J. Eur. Opt. Society-Rapid Publ. 22, 7( 2026) 69
Fig
. 12. Photo of the experimental setup arrangement of the passive Q-switched Nd: YAG laser cavity with saturated Cr: YAG absorber:( A) concave HR mirror( R = 500 mm),( B) laser head housing the Nd: YAG crystal and flashlamp,( C) Saturated absorber of C: YAG and( D) flat output coupler( T = 40 %).
Fig. 10. Maximum power of pulses produced by Nd: YAG laser in free running mode.
Fig
. 11. Microsecond pulse produced by Nd: YAG laser in free running mode.
Cr 4 +: YAG saturable absorber crystal with an initial transmission of 40 % is placed in the cavity. The cavity is completed by a flat output coupler with 40 % transmission at 1064 nm.
To optimize the temporal characteristics of the pulse train – specifically to minimize pulse width and maximize the number of generated pulses – we systematically varied the cavity geometry as outlined in Table 3. Fourconfigurations( A – D) with cavity lengths ranging from 275 mm to 465 mm were implemented.
Initial measurements focused on determining the threshold energy density required to initiate Q-switching in each configuration. As shown in Figure 13, the shortest cavity length( setup A, 275 mm) exhibited the lowest threshold fluence at 33 J / cm 2, while the longest cavity( setup D, 465 mm) required a threshold of 40 J / cm 2. This trend confirms that shorter cavities enable earlier saturation of the Cr: YAG absorber due to the reduced round-trip time for photons within the resonator, resulting in more efficient energy buildup and faster onset of Q-switching. In contrast, longer cavities necessitate more extensive energy storage
Fig. 13. Threshold energy density required for Q-switching operation to be started in four cavities( A, B, C, and D) with different lengths.
within the gain medium to reach the saturation point of the absorber and initiate lasing action. These observations are in strong agreement with established Q-switching dynamics, wherein the time required for population inversion and absorber saturation scales with the cavity length and photon lifetime within the resonator [ 21 – 24 ].
Figure 14 and Table 5 depict the relationship between input energy density and the number of pulses generated per burst in the four cavity configurations. The data clearly show that the number of pulses increases with both increasing input fluence and decreasing cavity length. Setup A( 275mm) producesupto22pulsesat50J / cm 2, whereas setup D( 465 mm) generates only 17 pulses under the same pump fluence. This behavior is attributed to the enhanced gain dynamics in shorter cavities, where faster photon circulation results in quicker gain extraction and a higher probability of multiple Q-switching events during each excitation cycle. In contrast, longer cavities slow down the energy extraction process, limiting the total number of pulses generated [ 25 – 29 ].