Berlin 2005 – wissenschaftliches Programm
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Q: Quantenoptik und Photonik
Q 59: Laserspektroskopie I
Q 59.4: Vortrag
Dienstag, 8. März 2005, 17:15–17:30, HU 2014a
Mid-infrared harmonic-frequency-comb spectrometer without moving parts — •Fritz Keilmann1, Markus Brehm1, Albert Schliesser1, and Daniel Van Der Weide2 — 1MPI für Biochemie, 82152 Martinsried (München), Germany — 2University of Wisconsin, Madison, WI 53711, USA
We demonstrate a new concept of broadband Fourier-transform infrared spectroscopy (FTIR) based on a multi-heterodyne detection principle. Two coherent mid-infrared beams that contain slightly offset harmonic frequency combs are superimposed on a photoconductive detector. The signal contains a radio-frequency harmonic spectrum that replicates the mid-infrared spectrum, so the latter can be retrieved by recording the detector signal vs time, much as an interferogram known in FTIR, with subsequent Fourier transformation. In our experiment, two independent 10 fs Ti:sapphire lasers generate both mid-infrared beams by difference-mixing in GaSe. The radio frequency is choosable by offsetting the pulse repetition rates. We demonstrate an interferogram acquisition duration as short as 10-6 s which could be interesting for taking snapshot infrared spectra of single transient events such as in high-field magnetospectroscopy or chemical reactions. We intend to exploit the advantage of diffraction-limited operation of this spectrometer for mid-infrared scattering-type near-field microscopy. F.Keilmann, C.Gohle and R.Holzwarth, Opt. Lett. 29, 1542 (2004).