Scheme of the experimental setup (see main text for details).
Oscilloscope screen shot showing the saw-tooth modulation of the injection diode current (black, bottom), the monitored laser intensity after the cavity (red, middle), and the periodic resonant photoacoustic signal of a water transition (blue, top). time base.
Peak photoacoustic signal of a weak water transition near 635 nm at various modulation frequencies.
(a) Iodine absorption lines; lower trace FTIR reference (Ref. 46), upper trace diode laser setup, showing the entire mode-hop free tuning range. The arrow indicates the range, which can be tuned without resetting the voltage on the piezomirror of the optical cavity. (b) Two very weak water lines (overtone transitions) observed within this tuning range; lower trace reference from the HITRAN database (Ref. 49), upper trace diode laser setup with resonant photoacoustic detection (OF-CERPAS).
Comparison of different detection schemes observing a very weak water overtone transition near 635 nm. Upper trace: novel diode laser-based PAS system (OF-CERPAS). Middle trace: CRDS. Lower trace: Integrated laser intensity after the cavity, corresponding to CEAS).
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