J. Eur. Opt. Society-Rapid Publ. 22, 7( 2026) 75
Fig
. 25.( a) Photo of the experimental setup and( b) Schematic of the cavity arrangement of passive Q-switched Nd: YAG laser with saturable Cr: YAG absorber for second harmonic generation.
Fig. 26. Train pulses generated from the second harmonic with a wavelength of 532 nm:( a) with time / div 400 ls,( b) with time / div 2 ms.
gradients inside the crystal, thereby suppressing one of the major contributors to pulses amplitude instability [ 38 ].
5. Studies have shown that in second-harmonic generation, operating with a larger beam waist( i. e., weaker focusing) equivalent to expansion of the input beam, significantly reduces thermal effects and thermal lensing in nonlinear crystals, thereby leading to considerably improved long-term stability of the frequencydoubled output [ 39 ].
When these measures are applied in combination, it is expected that the amplitude fluctuations of the 532 nm burst output will be limited and long-term stable performance will be achieved for more than 10 pulses, allowing the generation of nanosecond green pulse trains with high repetition rate and temporal stability.
Figure 27 illustrates the temporal profile of a single SHG pulse measured using a 200 ns / div oscilloscope setting. The pulse exhibits a full width at half maximum( FWHM) of 6 ns, a peak voltage of 65.2 mV, an intra-burst repetition