Laser physics and laser optics

Theoretical study of the influence of parameters of the amplifying and absorbing medium on the dynamics of coherent mode locking in a two-section laser

R. M. Arkhipov^a, M. V. Arkhipov^a, O. O. Dyachkova^ab, A. V. Pakhomov^ab, N. N. Rosanov<sup>a

a</sup> Ioffe Institute, St. Petersburg
^b Saint Petersburg State University

Abstract: A theoretical study of the influence of the parameters of the amplifying and absorbing media on the dynamics of coherent mode locking (CML) in a two-section laser is carried out. Based on analytical calculations and numerical modeling, the conditions for the formation of a stable CML regime with parameters characteristic of terahertz quantum cascade lasers (QCLs) are studied. Using the generalized area theorem, the existence and stability of the CML regime in such systems are proven. Numerical solution of nonlinear equations describing the interaction of radiation with the active and passive media made it possible to determine the key parameters affecting the CML dynamics. It is shown that the ratio of population relaxation times in the amplifying and absorbing media plays a critical role. The obtained results are important for the development of self-starting compact laser systems generating short pulses, in particular, for terahertz QCLs. Such systems are promising for use in ultrafast spectroscopy and other applications requiring stable generation of ultrashort pulses.

Keywords: coherent mode locking, two-section laser, quantum cascade laser, self-induced transparency, nonlinear dynamics.

Received: 15.04.2025
Revised: 28.04.2025
Accepted: 29.04.2025

DOI: 10.61011/OS.2025.06.60916.7912-25

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