Abstract

Today, lasers emitting around 1 μm wavelength have reached an outstanding maturity in terms of power levels, beam quality, compactness and temporal regimes. It would thus be desirable to have the same features at different wavelengths, especially in some spectral ranges where there is pressing needs for lasers with comparable performances as at 1 μm. For example, a number of different applications like surgery, spectroscopy or IR vision require laser sources in the 2 – 20 μm wavelength range [1]. To fulfill this need, different techniques are under study, some of them use gas lasers [2], frequency mixings in OPOs [3] or quantum cascade lasers [4], or frequency conversion by Stimulated Raman Scattering (SRS). The latter is becoming very promising because of the advent of Hollow-Core Photonic Crystal Fibers (HC-PCF) [5]. Recently, using this technique with an Yb-fiber pump pulsed laser of 27 ps and average power 14W, it has been possible to generate ultra-wide Raman frequency combs [6], from the UV to the IR, and to optimize the fiber parameters to favor the Raman conversion at the 1st order Stokes at 1.8 μm, resulting in pulses with duration was less than 20 ps, an energy of 33 μJ, and average power of ~9 W [7]. This results indicate that SRS in HC-PCF is a promising frequency convertor of picosecond lasers emitting at 1 μm. The question on how this frequency convertor perform at shorter pump pulses, however, remains. Also, so far there is no reported work on the pulse profile of Stokes radiation and how it compares to the pump when using USP pulses.

© 2019 IEEE