J. Eur. Opt. Society-Rapid Publ. 2025, 21, 14 Ó The Author( s), published by EDP Sciences, 2025 https:// doi. org / 10.1051 / jeos / 2025010 Available online at: https:// jeos. edpsciences. org
Journal of the European Optical Society-Rapid Publications
EOSAM 2024 Guest editors: Luca De Stefano and Raffaele Velotta
RESEARCH ARTICLE
Type-I intermittency route to the chaos in passively Q-switched Tm: YLF laser emitting at 2.3 lm
Matthieu Glasset, Hippolyte Dupont, Patrick Georges, and Frédéric Druon * Université Paris-Saclay, Institut d’ Optique Graduate School, CNRS, Laboratoire Charles Fabry, 91127 Palaiseau, France
Received 31 December 2024 / Accepted 26 February 2025
Abstract. We report on an original chaotic dynamic behavior of a Tm-doped Q-switched laser operating on the 3 H 4? 3 H 5 transition emitting at 2.3 lm using a Tm: YLF crystal, with optional co-lasing at 1.9 lm via the 3 F 4? 3 H 4 transition. This study specifically investigates the chaotic and intermittent dynamics originally observed in this laser. Experimental observations reveal an atypical type-I intermittency route to chaos, linked to cascade transitions and characterized using Poincaré maps, entropy calculations, and phase-space reconstructions. The analysis highlights synchronization losses between the Q-switched pulse train and relaxation oscillations in the 1.9 lm cascade laser as a driver of chaotic instabilities. These findings deepen the understanding of chaotic regimes in Tm-doped lasers and provide insights for optimizing the stability of MIR laser systems for advanced photonic applications. Further modeling is needed to fully elucidate the interplay of dual-wavelength dynamics and the observed chaotic behavior.
Keywords: Solid state laser, MIR laser, Tm-doped laser, Q-switch laser.
1 Introduction
The advancement of Q-switched lasers operating in the short-wave infrared( SWIR) to mid-infrared( MIR) spectrum represents a significant and promising area of research, with specific applications including atmospheric gas sensing, non-invasive blood glucose monitoring, and the pumping of mid-infrared optical parametric oscillators utilizing non-oxide nonlinear crystals. Of particular interest are wavelengths around 2.3 lm, which are well-suited to these applications. Trivalent thulium ions( Tm 3 +) possess an energy level structure that supports emission at around 1.9 lmviathe 3 F 4? 3 H 6 transition, as well as at 2.3 lmvia the 3 H 4? 3 H 5 transition. Extensive research has been conducted on Tm-doped materials under Q-switching regimes [ 1 – 5 ], with observations of chaotic behavior, particularly at 2.3 lm [ 6 – 9 ]. However, this sensitivity to instability and chaotic regimes has not yet been systematically analyzed. The study of chaotic dynamics for such lasers holds great interest as it depends on our understanding of laser stability issues. Indeed, Tm-doped lasers operating above 2 lm have in this matter a strong propension to reach chaotic regimes, since such materials often involve cascade energetic transitions. The 3 H 4? 3 H 5 laser transition at 2.3 lm( wavelength of interest here) is actually linked to the 3 F 4? 3 H 6 transition emitting at 1.9 lm via the long
* Corresponding author: frederic. druon @ institutoptique. fr
( e. g. 11 ms in Tm: YLF) intermediate metastable level: 3 F 4, cf. Figure 1a.
Interestingly, Q-switched Tm-doped lasers exhibit an unique intermittency route to chaos, an unusual behavior for Q-switched lasers, such as those that are doped with Nd for example. This atypical chaotic behavior with intermittency appears inherently linked to the cascade transitions within the laser, as described by De Valcárcel et al. [ 10 ]. Although intermittency routes to chaos have been documented in other laser systems, often induced through external coupling [ 11 – 16 ] or in multiple-cavity Q-switched systems [ 17 ], such behavior has not, to our knowledge, been previously reported in passively Q-switched systems.
We demonstrate here that a type-I intermittency route to chaos can be observed within a single Q-switched cavity, which is a very atypical route for passively Q-switching.
2 Experimental results
To make a detailed examination of the dynamic behavior of a Tm: YLF laser operating on the 3 H 4? 3 H 5 transition, emission at 2.3 lm alone or in cascade co-laser operation( 2.3 lm and1.9lm) have been studied. For this, as shown in Figure 1b, a Q-switched cavity operating at 2.3 lmusing a Cr: ZnSe saturable absorber crystal is performed. An optional“ cw” cavity emitting at 1.9 lm sharing the Tm: YLF gain crystal is also implemented to test the behavior
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