Direct Measurement of Temporal Transmission Distribution of a Saturable Absorber in a Passively Q-Switched Laser

Abstract

An in situ temporal decay and spatial distribution of the transmission of a Cr 4+ :YAG saturable absorber in a passively Q-switched Nd:YAG laser were measured simultaneously by a scanning transmission focused laser beam method. An excited ion decay time of 4 μs and a top hat (saturated) transmission distribution were clearly observed. The ratio of the ground-state absorption cross section and the excited-state absorption cross section (σ SAπ/ σ ESAπ ) for π-polarized light to the S 4 local symmetry axis of Cr 4+ center was measured at approximately 4.1-4.2. Using a theoretical fitting of the transmission distributions, we found the ground-state absorption cross sections to be at 1 × 10 −17 and 2.3 × 10 −19 cm 2 for π and for σ -polarized light to the S 4 local symmetry axis of Cr 4+ center, respectively. The value of the excited-state absorption cross section was also estimated correspond to 2.4 × 10 −18 cm 2 .

Amplified spontaneous emission suppression of a saturable absorber in a nanosecond double-pass laser amplifier

“…Several models have been reported to explain the saturation behavior of Cr:YAG. 16,[18][19][20][21][22] Among these, we employ the three-level model 16,18) because it is well-verified for nanosecond pulses, 16) which we are considering. The threelevel model describes the saturation behavior by using three coupled rate equations that represent the occupation densities of the three energy states.…”