Views
4 years ago

Characterization of the laser induced damage threshold of mirrors in ...

Characterization of the laser induced damage threshold of mirrors in ...

Chapter 5 Conclusion and

Chapter 5 Conclusion and Outlook 5.1 Conclusion We developed a setup for the detection of damage threshold via the detection of scattered light. It allows us to measure a reproducible change in scattering behavior, which we think is linked to the onset of a change of the surface topology. Currently we can measure up to fluences of 16 J cm 2 at a center wavelength of 780 nm, a spectral width of 50 nm [FWHM], a repetition rate of 500 Hz and a pulse duration of 60 fs. We evaluated the involved statistical and systematical errors and concluded an uncertainty of smaller than ±5% for the fluence calculations on the sample. Measurements were reproducible on different days with different calibration settings. However we showed, that there is a permanent coloration of the irradiated surface at fluences below the threshold fluence measured with our setup. It was not possible so far to verify our measurements with literature data. For the case of standard dielectric mirrors and fused silica substrate we measured too low values while we measured for a gold mirror something too high compared to the literature value. We have to postpone the answer on the question about the quality of our measurements to a later point, when we will have collected further data. Due to the simplicity of the setup it would be surprising though to find any major problems. We hope to have given a conclusive overview of the available literature about the damage threshold of wide bandgap dielectrica, while showing the controversity of the topic. Much has been investigated and much has been understood, anyhow no one is able to draw a coherent picture of the whole topic by now. 36

5.2 Outlook 5.2.1 Improvement of the setup Several major improvements need to be done in the future. To enable automated measurements of multiple spots the DC motor controlling the filter wheel should be replaced by a stepping motor in order to gain a more accurate and reproducible control over the filter wheel and a shutter needs to be introduced. A commercial shutter with a shuttering time of a few microseconds for the required aperture would have cost about 2000 $ so we decided to build one from a hard disk voice coil, following a recent paper[76]. By now we got a working prototype that needs further testing, it cost in total 25 $. Using a chopper wheel together with that shutter, would allow interesting single shot measurements and measurements with well defined trains of pulses. 5.2.2 Introducing a model for the better evaluation of the measurement data By now the determination of the damage threshold from the data is only done by looking on the scattering light curves. This is sufficient for the mere characterization of a dielectric mirror for laser design purposes. For the optimization of the damage threshold and the analization of similar mirror designs a mathematical model for the damage threshold extraction has to be developed, as we expect to see only changes of a few percent in the planned measurements. Several ideas have been proposed and need to be tested for their applicability. 5.2.3 Crosscheck with an established setup and verification of the results In order to get further information about the quality of our results a crosscheck with an established setup is planned. The Laser Zentrum Hannover (LZH) offers commercial damage threshold measurements of dielectric mirrors, using a similar setup as we do. A set of samples will be prepared at the LMU coating facility and the damage threshold of these samples will then be measured by both setups on the very same mirrors. This experiment will allow a more clear statement about the quality of our data than the already conducted comparisons with literature values. Further measurements must be done in order to investigate the pre scattering threshold optical modifications. It has to be shown that effects like the observed coloration do not influence the spectral properties of the mirror like the the group delay dispersion induced by the mirror or its spectral reflectivity. Otherwise our detection technique will 37

femtosecond laser induced breakdown spectroscopy (LIBS) - CSIR
Laser induced damage - Fusion Energy Research Program - UC ...
Microstructure and laser-induced damage threshold of ZrO2 ...
Effect of laser pulse duration on damage to metal mirrors for laser IFE
Laser Damage Threshold Measurements of Micro-Structure Based High Reflectors
Femtosecond laser-induced damage in dielectrics
Deterministic Nanosecond Laser-Induced Breakdown Thresholds In ...
Laser-induced damage in deuterated potassium ... - mfeit.net
Single-shot spatially resolved characterization of laser-induced ...
Progress on Laser Induced Damage Studies of Grazing Incidence ...
Characterization techniques for high brightness laser diodes
Short and ultrashort laser pulse induced bubbles on - University of ...
Spectroscopic characterization of laser-induced tin plasma
759 ablation threshold, laser wavelength influences on ... - Wiley-VCH
Modeling of Laser Induced Damage in NIF UV Optics
Extracting the distribution of laser damage precursors on ... - mfeit.net
Growth of Laser Initiated Damage in Fused Silica at 1053 ... - mfeit.net
Time-Resolved Studies of Laser-Induced Phase ... - Mazur Group
Modeling of Charge Trapping Induced Threshold ... - IEEE Xplore
Molecular dynamics simulations of laser-induced damage of ...
Fabrication of Microoptical Elements in Quartz by Laser Induced ...
Growth of Laser Damage in SiO2 under Multiple ... - mfeit.net
Temporal and spatial evolution of C2 in laser induced plasma from ...
Femtosecond Laser Induced Micro-welding of Silver and Copper
Invited paper Theory and design of chirped dielectric laser mirrors
Structural modifications in fused silica due to laser damage induced ...
Shielding properties of laser-induced breakdown in water for pulse ...
Nanosecond laser-induced breakdown in pure and Yb3+ doped ...
Study of ns and fs pulse laser-induced effects in biological-tissue ...