CC BY
18LS-I-4
Investigations on High Power Oscillators and Amplifiers Based on Birefringent Yb:LiLuF4 Single Crystal Fibers Grown by the
Micro Pulling Down
S. Pizzurro1, M. Tonelli2, A. Agnesi13, F. Pirzio1
1- Dip. di Ingegneria Industriale e dell'Informazione, University of Pavia, via Ferrata 5, IT-27100, Pavia, Italy 2- Mega Materials s.r.l and Dip. di Fisica, University of Pisa, Largo B. Pontecorvo 3, IT-56127 Pisa, Italy 3- Bright Solutions s.r.l., Via degli Artigiani 27, IT-27010 Cura Carpignano (PV), Italy
e-mail: _ federico.pirzio@unipv. it
Single crystal fibers (SCF) are a very attractive solution for power scaling of solid-state lasers owing to the convenient distribution of heat load along a relatively long, low-doped, thin crystal with a favorable surface-to-volume ratio. Micro pulling down (^-PD) growing technique is particularly suited to the realization of SCFs. Indeed, in addiction of been faster and cheaper than the traditional Czochralski method, it allows to directly obtain thin (down to < 1 mm) and long (several cm) SCFs with no additional processing of the grown crystal. To now, ^-PD technique was exploited mainly for cubic crystals, especially YAG, with remarkable results in particular with Yb3+ doping [1, 2]. Recently, we demonstrated for the first time successful growth of a birefringent Yb:LiLuF4 SCF (see Fig. 1 (a)) [3]. Birefringent Yb-doped fluoride SCFs, are particularly interesting for several reasons, e.g., they do not suffer of beam quality degradation at high thermal load due to depolarization, they benefit of the weaker thermal lens (and associated aberrations) of fluoride materials, and if pumped at 976 nm with commercial high-power laser diodes, they allow small quantum defect with laser emission at 1020 nm.
Fig. 1. (a) Examples of grown Yb:LLF SCFs; (b) Setup for multi-pass amplification experiments; (c) Laser oscillator best performance.
In this talk, we will present our latest results obtained both in multi-pass amplification (setup shown in Fig. 1 (b)) and laser oscillation, by pumping a 2%-doped, 42-mm long Yb:LiLuF4 SCF with a 135-W laser diode at 976 nm. For the amplification experiments we employed either a 1-W cw seeder, or a 150-J 100-ns PQS seeder at 5 kHz repetition rate. Four passes small signal gain G0~40 was achieved at ~85 W of absorbed pump power with a maximum output power of 8 W in cw experiments and a 1-mJ amplified pulse energy, when seeding with the PQS laser. In both cases, diffraction limited beam quality was obtained at the maximum pump power. In laser oscillator experiment, we achieved up to 25 W (see Fig. 1(c)), with M2~2 and ~40% slope efficiency in a simple confocal resonator layout.
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[3] F. Pirzio, S. Jun, S. Tacchini, A. Di Lieto, G. Piccinno, M. Tonelli, and A. Agnesi, "Multi-watt amplification in a birefringent Yb:LiLuF4 single crystal fiber grown by micro-pulling-down," Opt. Lett. 44, pp. 4095-4098, (2019).
