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Laser frequency comb ready to aid exoplanet search

14 Dec 2023

Optical benchmark will help astronomers detect tiny variations caused by gravitational pull of orbiting exoplanets.

The search for rocky, Earth-like exoplanets has received a boost, with the arrival of a new laser frequency comb at the European Southern Observatory’s La Silla Observatory in Chile.

Built by a team of laser experts at the Centre Suisse d’Electronique et de Microtechnique (CSEM) in Neuchâtel, the optical metrology device is installed within the Near-Infrared Planet Searcher (NIRPS) instrument, which analyzes light collected by La Silla’s 3.6 m telescope.

NIRPS achieved “first light” in June 2022, and it is hoped that the instrument will locate exoplanets representing the closest habitable worlds outside our own solar system.

“Commissioned by the University of Geneva, this device generates light with an exceptionally steady frequency spectrum, characterized by evenly spaced lines,” CSEM explains.

”It serves as an optical benchmark, aiding the measurement of a star’s radial velocity - a crucial metric for understanding the speed at which stars move towards or away from us.”

The laser frequency comb will calibrate the NIRPS spectrograph to unprecedented levels of accuracy and precision, improving the instrument’s ability to determine the behavior and characteristics of Earth‑like exoplanets.

Red dwarfs
The main goal of NIRPS is to use the radial velocity method to detect and characterize planets orbiting relatively cool stars known as red dwarfs, said by ESO to be the most common type of star found in the Milky Way.

As the planet orbits, its gravitational pull causes a slight wobble in the host star’s motion, alternately shifting the light that it emits towards the blue and red.

“With super-sensitive spectrographs such as NIRPS, the shifts can be measured and used to infer details of a planet’s mass and orbit,” states ESO.

Christopher Bonzon, CSEM’s manager for laser technologies, said in a release from the institution: “CSEM's laser frequency comb technology stands as the epitome of spectroscopic accuracy and stability.

“This system produces a stream of equidistant laser lines locked to a molecular transition and spaced by exactly 15 GHz using electro-optic modulation - far surpassing the scope of competing technologies.

“The frequency comb acts exactly like ruler in the spectral domain, providing the NIRPS spectrograph a reference to match data over the years.”

Geneva professor François Bouchy, also co-principal investigator of the NIRPS consortium, added: “[CSEM’s] laser frequency comb technology is essential for achieving the high performance and long‑term reliability that we need for the NIRPS spectrograph.

“Together, we hope to make new discoveries and contribute to the advancement of exoplanet science.”

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