27 August 2010 Frequency metrology of a photomixing source for gas phase spectroscopy
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Abstract
The availability of frequency combs has opened new possibilities for the measurement of optical frequencies. Photomixing is an attractive solution for high resolution THz spectroscopy of gases due to the narrow spectral resolution and ability to access the 100 GHz to 3.5 THz range. One limitation of present photomixing spectrometers is the accuracy with which the THz frequency is established. Measurement of the centre frequency gas phase molecular transitions requires an accuracy better than 100 kHz in order to allow spectroscopic constants to be determined. Standard optical techniques like those employed in wavelength meters can only provide accuracies in the order of 50 MHz. We have used a turnkey fibre based frequency comb and a standard photomixing configuration to realize a THz synthesizer with an accuracy of around 50kHz. Two ECDLs used to pump the photomixer are phase locked onto the frequency comb and provide a tuning range of 10 MHz. In order to extend the tuning range an additional phase locked ECLD has been added to obtain a range in excess of 100 MHz. The absorption profiles of many Doppler limited transitions of carbonyl sulphide and formaldehyde have been measured to validate this instrument.
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Francis Hindle, Francis Hindle, Gael Mouret, Gael Mouret, Chun Yang, Chun Yang, Arnaud Cuisset, Arnaud Cuisset, Robin Bocquet, Robin Bocquet, Michel Lours, Michel Lours, Daniele Rovera, Daniele Rovera, } "Frequency metrology of a photomixing source for gas phase spectroscopy", Proc. SPIE 7763, Terahertz Emitters, Receivers, and Applications, 77630C (27 August 2010); doi: 10.1117/12.859843; https://doi.org/10.1117/12.859843
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