A femtosecond (fs) laser beam machining method has been proposed to improve the quality of micromachining. At first, the coated silica sheet is prepared by pulsed laser deposition, then the coated silica is processed by the fs laser. After that, the aluminum film on a fused silica sheet is cleared out by hydrochloric acid (HCl) in a solution of 10%, and then the microhole array is formed on the silica which has better morphologies. Additionally, some mathematical models are constructed to analyze the diffusion of vapors and reflection of shock waves during the machining process. The theoretical results show that the aluminum film can effectively decrease the pressure gradient of the vapors and the reflection of shock wave pressure on the fused silica during the machining process. The simulation is consistent with experimental results. Finally, coating with a film or not has a great influence on the quality of micromachining, but the types of coating films have little influence. In a word, it is an excellent choice to improve the quality of fs laser processing by coating with a film on a fused silica sheet.
We investigate the damage characteristics and mechanism of neutral density filters consisting of metal film on K9 glass substrate by 1064-nm pulsed laser. The damage morphologies present marked differences with different laser pulse energies. Specifically, with the increase of laser fluence, the damage pits density increase as well, and at the same time, the cracks appear around the pits and interconnect, which lead to the abscission of film. The damage mechanism has been studied from the viewpoint of embedded impurities in the film. The theoretical results show that the difference between the thermodynamic properties of impurities and film can lead to thermos-elastic stress, which plays important roles in deformation of film, nucleation and propagation of cracks. Last, methods have been proposed to improve the laser damage resistance by controlling the size distribution of impurity particles and increasing the film tensile strength.
Semiconductor saturable absorber mirror (SESAM) mode locked Yb doped ultrafast lasers have been widely used in industrial applications. High laser stability against environment change and delivery process are required for industrial laser systems. A double Z-type ultrafast laser cavity was demonstrated experimentally and theoretically. Compared with the conventional Z-type cavity, this double Z-type cavity SESAM mode locked laser is less sensitive to misalignment and can tolerate more arm length changes while still staying cw mode locking.
Laser-induced plasma can expedite the deposition of incident laser energy and the laser-induced damage in optical glass is considerably affected by the magnitude and distribution of the plasma shock wave. The spatial distribution of energy deposition and expansion pressure of the laser plasma shock wave is analyzed based on the moving breakdown model. Furthermore, damage morphologies are discussed in light of the spatial distribution of pressure and glass properties. It was found that with the increase of laser pulse energy, the shock wave expands rapidly in the direction opposite to the incident laser, resulting in that the damage morphologies transform from sphere to spindle gradually. The laser energy deposits mostly in a narrow plasma channel. The diffusion of the plasma with high temperature and pressure leads to the shock wave; the intensity of which decreases sharply with the axial distance from the centerline. As a consequence, the glass near the centerline fractures and melts, and the refractive index also changes near the end of cracks.
Silicon is a key material to electro-photonic detectors, which makes the studies of laser induced damage of
silicon significantly important in laser detecting and military applications. The damage characters of silicon under
high-intensity nanosecond laser pulses have been investigated in this paper. The results show that the synergy of thermal,
shock and spectral radiation effects of laser plasma determines the damage characters in silicon. Due to thermal and
shock effects of laser plasma, the material is melt, vaporized, ionized and pushed out in laser irradiated area. This way,
pits are formed and the cool ejected effluents are distributed radially. The interference between scattered and incident
laser can form a periodic structure because of the periodic distribution of thermal stress in particular area. N, O and Si
characteristic spectrum in laser plasma suggests that colored film is the mixture of SiO<sub>x</sub>:SiN<sub>y</sub> from laser plasma under repetitive laser pulses.
Taking into account the effects of third-order nonlinear effects, transverse walk-off and diffraction etc., we have performed theoretical analysis and numerical simulation for third-harmonic generation (THG) in potassium dihydrogen phosphate (KDP). The results show that the efficiency of the THG decreases as the ratio of phase ripples of the input beam increases. The results also indicate that increasing the conversion efficiency of THG can improve the beam quality of the third-harmonic wave.
Considering the fact that holes contained in spatial filters may also serve to isolate ghosts in different areas, we have proposed an optical matrix method for locating the near-axial ghosts in high power laser systems. We also analyze practical criteria for distinguishing real and virtual ghosts. Our model can be used to calculate arbitrary order ghosts of laser amplifier systems.