Effect of defects on long-pulse laser-induced damage of two kinds of optical thin films
ABSTRACT In order to study the effect of defects on the laser-induced damage of different optical thin films, we carried out damage experiments on two kinds of thin films with a 1 ms long-pulse laser. Surface-defect and subsurface-defect damage models were used to explain the damage morphology. The two-dimensional finite element method was applied to calculate the temperature and thermal-stress fields of these two films. The results show that damages of the two films are due to surface and subsurface defects, respectively. Furthermore, the different dominant defects for thin films of different structures are discussed.
Conference Paper: Long-pulse laser design and experimental work[Show abstract] [Hide abstract]
ABSTRACT: Long pulse laser starts to have a prominent role in many applications. So, How to design and calculate the parameters of the high power long-pulse solid-state laser is illustrated, experimentally and arithmetically. How to design a pumping chamber is illustrated, with a double-ellipse cavity. Optical resonator losses are got experimentally in details. Efficiency factor and system slope efficiency are calculated experimentally. Illustration for how to get the optimum mirror reflectivity is mentioned. Beam waist and beam divergence also studied experimentally. The designed system has 10J output energy with pulse width 20msec for efficiency factor 1.1% and a combined loss 0.181 inside resonator. Average system efficiency, gain coefficient and fluorescence power for four different output mirror reflectivity are 0.328%, 0.00994cm-1 and 144.92W respectively. 6KW/cm2 power density inside resonator is obtained which corresponds to 585W maximum output power. An optimum mirror reflectivity 57% is for 208.2KW input power. The beam waist and beam divergence are recorded to be 0.66cm and 8.86mrad. Calculations show that, 11.7J output energy can be obtained by more optimization based on the designed system.ISPDI 2013 - Fifth International Symposium on Photoelectronic Detection and Imaging; 09/2013
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ABSTRACT: A facile sol–gel procedure has been developed for the synthesis of colloidal alumina nanocrystals. For the first time, optical characterization procedures were employed to study the quantum confinement effects in optical properties of the prepared Al2O3 sol. Accordingly, the hyperbolic band model was used to determine the optical band gap of colloidal alumina nanocrystals. X-Ray diffraction pattern was used to study the crystallographic phase of the dried gel. Morphological characterization was performed using scanning electron microscopy (SEM). Inductively Coupled Plasma (ICP) emission spectroscopy was used to determination purity of the Al2O3 powder. High-resolution TEM showed that the diameter of colloidal nanocrystals is about 10 nm. Photoluminescence spectroscopy demonstrated that quantum yields for colloidal nanocrystals are 68% with 300 nm excitation wavelength. The experimental observations confirm that highly stable alumina sol with strong UV emission was synthesized. The mentioned optical properties have not been reported before.Journal of the American Ceramic Society 03/2015; DOI:10.1111/jace.13546 · 2.43 Impact Factor
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ABSTRACT: In this study multilayer thin film optical coatings, which are indispensable parts of optical systems are investigated from a heat transfer point of view. Laser irradiation induced temperature distribution on a multilayer coating stack is obtained by discretizing the heat diffusion equation using the finite volume method. In order to obtain mathematical representation of the energy flow and Electric Field Intensity (EFI) through the stack, Maxwell equations are solved by using the commercial software MacLeod®. Laser energy, which is absorbed by the multilayer stack in terms of heat, is calculated as a function of space and time by using the computed EFI, coating materials' optical properties and Gaussian laser beam parameters. Computed heat load is used in the finite volume solver ANSYS FLUENT® through a user defined function. Temperature distribution on a 19 layer HR multilayer coating stack irradiated by 1064 nm laser beam are obtained for both quarter wave and non-quarter wave designed configurations. Results of numerical simulations show that maximum temperature rise is seen in the first high index layer for quarter wave design (QWD). In addition to that, high temperatures are also seen in film/film interfaces, which is associated to both EFI distribution on the stack and wide differences in material properties between high and low index film layers. Non-quarter wave design (NQWD) is seen to be successful in decreasing temperatures at high index layers and at film/film interfaces. But it also changes the EFI distribution inside the multilayer stack, increasing absorbed laser energy and resulting in higher temperatures at modified low index layers.Laser-Induced Damage in Optical Materials: 2013, Boulder Colorado; 12/2013