Effect of Wet Expansion Behavior on Polyimide Membrane Diffractive Lens

Guohan Gao,Bin Fan,Chunlin Guan,Danbo Mao

doi:10.3390/coatings9090559

Abstract

Optical polyimide (PI) membrane is a potential substrate to fabricate a diffractive primary lens in large aperture space-borne telescope. In this paper, we investigated the wet expansion behavior of PI via a strain gauge method and measured the coefficient of wet expansion (CWE) of PI membrane supported by different fixtures. The CWE of silica-fixed, ring-fixed, and free state PI membrane were near zero, 5 ppm/%, and 10 ppm/% respectively. It is found that Fresnel zone lens (FZL), based on PI membrane with lower CWE, achieve a better imaging quality with smaller wave-front errors. The underlying mechanisms and methods to improve imaging quality of ring-fixed FZL are discussed. This work provides direction in fabricating a flexible membrane diffractive lens with applicable imaging quality.

Highlights

Polyimide (PI), with unique properties such as good space environmental adaptability, excellent chemical stability, and mechanical properties, has been widely applied in aerospace engineering, micro manufacturing, display panels industry, and so on [1]
The black line refers to expansion trend and its slope equals coefficient of wet expansion (CWE) of free, the blue line refers to sample under 5 MPa initial stress, and the black line refers state PI membrane
The black line refers to expansion trend and its slope equals CWE of free state PI membrane

Summary

Introduction

Polyimide (PI), with unique properties such as good space environmental adaptability, excellent chemical stability, and mechanical properties, has been widely applied in aerospace engineering, micro manufacturing, display panels industry, and so on [1]. A Fresnel zone lens (FZL) is fabricated by photolithography and subsequent etching process to form concentric rings in an optical substrate, and act as a diffractive lens. Further research needs to assess the way wet expansion behavior affects. Further research needs to assess the way wet expansion behavior affects imaging quality of PI membrane FZL. Schematic of of Polyimide (PI) membrane Fresnel zone lens (FZL) This behavior the diffraction pattern, if theon temperature and to humidity change from. PI membrane’s anisotropy and dimensional stability and possible approaches to eliminating the effect of wet expansion behavior on wave-front error. Found that coefficient of wet expansion (CWE) varies in different directions, and anisotropy behavior was correlated to molecular orientation [22].

Results and Discussion

Results

Humidity

Effect

On humidity

Conclusions