Mid-infrared Frequency Comb Spanning an Octave Based on an Er Fiber Laser and Difference-Frequency Generation
We describe a coherent mid-infrared continuum source with 700 cm-1 usable bandwidth, readily tuned within 600–2500 cm-1 (4–17 μm) and thus covering much of the infrared "fingerprint" molecular vibration region. It is based on nonlinear frequency conversion in GaSe using a compact commercial 100-fs-pulsed Er fiber laser system providing two amplified near-infrared beams, one of them broadened by a nonlinear optical fiber. The resulting collimated mid-infrared continuum beam of 1 mW quasi-cw power represents a coherent infrared frequency comb with zero carrier-envelope phase, containing about 500,000 modes that are exact multiples of the pulse repetition rate of 40 MHz. The beam's diffraction-limited performance enables long-distance spectroscopic probing as well as maximal focusability for classical and ultraresolving near-field microscopies. Applications are foreseen also in studies of transient chemical phenomena even at ultrafast pump-probe scale, and in high-resolution gas spectroscopy for e.g. breath analysis.
KeywordsInfrared laser Infrared continuum source Mid-infrared supercontinuum Frequency-comb beam Mid-infrared frequency comb
We acknowledge helpful dicussions with Marco Marangoni and Albert Schliesser.
- 1.Griffiths, P. R. & Haseth, J. A. d. Fourier Transform Infrared Spectroscopy (Wiley, 2007).Google Scholar
- 7.Röseler, A. Infrared spectroscopic ellipsometry (Akademie-Verlag, 1990).Google Scholar
- 10.Keilmann, F. & Hillenbrand, R. in Nano-Optics and Near-Field Optical Microscopy, eds. A. Zayats and D. Richards, ISBN 978-1-59693-283-8 (ArtechHouse, 2009).Google Scholar
- 13.Schliesser, A., Picque, N. & Hänsch, T. W. Mid-infrared frequency combs. In prep. (2012).Google Scholar
- 14.Wang, C. Y. et al. Mid-infrared optical frequency combs based on crystalline microresonators. arxiv:1109.2716v1 (2011).Google Scholar
- 18.Amarie, S. & Keilmann, F. Broadband-infrared assessment of phonon resonance in scattering-type near-field microscopy. Physical Review B 83, 45404-1–45404-9 (2011).Google Scholar
- 19.Ruehl, A. et al. Widely tunable mid-IR frequency comb source based on difference frequency generation. arXiv:1203.2441v1 (2012).Google Scholar
- 23.Huth, F. et al. Nano-FTIR absorption spectroscopy of molecular fingerprints at 20 nm spatial resolution. Nanoletters (2012).Google Scholar