We demonstrate the possibility of using a femtosecond laser to measure with high accuracy the frequency of a far-infrared (FIR) monochromatic source, such as an optically pumped molecular laser, by generating in a suitable mixer a signal in the radio-frequency region at the frequency difference between n steps of a femtosecond comb and the FIR source. All the couples of modes lying a distance of n steps from one another contribute coherently to the heterodyne signal. The technique has been tested up to 670GHz.
© 2005 Optical Society of America
(040.2840) Detectors : Heterodyne
(120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.4050) Lasers and laser optics : Mode-locked lasers
(260.3090) Physical optics : Infrared, far
N. Beverini, G. Carelli, A. De Michele, E. Maccioni, B. Nyushkov, F. Sorrentino, and A. Moretti, "Coherent multiwave heterodyne frequency measurement of a far-infared laser by means of a femtosecond laser comb," Opt. Lett. 30, 32-34 (2005)