Ultraviolet frequency combs for precision cosmology

Laser Frequency combs at high repetition rates (> 10 GHz) are ideally suited to calibrate astronomical spectrographs, supporting precise and accurate spectroscopy of astronomical objects. Leveraging periodically-poled lithium niobate nanophotonic waveguides we demonstrate for the first time the calibration of an astronomical spectrograph with a laser frequency comb at blue and ultraviolet wavelengths, relevant to optical precision cosmology.

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Ultraviolet (UV) and visible (VIS) wavelengths laser frequnecy comb as seem by the SOPHIE spectrograph at the Observatoire de Haute Provence (OHP).

Ultraviolet wavelength, below 400 nm, are important for cosmological studies, including those that aim at measuring the cosmic expansion in ‘real time’. However, it is exceedingly challenging to create high-repetition combs at ultraviolet wavelength, due to their intrinsically low pulse energy. Here, we utilize highly-efficient and broadband harmonic generation in nanophotonic lithium niobate waveguides, to achieve such combs and demonstrate the calibration of the SOPHIE spectrograph at the Observatoire de Haute Provence (OHP).

Reference: 
Ultraviolet astronomical spectrograph calibration with laser frequency combs from nanophotonic waveguides; Markus Ludwig, Furkan Ayhan, Tobias M. Schmidt, Thibault Wildi, Thibault Voumard, Roman Blum, Zhichao Ye, Fuchuan Lei, François Wildi, Francesco Pepe, Mahmoud A. Gaafar, Ewelina Obrzud, Davide Grassani, François Moreau, Bruno Chazelas, Rico Sottile, Victor Torres-Company, Victor Brasch, Luis G.Villanueva, François Bouchy, Tobias Herr; arXiv:2306.13609