The Study Of Ciliary White Light Of Femtosecond Laser Ablation On BK7Glass

In recent decades, scientists have been committed to the research of laser ablation technique. Femtosecond laser ablation has great advantages in practical applications compared with the outdate method using nanosecond laser, because there is no obvious collateral damage to the surroundings owing to shock waves and heat conduction produced in the ablation process. Laser ablation technique has been intensively studied and applied to many research fields and applications, such as nanoparticle manufacturing, micromachining surgery, thin film deposition, and laser induced breakdown spectrometry, etc. Femtosecond laser ablation involves various linear and nonlinear optical processes, which are very important to have a further understand the various phenomena in the process of ablation. So far, a lot of investigations on the fundamental mechanism and fabricated nanostructures on the surface of materials have been done, but truly no much attention has been paid for the ablating laser itself. The main research of this thesis is the interaction of ultra-intense femtosecond pulse laser and the transparent BK7glass.Firstly, the linear refractive index of BK7glass was measured with the third order harmonic method. The intensity of the third order harmonic produced by a three frequency doubling crystal was the strongest when two parallel femtosecond laser beams with equal energy were coincident in time and space. In addition, theoretical analysis and experimental verification have been performed, and the refractive index of BK7glass has been obtained by processing the experimental data before and after putting the sample into the light path. It turned out that the measured refractive index of the sample is in good agreement with the actual data, which verified the validity of this technique to measure the linear refractive index of materials. Compared with the traditional measuring methods, this technique can be operated simply, which has no limit on the range of the refractive index, and the sample is processed easily. Thus, the method of third-order harmonic has very important practical value.Secondly, ciliary white light was observed by femtosecond laser pulse ablation on BK7glass in air. By varying the distance of laser focus from the front surface of BK7glass, we investigated the evolution of laser emission patterns from the back surface. The full spectrum and angular distribution spectrum of the ciliary white light were also measured to acquire the variation of emission spectra, which are important to study the properties of the ciliary white light and have great role in promoting the development of laser ablation monitoring technology.