Passive Q-Switching by Cr4+:YAG Saturable Absorber of Buried Depressed-Cladding Waveguides Obtained in Nd-Doped Media by Femtosecond Laser Beam Writing.

Gabriela (Salamu),Nicolaie Pavel

doi:10.3390/ma11091689

Gabriela (Salamu), Nicolaie Pavel

Open Access

https://doi.org/10.3390/ma11091689

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Abstract

We report on laser performances obtained in Q-switch mode operation from buried depressed-cladding waveguides of circular shape (100 μm diameter) that were inscribed in Nd:YAG and Nd:YVO4 media by direct writing with a femtosecond laser beam. The Q-switch operation was realized with a Cr4+:YAG saturable absorber, aiming to obtain laser pulses of moderate (few μJ) energy at high (tens to hundreds kHz) repetition rate. An average power of 0.52 W at 1.06 μm consisting of a train of pulses of 7.79 μJ energy at 67 kHz repetition rate, was obtained from a waveguide realized in a 4.8 mm long, 1.1-at % Nd:YAG ceramics; the pulse peak power reached 1.95 kW. A similar waveguide that was inscribed in a 3.4 mm long, 1.0-at % Nd:YVO4 crystal yielded laser pulses with 9.4 μJ energy at 83 kHz repetition rate (at 0.77 W average power) and 1.36 kW peak power. The laser performances obtained in continuous-wave operation were discussed for each waveguide used in the experiments. Thus, a continuous-wave output power of 1.45 W was obtained from the circular buried depressed-cladding waveguide inscribed in the 1.1-at %, 4.8 mm long Nd:YAG; the overall optical-to-optical efficiency, with respect to the absorbed pump power, was 0.21. The waveguide inscribed in the 1.0-at %, 3.4 mm long Nd:YVO4 crystal yielded 1.85 W power at 0.26 overall optical efficiency. This work shows the possibility to build compact laser systems with average-to-high peak power pulses based on waveguides realized by a femtosecond (fs) laser beam direct writing technique and that are pumped by a fiber-coupled diode laser.

Highlights

The experiments performed by Davis et al [1] demonstrated that a femtosecond laser beam can induce stable damages and changes of the refractive index in various glasses
We reported high-average power Q-switch laser operation from circular, depressed-cladding waveguides that were inscribed in Nd:YAG/Cr4+ :YAG composite crystals; worthy of mention was that the optical pump was made with a fiber-coupled diode laser [27]
Of depressed-cladding waveguides that were inscribed in Nd:YAG ceramics and Nd:YVO4 crystals

Summary

Introduction

The experiments performed by Davis et al [1] demonstrated that a femtosecond (fs) laser beam can induce stable damages and changes of the refractive index in various glasses. In the case of crystals the stress field induces an increase of the refractive index in the zones adjacent to that where laser irradiation is performed [3]. Based on this finding, wave-guiding was realized between two such written tracks that were positioned at a narrow distance (up to a few tens of μm) from each other; single-transverse mode operation was obtained in this way [4,5]. A tubular waveguide is obtained with this technique, by using a core of the crystal with unmodified properties around which many parallel

Results

Discussion

Conclusion