Continuous ultraviolet to blue-green astrocomb

• Published in: Nature communications Vol. 15; no. 1; pp. 1466 - 8
• Main Authors: Cheng, Yuk Shan, Dadi, Kamalesh, Mitchell, Toby, Thompson, Samantha, Piskunov, Nikolai, Wright, Lewis D., Gawith, Corin B. E., McCracken, Richard A., Reid, Derryck T.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 17.02.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 639/33/34/2810; 639/33/34/862; 639/624/1111/1112; Absorption; Accuracy; Bandwidths; Broadband; Calibration; Doppler effect; Extrasolar planets; Fabry-Perot filters; Humanities and Social Sciences; Infrared lasers; Laser applications; Lasers; multidisciplinary; Sapphire; Science; Science (multidisciplinary); Second harmonic generation; Silicon nitride; Spectrographs; Spectrum allocation; Telescopes; Ultraviolet radiation; Velocity; Waveguides
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-45924-6

Cosmological and exoplanetary science using transformative telescopes like the ELT will demand precise calibration of astrophysical spectrographs in the blue-green, where stellar absorption lines are most abundant. Astrocombs—lasers providing a broadband sequence of regularly-spaced optical frequencies on a multi-GHz grid—promise an atomically-traceable calibration scale, but their realization in the blue-green is challenging for current infrared-laser-based technology. Here, we introduce a concept achieving a broad, continuous spectrum by combining second-harmonic generation and sum-frequency-mixing in an MgO:PPLN waveguide to generate 390–520 nm light from a 1 GHz Ti:sapphire frequency comb. Using a Fabry-Pérot filter, we extract a 30 GHz sub-comb spanning 392–472 nm, visualizing its thousands of modes on a high-resolution spectrograph. Experimental data and simulations demonstrate how the approach can bridge the spectral gap present in second-harmonic-only conversion. Requiring only ≈ 100 pJ pulses, our concept establishes a new route to broadband UV-visible generation at GHz repetition rates. Astrocombs serve as precision calibrators for astrophysical spectrographs by providing a regular sequence of optical lines on a multi-GHz grid. Here, the authors report the first broadband astrocomb in the UV to blue-green spectral region, where stellar absorption lines are most abundant.