We have optimized the input pulse width and injection time to achieve the highest possible output pulse energy in a double-pass laser amplifier. For this purpose, we have extended the modified Frantz-Nodvik equation [1] by simultaneously including both spontaneous emission and pump energy variation. The maximum achieved fluence of the output pulse was 2.4 J/cm 2 . An input pulse energy of 1 J could be maximally amplified to output pulse energy of 12.17 J, where the optimal values of the pulse width and injection time of the input pulse were 168 and 10 , respectively, with the effective pump energy being 8.84 J.
The optimization of solid-state laser cavities requires a deep understanding of the gain module, the most critical laser component. This study proposes a procedure for evaluating the performance of the solid-state laser gain module. The thermal effect and energy storage characteristics are the performance criteria. A normalized heating parameter was calculated as a quantitative indicator of the performance criteria. We proposed a method to quantify the heat dissipated into the gain medium using the wavefront distortion, thermal deformation theory of the gain medium, and the ray transfer matrix method. The suggested procedure was verified by evaluating the flashlamp type Nd:YAG rod gain module, but it can also even be extended to other solid-state laser gain modules by applying the appropriate thermal deformation theory.
We introduce the laser-induced surface processing (LISP) method that imparts hydrophilicity and hydrophobicity using a Nd:YAG nanosecond laser, especially the high-fluence (HF) condition for fast processing and the low-fluence (LF) condition to control the surface wettability. A prime example of HF processing is laser shock peening, where we show the potential to achieve both strength enhancement and wettability in materials. This could be a new advantageous feature in areas such as reactor maintenance. We combined a beam homogenizer with LISP to increase processing efficiency. The beam homogenizer realizes a uniform fluorescence distribution in the beam area and, at the same time, makes the beam rectangular to increase work efficiency. The maximum contact angle was 123.8° for the zircaloy-4 specimen through HF processing with the beam homogenizer. We also showed that nanosecond laser-induced periodic surface structures could be generated by combining LF processing with specific conditions of a beam homogenizer. This could produce a superhydrophobic surface with contact angles up to 166° on zircaloy-4 or achieve a near superhydrophilic surface with a contact angle of 17.9° depending on the processing conditions.
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