CW, Q-switched and mode-locking oscillations at 2.1 μm in novel Tm<sup>3+</sup>:Lu<inf>2</inf>O<inf>3</inf> ceramics lasers

Abstract

Summary form only given. Solid-state lasers at 2.1 μm having many applications for medical surgery, atmospheric wind lidar, gas detection, material processing and pumping of mid-IR optical parametric oscillators are attracting great interest in the last years. Tm- and Ho-doped sesquioxides (Tm3+:Lu2O3, Tm3+:Sc2O3, Ho: 3+:Lu2O3 and others) having an extraordinary long-wavelength 2-μm luminescence band and a high thermal conductivity open up new opportunities for highly efficient laser generation at around 2.1 μm [1]. Transparent laser ceramic materials are attracting great interest as a substitute for the single crystals. Recently, the high-quality sesquioxides ceramics doped by Nd3+ or Yb3+ ions have demonstrated good potential for the efficient laser oscillation. This presentation is an overview of our investigations of the 2.1- μm lasers based on the novel Tm3+:Lu2O3 ceramics with diode or laser pumping at 796 or 810 nm [2-6].Structural, optical and spectroscopic properties of novel Tm3+:Lu2O3 ceramics, produced by “Konoshima Chemicals Co.” (Japan), were studied [2-4]. The average grain size is determined to be ~ 0.55 μm. The absorption spectra show good opportunities for diode or laser pumping at 796 nm and 811 nm. The ceramics have high mid-IR transmittance of up to 7 μm. Strong luminescence lines centered at 1942 nm, 1965 nm and 2066 nm were detected. The thermal conductivity and the thermal index gradient of the ceramics were determined (by kinetic-resolvable interferometric and grating testing methods) to be comparable with the single crystal [4]. 2.1-μm laser-oscillators based on Tm3+:Lu2O3 ceramics pumped by 796-nm or 810-nm laser diodes were created and studied [2,3]. CW operation with average power of ~ 35W and optical-to-optical efficiency of ~ 34% and the slope efficiency (with respect to absorbed power) of ~ 44% was demonstrated. The oscillations wavelength was tuned in spectrum region of 2060 - 2098 nm. 1-10 kHz periodically-pulsed generation was realized by active Q-switching (by a quartz acousto-optic modulator). The average power of the Q-switched radiation reached 7 W, corresponding peak power was up to 10 kW. Cr2+:ZnSe saturable absorber was also investigated as an passive Q-switcher of the ceramics lasers. An ion-implanted InGaAsSb quantum-well-based SESAM was applied for realization of the passive modelocking oscillations in the Tm3+:Lu2O3-ceramic lasers [5]. Transform-limited pulses as short as 180 fs were generated at 2076 nm with an average output power of 400 mW and a pulse repetition frequency of 121.2 MHz. An output power up to 750 mW was reached at the longer pulse duration of 382 fs. Femtosecond pulse generation tuned in 2030-2100 nm spectral range was realized. A single-layer graphene was used also for mode-locking in the ceramics Tm:Lu2O3 laser [6]. The transformlimited 410 fs pulses with a spectral width 11.1 nm at 2067 nm were registered. The maximum average output power was 270 mW, at a pulse repetition frequency of 110 MHz. This is a convenient high-power transform-limited ultrafast laser at 2 μm for various applications, such as laser surgery and material processing.