Pump-probe spectroscopy of molecular systems requires high average power, short pulse, mid-infrared sources. Today OPO deliver wavelengths up to 4 µm and THz systems supply wavelengths beyond 20 µm. To achieve tunable wavelengths in between these two regions, the signal and idler beams of the OPO can be difference frequency mixed again. This two-step nonlinear process necessarily leads to average power much less than the OPO pump, which is typically a 1 W Ti:sapphire laser. In this paper, we report initial experimental results of two-wavelength amplification in a Yb-doped DCF fiber. Yb:fibre amplifiers have been shown to deliver short pulses at average power levels of up to 20 W .The goal of the work is to generate high average power (<1W) pump and signal beams for difference frequency generation at around 15 µm.
A schematic of the experimental is shown in Fig.1. A photonics crystal fiber is pumped by a mode-locked Ti:Sapphire laser to create supercontinuum, from which we can select the two seed wavelengths by using a standard zero dispersion grating line that has been adapted to have individual mirrors in the focal plane for the two different colours. The Yb:fibre is pumped by a 915nm diode laser. As shown in Fig. 2, at a pump power of 2.1 W, 500 gain was achieved yielding 150 mW total power(1055 and 1095 nm).
References:1. D. Nickel et al, Opt. Commun. 190, 309 (2001)