Laser systems based on a fiber doped with the rare earth metal thulium make it possible to study a wide range of light wavelengths from 1600 to 2500 nm. Atmospheric transmission with low losses, the possibility of deep penetration into biological tissues, as well as the presence of a large number of absorption lines of gasses and biomolecules determine the demand for efficient light sources operating in this wavelength range. Monitoring greenhouse gasses in the environment, processing polymers or semiconductors, optical coherence tomography, nonlinear microscopy, and optical communication are just some of the ultrafast laser uses made possible or improved by the development of Tm-doped fiber systems.
Working together, researchers at the NSU Department of Physics Laboratory of Photonic Technology and Machine Learning for Sensor Systems, the Leibniz Institute of Photonic Technology (Germany), the Institute of Photonics and Electronics (Czech Republic), iXblue Photonics (France), Ulyanovsk State University, and the University of Mons (Belgium) conducted a study on a new compact design for a thulium fiber laser with radiation mode self-locking and the possibility of spectral tuning in a wavelength range from 1873 to 1962 nm. This system provides a simple approach to the generation of ultrashort pulses with the ability to tune the wavelength and operating modes in a wide range, which is not affected by stability or laser power limitations. The results of this research were published in the Communications Physics journal.
Anastasia Bednyakova, Candidate of Physical and Mathematical Sciences and Senior Researcher at the Laboratory, described their work,
The thulium-doped fiber light guide performs three roles in the resonator: it serves to amplify the signal, is a simple and highly integrated saturable absorber, and simultaneously allows you to control the radiation wavelength by controlling the level of active medium excitation. My colleagues and I performed a detailed experimental and numerical study of a highly doped (0.8 mol%) active fiber enriched in thulium ionic clusters. The results of numerical simulation based on the nonlinear Schrödinger equation and the three-level model of the amplifying medium are in good agreement with experiments, demonstrating the same tuning range. It is important to note that the highest laser efficiency is observed at a feedback coefficient of 20%, which makes it possible to obtain soliton pulses with a duration of 580 fs at a wavelength of 1877 nm with an output pulse energy of 1.5 nJ,
This research was supported by the Russian Federation Ministry of Science and Higher Education (project # FSUS-2021-0015 and 075-15-2021-581) and the Russian Science Foundation (project no. 18-12-00457).