Towards a Visible to Mid-Infrared Astrocomb for the Extremely Large Telescope

The Extremely Large Telescope (ELT), currently under construction in Chile, aims to investigate exoplanet atmospheric spectroscopy, star / planet formation and evolution, and cosmology and fundamental physics with a broadband high-resolution spectrograph, designated ELT-HIRES. Comprising four modules covering wavelengths from 370–2500 nm, this instrument requires laser comb calibration with mode spacings from 32 GHz (<600 nm) to 6 GHz (>1950 nm). As illustrated by our recent review paper [1], approaches to date based on nonlinear broadening of a single ultrafast oscillator still fall significantly short of the required coverage. Here we present a new approach yielding a nearly-continuous 500–2200 nm 1-GHz comb from dual supercontinua sources pumped by an 805-nm Ti:sapphire oscillator and phase coherent 1610-nm pulses from a degenerate optical parametric oscillator (OPO) [2].