Measuring optical frequencies in the 0–40 THz range with non-synchronized electro–optic sampling

Reviews and Highlights	Quantum Science	Molecular and Soft-matter	Ultrafast Nano-optics and Nanophotonics	Mineralogy and Geochemistry

Peter Gaal, Markus B. Raschke, Klaus Reimann, and Michael Woerner
Nature Photonics 1, 577 (2007).
DOI PDF

Measurements using optical frequency combs are now important in high-precision spectroscopy. However, measurement techniques described so far are either restricted to narrow frequency ranges or are difficult to implement in the far-infrared regime. Here we present a time-domain method for the direct measurement of optical frequencies in the mid- and far-infrared spectral region. The method is analogous to a sampling scope, with the electric field of the source measured by electro-optic sampling using the light pulses from a femtosecond laser as a probe. The highest optical frequency that can be measured with our ‘sampling scope’ is determined by the pulse length of the femtosecond laser. When 12-fs probe pulses are used, a measurement of up to 40 THz, corresponding to a wavelength of 7.5 mm, is possible.