Eye-Safe KGd(WO4)2 Raman Lasers: Comparative Study of Pumping of Nd:KGd(WO4)2 Lasers With 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 Working Transitions**

This is a comparative study of eye-safe extracavity KGd(WO4)2 (KGW) Raman lasers that convert multimode emission from pulsed Nd:KGW lasers operating on the 4F3/2 → 4I11/2 and 4F3/2 → 4I13/2 transitions into the third Stokes component at λ = 1500 nm and the first Stokes component at λ = 1507 or 1538 nm. For equal sizes of the Raman and laser sections of a Raman laser emitting the third Stokes component, the pulse energy is higher (~14.2 mJ) and the divergence of the Stokes beam is lower (~9.4 mrad) for a lower energy of the Nd:KGW laser (~6.7 J). For pump pulse energies of 29–34 mJ, all the Raman lasers have essentially the same optical lasing efficiency of up to 36%. In terms of the electrical energy delivered to the flashlamp, however, the overall efficiency of the Raman laser for the third Stokes component is a factor of ~1.7 higher. The duration of the Raman pulses is comparable to that of the pump pulses and is ~20 ns for the first Stokes components. The pulse in the third Stokes component is shorter by a factor of 2.5–3. Given the different pump levels and the differences in the thermallyinduced optical distortions of the Nd:KGW laser components, the energy density distribution for beams of the first Stokes components is elliptical, while that of the third Stokes components is almost circular. The possibility of simultaneous lasing at wavelengths of 1507 and 1538 nm with parallel and mutually orthogonal polarizations of the Stokes waves is demonstrated.