Abstract

Midinfrared frequency combs are a promising tool for new applications in chemical imaging and sensing, as they can directly access molecular vibrations in the molecular fingerprint wavelength region [1]. Practical laser sources are moving steadily from few micrometer wavelengths further into the fingerprint region to the 10 µm region. For practical applications of midinfrared light, difference frequency generation (DFG) with well-developed fiber laser technology provides a highly-integrated, compact, and robust frequency comb source. Difference frequency generation fits naturally with fiber lasers, given the midinfrared photon energy difference between Er and Tm amplifier wavelengths. The recent availability of orientation-patterned GaP (OP-GaP) has made this much more practical, with its large transparency window, good nonlinearity, and flexibility from quasi-phase matching [2]. We use the difference frequency from Er and Tm amplifiers to generate 25 mW of midinfrared centred at 8 µm wavelength, and show that the output is a frequency comb, with a stable repetition rate and tunable carrier-envelope offset (CEO) frequency.

© 2017 IEEE