Fiber-laser in-band pumping enables novel 2 μm high-power short-pulse laser

A research team has developed novel 2 μm high-power short-pulse lasers based on a new technique of fiber-laser in-band pumping at 1611 nm and Kerr-lens mode locking with a new Tm-doped gain medium.

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Highly efficient high-power short-pulse lasers in the 2 μm wavelength range based on thulium (Tm3+)-doped materials have a variety of applications that include materials processing (such as polymer-to-metal joining), lidar, mid-infrared (mid-IR) optical parametric oscillators (OPOs) that produce wavelengths up to 12 μm, and mid-IR supercontinuum generation. They also would enable direct coherent soft x-ray generation via high-order harmonic generation (HHG). For these applications, a light source with much higher conversion efficiency, average power, pulse energy, and shorter pulse duration is desirable.

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Now, Masaki Tokurakawa and colleagues at the Institute for Laser Science, University of Electro-Communications (UEC; Tokyo, Japan) have developed novel 2 μm high-power short-pulse lasers based on a new technique of fiber-laser in-band pumping at 1611 nm and Kerr-lens mode locking with a new Tm-doped gain medium provided from the University of Hamburg by researcher Christian Kränkel.

Pulses as short as 115 fs and an output power of 420 mW with a conversion efficiency of approximately 20% were obtained. At a longer pulse duration of 298 fs, the laser reached an average power of more than 1 W. Compared with prior semiconductor saturable-absorber mirror (SESAM) mode-locked Tm-doped lasers pumped by titanium:sapphire (Ti:sapphire) lasers, this new method enabled generation of much higher output power and shorter pulse duration with higher conversion efficiency. The researchers say that this is the first Kerr-lens mode-locking at a wavelength of 2 μm, opening up possibilities for new highly efficient high-power short-pulse lasers at 2 μm. In the future, sub-50-fs pulse generation at this wavelength range is possible. Reference: M. Tokurakawa et al., Opt. Lett., 42, 3185–3188 (2017); https://doi.org/10.1364/OL.42.003185.

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