Abstract
We report the generation of mid-infrared (~2 µm) high repetition rate (MHz) sub-100 ns pulses in buried thulium-doped monoclinic double tungstate crystalline waveguide lasers using two-dimensional saturable absorber materials, graphene and MoS2. The waveguide (propagation losses of ~1 dB/cm) was micro-fabricated by means of ultrafast femtosecond laser writing. In the continuous-wave regime, the waveguide laser generated 247 mW at 1849.6 nm with a slope efficiency of 48.7%. The laser operated at the fundamental transverse mode with a linearly polarized output. With graphene as a saturable absorber, the pulse characteristics were 88 ns / 18 nJ (duration / energy) at a repetition rate of 1.39 MHz. Even shorter pulses of 66 ns were achieved with MoS2. Graphene and MoS2 are therefore promising for high repetition rate nanosecond Q-switched infrared waveguide lasers.
Highlights
Waveguide (WG) lasers emitting in the spectral range of ~2 μm are of interest for spectroscopy, telecom and environmental sensing applications [1]
We report the generation of mid-infrared (~2 μm) high repetition rate (MHz) sub100 ns pulses in buried thulium-doped monoclinic double tungstate crystalline waveguide lasers using two-dimensional saturable absorber materials, graphene and MoS2
Two-dimensional materials are promising saturable absorber (SA) for WG lasers emitting at ~2 μm
Summary
Waveguide (WG) lasers emitting in the spectral range of ~2 μm are of interest for spectroscopy, telecom and environmental sensing applications [1]. When employed in a passively Q-switched (PQS) laser, “fast” SAs provide the generation of nanosecond (ns) pulses at high repetition rates in the range of hundreds of kHz – few MHz. Graphene is the most prominent example of 2D materials. We employ few-atomic-layer graphene and MoS2 as saturable absorbers in fs-DLW Thulium channel WG lasers based on a monoclinic crystal, for the first time, to the best of our knowledge. Fs-DLW induces a spatially localized modification of the material compromising its crystallinity and its index of refraction, as well as inducing anisotropic stress fields surrounding each laser-written track [28] The latter will result in a local variation of the optical indicatrix due to the photo-elastic effect leading to an additional phase shift for rays propagating through such a structure. The crystal was replaced by a 1951 USAF resolution test target (R1DS1, Thorlabs) to determine the mode size at the OC
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