fitting algorithm is applied to the data processing. The principal of method and construction of system are described, the results of computer simulation testing are presented as well. It is shown that this method is especially useful for wavefront sensing of an active optical system operated on a satellite without any guide star or reference surface.
The methods of surface irregularity testing and characteristic parameter measurement for aspherical mirrors are studied experimentally and computer-simulatively. An accurate method for paraxial curvature radius measurement of aspherical mirrors by a special micrometric rod, in the meantime of testing of surface irregularity, is described. Finally, the measurement accuracy is analyzed.
An adaptive phase-shifting interferometry, insensitive to the disturbance of constant term of phase perturbations induced by environmental vibration and air turbulence is introduced. Where high frequency intensity modulation of laser beam and phase lock-in as well as the closed loop control techniques are used. The wobble of interference fringes can be compensated, and sequentially be locked at arbitrarily chosen phases for phase-shifting testing. Comparing with other similar techniques, here the depth of signal modulation is not limited by the magnitude of optical path difference (OPD) and the fringe contrast is not reduced by the modulation, hence a high SNR can be obtained. The experimental results and conclusions are presented.
Using the technique of capacitance micrometry it is possible to measure very small displacements. Here, a microcomputer- controlled scanning Fabry-Perot interferometer is presented. In each scanning step, the parallelism of Fabry-Perot interferometer is monitored and adjusted in real-time with the aid of three capacitance micrometers - it is the feature of this system, where the readjustment and scanning are realized with three electrostrictive actuators, and the parallelism and the spacing of the mirrors are controlled by three capacitance micrometers. The light information from the interferometer is detected by a photo-detector. All of these are controlled by a microcomputer in order to realize the scanning and real-time control of Fabry-Perot interferometer. This system removes the problem of the nonlinear response and hysteresis associated with electrostrictive actuators and allows precise control of both parallelism and spacing of the mirrors.
The static response function f(x,y) of bimorph mirror is calculated with the algorithms of Gaussian iteration and Monte-Carlo, while the performance of bimorph mirror deduced by Kokorowski is described using Poisson's equation, which meets the Neumann boundary conditions. The Zernike polynomials are fitted separately with whole set of response functions which are taken as base functions. The optimization of bimorph mirror is considered for a given pattern and the low order aberrations. The effectiveness of correction is analyzed theoretically and experimentally. The optical performed is analyzed and tested thereafter.
Optical angle gauge is one of the measuring instruments standardized by the National Metrological System of Chian for verification of plane angle. In this paper a new method for verifying the optical angle gauge is described and a related photoelectric goniometer developed by ourself is introduced. As a datum instrument for measuring deviation angle of optical wedge, its maximum error is less than 0.1 inch. In addition, some examples of its application for calibrating indication error of various angle measuring devices are presented, and its distinctive advantages, especially in calibrating 2D autocollimators, are demonstrated.
An experimental setup of photon counting real-time image acquisition system is introduced, wherein a photon image head (an image intensifier with high radiant emittance gain) is coupled with a high frame rate CCD camera by a super powerful relay lens. The restrictions on luminous emittance of object are analyzed for multiphoton and single photon imaging modes. The methods of determining readout noise are introduced. The application examples of system in adaptive optics wavefront sensor operated with a faint object, and in experimental study on the optical wave-particle duality and the uncertainty relation are presented.
A detailed analysis of the characteristics, regularities, and relationships of the centroiding errors of image spots caused by discrete and limited sampling, photon noise, and readout noise of the detector in a Hartmann-Shack wavefront sensor, wherein an image intensified charge-coupled device used as a photon detector is presented. The theoretical analysis and experimental results herein prove useful for optimum design and application of the sensor.
An experimental set-up of H-S (Hartmann-Shack) wavefront sensor using an ICCD (intensified charge coupled device) as a photon detector is introduced. The centroiding errors of image spots caused by discrete and limited sampling, photon noise, and read-out noise are analyzed theoretically and experimentally.
The limitations of a Hartmann type wavefront sensor are theoretically and experimentally
studied based on photon counting technique. An experimental set-up for
simulation of single subaperture adaptive astronomical telescope is described. The
results of experiments and analyses show that a star of the 8th magnitude can be
dealt with by this kind of wavefront sensors within 1 ms of time and with A/1O of
wavefront distortion detection sensitivity. As for calibration of experiments, an
algorithm related to luminous flux at entrance pupil of telescope and its corresponding
photo-electron rate detected by the wavefront sensor is presented and yenfied
An experimental study on the Hartmann type wavefront tilt sensor is carried out at photon noise limitation. The experimental results and analyses show that A/10 sensitivity of wavefront tilt detection for space objects with about 8th astro- nomical magnitude within 1 ms of time has been achieved. An algorithm and computer program related to the luminous flux and corresponding photo-electron rate for wavefront sensor based on photon counting technique has been established and verified by experiments.