Compact green Ti:sapphire astro-comb with a 43 GHz repetition frequency
Eunmi Chae, Eiji Kambe, Kentaro Motohara, Hideyuki Izumiura, Mamoru Doi, Kosuke Yoshioka
Abstract
A compact green astro-comb with a 43 GHz repetition rate is developed based on a Ti:sapphire optical frequency comb (OFC) and a mode-selecting cavity. The OFC’s large repetition rate of 1.6 GHz eases the requirements for the mode-selecting cavity. Unnecessary frequency modes of the OFC are suppressed down to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>5</mml:mn> <mml:mo>×</mml:mo> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> at 535–550 nm using a single mode-selecting cavity with 70 MHz linewidth. The radial velocity precision <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mi>σ</mml:mi> <mml:mo>∼</mml:mo> <mml:mn>1.4</mml:mn> <mml:mspace width="thinmathspace"/> <mml:mspace width="thinmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">m</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> </mml:math> is achieved at the high dispersion echelle spectrograph for the Okayama 188 cm telescope of the National Astronomical Observatory of Japan using our astro-comb. With further improvements of the mode-selecting cavity and removal of fiber modal noises, our system will provide a simple, compact, and precise astro-comb setup in the visible wavelength region.