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J. Eur. Opt. Society-Rapid Publ. 22, 7( 2026)
Fig
. 17. Train taps produced by cavity arrangement C:( a) 35 J / cm 2 = 3,( b) 40 J / cm 2 = 9,( c) 47 J / cm 2 = 16,( d) 50 J / cm 2 = 20.
Fig. 18. Train taps produced by cavity arrangement D:( a) 40 J / cm 2 = 5,( b) 47 J / cm 2 = 11,( c) 50 J / cm 2 = 17.
coefficient of the crystal is less than 0.001 cm �1 at both 1064 nm and 532 nm, resulting in a transmission exceeding 99.95 % across the 5 mm length at these wavelengths. To isolate the 532 nm pulses for measurement and further confirm the AR coating’ s performance by separating residual fundamental light, a dielectric filter was placed immediately after the KTP crystal, designed to reflect the 1064 nm fundamental radiation(> 99 % reflection) while transmitting the 532 nm second-harmonic output with high efficiency(> 95 % transmission). To safeguard the KTP crystal from optical damage due to intracavity intensities, and to optimize the phase-matching conditions for efficient frequency doubling, the crystal was positioned externally, beyond the laser resonator. The complete schematic of the SHG experimental and semantical setup is shown in Figure 25.
In addition to the external placement of the nonlinear crystal, a polarizer was installed at a precise Brewster angle of 54.7 ° near the concave high-reflectivity mirror to enforce linear polarization of the fundamental laser beam, thereby enhancing the conversion efficiency via improved phase matching. A short-pass optical filter was employed immediately before the KTP crystal to isolate and transmit only the frequency-doubled component at 532 nm while rejecting residual 1064 nm radiation. The overall cavity length in this SHG configuration was 363 mm.