空间类地行星探测的偏振成像关键技术研究

The Earth-like planet detection requires an imaging contrast of 10E(-10) in the visible wavelength, which poses a serious challenge to the exoplanet imaging technology. In this proposal, a key technique named Polarimetry Imaging for Space-based Earth-like planet detection (PISE) was proposed. The PISE technique has several advantages compared with other imaging techniques such as polarization differential imaging and high-contrast dark hole: (1) The PISE technique can provide an imaging contrast gain of 1000 times in the visible wavelength, which can achieve a total imaging contrast of 10E(-10) when combining with a high-contrast coronagraph we previously developed, which meets the requirement of Earth-like planet imaging; (2) The PISE technique can measure all the Stokes parameters of the planetary light, and the polarimetric accuracy can achieve the order of magnitude of 10E(-4), which paves the way for the high-accuracy polarization measurements of the light signals from the Earth-like planet; (3) The PISE technique can cover an entire area within the field of view of the CCD camera with a single imaging procedure, and its detection efficiency is high. The proposal will lay a technical foundation for space-based Earth-like planet detection for China.

探测类地行星需要在可见光波段实现10E(-10)的成像对比度，这对系外行星成像技术提出了严峻的挑战。对此，本项目基于液晶可变相位延迟器提出空间类地行星探测的偏振成像（Polarimetry Imaging for Space-based Earth-like planet detection，简称PISE）关键技术。相比于偏振差分成像技术以及高对比度暗区技术，PISE技术的优势为：（1）PISE技术能够在可见光波段实现1000倍的成像对比度增益，联合研制的高对比度星冕仪在可见光波段达到10E(-10)的成像对比度，满足探测类地行星的要求；（2）PISE技术能够测量行星光的全部Stokes参量，而且偏振测量精度达到10E(-4)量级，为类地行星光信号的偏振精测奠定基础；（3）PISE技术进行一次成像就能够覆盖探测器视场内的整个区域，探测效率高。本项目将为我国开展空间类地行星探测奠定技术基础。

类地行星直接成像是当今天文学研究的一个前沿和热点，其终极目标是探测发现位于宜居带内的类地行星，并进一步确认是否存在地外生命信号，有望回答“人类在宇宙中是否孤独”这一基本科学问题。然而，对类地行星成像探测时需要在可见光波段实现10E-10的超高成像对比度，这对系外行星直接成像技术提出了严峻挑战。对此，本项目开展了基于液晶可变相位延迟器的空间类地行星探测偏振成像关键技术（简称PISE）研究，主要包括：LCVR的驱动电压——相位延迟量高精度定标、基于LCVR的偏振调制与偏振解调、实验系统的响应函数计算等内容。实验结果表明：（1）PISE偏振技术在可见光波段实现了1000倍的成像对比度增益，联合研制的高对比度星冕仪可以达到10E-10的成像对比度。（2）PISE偏振技术能够获得行星光的全部Stokes参数，并且偏振精度达到10E-4量级。（3）PISE偏振技术的探测效率高，可以实现对2λ/D以外整个区域的偏振成像探测。综上所述，本项目研究成果能够为我国未来开展类地行星的空间偏振探测奠定技术基础。