Study On Femtosecond Laser Machining Technology And Processing Mechanism For KDP Crystals

Laser processing3-D microstructures inside KDP crystals is an effective way tosuppress the transverse stimulated ramam scattering（TSRS）in high power lasers. Asimulation study on the transmission characteristics of focused laser inside KDP crystal andthe mechanism of interaction between laser and crystal were carried out to investigate thefeasibility of laser processing3-D microstructures and the effects of laser parameters on themachining accuracy, efficiency and yield. The results show that the mainly interactionalmechanism between ultrafast laser and KDP crystal is the nonlinear effects of multiphotonionization, collision ionization, etc. In addition, it also shows that machining process is tinilyinfluenced by absorption characteristics of material, however, it’s closely related with thelaser peak power. The peak power density, spot distortion and position deviation of laserfocus, are main factors which influence the machining accuracy and cause crystalfragmentation. The machining accuracy can be prominently increased after compensated bysoftware using simulation results. The size and shape of the E-ray focus will distort and itspeak power density decreases rapidly with the increasing of angle between incident laser andcrystal optical axis (θ). The results show that the effect of the E-ray will make the processingefficiency increase more than double when θ is less than15°, and can be neglected in thelow-energy or easily causes crystal fragmentation in high-energy when θ is greater than30°,in this case the e-ray should be shielded.The experimental research of laser machining3-D microstructures has been carried out.The results show that the mutual interference among microstructures and the internal stressaccumulation in machining process are main factors influencing processing quality.Therefore, optimizing grain spacing on the basis of simulation results and usingsectionalized and fractional processing method should be done to eliminating the influenceof internal stress accumulation. The light isolation property of3-D microstructures is mainlyabsorption, diffuse reflection and transmission. In transmission lights, the ratio betweenscattered light and parallel light is5.8:1.2, and the scattering angle is approximately39.6°.Using this technique, in addition, femtosecond laser cutting silica glass has been researched.Furthermore, the results indicate that we should try to use laser, which has high repeatfrequency, low pulse energy and short pulse width, in order to ensure the cutting efficiencyand increase the cutting quality.