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

By: P. Gaal, M. B. Raschke, K. Reimann, and M. Woerner

Nature Photonics 1, 577 (2007)

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.