Spectral Dynamics of Quantum Cascade Lasers Generating Frequency Combs in the Long-Wavelength Infrared Range
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Spectral Dynamics of Quantum Cascade Lasers Generating Frequency Combs in the Long-Wavelength Infrared Range V. V. Dudeleva, D. A. Mikhailova, A. V. Babicheva, S. N. Loseva, E. A. Kognovitskayaa,b, A. V. Lyutetskiia, S. O. Slipchenkoa, N. A. Pikhtina, A. G. Gladyshevc, D. V. Denisovb, I. I. Novikova,c,d, L. Ya. Karachinskya,c,d, V. I. Kuchinskiia, A. Yu. Egorovd, and G. S. Sokolovskiia,* a
b
Ioffe Institute, St. Petersburg, 194021 Russia St. Petersburg State Electrotechnical University LETI, St. Petersburg, 197376 Russia c Connector Optics LLC, St. Petersburg 194292 Russia d ITMO University, St. Petersburg, 197101 Russia *e-mail: [email protected] Received March 10, 2020; revised March 10, 2020; accepted March 11, 2020
Abstract—We have studied the spectral and dynamic characteristics of quantum cascade lasers emitting in the long-wavelength infrared range. It is shown that lasers with a short cavity (~1 mm) make it possible to obtain frequency combs in a very wide spectral range. We have investigated the spectral dynamics in the frequency comb generation regime. It is demonstrated that the intensity of longitudinal laser modes varies during a pump pulse propagation. We have observed simultaneous generation of all longitudinal modes of a frequency comb over a pump pulse segment with a constant amplitude. DOI: 10.1134/S106378422008006X
INTRODUCTION Intense investigations aimed at designing quantum cascade lasers (QCLs) operating in the long-wavelength infrared range are associated with the presence of intense absorption lines of many chemical compounds, as well as with the use of the second transparency window of the atmosphere. Therefore, gas analysis, monitoring of the state of the ambient environment, and nondestructive remote control, as well as wireless optical communication, are among the possible applications of such QCLs. For this reason, the development of systems for spectral express analysis is a topical problem. The most promising approach is associated with systems based on the interference of two frequency combs with a small difference in the intermode spacing [1]. An important feature of the method is simultaneous generation of all modes in the frequency comb for obtaining an interpretable interference pattern at the photodetector. It should be noted that a group of scientists [2, 3] was awarded a Nobel Prize in physics in 2005 for the application of frequency combs in the atomic transition spectroscopy. At present, active research works are being undertaken for obtaining frequency combs from QCLs operating in the long-wavelength infrared range [4–9] using the active mode locking methods [4–7] as well as due to the emerging self-pulsations in QCLs [8, 9]. This study is devoted to analysis of still
unclear aspects of QCL spectral dynamics during the generation of frequency combs. 1. EXPERIMENTAL SAMPLES We study the generation of frequency combs by QCLs emitting at wavelength close to 8 μm, as well as their dynamics. The test QCLs were prepared based on the heterostructure described in detail i
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