High average power quasi-CW single-mode green and UV fiber lasers

Visible Raman-Shifted Fiber Lasers for Biophotonic Applications

“…The relatively low SHG conversion efficiency obtained for the Raman-shifted systems in Ref. [28] is in part due to the modest nonlinear coefficient of LBO. As discussed in Section I-B, significantly higher effective nonlinear coefficients can be obtained using PP crystals, at the expense of a vastly reduced spectral acceptance bandwidth.…”

“…This can limit the SHG conversion efficiency due to the finite spectral acceptance bandwidths of frequency-doubling crystals. The impact of the finite spectral acceptance bandwidth was demonstrated by Avdokhin et al [28], where a Yb:fiber MOPA system was Raman-shifted to 1178 nm and 1230 nm and then frequency-doubled using LBO. The Yb:fiber MOPA system operated at 1064 nm with a pulse duration of approximately 2 ns at a repetition rate of 25 MHz.…”

620 nm Source by Second Harmonic Generation of a Phosphosilicate Raman Fiber Amplifier

“…Fiber-based, nanosecond-pulsed sources in the red spectral region are useful for a number of biophotonics imaging applications, including stimulated emission-depletion microscopy (STED) [1]. Typical Raman fiber-based sources operating in this region utilise multiple Raman shifts in silica fiber pumped by ytterbium-doped fiber (Yb:fiber) systems operating around 1 µm, followed by second harmonic generation (SHG) in a bulk crystal such as lithium triborate or lithium niobate [2,3]. An alternate method is to first frequency double Yb:fiber systems to the green, before repeatedly Raman shifting in silica fiber [1].…”

Watt-level Nanosecond 589 nm Source by SHG of a Cascaded Raman Amplifier

“…The frequency-doubling of Yb:fiber master oscillator power amplifier (MOPA) schemes into the green is a well established technique that has been scaled to average powers up to 700 W [3]. It is difficult to operate high-gain Yb:fiber MOPA systems beyond 1100 nm, however, due to the larger emission cross-section at shorter wavelengths that results in issues with amplified spontaneous emission (ASE).…”

“…Stimulated Raman scattering in optical fibers can be used to efficiently frequency-downshift the output of Yb:fiber systems but the broadband nature of the Raman gain spectrum results in the formation of Raman ASE with a bandwidth of several nanometres. This bandwidth can severely limit the second-harmonic generation (SHG) conversion efficiency if it exceeds the spectral acceptance bandwidth of the SHG crystal [3]. This is a particular issue if the fundamental has modest peak-power, since the high nonlinear coefficients of periodically poled (PP) crystals are required for efficient SHG.…”