Dynamic spectral tailoring of a 10 GHz laser frequency comb for enhanced calibration of astronomical spectrographs

• DOI: 10.48550/arxiv.2502.05401
• Publication Date: 2025-02-07
• Authors: Pooja Sekhar; Connor Fredrick; Ping Zhong; Abijith S. Kowligy; A. Cingöz; Scott A Diddams
• Keywords: Optical frequency comb

Laser frequency combs (LFCs) are an important component of Doppler radial velocity (RV) spectroscopy that pushes fractional precision to the $10^{-10}$ level, as required identify and characterize Earth-like exoplanets. However, large intensity variations across LFC spectrum arise in nonlinear broadening limit range comb lines can be used for optimal wavelength calibration with sufficient signal-to-noise ratio. Furthermore, temporal spectral-intensity fluctuations LFC, coupled flux-dependent detector defects, alter instrumental point spread function (PSF) result spurious RV shifts. To address these issues improve precision, spectral flattening is crucial LFCs maintain a constant photon flux per mode. In this work, we demonstrate dynamic shaping setup using spatial light modulator (SLM) over 800nm 1300nm. The custom compensates amplitude real time also correct wavelength-dependent spectrograph transmission, achieving profile delivers readout necessary maximizing precision. Importantly, out-of-loop properties flattener verify twofold improvement stability. This technique, combined our approach pumping waveguide broadener out-of-band at 1550 nm, reduces range. While region tailored employed Habitable-zone Planet Finder (HPF) spectrograph, method broadly applicable any astronomical calibration.