Dual-comb spectroscopy of water vapor with a free-running semiconductor disk laser

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Science  16 Jun 2017:
Vol. 356, Issue 6343, pp. 1164-1168
DOI: 10.1126/science.aam7424

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Two different combs from a single source

Combs of light divide the optical frequency spectrum into closely spaced tines that can measure molecular absorption spectra with exceptional precision. One appealing method to extend this precision down into the microwave regime is to simultaneously use two slightly distinct combs that differ in spacing by the magnitude of a microwave frequency. The challenge is ensuring that the combs remain synchronized. Link et al. solve this problem by generating both combs from the same semiconductor laser source. The resultant dual comb delivers highly accurate spectra of water vapor, and the approach could be generalized across the optical spectrum by tuning the semiconductor source.

Science, this issue p. 1164


Dual-comb spectroscopy offers the potential for high accuracy combined with fast data acquisition. Applications are often limited, however, by the complexity of optical comb systems. Here we present dual-comb spectroscopy of water vapor using a substantially simplified single-laser system. Very good spectroscopy measurements with fast sampling rates are achieved with a free-running dual-comb mode-locked semiconductor disk laser. The absolute stability of the optical comb modes is characterized both for free-running operation and with simple microwave stabilization. This approach drastically reduces the complexity for dual-comb spectroscopy. Band-gap engineering to tune the center wavelength from the ultraviolet to the mid-infrared could optimize frequency combs for specific gas targets, further enabling dual-comb spectroscopy for a wider range of industrial applications.

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