Acknowledgements

In another experiment, we fixed the exposure time at 10 s, varied the relative phase of the twocolor beams and examined the ablated holes afterwards. In Figure 11(a), we have plotted diameters of holes drilled in copper sheets as a function of relative phases between the fundamental (ω1) and second harmonics (ω2) of the synthesizing laser. Pictures of the drilled holes are also presented. Similar results for stainless steel are shown in Figure 11(b). These data clearly show the dependence of ablation rate on the synthesized waveform, that is, relative phase of the fundamental (ω1) and second harmonic (ω2) of the single-frequency Nd:YAG laser.

Figure 10. Numerical simulation of the peak strength of the laser waveform synthesized by two-color laser fields with various relative phases between the fundamental and the second harmonic (a) Δφ = 0, (b) Δφ = π/2, (c) Δφ = π, and (d) Δφ

As an application of the high-power laser system based on synthesized waveforms, we studied harmonic generation by three-color waveform synthesis in inert gas systems. In third-order nonlinear optics, the interaction between three-color beam and inert gases can be used to generate fourth to ninth harmonics of the laser fundamental output. For fourth-harmonic generation, there are three kinds of four-wave mixing processes: ω<sup>4</sup> = ω<sup>i</sup> + ω<sup>j</sup> + ωk, ω<sup>4</sup> = ω<sup>i</sup> + ω<sup>j</sup> ωk, where i, j, k = 1, 2, 3. For fifth-harmonic generation, there are three possible processes:

5. Summary

= 3π/2, respectively.

168 High Power Laser Systems

This work was supported by grants sponsored by the National Science Council (now Ministry of Science and Technology or MoST) of Taiwan (NSC 98-2112-M-009-015-MY3) and Phase II of the Academic Top University Program of the Ministry of Education, Taiwan.
