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22 July 2016 12.5-GHz-spaced laser frequency comb covering Y, J, and H bands for infrared Doppler instrument
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In order to detect Earth-like planets around nearby red dwarfs (in particular late-M stars), it is crucial to conduct precise radial velocity measurements at near-infrared wavelengths where these stars emit most of the light. We have been developing the Infrared Doppler (IRD) spectrograph which is a high dispersion spectrograph for the Subaru telescope. To achieve 1m/s RV measurement precision, we have developed a direct generation of laser frequency comb (LFC) that uses high-repetition-rate pump pulse synthesized by a line-by-line pulse-shaping technique. Our LFC generator has some advantages including simple and easy frequency stabilization, all fiber-optic configuration, and broadband calibration by the precise frequency shift of all modes in the LFC. We have successfully generated a 12.5-GHz-spaced comb spanning over 700 nm from 1040 to 1750 nm. The frequency stability was measured by optically heterodyning the comb with an acetylene-stabilized laser at 1542 nm as a reference light. The LFC showed a frequency stability of less than 0.2 MHz and an almost constant spectrum profile for 6 days. The original LFC that has just produced from highly nonlinear fibers needs some optical processing including spectrum shaping, depolarization, and a mode scramble in a multi-mode fiber before it is input into a spectrograph for the calibration. We have investigated the optical processing of the LFC which is necessary for the precise spectrograph calibration. Keywords: laser frequency comb, infrared, spectrograph, Doppler shift
© (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
T. Kokubo, T. Mori, T. Kurokawa, K. Kashiwagi, Y. Tanaka, T. Kotani, J. Nishikawa, and M. Tamura "12.5-GHz-spaced laser frequency comb covering Y, J, and H bands for infrared Doppler instrument", Proc. SPIE 9912, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation II, 99121R (22 July 2016);

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