生命特征检测偏振仪LSDpol的设计
Design of the Life Signature Detection Polarimeter LSDpol
摘要：
许多生物产生的手性分子，如氨基酸和糖，显示出对左手或右手的偏好（同手性）。因此，被诸如藻类和树叶之类的生物材料反射的光表现出强烈依赖于波长的少量圆偏振。我们的生命特征检测旋光仪（LSDpol）经过优化，可测量这些生命特征。LSDpol是一款紧凑型分光偏振计概念，没有移动部件，可即时测量视场内的线偏振和圆偏振，灵敏度优于1 e-4。我们希望在地面和飞机上验证其性能后将该仪器送入轨道。LSDpol是基于一个空间变化的四分之一波长延迟，这是实现与图案化的液晶。它是第一个最大化偏振灵敏度的光学元件。由于这种模式以及光谱仪的入口狭缝必须成像到检测器上，因此狭缝用作孔径，并且内部场光阑限制视场。延迟器的快轴角度沿一个空间维度线性变化。采用固定的四分之一波长延迟器和偏振光栅作为色散器和偏振分束器。圆偏振和线偏振由此在整个频谱上以不兼容的调制频率编码，这最小化了从线偏振到圆偏振的潜在串扰。
英文摘要：
Many biologically produced chiral molecules such as amino acids and sugars show a preference for left or right handedness (homochirality). Light reflected by biological materials such as algae and leaves therefore exhibits a small amount of circular polarization that strongly depends on wavelength. Our Life Signature Detection polarimeter (LSDpol) is optimized to measure these signatures of life. LSDpol is a compact spectropolarimeter concept with no moving parts that instantaneously measures linear and circular polarization averaged over the field of view with a sensitivity of better than 1e-4. We expect to launch the instrument into orbit after validating its performance on the ground and from aircraft. LSDpol is based on a spatially varying quarter-wave retarder that is implemented with a patterned liquid-crystal. It is the first optical element to maximize the polarimetric sensitivity. Since this pattern as well as the entrance slit of the spectrograph have to be imaged onto the detector, the slit serves as the aperture, and an internal field stop limits the field of view. The retarder's fast axis angle varies linearly along one spatial dimension. A fixed quarter-wave retarder combined with a polarization grating act as the disperser and the polarizing beam-splitter. Circular and linear polarization are thereby encoded at incompatible modulation frequencies across the spectrum, which minimizes the potential cross-talk from linear into circular polarization.
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