## 2 Experimental Hardware  
A block scheme of the experimental setup is shown in Figure 1.  
To study wavelength conversion in a KGW Raman laser, we arranged a relatively simple high-energy Nd: YAG laser that could operate in pulse-burst mode (PB mode), as well as in single-pulse mode (SP mode), using two different power supplies. It should be mentioned that operation in SP mode allows us to simplify and accelerate the laser alignment procedure, optimize the Raman laser parameters, etc. The Nd: YAG laser included a flash-lamp-pumped electro-optically Q-switched multimode oscillator, followed by a single-stage amplifier. The laser's Pockels cell driver had a variable Q-switching rate up to 10 kHz, to produce pulse bursts within a 10 ms flash lamp pump pulse, as well as to produce single pulses in combination with a 200 \(\upmu\)s flash lamp pulse when operated in SP mode. The laser's characteristics are shown in Table 1.  
SHG was obtained using a 5 mm length KTP crystal. The SHG efficiency in PB mode reached 50%, and the maximum burst energy at 532 nm was 23 J. The minimum subpulse duration here was 10 ns. In SP mode, the maximum pulse energy was 0.4 J, and the minimum pulse duration was 5 ns.  
The optical scheme of the external-cavity Raman laser is shown in Figure 2. The laser included a 7 \(\times\) 7 \(\times\) 50 mm \"Np\"-cut KGW crystal from Eksma Optics, with two flat mirrors: a pump and an output. The pump mirror had 93-95% transmission at 532 nm and 99.5% reflection within 550-670 nm. The output mirror had 99.5% reflection at 532 nm, to produce double-pass pumping. The reflection coefficients of the output mirrors at other wavelengths were varied, to determine the optimum values to selectively generate the first, second, or third Stokes order. Both mirrors were placed close to the ends of the KGW crystal, so the resonator length was 52-54 mm.  
\begin{table}
\begin{tabular}{c c} \hline \multicolumn{2}{c}{Pulse-Burst Mode} \\ \hline Burst repetition rate & 1–1.5 Hz \\ \hline Subpulse repetition rate within the burst & 5–10 kHz \\ \hline Burst duration & 10 ms \\ \hline Subpulse duration & 12–15 ns \\ \hline Maximum burst energy & 45 J \\ \hline \multicolumn{2}{c}{Single-Pulse Mode} \\ \hline Maximum pulse repetition rate & 10 Hz \\ \hline Minimum pulse duration & 6 ns \\ \hline Maximum pulse energy & 0.8 J \\ \hline \end{tabular}
\end{table}
Table 1: The characteristics of the Nd: YAG laser.  
Figure 1: The experimental setup.  
A pumping radiation of 532 nm was transmitted through a single microlens array (MLA) homogenizer, and focused into a KGW crystal via a condenser lens, producing a sharp 4.1 \(\times\) 4.1 mm rectangular cross-section channel along the crystal. The polarization of the 532 nm radiation was set to be parallel to the axis N\({}_{\rm m}\), to obtain a Stokes shift of 901 cm\({}^{-1}\).  
The laser energy in SP mode at all wavelengths was measured with a J-50-YAG pyroelectric detector from Coherent and, in PB mode, with a 30(150) A-LP2-18 thermophile sensor from Ophir. The subpulse duration was determined using a UPD-50-UD photodetector from Alphalas (50 ps rise time), and an Infinium DSO80804B digital oscilloscope with an 8 GHz bandwidth. The time dependence of the subpulses in PB mode was recorded using DET 36 photodetectors from Thorlabs, and a Tektronix 5204B oscilloscope. The spectrum of Raman laser generation was registered using a Flame-S-VIS-NIR-EO miniature spectrometer from Ocean Insight.