[Thermodynamics process of laser drilling on copper surface].

The laser drilling experiment was carried out on the copper surface by ns laser pulse, then the micro-morphology of the micro-hole was observed and the thermodynamic process was analyzed accordingly. The research results show that micro-hole is made of the pit in the center and surrounding uplift. The pit becomes deeper with the incident laser pulse energy. The thermodynamic analysis indicates that laser drilling on the metal requires two basic conditions: the first is the deposition of laser pulse energy, which makes the occurrence of melting, vaporization and ionization. Such phase transition can make the materials easy to remove and the laser plasma can accelerate the laser pulse energy deposition as the secondary heat source. The second condition is the production of the laser plasma shock wave, it can eject the materials of phase transition effectively and timely, thus the micro hole can be formed.

[The influence of laser induced damage points on characters of the laser transmission].

The production and increase of damage points in optical components under high energy repetitive pulsed lasers is closely dependent on the effects of light beam intensity modulation. In the present paper, the appearance of laser-induced damage points on surface of K9 glass was observed. The damage is increased toward center. In this way, the center of the focus of laser beam is fully cracked, and the shell-like factures and the refractive-index changing region, which is caused by phase transition, are arranged outward orderly. The transmittance spectrum through the K9 glass and damage point were measured, indicating that the optical transmittances can reduce by over 20% and the declining rate is related to the area of damage points instead of the wavelength, which means that the full fracture of the material will absorb laser energy completely and is similar to the black body. The laser density detection with CCD shows that the damage points can cause the distortion of laser transmission and the scattering effect plays a major role. This kind of modulation effects by damage points can cause inhomogeneity of the laser light intensity distribution, which can induce diffusion of damage in optical components.

[Study on characteristics of laser ablation in KTP crystal and its influence on the Raman spectroscopy].

The research and development of the KTP crystal with high threshold is of very importance for its application in high-energy laser systems. Ablation characteristics in KTP crystal as well as their influence on the Raman spectroscopy were studied by UV laser with high repetition frequency. The research results show that the laser plasma effects are the main reasons for the damage in the KTP crystal. The inverse bremsstrahlung absorption effect can increase the deposition of the laser pulse energy greatly; the ionization effect can make the crystal dislocated completely; shock wave effect can push away the mixture of melted, vaporized and ionized materials and cause cracks in the pit. Through investigation and comparison of the Raman spectroscopy before and after the laser ablation, it was found that the distribution characteristics of Raman peaks are almost the same, suggesting that the basic structures of KTP crystal do not change. But almost all the Raman characteristic peaks' R1R values have changed and the widths are broadened, which means that the crystalline degree has been decreased. The Raman peaks of TiO6 and PO4 oxygen polyhedron shift to the lower wave number, which indicates that bonding force becomes weaker and the KTP crystal can be damaged easily.

[Study on the damage of SiO2 thin films on LiNbO3 crystal in optical parametric oscillator by XRD spectrometry].

In an attempt to elucidate the damage in high transmission thin films on LiNbO3 crystal in optical parametric oscillator, the authors employed XRD spectrometry to investigate the spectrum of laser-induced damage in thin film as well as the morphology of the damage. The authors observed that the damage of thin film was characterized by the depressions/craters in the surface of the films, which were surrounded by a deposition layer with the deceasing thickness from the center of the craters. The XRD measurements indicate that the film was crystallized. The authors analyzed the causes of morphologies and the mechanism of crystallization with the aid of the model for impurity-induced damage in thin solid films. The crystallization was due to the solidification of liquid and gaseous mixtures that result from the strong absorbing to the incident laser. The crater was generated because the mixtures were ejected under the extensive pressure of the laser plasma shock wave. During the process that the mixtures deposit around the craters, the density of the mixtures will decrease and crystallization takes place. As a result, the color of the deposition layer becomes lighter from inside to outside, and the crystallization of the thin film materials was observed by XRD spectrometry.