With the continuous deepening of research and development in the field of aerospace, the requirements for aerospace payloads are also increasing. The stray light received by the spaceborne telescope in the space environment will be one of the most important factors affecting its performance. The optical mechanical surface of spaceborne telescope will deviate from the original design due to various objective factors during the whole link process, and the actual optical mechanical surface is not ideal. In order to ensure that it can work normally, it is necessary to simulate and analyze the stray light situation of the whole link. This paper mainly introduces the complex environment and complex characteristics experienced from the ground section to the orbit section, analyzes and summarizes the sources of stray light, and finally proposes a framework for establishing a digital twin model of stray light for spaceborne telescopes. Through data-driven and model-driven methods, finally build a complete set of ground, launch, and in-orbit digital twin models.
In order to solve the serious problem of ordinary biological microscopic objective lenses including field distortion, chromatic aberration and low resolving power, a high-resolution infinite conjugate microscopic objective with three fourth-order Zernike polynomial surfaces has been presented in this paper. The numerical aperture of microscopic system is 1.1 with 2.6mm focal length, which can be equipped with most field lens. The design and analysis results show that the par focal distance of the objective lens is 45mm, and the incidence angle and refraction angle of the optical surface of the lens are less than 60°, which meets the international standard of the microscopic objective lens. The optical Modulate Transfer Function (MTF) curve is close to the theoretical diffraction limit and the RMS wavefront error of the high-performance microscopic objective satisfied Marechal criterion. In addition, the tolerance analysis results show that the system can be processed based on the existing machining methods, despite the wavefront aberration RMS will deteriorate to 0.25λ. The whole system can be used in genetic testing research and mirror test, which is expected to promote the development of medical testing and industrial test and become one of new generation of diagnostic tools.
In this paper, a new type of wheel polishing tool is designed. Through the bevel gear structure, only one motor is used to realize the revolution and rotation of the polishing wheel, which makes the structure simple, small inertia, and stable operation. Traditional polishing wheels have a three-layer structure: internal rigid hub, middle flexible rubber, and external polishing pad. It is found through experiments that the hardness of rubber has a greater influence on the tool influence function (TIF). Therefore, by optimizing the hardness of the rubber, we obtained a TIF very close to the Gaussian shape, which is conducive to the rapid convergence of the surface error. Finally, the effects of polishing wheel speed, polishing pressure and polishing time on the TIF, as well as the stability of the TIF, are studied through experiments. Experiments show that: (1) There is no linear relationship between the removal efficiency of the polishing wheel, the polishing wheel speed, and the polishing pressure, but as the parameter increases, the increase in the removal efficiency slows down; (2) There is a good linear relationship between the removal amount of the polishing wheel and time; (3) The TIF is very stable, and the stability of the TIF reaches 98%.
An ABB IRB6640 industrial robot is used as a processing platform for optical polishing. The relationships of coordinate systems are defined, the algorithm of coordinate transformation, Euler angles and quaternion are provided. M-like removal function and Gaussian-like removal function are used to simulation process an off-axis aspheric surface. The surface error after polishing by M-like removal function is 1.5 to 2.5 times bigger than Gaussian-like removal function. This proves that M-like removal function also has good convergence speed. Then, the pentagram polishing head is used to polish a Φ600mm off-axis paraboloid surface. After 15 cycles, about 120 hours processing, PV converges from 5.8μm to 0.836μm, RMS converges from 1.2μm to 0.054μm, PV and RMS respectively converge 85% and 95%. The experiment shows M-like removal function has good convergence speed.
The manufacturing and testing of a surface modified silicon carbide mirror with a bowl-shaped structure was introduced. The entire process flow includes pre-modification silicon carbide substrate processing, silicon carbide substrate surface modification, and silicon modified layer processing. Firstly, before the modification, the conventional processing method of silicon carbide was used, and the effect of the support form on the figure was eliminated by multiple direction rotation testing.At the same time, the self-aligned compensation cross-test was completed and the accuracy of the aspherical surface coefficient was verified. In addition, the polishing process of the silicon modified layer material was studied, and the optimum process parameters suitable for polishing the silicon modified layer material were found out. Based on the above experiments, the modified optical processing adopts a combination of two kinds of polishing technology: flexible chemical mechanical polishing (FCMP)and ion beam figuring (IBF).The surface roughness and surface finish of silicon modified layer are improved by flexible chemical mechanical polishing technology. The high figure accuracy of silicon modified layer is achieved finally by ion beam figuring technology. Finally, the final result of the mirror after IBF is:the RMS values of the figure and roughness in the Φ450 mm aperture is 0.01λ (λ=632.8 nm) and 0.52 nm. The mirror's processing results fully meet the design specifications.
Based on the wavefront aberration theory and the coordinates transform, the free form optical induced aberration’s characteristic of optical system has been analyses in this paper. The optical wavefront error and the free form surface can be express as Fringe Zernike polynomial; the free form optical on the surface (Stop or Entrance pupil or Exit pupil) affects all the field angles equally. If the surface is not the pupil of optical system, the aberration observed is different from the free form itself because the footprint of the beam for an off-axis field point only covers part of the surface. For the Fringe Zernike surface figure on a surface not at pupil, it will transform into lower order Fringe Zernike aberration in the optical system, the relationship between different Fringe Zernike aberration and field is different, and the location zero for the lower aberration always reside at the center of the field of view.
The increased sensitivity of space-based sensors has imposed greater stray light performance goals on telescope design. To meet the demand, a stray light test station for measuring point source transmission (PST) has been built with a lower threshold and higher accuracy. The station is nearly all black with dimensions of 28m long by 8m wide by 9m high. it is coupled with a double cylindrical chamber that reflects the specular light away from the instrument under test. The chamber is a Class 6 cleanroom. The station will allow measuring the instruments with up to a 1 meters diameter, and to perform these measurements at visible and infrared wavelengths. The instrument under test will allow to scan at azimuth angles ±110°, and at elevation ±15°. The tests were performed to estimate stray light characteristics of two optical instruments. Test results demonstrated PST performance below 1×10-7 at visible wavelengths, and 1×10-6 at infrared wavelengths.
A three-dimensional kinematic model of spherical mirror is developed by coordinate transformation theory. Based on the
model and Preston equation, material removal rate for polishing with constant pressure can be obtained. Then the fitted
parameters are determined for special process tools (pentagon tool and Uniform Removal Tool), Conclusions beneficial
to glass polishing in practice are arrived. The simulate results can describe visually the material removal law of mirror
under so many kinematic parameters. The work discussed above is of importance to polish flat mirror, spherical mirror
and aspheric mirror with one-axis polisher.
Determine the misalignment of optical element quickly and exactly is the key to the technology of computer-aided
alignment (CAA). For alignment a three-mirror off-axis field bias system, the sensitivity matrix method was used to
simulate the alignment process. The results of simulation show that the sensitivity matrix method was not convergence. A new CAA method to get misalignment was put forward; the misalignment was obtained by programming the function of optical design software CODE V’s auto-optimization option. The system’s alignment characteristic was analysis and made use of this new method put up a computer simulation. The results of simulation show that the misalignment determined by only once auto-optimization and guidable to alignment of this system. After alignment, the optical system produced a measured wave front error across the all image plane less than 0.08 waves RMS at λ=0.6328μm.
Null testing of off-axis conic surface at the pair of conjugate foci can add sensitivity resulting from double pass off the
test piece. However, the alignment procedure of the test is difficult. The main reason is that the return wavefront from
off-axis aspheric surface is not rotationally symmetric so that the observer cannot tell if the wavefront asymmetries are
due to surface or misalignment errors. In this paper, we analyze the effect of misalignments on test results with the
optical path method, and derive an equation for misalignment-induced aberrations. Next we present an optimum method
for the removal of alignment errors. As an example the method is applied to the alignment of an off-axis mirror. After
several alignments, a misaligned test system giving 0.093λ rms wavefront error can be adjusted to 0.024λ, at 0.6328
microns.
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