Study On Laser Induced Damage Identification Technology Based On Terahertz

The laser-induced damage of optical elements has always been the main limiting factor for the development of high-energy and high-power laser system.Therefore,the development of laser technology is closely related to the ability of optical components to resist laser damage.Only by quantitatively measuring the laser damage threshold of an optical element,it is possible to improve its ability to resist laser damage.Before testing the laser damage threshold of an optical element,it is essential to identify the damage.How to quickly and effectively identify the laser-induced damage of an optical element has become a research hotspot.Terahertz spectroscopy,with its advantages of strong penetrability,high spectral resolution,convenience,high efficiency and safety,has a broad application prospect in the detection of material defects,and provides a new research idea for laser-induced optical element damage identification.Therefore,in this thesis,terahertz spectroscopy technology is combined with laser-induced damage recognition technology to study the laser-induced optical elements damage identification.In this thesis,the laser-induced damage technology and terahertz spectroscopy technology are studied.The laser-induced damage optical element are obtained by using the laser-induced damage test platform,and the damaged and undamaged optical elements are tested in the transmission terahertz time-domain spectroscopy system.Based on the previous research,the optical parameter calculation model of the optical element in the terahertz band was derived,and the algorithm programming was performed using MATLAB language to achieve the optical parameter calculation of the uncoated optical element and the Single-layer optical element.And the terahertz time-domain waveform,frequency-domain waveform,refractive index spectrum and absorption coefficient spectrum of the damaged and undamaged optical elements are obtained,and the terahertz information identifying the laser-induced damage of the optical element is obtained by comparison and analysis.The specific work are as follows:（1）Using the laser-induced damage test platform,laser pulses of different energies irradiate on Silicon chip,K9 glass,fused Silica,and Ti O₂film on Si substrate,and makes them damaged,these damaged optical elements were used as damage samples tested by terahertz spectroscopy.（2）Testing undamaged and damaged the Silicon chip,K9 glass,fused Silica,and Ti O₂film on Si substrate in use of the transmission terahertz time-domain spectroscopy system to obtain the corresponding terahertz time-domain waveform.By comparison and analysis,it is found that the time-domain peak-peak value of the damaged Silicon chip,K9 glass and fused Silica are all lower than ones of the undamaged,while the time-domain peak-peak value of the damaged Ti O₂film on Si substrate is higher than the undamaged.（3）Deducing the terahertz optical parameter models of uncoated optical elements and Single-layer optical elements and writing the corresponding algorithm programs in the MATLAB language environment.Processing the terahertz time-domain data of the laser-induced damage and undamaged of Silicon chip,K9 glass,fused Silica,and Ti O₂film on Si substrate to obtain their corresponding terahertz frequency-domain waveforms,refractive index spectra,and absorption coefficient spectrum.（4）The terahertz frequency-domain waveform,refractive index spectrum,and absorption coefficient spectrum of Silicon chip,K9 glass,fused Silica,and Ti O₂film on Si substrate are compared and analyzed before and after laser-induced damage.The results show that the frequency-domain amplitude of the damaged Silicon chip,K9 glass,and fused Silica are lower than ones of the undamaged,while the frequency-domain amplitude of the damaged Ti O₂film on Si substrate is higher than the undamaged;the refractive index of the damaged Silicon chip,fused Silica,and Ti O₂film on Si substrate are less than ones of the undamaged,while the refractive index of the damaged K9 glass is basically unchanged;the absorption coefficient of the damaged Silicon chip,K9 glass,and fused Silica are larger than ones of the undamaged,while the absorption coefficient of the damaged Ti O₂film on Si substrate is smaller than the undamaged.The above analysis shows that the terahertz time-domain peak-peak value,frequency-domain amplitude,and absorption coefficient of Silicon chip,K9 glass,fused Silica,and Ti O₂film on Si substrate after laser-induced damage have changed comparing to ones of the undamaged.Therefore,they can be used to identify laser-induced damage of uncoated optical elements and Ti O₂film on Si substrate.