Characterization of point defects in nonlinear optical materials

Thermoluminescence (TL), optical absorption, and electron paramagnetic resonance (EPR) were used to characterize point defects in LiNbO3 and LiTaO3 Crystals. A broad TL emission, peaking at 440 nm, is observed near 94 K from LiNbO3 when the crystal is irradiated at 77 K and then rapidly warmed. From the LiTaO3 crystals two overlapping TL peaks occur at 94 and 98 K, with each showing a 350-nm maximum in spectral emission. These peaks are observed after 77-K exposure of the crystals to x rays or lasers (266, 325, or 355 nm). During excitation of these crystals at 77 K, holes are trapped on oxygen ions adjacent to lithium vacancies and electrons are trapped on niobium and tantalum ions at regular lattice sites. These defects have characteristic EPR spectra, and the trapped electron center has an optical absorption band peaking at 1200 nm in LiNbO3 and 1600 nm in LiTaO3. Upon warming, the electrons become thermally unstable and migrate to the trapped-hole sites where radiative recombination occurs.;Optical absorption and EPR were used to characterize the production and thermal decay of point defects in KD2PO4. A crystal was irradiated at 77 K with x rays and then warmed to room temperature. Immediately after the irradiation broad optical absorption bands were formed at 230, 390, and 550 nm. These bands thermally decayed in the 80 to 140 K range. Another absorption band near 450 nm appeared as the three bands disappeared. Correlations with EPR data suggest that the band at 230-nm is associated with interstitial deuterium atoms, the two bands at 390 and 550 nm are associated with self-trapped holes, and the band at 450 nm is associated with holes trapped adjacent to deuterium vacancies.;Results from quantum-mechanical calculations performed with Gaussian 98 were correlated with hyperfine data from EPR measurements for several point defects in KH2PO4. The point defects modeled with calculations are: the self-trapped hole, the proton vacancy, the silicon hole, and the oxygen vacancy. Primary results from the calculations include the minimum energy, the isotropic Fermi contact coupling terms, and the lattice relaxation

Growth and Characterization of some amino acid doped nlo materials crystals

The recent advances in science and technology have brought a great demand of various crystals with numerous applications. A field of multidisciplinary nature in science and technology has been emerged, known as crystal growth, which deals with the crysta

The Effect of Surface Processing Methods on the Laser Induced Damage Threshold of Fused Silica

High peak power laser systems, such as National Ignition Facility (NIF), Laser Mega Joule (LMJ), and High Power laser Energy Research facility (HiPER), include a large amount of optics. Fused silica glass is one of the most common optical materials which is used in these high peak power laser systems owing to its excellent optical properties, especially for the 355nm ultraviolet laser. However, it is generally found that fused silica optics damage under irradiation with a high peak power laser beam, and the laser induced damage (LID) becomes the limit to increasing the laser power. Theoretically, the laser induced damage threshold (LIDT) of fused silica substrates is high, while it drops significantly due to the poor surface quality created in the manufacturing process. This project aims to find a series of fused silica optical surface processing techniques which are able to improve the surface quality and increase its LIDT when irradiated using high peak power lasers. This work consists of the following contents： 1. According to the mechanisms of LID, the effects of surface structural defects and contaminants on the LID are analysed and some simulation work is done. 2. By means of the Magnetorheological Finishing (MRF) method, surface structural defects, i.e. surface and sub-surface damage, are removed because the MRF method is a non-fracture polishing process. 3. Parameter optimisation in the MRF process is done by the Taguchi designing method. This optimisation mainly focuses on the surface roughness because it is also another factor that limits the LIDT. 4. Two post polishing treatments, Ion Beam Etching (IBE) and a HF-based etching process (buffered oxide etch (BOE)), are used in this work to remove contaminants left by the former polishing steps (conventional polishing and MRF processes). 5. A series of LIDT tests are done to verify the validity of the above work. Results show that the MRF process, BOE etching and IBE treatment are all useful in improving the LIDT of fused silica optics. The main contribution to knowledge of this work is that this work provides a series of processing techniques to increase the LIDT of fused silica optics. These techniques involve the MRF procedure, IBE method and BOE etching in sequence after the conventional grinding and lapping processes. These processing techniques are validated by several groups of LIDT tests