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Laser frequency comb in astronomy research

Answering fundamental questions in astronomy such as the expanding universe theory, depend on the possibility of measuring the slow drift of cosmological redshifts which are inherent in any evolving universe.

However, such an observation requires very high accuracy of the measured spectrograms since the expected redshifts are exceedingly small.  While modern telescopes might be able to distinguish even tiny shades of colour, a correct interpretation of the measured absorption and emission lines in a spectrogram is hindered by missing calibration sources throughout the measured spectrograms. It is exactly at this point where laser frequency combs (LFCs), with their evenly distributed, stable comb lines, act as a very stable, reproducible calibration tool for astronomers.

Since May 2016, Heriot-Watt University (HWU) in Scotland employs a LFC in the Southern African Large Telescope (SALT), 400 km from Cape Town, South Africa. SALT is the largest single optical telescope in the southern hemisphere, and is able to view the light from stars and galaxies that are a billion times fainter than can be seen with the eye! The high resolution spectrograph (HRS) at SALT covers the visible spectrum from 370 nm to 890 nm and is used to analyse the colour content of distant stars and galaxies. Now, with use of the LFC, these colours can be measured with even greater precision. The employed LFC is a Laser Quantum gigajet Ti:Sa femtosecond laser running at 1 GHz repetition rate which is pumped by its industry-leading finesse pump laser. The gigajet delivers up to 1.8 W of average power at 1 GHz with optical pulse durations as short as 15 fs and represents the preceding product of the turn-key laser system taccor.

Laser Quantum has recently launched a complete frequency comb system, the taccor comb, an extension to the already successful taccor family. The taccor comb comes with stabilised repetition rate and carrier-envelope offset frequency, and extends the turn-key and long-term stable operation of the 1 GHz taccor to frequency comb applications. To find out more about the newly developed taccor comb, please click here.

For more information on SALT and the ongoing collaboration with HWU please visit the nightly log and the website of the South African Astronomical Observatory (SAAO)

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