Wavelength calibration of a high resolution spectrograph with a partially stabilized 15-GHz astrocomb from 550 to 890 nm

• Published in: Optics express Vol. 25; no. 6; p. 6450
• Main Authors: McCracken, Richard A., Depagne, Éric, Kuhn, Rudolf B., Erasmus, Nicolas, Crause, Lisa A., Reid, Derryck T.
• Format: Journal Article
• Language: English
• Published: United States 20.03.2017
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.25.006450

A visible astrocomb spanning 555-890 nm has been implemented on the 10-m Southern African Large Telescope, delivering complete calibration of one channel of its high-resolution spectrograph and an accurate determination of its resolving power. A novel co-coupling method allowed simultaneous observation of on-sky, Th-Ar lamp and astrocomb channels, reducing the wavelength calibration uncertainty by a factor of two compared to that obtained using only Th-Ar lines. The excellent passive stability of the master frequency comb laser enabled broadband astrocomb generation without the need for carrier-envelope offset frequency locking, and an atomically referenced narrow linewidth diode laser provided an absolute fiducial marker for wavelength calibration. The simple astrocomb architecture enabled routine operation by non-specialists in an actual telescope environment. On-sky spectroscopy results are presented with direct calibration achieved entirely using the astrocomb.