Abstract
The microstructures on flexible membrane substrate prepared by the traditional methods may introduce large morphology and position errors, making it hard to achieve clear imaging. In this paper, we present a high precision fabrication method composed of two steps: unstressed fixation of the polyimide membrane and high precision fabrication of diffractive microstructures on the flexible membrane substrate. By using precise spin-coating technology, we get 25 μm thick polyimide membranes, whose coefficient of thermal expansion is almost zero. To prepare high precision microstructures, we propose an aerated membrane method, by which the flexible membrane substrate and the photoresist on it can attach tightly to the mask under the air pressure difference between the upper and lower surfaces of the membrane substrate during the contact lithography. The results show that the wave-front error obtained by this method is less than 1/30λ RMS (F# = 25@632.8 nm) at 400 mm aperture, indicating the microstructures have excellent morphologies and high position accuracy.
Highlights
Geostationary orbit satellites have attracted worldwide attention due to the high time efficiency and continuous detection capability, but in order to achieve the meter-level target resolution, the aperture of the primary mirror needs to reach more than 20 m [1]
We present a high precision fabrication method composed of two steps: unstressed fixation of the polyimide membrane and high precision fabrication of diffractive microstructures on the flexible membrane substrate
The ultrathin flexible membrane substrate diffractive optical element with high precision microstructures is shown as Fig. 10
Summary
Geostationary orbit satellites have attracted worldwide attention due to the high time efficiency and continuous detection capability, but in order to achieve the meter-level target resolution, the aperture of the primary mirror needs to reach more than 20 m [1]. In order to meet the requirements of high precision imaging, it is necessary to have a high accuracy wave-front sensor to detect the morphology errors of the sub-mirrors and correct them by actuators in real time, and need a high precision on-orbit deployable structure [3]. The use of large aperture membrane reflectors makes telescope systems extremely lightweight, it requires a high accuracy surface shape control system, which. The diffractive imaging system with the membrane material whose thickness is less than 30 μm has the characteristics of lightweight (only 1/6–1/50 of the reflective system), low morphology error requirements, space deployable capacity and easy replication, which has great potential in the field of high-resolution imaging in the geostationary orbit [4]
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