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Comb-assisted subkilohertz linewidth quantum cascade laser for high-precision mid-infrared spectroscopy
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View: Figures


Image of FIG. 1.
FIG. 1.

Schematic of the experimental setup. There are three main parts: the beat-note detection between QCL and DFG for the phase-lock, the high-finesse cavity for FNPSD analysis, and the saturation spectroscopy signal detection for the absolute frequency measurement of the CO2 transition. See Refs. 9 and 23 for more details.

Image of FIG. 2.
FIG. 2.

Beat-note signal between the DFG radiation and the phase-locked QCL. The inset shows the same beat-note with a narrower span and resolution bandwidth. In both cases, the width of the peak (FWHM) is limited by the RBW of the spectrum analyzer.

Image of FIG. 3.
FIG. 3.

QCL FNPSDs in free-running (trace a) and phase-locked (trace b) conditions, acquired by using a CO2 line and the high-finesse cavity as frequency-to-amplitude converters, respectively. The cavity has been used also to measure the FNPSD of the DFG radiation (trace c) and that of the QCL, when it is frequency-locked to a molecular line as in our previous work 22 (trace d).

Image of FIG. 4.
FIG. 4.

Dependence of the center of the Lamb dip of the CO2 ( ) P(29) transition on pressure, with the corresponding linear fit. For clarity, the constant value of 69 297 478 MHz has been subtracted from the absolute frequency values. Inset: example of a single Lamb-dip acquisition (black squares). Experimental conditions: lock-in amplifier time constant 10 ms, chopper frequency 616 Hz, frequency scan with 60-MHz span, and 50 kHz steps. The fit with a Voigt function (green line) and the residuals are also plotted.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Comb-assisted subkilohertz linewidth quantum cascade laser for high-precision mid-infrared spectroscopy