Time-resolved spectral characterization of a pulsed external-cavity quantum cascade laser

Jean-Michel Melkonian; Myriam Raybaut; Antoine Godard; Johan Petit; Michel Lefebvre

doi:10.1117/12.971429

30 October 2012 Time-resolved spectral characterization of a pulsed external-cavity quantum cascade laser

Jean-Michel Melkonian, Myriam Raybaut, Antoine Godard, Johan Petit, Michel Lefebvre

Proceedings Volume 8546, Optics and Photonics for Counterterrorism, Crime Fighting, and Defence VIII; 854607 (2012) https://doi.org/10.1117/12.971429
Event: SPIE Security + Defence, 2012, Edinburgh, United Kingdom

Abstract

Spectrally tunable narrow-linewidth mid-infrared sources are used in a variety of spectrometric optical systems for detection, identification, and/or quantification of chemical species. However, in the pulsed regime they often display a varying spectrum in time, either from shot-to-shot or during the pulse itself, with consequences on the measurement accuracy, resolution, and repeatability. This is, for instance, the case of pulsed quantum cascade lasers (QCL), mainly because of strong transient thermal effects in the optical waveguide. Unfortunately, little information has been published on this subject because mid-infrared time-resolved spectrometers are extremely scarce. In this paper, we explain how this can be circumvented by using time-gated frequency upconversion in a nonlinear crystal. We apply this principle to characterize a pulsed external cavity QCL (EC-QCL) at 7.8 μm, using AgGaS₂ as the nonlinear crystal and a Q-switched Nd:YAG laser as the pump source. The upconverted near infrared spectrum is conveniently analyzed with a high resolution lambdameter and an optical spectrum analyzer. We evidence frequency chirp at an average rate of -50 MHz/ns and mode hops spanning 15 GHz for the EC-QCL. These results are compared to published data.

Citation Download Citation

Jean-Michel Melkonian, Myriam Raybaut, Antoine Godard, Johan Petit, and Michel Lefebvre "Time-resolved spectral characterization of a pulsed external-cavity quantum cascade laser", Proc. SPIE 8546, Optics and Photonics for Counterterrorism, Crime Fighting, and Defence VIII, 854607 (30 October 2012); https://doi.org/10.1117/12.971429

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