Direct exoplanet spectroscopy aims to measure the spectrum of an exoplanet while simultaneously minimizing the light collected from its host star. Isolating the planet light from the starlight improves the signal-to-noise ratio (S/N) per spectral channel when noise due to the star dominates, which may enable new studies of the exoplanet atmosphere with unprecedented detail at high spectral resolution (>30,000). However, the optimal instrument design depends on the flux level from the planet and star compared to the noise due to other sources, such as detector noise and thermal background. Here we present the design, fabrication, and laboratory demonstration of specially-designed optics to improve the S/N in two potential regimes in direct exoplanet spectroscopy with adaptive optics instruments. The first is a pair of beam-shaping lenses that increase the planet signal by improving the coupling efficiency into a single-mode fiber at the known position of the planet. The second is a grayscale apodizer that reduces the diffracted starlight for planets at small angular separations from their host star. The former especially increases S/N when dominated by detector noise or thermal background, while the latter helps reduce stellar noise. We show good agreement between the theoretical and experimental point spread functions in each case and predict the exposure time reduction (∼33%) that each set of optics provides in simulated observations of 51 Eridani b using the Keck Planet Imager and Characterizer instrument at W. M. Keck Observatory.

直接系外行星光谱仪旨在测量系外行星的光谱，同时最大限度地减少从其主星收集的光。当由恒星引起的噪声占主导地位时，将行星光与星光隔离可提高每个光谱通道的信噪比 (S/N)，这可能会在高光谱分辨率 (>30,000) 下以前所未有的细节对系外行星大气进行新的研究）。然而，最佳仪器设计取决于行星和恒星的通量水平与其他来源的噪声相比，例如探测器噪声和热背景。在这里，我们展示了专门设计的光学器件的设计、制造和实验室演示，以使用自适应光学仪器在直接系外行星光谱学的两个潜在方案中提高信噪比。第一个是一对光束整形透镜，通过提高行星已知位置的单模光纤的耦合效率来增加行星信号。第二个是灰度变迹器，它可以减少与主星小角度间隔的行星的衍射星光。前者在受探测器噪声或热背景支配时尤其会增加 S/N，而后者有助于降低恒星噪声。我们在每种情况下显示了理论和实验点扩散函数之间的良好一致性，并预测了每组光学器件在使用 WM Keck 的 Keck Planet Imager and Characterizer 仪器对 51 Eridani b 的模拟观测中提供的曝光时间减少（~33%）天文台。