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


Measurements using optical frequency combs1,2,3,4,5,6 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 sampling7,8,9,10,11,12,13 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 µm, is possible9.

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Figure 1: Schematic of the experimental set-up.
Figure 2: Experimental results for the electro–optic signal.
Figure 3: Autocorrelation of the electro–optic signal for different measurement times ΔT.
Figure 4: Spectra of the data.


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The authors acknowledge financial support by the Deutsche Forschungsgemeinschaft.

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Correspondence to K. Reimann.

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Gaal, P., Raschke, M., Reimann, K. et al. Measuring optical frequencies in the 0–40 THz range with non-synchronized electro–optic sampling. Nature Photon 1, 577–580 (2007).

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