In order to measure the transmittance for a large field of view (FOV), a system based on scanning LED is developed. The system mainly consists of tunable LEDs, a glass diffuser and a camera. The LED panel would display different colors in the CIE color space. An algorithm of converting the light wavelength to the RGB values is adopted. The images are captured using a monochrome camera. Depending on the number of colors displayed, the transmittance map for the entire spread of visible colors can be determined. Results are compared with those measured through a spectrometer. The spectral transmittance for the two methods exhibit good similarity. The system provides a means of measuring transmittance with no moving parts and can be extended to other hyperspectral imaging applications.
Lensless digital holography could improve the resolution of digital holography reconstruction and has drawn wide attention. The complex wave-front could be reconstructed through Fourier transformation of a single hologram. It’s crucial to reconstruct the phase precisely. However the phase constructed from a single hologram usually contains a quadratic aberration. Many methods are proposed to remove the item. In this paper the method of lateral shearing interferometry is studied to compensate the quadratic aberration. First we show the aberration in lensless digital holography and the lateral shearing interferometry. Then numerical simulations are carried out to test the method. It can be concluded that the method of linear fitting could effectively extract the quadratic aberration. The drawback is that the quadratic phase information extracted could not discern the additional aberration and the quadratic item included by the object wave field. A small local smooth area couldn’t guarantee good estimation of quadratic aberrations. A larger area could get better results even in the presence of noises. However the aberration compensation depends greatly on noises. The reason of larger residual aberrations in the presence of noises is that noises influence greatly on the phase reconstruction including unwrapping.
The support systems of primary mirrors usually consist of axial supports and lateral supports. The surface of an active
thin mirror is maintained through actuators on back of the mirror. The axial and lateral supports are designed for a 1.2 m
thin mirror with the aspect ratio of 24. The 36 axial supports are equally distributed on three rings and normalized
radiuses are 0.275, 0.583 and 0.897 respectively. The numbers of axial supports for each ring are 6, 12 and 18
respectively. Three lateral support units are equally distributed at the outer edge of the mirror. The optimum surfaces are
2.7 nm and 12 nm RMS respectively when the mirror is mounted horizontally and vertically. It’s also demonstrated that
the active supports could correct most of manufacture errors.
Active optics is one of the key technologies for constructing modern large telescope. It's necessary to study the
performance of an active optics system theoretically in advance. In this paper we built a 1.2 m active thin-mirror model
with 36 axial supports and 3 lateral supports. In order to ensure the active optics system and select appropriate force
actuators, we carried out following analyses through FEA: the ability of the active optics system to duplicate the first 15
Zernike modes and the first 15 natural resonance modes; mirror deformations before and after active force corrections
under gravitational loads; the maximum stresses of the mirror while fitting Zernike modes of 1 micron PV amplitude;
requirements of the force accuracy and the maximum load for the force actuators. Through above analyses over the
theoretical performance of the 1.2 m active thin-mirror, it can be concluded that: the support system is effective to
maintain the mirror surface; the maximum stresses of the mirror while fitting aberrations are within the allowable stress
of the glass material; the force resolution is about 0.5 N and the maximum load for the force actuators is about 400 N. As
a result fundamentals are set up for constructing a practical active mirror.
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