## 3 Results and Discussion
### Energy Characteristics of Pulse-Burst Generation  
The best values for the energy characteristics of the Raman laser in PB mode were obtained when the Q-switching rate and, correspondingly, the subpulse repetition rate, were 7.6-8 kHz. We obtained 75-78 subpulses in the burst (see Figure 3). The maximum electric pump energy applied to flash lamps operating in PB mode exceeds 1500 J, so the average pump power, even at 1 Hz, can exceed 1.5 kW. It caused a considerable thermal birefringence in the Nd: YAG laser rods, and the reduction in Nd: YAG laser energy after the start. Correspondingly, the burst energies at 532 nm and all Stokes wavelengths also decreased. The temporal decrease in the burst energy at 532 nm and 589 nm is shown in Figure 4.  
At the same time, we can see that the efficiency of 589 nm generation remains practically unchanged after more than 2 min of laser operation. This means that **E\({}_{\textbf{589}}\)** reduces only in proportion to the reduction in **E\({}_{\textbf{532}}\)**, indicating that, for our pumping spot size, the thermo-optical distortions that are created in the KGW crystal during Raman laser generation are actually small, and do not exert a notable additional influence on the Raman laser energy. Figure 3: The oscillograms of the burst pulse at an 8 kHz Q-switching rate: pink, 532 nm pump radiation; yellow, 589 nm Raman radiation. The frame width is 10 ms. Figure 5 shows the dependence of the burst energies of the first, second, and third Stokes orders on a 532 nm pump energy. The energy values indicated here were measured at the fifth burst after the start. At the maximum 532 nm pump energy \(\mathbf{E_{532}}\) = 23 J, we obtained a burst energy \(\mathbf{E_{559}}\) = 13 J at 559 nm, \(\mathbf{E_{589}}\) = 11.6 J at 589 nm, and \(\mathbf{E_{621}}\) = 8 J at 621 nm. This is the first time that such a level of energy in Raman lasers for the visible spectral range has been  
Figure 4: The temporal behavior of the laser burst energy and Raman laser efficiency. The burst repetition rate is 1 Hz. The electrical pump energy applied to Nd: YAG laser flash lamps is 1250 J, which is \(\sim\)80% of the maximum available pump energy. Figure 5: The dependence of the Raman laser burst energy on 532 nm pump burst energy for the generation of 559 nm, 589 nm, and 621 nm Stokes orders. The 589 nm order was generated using output mirror 1 (Table 2). The burst repetition rate is 1 Hz. realized. The maximum energy achieved here at 559 nm is eight times higher than that previously reported in [4] for 1180 nm. The maximum energy efficiencies, \(\eta\), here, are 56%, 50%, and 35% for 559 nm, 589 nm, and 621 nm, respectively. The increase in the Nd: YAG laser's burst repetition rate from 1 Hz to 1.5 Hz was followed by an additional decrease in burst energies at all wavelengths at the given electric pump level. In Figure 6, we combine the burst energy data obtained at 1.0 and 1.5 Hz. One can see that all the dots lie on the same straight line. This means that the Raman laser efficiency does not reduce when the burst repetition rate increases from 1 Hz to 1.5 Hz. At 1.5 Hz, thermal distortions, of course, are larger than at 1 Hz, but this does not cause a reduction in efficiency. In our opinion, this also confirms the conclusion, which was expressed earlier, that thermo-optical distortions in a KGW crystal under our operational conditions do not cause a notable deterioration in the laser energy. Thus, we can expect to obtain larger output energies and average powers from a KGW Raman laser in PB mode by improving the characteristics of Nd: YAG lasers. The efficiency of the Raman laser generation achieved in PB mode was 12-20% lower than that obtained in SP mode at an equal pump energy density (considering the average energy density of individual subpulses in a 532 nm burst).