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Universität zu Köln
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Mathematisch-Naturwissenschaftliche Fakultät
Fachgruppe Physik

I. Physikalisches Institut

OPO - Optic Parametric Oscillator System

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Spectroscopy in the mid-infrared needs widely tunable laser sources with small linewidths. While lead salt diode lasers are used in our group for spectroscopic applications, they lack the broad tuning range to cover large regions with different vibrational transitions of different molecules.
The Cologne spectroscopy group is working to extend its spectral coverage in the mid-infrared region with the setup of an optical parametric oscillator. In its first implementation, it will provide radiation in the range of 2.5 to 3.5 microns with a small linewidth (< 10 MHz is expected) for high resolution spectroscopy of C-H stretching vibrations (e.g. CH5+, see also Ion trap).
Fig. 1 shows the working principle of an OPO. A high power "pump" laser beam (Nd:YAG, 1064 nm, 10 W cw) penetrates a crystal with high second-order nonlinear susceptibility. The nonlinearity results in converting some pump photons into pairs of photons with the energy being conserved (Fig. 2). Feedback from a high finesse cavity is necessary for further stimulation of the process and for frequency selection.
Contact: Jürgen Krieg

OPO energy
Figure 1: Working principle of an OPO. Figure 2: