Green pulse regenerative amplification using a Pr³⁺:LiYF₄ crystal pumped by GaN blue laser diodes

Direct regenerative amplifications of green pulses (522 nm) were investigated using a Pr³⁺-doped LiYF₄ crystal pumped by GaN blue laser diodes. Green pulses with two different temporal duration regimes, i.e. sub-picosecond (sub-ps) and sub-nanosecond (sub-ns), were prepared from the second harmonic generation of the mode-locked Yb³⁺-doped fiber laser at the repetition rate of 100.86 kHz and used as a seed for the comparison of the amplification processes. For the sub-ps (0.63 ps) and sub-ns (0.3-0.4 ns) seeds, the amplifications resulted in 1.25 µJ and 1.53 µJ in the pulse energies, 0.60 nm and 0.27 nm bandwidths, and the beam qualities of (M²x = 2.26, M²y = 1.25) and (M²x = 1.47, M²y = 1.23), respectively. A comparison of the B integrals confirmed that the wider bandwidth and the lower beam quality of the sub-ps seed amplification versus the sub-ns seed amplification were caused by the nonlinear effects in the sub-ps amplification.