Kamalesh Dadi | Searcharxiv

arXiv2026

Demonstration of a Single-Laser-Diode-Pumped Ti:Sapphire Astrocomb on the Southern African Large Telescope

Astrocombs -- broadband lasers comprising thousands of narrow, uniformly spaced and atomically-referenced spectral lines -- offer gold-standard wavelength calibration for ground-based optical telescopes, with the potential for the cm/s precision needed for radial-velocity follow-ups of exoplanet candidates from photometric space missions like Kepler, TESS and PLATO. Current astrocombs, particularly those operating in the visible spectrum, are complex and expensive, putting them beyond the reach of many observatories. Here, we present the first on-instrument demonstration of a new and simple astrocomb concept, providing calibration light across nearly the entire 550 nm to 890 nm red channel of the Southern African Large Telescope's High Resolution Spectrograph (SALT-HRS). An octave-spanning supercontinuum generated in a silicon nitride waveguide by a GPS-referenced diode-pumped Ti:sapphire laser is filtered to 21 GHz before fibre delivery to the spectrograph. Using the astrocomb, we obtain the wavelength solution for one order of SALT-HRS and the wavelength-dependent line-spread function of the instrument. With potential for further extension into the blue spectral region, this uniquely simple architecture brings visible-to-infrared astrocomb technology within the reach of a wider range of astronomical observatories.

astro-ph.IM↗

arXiv2023

Continuous Ultraviolet to Blue-Green Astrocomb

The characterization of Earth-like exoplanets and precision tests of cosmological models using next-generation telescopes such as the ELT will demand precise calibration of astrophysical spectrographs in the visible region, where stellar absorption lines are most abundant. Astrocombs--lasers providing a broadband sequence of ultra-narrow, drift-free, regularly spaced optical frequencies on a multi-GHz grid--promise an atomically-traceable, versatile calibration scale, but their realization is challenging because of the need for ultra-broadband frequency conversion of mode-locked infrared lasers into the blue-green region. Here, we introduce a new concept achieving a broad, continuous spectrum by combining second-harmonic generation and sum-frequency-mixing in an aperiodically-poled MgO:PPLN waveguide to generate gap-free 390-520 nm light from a 1 GHz Ti:sapphire laser frequency comb. We lock a low-dispersion Fabry-Perot etalon to extract a sub-comb of bandwidth from 392-472 nm with a spacing of 30 GHz, visualizing the thousands of resulting comb modes on a high resolution cross-dispersion spectrograph. Complementary experimental data and simulations demonstrate the effectiveness of the approach for eliminating the spectral gaps present in second-harmonic-only conversion, in which weaker fundamental frequencies are suppressed by the quadratic \{chi}^((2)) nonlinearity. Requiring only ~100 pJ pulse energies, our concept establishes a practical new route to broadband UV-visible generation at GHz repetition rates.

physics.optics↗