Diffractive telescope technology is an innovation solution in construction of large light-weight space telescope. However, the nondesign orders of diffractive optical elements (DOEs) may affect the imaging performance as stray light. To study the stray light characteristics of a diffractive telescope, a prototype was developed and its stray light analysis model was established. The stray light characteristics including ghost, point source transmittance, and veiling glare index (VGI) were analyzed. During the star imaging test of the prototype, the ghost images appeared around the star image as the exposure time of the charge-coupled device improving, consistent with the simulation results. The test result of VGI was 67.11%, slightly higher than the calculated value 57.88%. The study shows that the same order diffraction of the diffractive primary lens and correcting DOE is the main factor that causes ghost images. The stray light sources outside the field of view can illuminate the image plane through nondesign orders diffraction of the primary lens and contributes to more than 90% of the stray light flux on the image plane. In summary, it is expected that these works will provide some guidance for optimizing the imaging performance of diffractive telescopes.
Using lightweight, replicated diffractive optics, we can construct extremely large aperture telescopes in space.The transmissive primary significantly reduces the sensitivities to out of plane motion as compared to reflective systems while reducing the manufacturing time and costs. This paper focuses on the design, fabrication and ground demonstration of a 460mm diffractive transmissive telescope,the primary F/# is 6, optical field of view is 0.2° imagine bandwidth is 486nm~656nm.The design method of diffractive optical system was verified, the ability to capture a high-quality image using diffractive telescope collection optics was tested.The results show that the limit resolution is 94lp/mm, the diffractive system has a good imagine performance with broad bandwidths. This technology is particularly promising as a means to achieve extremely large optical primaries from compact, lightweight packages.
Micro-structure optical elements are gradually applied in modern optical system due to their characters such as light weight, replicating easily, high diffraction efficiency and many design variables. Fresnel lens is a typical micro-structure optical element. So in this paper we take Fresnel lens as base of research. Analytic solution to the Point Spread Function (PSF) of the segmented Fresnel lens is derived based on the theory of optical diffraction, and the mathematical simulation model is established. Then we take segmented Fresnel lens with 5 pieces of sub-mirror as an example. In order to analyze the influence of different offset errors on the system’s far-field image quality, we obtain the analytic solution to PSF of the system under the condition of different offset errors by using Fourier-transform. The result shows the translation error along XYZ axis and tilt error around XY axis will introduce phase errors which affect the imaging quality of system. The translation errors along XYZ axis constitute linear relationship with corresponding phase errors and the tilt errors around XY axis constitute trigonometric function relationship with corresponding phase errors. In addition, the standard deviations of translation errors along XY axis constitute quadratic nonlinear relationship with system’s Strehl ratio. Finally, the tolerances of different offset errors are obtained according to Strehl Criteria.
Stitching Fresnel lens are designed for the application in the micro-focus X-ray, but splicing errors between sub-apertures will affect optical performance of the entire mirror. The offset error tolerance of different degrees of freedom between the sub-apertures are analyzed theoretically according to the wave-front aberration theory and with the Rayleigh criterion as evaluation criteria, and then validate the correctness of the theory using simulation software of ZEMAX. The results show that Z-axis piston error tolerance and translation error tolerance of XY axis increases with the increasing F-number of stitching Fresnel lens, and tilt error tolerance of XY axis decreases with increasing diameter. The results provide a theoretical basis and guidance for the design, detection and alignment of stitching Fresnel lens.
This paper describes a pentaprism scanning combined with sub-aperture stitching interference method to test large
aperture optical system wave-front. This method uses pentaprism scanning and interferometer testing sub-aperture
optical system wave-front, after testing all the sub-aperture wave-front and then using average error stitching algorithm
to reconstruction full-aperture optical system wave-front. It makes use of the pentaprism easily to adjust and
interferometer's high-precision characteristic. Analyzed the mechanical precision of turntable and electric guide, when
the turntable sway angle is less than 8', location accuracy is less than 1.194' and the electric guide linearity is less
than 8'location accuracy is less than 83.3μm, can meet the testing requirements. We used 40mm sub-aperture testing
312mm full aperture wave-front PV is 0.2197λ and RMS is 0.0536λ. Compared the stitching results with Zygo
interferometer directly full aperture testing verified the accuracy of the method and provides a new idea for testing a large aperture optical wave-front.
Two-mirror optical system has been widely used for large telescope, infrared and ultraviolet optical systems. Subaperture
stitching interferometry technique has been developed for low cost and effective test of large optical system. The
principle of error averaging subaperture stitching algorithm for testing two-mirror optical system wavefront is introduced
in this paper. A two-mirror optical system is simulated by zemax software, a reasonable mathematical model is
established and computer simulation experiment is carried out. Compared the stitching results with zemax software, the
relative error of PV and RMS is 0.76% and -0.44%respectively. The PV and RMS of wavefront phase distribution
residual are 0.0097λ and 0.0013λ .It is proved that the model and method are accurate and feasible to test optical
system.
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