Many of the investigations of contamination related laser damage to date have been largely phenomenological. These papers can provide some direction in the quest for determining and maintaining adequate laser cleanliness levels. Purely optical analyses of laser contamination effects likewise provide direction. Neither the phenomenological nor the purely classical optical methods provide a solid basis for the determination of a safe or acceptable contamination level. This is borne out by the present state of the art. Investigation of the purely physical, optical, or chemical properties of the contamination is insufficient and incomplete. It is necessary to look at the combined physical, chemical and optical properties of the laser system, which includes the contamination. Determination of some key properties of the laser/contaminant system and their interactions has been carried out and the results are promising.

Laser and instrument systems used for space flight have extreme requirements for cleanliness. Many of these systems specify or require cleanliness target values approaching one monolayer of non-volatile residue (NVR) or even less in some cases. This opens up a completely new series of challenges that are added to the challenges facing contamination control and contamination analysis personnel. As the amount of molecular contamination on a surface approaches zero, the behavior of the contaminant changes. These behavioral changes require knowledge of the surfaces and the contamination beyond whether bulk material is soluble in the solvent. As the thickness of the contamination drops below a few monolayers, the bulk properties become nearly irrelevant. Knowledge of the interactions of the contaminant with the surface becomes critical. This includes both the equilibrium and kinetics of the surface adsorption. The paper will address the fundamental physical, procedural, philosophical, and technical aspects of cleaning surfaces to the monolayer level.

Several methods for creating color laser-induced images are discussed. The first group of the methods is based on the creation of laser-induced damages with specific space shapes so as they lay out white light into spectrum. The second group is based on the creation of the color centers. The third group uses special types of transparent materials like photosensitive glass.

Excimer laser radiation changes the optical properties of fused silica. These changes include radiation induced absorption and changes of the index of refraction, which in turn determine the expected lifetime of silica lenses used in optical microlithography. A fully automated experimental setup designed for the marathon exposure of samples at low energy densities was employed. Measurements of the induced absorption, of the H₂ content using Raman spectroscopy as well as wavefront measurements were performed. A model to predict the aging behavior of silica in optical microlithography systems due to defect generation has been developed for both ArF laser irradiation and KrF laser irradiation. The model includes linear and nonlinear defect generation, relaxation processes and the consumption of hydrogen and describes the radiation induced changes of the index of refraction, the increase as well as the decrease. The model calculations were derived by analytical and numerical methods. A very good agreement in the range of parameters used in the experiments is observed.

A continuous CO₂ laser is used to locally re-fuse silica and avoid growth of 3ω laser damaged sites. Temperature evolution on each spot is monitored by a radiometry diagnostic. Important temperature variations are observed from site to site at a mm scale. Such variations can only be induced by a non homogeneous, high temperature, thermal conductivity. Real time retroaction, on silica exposure to laser radiation, enables us to control surface silica evaporation and etching depth. The 3ω laser induced damage threshold test of the re-fused sites shows that the limit for the mitigation rate lies in the surrounding silica surface.

This paper presents an interpretation of the meaning of the result of a damage measurement. The motivation of this work is to understand under what conditions identical results can be expected from measurements on samples coming from the same production process. The interpretation is developed from the properties of a generalized probability of damage that represents the manufacturing process, M(φ). The probabilities of damage for each sample in the production run, P(φ) is modeled as a sampling of M(φ). The P(φ) are then analyzed using first order statistics to determine the likely outcomes of the measurements. It is hoped that this work will begin to shed some light on questions of damage test sample to sample variation and repeatability. This work is also intended to help develop consensus on expectations for measurement accuracy and precision.

This paper presents a derivation of the field magnitude for laser beams of finite extent incident on coated total internal reflection (TIR) surfaces. The work presented is a continuation of efforts presented previously at this meeting. This analysis includes the effects of the Goos-Hanchen shift and a generalized coating on the TIR. This paper shows that inclusion of the Goos-Hanchen shift in the analysis results in vastly different E field magnitudes as a function of angle of incidence that previous work. This new behavior includes a null in the field for the S polarization.

HfO₂/SiO₂ dielectric mirrors for 355 nm, prepared by conventional electron beam deposition, had been investigated with respect to their laser damage resistance. Two kinds of HfO₂ with different purity were chosen as the high index material, whose impurity contents were evaluated by Glow Discharge Mass Spectrometer (GDMS) and X-ray Photoelectron Spectroscopy (XPS). Laser damage testing was performed both in the “1-on-1” and the “s-on-1” regime, using 355 nm pulsed laser with a pulse width of 8 ns. It was found that the laser induced damage threshold (LIDT) for single-shot was much higher than that for multishot. A phenomenon displayed that the impurity of zirconium was a critical hindrance in improving the LIDT in the single-shot process, but such an effect was not shown in the multishot process. The damage mechanism is different in the two manner of radiation, the main cause of the damage in single-shot is impurity absorption and that in the multishot is accumulation of structural defects. Optical microscopy and surface profiler was employed in mapping laser-induced damage morphology features after irradiation.

When sufficient intense laser pulse interacts with semi-conductors, permanent damage results due to formation of scattering centers in the semi-conductor surface. Reflectance of the damaged surface is reduced as compared to the smooth surface. Generally, damage threshold is defined as a value for which the reflectance is decreased by more than 10%. It is interesting that reflectance change can be seen below the damage threshold value. In the present work it has been shown that these changes occur at the rate of 0.5% per pulse. These changes are not due to any type of irreversible process in the material and slow but continuous decrease can be seen in the reflectance if the number of pulses is increased. Although when the fluence is increased, remarkable change can be seen in the reflectance decrease for the first pulse (in some cases, for 2-3 pulses), but if the number of incident pulses are further increased, the slow and continuous decrease is shown in reflectance value. The present experiments were performed in the CdZnTe <111> single crystal surface exposed to Nd:YAG laser (pulse duration: 20ns, prs:1pps, wavelength: 1.064µm) in the ambient air.

In this paper homogeneous model for surface roughness in identical layer system has been presented. It has been shown that reflectance change in non-absorbing layer is directly proportional to the square of total thickness of the layers. The reflectance in the visible range of the wavelength changes (decreases) substantially when the roughness factor or the number of layers are increases. In the present model the reflectance of the double layer system can be explained with the help of only one parameter that is roughness factor σ.

Most of the applications that require frequency agile solid state laser systems for use in the mid-infrared are centred on the development of optical parametric oscillators. These exploit the non-linear optical characteristics of non-centrosymmetric materials, in particular the chalcopyrite class of materials that includes AgGaSe₂ and ZnGeP₂. Whilst such materials are generally difficult to produce, major strides have been made in recent years to optimise crystal growth processes which have enabled the generation of moderate laser output powers. Other approaches have been centred on the use of periodically poled lithium niobate and diffusion bonded gallium arsenide. The latter system is particularly attractive because it exploits a readily available crystalline material, but its implementation is difficult because of the need for an ultra-clean processing environment and relatively high bonding temperatures. This paper describes progress in the development of a new, low-temperature approach for achieving quasi-phase matched gallium arsenide by bonding with an index-matched chalcogenide glass. A major advantage of this approach is the tolerance to GaAs wafer thickness variations and to defects at the surface of the GaAs wafers. Several glass compositions in the germanium-arsenic-selenium-tellurium system have the desired refractive indices, but only some provide the characteristics necessary to ensure the formation of stable low-loss bonds. The glass bonding process begins by RF sputtering films of the glass from pre-manufactured targets onto each side of individual GaAs substrates. These coated substrates are then assembled in a vacuum oven and uniaxially pressed under carefully controlled conditions until a single composite assembly is formed. Issues such as glass purity, the integrity of the sputtering process and choice of pressing conditions are important in ensuring that a high quality non-linear crystal is produced.

There are many applications driving the need for frequency agile solid state laser systems for use in the mid-infrared. Most of these are centred on the development of optical parametric oscillators (OPOs), which exploit the non-linear optical characteristics of non-centrosymmetric materials. In a new approach highlighted in a companion paper, OPO elements are formed by bonding gallium arsenide wafers precoated with RF sputtered films of a quaternary chalcogenide glass. The conditions used for sputtering the glass films are critical in ensuring the realisation of reliable bonds, where the glass is required to be index matched to the GaAs within very close tolerances. Issues such as glass composition, purity, porosity, devitrification and optical absorption are all key factors in determining the success of the approach. This paper describes a summary of some of the results achieved, emphasising the degree of control necessary for both the sputtering process and the preparation of the sputtering targets. Composition changes on sputtering can influence the refractive index of the glass and can easily introduce levels of insertion loss that are unacceptable by the time that stacks containing 50 or more individual phase-matched GaAs elements have been produced. Oxygen-related impurities are also easily introduced from a variety of sources and can degrade performance levels further. Such difficulties have been overcome and a reproducible technique for fabricating glass-bonded GaAs crystals has been developed. Optimised conditions for thermal bonding pairs of glass coated GaAs wafers are also reported.

A new laser calorimetric technique has been developed to enable absorption, transmission and heat capacity measurements to be made on arbitrarily shaped crystals and other optical materials. Samples are mounted inside a unique cradle device, which ensures minimal heat exchange with the sample's surroundings. A transmission map of the sample is formed by moving the sample, under computer control, through a fixed laser beam. The absorption of the sample at specific points is obtained by recording the temperature rise of the sample due to heating by the laser beam. Spatially resolved measurements are reported for a number of materials including ZnGeP₂ and quasi-phase matched GaAs, and correlated with transmission characteristics obtained using a mid-IR band InSb camera.

The standing-wave electric-field profile within multilayer coatings is significantly perturbated by a nodular defect. The intensity, which is proportional to the electric field squared, is increased in the high index material by ≥3x at normal incidence and ≥12x at 45 degrees incidence angle. Therefore is it not surprising that nodular defects are initiation sites of laser-induced damage. In this study, the impact of reflectance-band centering and incident angle are explored for a 1 μm diameter nodular defect seed overcoated with a 24 layer high-reflector constructed of quarter-wave thick alternating layers of hafnia and silica. The modeling was performed using a three-dimensional finite-element analysis code.

Photothermal microscopy is a useful nondestructive tool for the identification of fluence-limiting defects in optical coatings. Traditional photothermal microscopes are single-pixel detection devices. Samples are scanned under the microscope to generate a defect map. For high-resolution images, scan times can be quite long (1 mm² per hour). Single-pixel detection has geen used traditionally because of the ease in separating the laser-induced topographical change due to defect absorption from the defect surface topography. This is accomplished by using standard chopper and lock-in amplifier techniques to remove the DC signal. Multi-pixel photothermal microscopy is now possible by utilizing an optical lock-in technique. This eliminates the lock-in amplifier and enables the use of a CCD camera with an optical lock in for each pixel. With this technique, the data acquisition speed can be increased by orders of magnitude depending on laser power, beam size, and pixel density.

We have developed techniques using small-beam raster scanning to laser-condition fused silica optics to increase their damage threshold. Further, we showed that CO₂ lasers could be used to mitigate and stabilize damage sites while still on the order of a few tens of microns in size, thereby greatly increasing the lifetime of an optic. We recently activated the Phoenix pre-production facility to condition and mitigate optics as large as 43 cm x 43 cm. Several full-scale optics have been processed in Phoenix. The optics were first photographed using a damage mapping system to identify scratches, digs, or other potential sites for initiation of laser damage. We then condition the optic, raster scanning with the excimer laser. The first scan is performed at a low fluence. A damage map is then acquired and any new damage sites or any sites that have grown in size are mitigated using the CO₂ laser. The process is repeated at successively higher fluences until a factor of 1.7 above the nominal operating fluence is reached. After conditioning, optics were tested in a large beam 3ω laser and showed no damage at fluences of 8 J/cm² average.

Using the Phoenix pre-production conditioning facility we have shown that raster scanning of 3ω optics using a XeF excimer laser and mitigation of the resultant damage sites with a CO₂ laser can enhance their optical damage resistance. Several large-scale (43 cm x 43 cm) optics have been processed in this facility. A production facility capable of processing several large optics a week has been designed based on our experience in the pre-production facility. The facility will be equipped with UV conditioning lasers -- 351-nm XeF excimer lasers operating at 100 Hz and 23 ns. The facility will also include a CO₂ laser for damage mitigation, an optics stage for raster scanning large-scale optics, a damage mapping system (DMS) that images large-scale optics and can detect damage sites or precursors as small as ≈15 μm, and two microscopes to image damage sites with ≈5 μm resolution. The optics will be handled in a class 100 clean room, within the facility that will be maintained at class 1000.

A process whereby laser-initiated surface damage on KDP/DKDP optics is removed by spot micro-machining using a high-speed drill and a single-crystal diamond bit, is shown to mitigate damage growth for subsequent laser shots. Our tests show that machined dimples on both surfaces of an AR coated doubler (KDP) crystal are stable, for 526 nm, ~3.2 ns pulses at ~12 J/cm² fluences. Other tests also confirmed that the machined dimples on both surfaces of an AR coated tripler (DKDP) crystal are stable, for 351 nm, ~3 ns pulses at ~8 J/cm². We have demonstrated successful mitigation of laser-initiated surface damage sites as large as 0.14 mm diameter on DKDP, for up to 1000 shots at 351 nm, 13 J/cm², ~11 ns pulse length, and up to 10 shots at 351 nm, 8 J/cm², 3 ns. Details of the method are presented, including estimates for the heat generated during micromachining and a plan to implement this method to treat pre-initiated or retrieved-from-service, large-scale optics for use in high-peak-power laser applications.

Laser damage of large optics initiates at material imperfections. Absorbers of very small, nanoscale size are possible initiators. We will analyze experimental implications of assuming that the damage is initiated by a size distribution of nanoabsorbers. We will demonstrate that the model predicts damage fluence pulselength scaling consistent with experiment. The size distribution of nanoabsorbers is related to the resulting damage site density and to the shape of the damage probability curve (S-curve). Conditioning of KDP crystals can be explained within the same model. The relative efficiency of various conditioning strategies is discussed.

Cracks can affect laser damage susceptibility in three ways. These are field intensification due to interference, enhanced absorption due to trapped material in the cracks, and increased mechanical weakness. Enhanced absorption is the most important effect.

A numerical model of CO₂ laser mitigation of damage growth in fused silica has been constructed that accounts for laser energy absorption, heat conduction, radiation transport, evaporation of fused silica and thermally induced stresses. This model will be used to understand scaling issues and effects of pulse and beam shapes on material removal, temperatures reached and stresses generated. Initial calculations show good agreement of simulated and measured material removal. The model has also been applied to LG-770 glass as a prototype red blocker material.

We have demonstrated a simple experimental technique that can be used to measure the nonlinear absorption coefficients in glasses. We determine BK7, UG1, and UG11 glasses to have linear absorption coefficients of 0.0217 ± 10% cm^-1, 1.7 ± 10% cm^-1, and 0.82 ± 10% cm^-1, respectively, two-photon absorption cross-sections of 0.025 ± 20% cm/GW, 0.035 ± 20% cm/GW, and 0.047 ± 20% cm/GW, respectively, excited-state absorption cross-sections of 8.0 x 10^-18 ± 20% cm², 2.8 x 10^-16 ± 20% cm², and 5 x 10^-17 ± 20% cm², respectively, and solarization coefficients of 8.5 x 10^-20 ± 20% cm², 2.5 x 10^-18 ± 20% cm², and 1.3 x 10^-19 ± 20% cm², respectively. For our application, nonlinear effects in 10-cm of BK7 are small (≤ 2%) for 355-nm fluences < 0.2 J/cm² for flat-top pulses. However, nonlinear effects are noticeable for 355-nm fluences at 0.8 J/cm². In particular, we determine a 20% increase in the instantaneous absorption from linear, a solarization rate of 4% per 100 shots, and a 10% temporal droop introduced in the pulse, for 355-nm flat-top pulses at a fluence of 0.8 J/cm². For 0.5-cm of UG1 absorbing glass the non-linear absorption has a similar effect as that from 10-cm of BK7 on the pulse shape; however, the effects in UG11 are much smaller.

Existing Petawatt class lasers today based on Nd:glass architectures operating at nominally 500 J, 0.5 ps use meter-scale aperture, gold-overcoated master photoresist gratings to compress the amplified chirped pulse. Many lasers operating in the >1kJ, >1ps regime are in the planning stages around the world. These will require multilayer dielectric diffraction gratings to handle larger pulse energy than can be accommodated with gold gratings. Models of the electric field distribution in the solid material of these gratings suggest that high aspect-ratio structures used at high incidence angles will have better laser damage resistance. New tooling for transfer etching these submicron-grating patterns and for nondestructive critical-dimension measurement of these features on meter-scale substrates will be described.

The selection of coating materials for the design and production of optical components has to satisfy at least two criteria: (1) the component’s spectral performance requirements and (2) the survivability in the system’s operational environment. In many instances tradeoffs are required to satisfy both conditions. This paper offers tradeoffs in the material selection and deposition process conditions that provide high performance, stable coating structures for optical components in the deep ultraviolet (DUV) for excimer laser microlithography and micromachining applications. A critical necessity of these coatings is long lifetime survivability under the continuous operation of high fluence, pulsed laser irradiation; the continuous operation can number in the tens of billions pulses. Spectral performance data and lifetime survivability data will be presented.

We begin with a short discussion of existing approaches to the description of nonequilibrium processes and the possibility of how to overcome the problem of the definition of temperature in this case. Next, we explain why the equations of fluxes and conductivities as derived in standard solid state theory have to be reconsidered. Starting from the Boltzmann equation then we derive expressions for the thermal and electrical conductivity with new qualitative and quantitative properties. These results are supported by comparison with experiments.

First, we give a briefly critically discuss the existing definitions of melting and damage thresholds and the different kinds of experimental determinations of the thresholds. Then we investigate the thermal and athermal melting of oxides (wide-band gap semiconductors) and of silicon by solving a rate equation for the excited electrons and a by complete self-consistent solution of a coupled system of differential equations for the electron density and for the electron and phonon temperatures. In particular, we direct our attention to the still open question about the value for the critical electron density in the case of athermal melting.

We investigate theoretically the stimulated Brillouin scattering (SBS) which occurs during damage experiments on thick fused silica samples. A 3D time dependent model shows that for conditions equivalent to the experimental ones, the Stokes fluence at the front surface is of the same order as the incident laser fluence increasing in this way the damage probability of this face. The effect of self-focusing on this process is presented.

Evolution of damage in mirror polished samples of HgCdTe, CdTe & CdZnTe has been studied for three fluence regimes-Damage Threshold (F_th), Five Times Damage Threshold (5F_th), Ten Times Damage Threshold (10F_th) with multiple pulses of a Q-switched 1.06 μm Nd:YAG laser of 20ns pulse duration. Damage morphology observed under Scanning Electron Microscope (SEM) seem to evolve almost in similar fashion with increasing number of pulses as well as incident energy in HgCdTe and CdZnTe on account of uniform heating through a significant depth through the sample surface whereas in case of CdTe, effect of subsurface superheating is evident. Thermal modeling has been done to explain the evolution of laser damage.

An investigation of ultra short pulse damage threshold of AR coated beta-barium borate (BBO) used for SHG or as Q-switching material has been carried out. As a laser source, a CPA Ti:Sapphire laser system operating at a wavelength of 775 nm tuned to various pulse durations (150 fs, 1 ps, 3 ps) has been used. The online damage detection system is based on a scatter probe unit. It is capable of counting the number of pulses prior to damage and logging of the damage level, and allows for the interruption of irradiation immediately after damage. For S-on-1 irradiation and pulse numbers of up to 10⁴ per site, LIDTs of 0.3, 0.8 and 1.9 J/cm² were detected for the given pulse durations. Characteristic damage curves were measured according to the ISO standard 11254 2.0. Coating delamination was observed as the damage morphology.

During the first steps of optical silica substrate preparation, cracks due to mechanical stress appear on the surface in a thickness of a few microns. The following stage of polishing is useful to reduce those cracks and to decrease the roughness thanks to specific abrasive liquids. The consequence of this process is a contamination of the silica on the considered layer. These different contaminants could be suspected to be precursor centers of laser damage. An estimation of this critical thickness can be done by studying the morphology of the laser-induced damages. Results obtained by observation after irradiation with an atomic force microscope confirms that a thickness of a few microns seems to be involved. The study proposed here, consists in an investigation of the layer which is responsible of surface damages. We use a statistical model previously developed to determine the precursors density from laser damage probability curves. At first, we will present results based on the study of liquids used for the polishing of bare silica glasses. Subsequently, we will correlate these results with the laser-induced damage threshold of the substrates. Finally, we will describe a method allowing us to measure the thickness of this surface contamination layer. To illustrate our purpose, we will present results achieved on bare silica.

Non destructive detection, localization and characterization of nanocenters today remains a challenge for investigation of laser-induced damage in optical materials. In this study we propose an attempt to reach this aim via optical techniques, and extract size and complex index of nanocenters. The procedure is described and results are given for SiO₂ thin film samples. All conclusions are discussed in regard to assumptions.

Mixtures of two non-absorbing and index-matched materials with contrasting nonlinear optical response have been shown to optically limit above a critical fluence of pulsed nanosecond laser light. Under these conditions, index mismatch is induced between the disparate phases leading to strong Tyndall scattering. The effect has been demonstrated previously by the authors in both solid-liquid mixtures (hexadecane and calcium fluoride), and surfactant-stabilized liquid-liquid emulsions consisting of dichloroethane as the organic phase and a concentrated aqueous phase of sodium thiocyanate (NaSCN). Materials used in these studies exhibit low absorption coefficients over extended wavelength regions allowing for a broadband response of the limiter. Recently, limiting has been observed at 532 nm in a polymer composite consisting of barium fluoride and poly-(n-butyl acrylate). A modified open-aperture z-scan method was used to quantify optical limiter performance in this system. Modeling studies provide the basis for designing optical limiters based upon this light scattering mechanism and show the importance of size resonance and constituent optical properties on limiter performance.

The dielectric constant of several oxide dielectric thin-films (TiO₂, Ta₂O₅ and HfO₂) excited close to the laser-induced damage threshold is retrieved from reflection and transmission measurements with a 40-fs time resolution. The experiments were compared with the results of a numerical solution of the coupled Boltzmann equations for conduction band electrons and phonons, including nonlinear carrier excitation and relaxation processes as well as defect formation. The observed fast sub-100-femtosecond decay is shown to be caused by the interaction of non-equilibrium electrons with phonons and is in qualitative agreement with the results of the computer simulation. The observed sign reversal of the real part of the dielectric function from negative to positive after several hundred femtoseconds is attributed to the formation of self-trapped excitons (STE's) in the forbidden bandgap. Both real and imaginary part of the dielectric function are successfully modeled with the Boltzmann equation when defect formation is included. The simulations show that STE formation leads to efficient, non-thermal excitation of phonon modes on a sub-picosecond time scale.

We report on the physical and optical characteristics of the laser-hardened, solid-state host material polymer-filled nanoporous glass (PFNPG). PFNPG consists of a nanoporous glass structure (average pore size =~7 - 10 nm and matrix porosity =~38 - 40%) filled with a damage-resistant polymer. We have previously used this material as a host matrix for solid-state dye lasers, and in this study have applied it to nonlinear filters. The objectives were twofold: (1) to fabricate PFNPG samples with a high laser damage threshold under f/5 focusing conditions; and (2) to successfully dope a nonlinear absorbing dye into this matrix at millimolar concentrations. Undoped PFNPG plates showed damage thresholds of =~42 J/cm², a value significantly higher than that observed for a bulk polymer in the same test bed. PFNPG samples doped with the nonlinear dye Zn-TPP showed even greater damage resistance. Samples with dye concentrations ≥1 mM showed good nonlinear filtering.

Polishing of optical components produces defects in the subsurface resulting in a decrease in their performance. These defects can be large, like cracks, but also punctual, like oxygen vacancies or non-bridging bonds. Under electronic excitation, punctual defects can produce luminescence (also called cathodoluminescence) and/or can trap electrical charges. In a first work, we have shown that the cathodoluminescence technique is a good way to detect punctual defects (color centers) in silica. In this work, we have improved our cathodoluminescence technique in order to measure the depth profiling of color centers. We have also used the “Charge Contrast Imaging” technique in environmental SEM to observe directly sub-surface scratches generated by polishing.

Approximately 40 different reservoir and surface rock samples were lased using high power COIL (λ = 1.315 μm), CO₂ (λ = 10.6 μm) and Nd:YAG (λ = 1.06 μm) lasers. Spectrum of the samples in the wavelength region from 0.35 to 15.387 μm was obtained. The objectives of this research are to make a detailed study of the spectral properties and optic signatures of rock samples, including reservoir rocks collected from a depth of more that 8,000 ft, in order to predict the energy absorbed when a laser hits a rock. The optical coefficients [extinction/reflection (E), scattering (S), absorption (K) and emission (F)] of these rocks are critically investigated against rock chemistry, grain size, mode of occurrence, porosity, cementing matrix and rock textures, and total organic content. This research, initiated for the petroleum industry, develops a relationship between reflectance and rock properties that are commonly known and used as correlation parameters for other reservoir characterization uses. Our results show that: (1) More than 25% of the COIL and Nd:YAG laser energy is reflected and/or scattered by rocks with more than 85% SiO₂ content. (2) Surface and reservoir sandstones have almost the same spectral features and hence similar optic coefficients. (3) Rocks with high porosity have greater reflection coefficients (at the COIL and Nd:YAG wavelengths) compared to those having lower porosity. (4) The reflectance at the CO₂ laser wavelength (10.6 μm) is not a function of porosity or grain size.

Pulse duration and band-gap scaling of the laser breakdown threshold fluence of oxide dielectrics were measured using various (TiO₂, Ta₂O₅, HfO₂, Al₂O₃, and SiO₂) single layer thin films. The observed scaling with pulse duration was explained by an empirical model including multi-photon and avalanche ionization, and conduction band electron decay. The results suggest the formation of self-trapped excitons on a sub-ps time-scale, which can cause significant energy transfer to the lattice. At constant pulse duration, the band-gap scaling was found to be approximately linear. This linear scaling can be explained by the Keldysh photo-ionization theory and avalanche ionization in the flux-doubling approximation.

The focus of this paper will be on the analytical techniques used to study laser/rock destruction. High-power COIL, CO₂, and Nd:YAG lasers were used to drill holes, melt, crack, and vaporize rock samples. Rock types used in the research include: surface sandstones, reservoir sandstones, surface shale, reservoir shale, surface limestone and dolomite, and granite. Physical and chemical properties of the unlased and lased rocks are analyzed. X-Ray Fluorescence (XRF) is used to determine rock chemistry while carbon content is determined by a coulometer. Permeability is determined by the Pressure-Decay Profile Permeameter (PDPK), and Computerized Tomography (CT) imaging is used to calculate the volume of material removed by laser and pixel porosity and density around the lased holes. Thermal properties, such as endothermic and exothermic reactions, clay disassociation, and melting temperatures, are determined using Simultaneous Thermal Analysis (STA). Scanning Electron Microscope with Energy Dispersive Spectrometer (SEM-EDS) is used to map laser-induced fractures and mineralogical transformations. Mineral assemblages, rock texture, and average porosity are determined using petrographic thin sections.

High performance optical coatings are an enabling technology for many applications - navigation systems, telecom, fusion, advanced measurement systems of many types as well as directed energy weapons. The results of recent testing of superior optical coatings conducted at high flux levels will be presented. The diagnostics used in this type of nondestructive testing and the analysis of the data demonstrates the evolution of test methodology. Comparison of performance data under load to the predictions of thermal and optical models shows excellent agreement. These tests serve to anchor the models and validate the performance of the materials and coatings.

High-power solid-state ultraviolet (UV) lasers by using a have been in high demand because of their convenient operation procedure. An effective technique for UV generation is cascaded sum-frequency generation pumped by the output of near-IR solids-state lasers. The performance of such solid-state UV lasers appears to depend on the ability and reliability of nonlinear optical (NLO) crystals that are employed for laser frequency conversion. Discovery of CsLiB₆O₁₀(CLBO) crystals have enabled the production of such practical high-power all solid-state UV lasers. In 2001, UV output power up to 23.0 W by fourth harmonic generation of Nd:YAG laser was achieved. It is fact that laser-induced damage of NLO crystal is a limiting factor on reliable operation of high-power solid-state UV lasers. Bulk laser-induced damage of NLO crystal is related to the crystal's quality. In this paper, we have investigated the relationship among the bulk laser-induced damage threshold (LIDT), dislocation density and absorption of laser light in CLBO crystals with various crystallinity. The bulk LIDT of CLBO increased with decreasing dislocation density. High-quality crystals with a higher LIDT (15 - 18 GW/cm²) have a lower dislocation density of 6.6 x 10³/cm² than that of conventional CLBO (~15.0 x 10³/cm²). The relationships between crystal quality and absorption of laser light will be presented.

In order to understand the role played by nanodefects in optical breakdown of dielectrics, the interaction of an intense laser field with model dielectric samples containing metallic nanoparticles is studied both theoretically and experimentally. A theoretical study of the metal conduction electrons dynamics in the laser field predicts an efficient injection of carriers from the metallic inclusion to the conduction band of the dielectric, which leads to a strong local increase of the optical absorption in the initially transparent matrix. This prediction is tested experimentally by using time-resolved spectral interferometry to measure excitation densities as a function of the laser intensity in silica samples doped with gold nanoparticles, which are compared with similar measurements in pure silica.

Variable experimental conditions were used to measure the occurrence of front surface, rear surface and filamentation damage in synthetic fused silica windows. Experiments were performed at 355 nm with a table-top beam of mm-size, and at 351 nm with ALISE laser, a 100 J installation. The 351 nm beam was about 3 cm wide at the entrance surface; it was single-mode temporally, with or without a frequency modulation which has the function of widening the spectrum to decrease Stimulated Brillouin Scattering. The 355 nm was single-mode temporally. Thin windows showed very scarce front damage and no filament damage at intensities which cause a high density of rear surface damage. Without any spectral widening, the thicker windows (4.3 cm) showed appreciable amount of front surface damage; filaments were observed and but no filaments. When a spectral modulation was added, front surface damage vanished, filaments and rear surface damage were observed.

The purpose of this paper is to gather experimental elements allowing for the prediction of laser damage on full size components installed on high power Nd-glass laser lines. Damage can initiated on material defects, which aren’t known in their nature, but the density of which can be measured. On transmissive optics, depending on the component thickness, and on the intensity distribution at the front surface, rear surface damage can also appear due to self-focusing of hot spots. These two contributions produce damage sites that are prone to grow. The growth rate has been shown to be proportional to the damaged area. The resulting exponential growth is the major limitation to the lifetime of optics. A representation of these phenomena in the plane Intensity/Fluence gives a practical description of the impact of laser damage on the lifetime of optical components. It also enlightens the comparison between different operating conditions.

Experiments have been performed to measure the rate of laser-induced damage growth at the rear surface of fused silica windows at 1064, 1053 and 351 nm. One test bench delivered 9 ns monomode gaussian pulses at 10 Hz and 1064 nm. The size of the focused beam on the sample was a few mm². Another test bench delivered 2.5 ns single or multimode pulses at 1053 and 351 nm. The focused spot on the sample was a few cm². We compare and discuss our laboratory experimental results, the larger scale ALISE laser data and other results obtained at LULI.

Si wafer was polished accurately with ArF laser irradiation in the presence of the hydrofluoric acid water solution. The highest surface accuracy of Si wafer is needed for the Si substrate for using extremely ultra violet (EUV) lithography. Then we tried to polish the SiO2 with hydrofluoric acid water solution, which was photo-oxidized Si wafer surface with active oxygen. The active oxygen was photo-dissociated from water (H2O). The Si wafer surface was pressurized at 50g/cm2 on the fluorocarbon-polishing mat. Next the hydrofluoric acid water solution is infiltrated into the thin gap between the sample and the fluorocarbon. And ArF laser is irradiated through the fluorocarbon turntable. By this irradiation, the Si wafer surface was oxidized and produced SiO2. The moment it is dissolved by HF solution. After the etching, the polishing progresses by the friction with the fluorocarbon. The surface roughness was obtained 3 nm with 30 minute polishing with the ArF laser irradiation (20 mJ/cm2, 100 pps) in 15% HF/H2O ambience.

The Z-scan method has been widely used for the estimation of the nonlinear refractive index and the nonlinear absorption coefficient of various materials which usually show quite important nonlinear behaviors. However, it still remains difficult to perform accurate measurements of small nonlinear phase shifts since the major drawbacks of the method are an important multiplicative noise and a great sensitivity to the incident beam spatial quality and to the pulses temporal profile. In order to measure accurately the nonlinear refractive index of optical glasses in the nanosecond regime we had to improve the Z-scan method sensitivity and to reduce drastically the numerous possible errors. We have developed and optimized a Z-scan experimental setup which is well-adapted for the metrology of the nonlinear refractive index.

Self-focusing is one of the dramatic phenomena that may occur during the propagation of a high power laser beam in a nonlinear material. This phenomenon leads to a degradation of the wave front and may also lead to a photoinduced damage of the material. Realistic simulations of the propagation of high power laser beams require an accurate knowledge of the nonlinear refractive index γ. In the particular case of fused silica and in the nanosecond regime, it seems that electronic mechanisms as well as electrostriction and thermal effects can lead to a significant refractive index variation. Compared to the different methods used to measure this parmeter, the Z-scan method is simple, offers a good sensitivity and may give absolute measurements if the incident beam is accurately studied. However, this method requires a very good knowledge of the incident beam and of its propagation inside a nonlinear sample. We used a split-step propagation algorithm to simlate Z-scan curves for arbitrary beam shape, sample thickness and nonlinear phase shift. According to our simulations and a rigorous analysis of the Z-scan measured signal, it appears that some abusive approximations lead to very important errors. Thus, by reducing possible errors on the interpretation of Z-scan experimental studies, we performed accurate measurements of the nonlinear refractive index of fused silica that show the significant contribution of nanosecond mechanisms.

In the context of high power laser applications, laser-induced-damage in fused silica is still a limitation which need more study. To obtain better understanding of induced-breakdown processes, pure silica "model" samples, seeded with 100-250 nm diameter gold nanoparticles have been prepared. The aim in using these samples is to observe the mechanism of damage initiation that can be attributed to inclusions of nano-metric size. These samples were studied in a series of experiments using a photothermal microscope coupled with an experimental set-up allowing damage threshold measurement at wavelength 1064 nm. This installation is of great interest because it enables us to combine the laser irradiation of the sample with the optical absorption measurement. An evaluation of the silica transformation as a function of the fluence of irradiation can thus be obtained from the experimental results. These experimental data are completed with "Nomarski" and "atomic force" microscope observations, and then interpreted. Finally, we compare our results to numerical simulations performed with a 1-D hydrodynamic code. These simulations indicate that the threshold for melting the gold inclusion as a function of the incident laser fluence exceeds the threshold at which the absorption of the inclusion decreases.

In order to understand the mechanisms of laser damage initiation, we study “model” samples constituted of pure silica seeded with 3 nm gold particles. Numerical simulations are performed with a 1-D hydrodynamic code to determine the laser light absorption by a spherical nanoparticle. This code also simulates the thermal conduction, radiative transfer and ionization by UV light emitted by the heated metallic particles. The setup used for experimental studies is a high resolution, high sensitivity photothermal microscope. This setup allows correlation between optical absorption and laser irradiation. We observe the silica transformation in terms of absorption modification as a function of the irradiation fluence. The morphology of irradiated samples surface is observed thanks to “Nomarski” and “atomic force” microscopy and compared to photothermal microscopy results. A correlation is observed between flaked silica and strongly absorbing areas.

Silica glasses can be used as optical material in various applications such as deep-ultraviolet lithography and nuclear fusion, because they have no internal absorption and extremely small defects. In these applications, laser-induced bulk damage is an important factor in practical use. The laser-induced damage threshold (LIDT) is expected to depend on the types and production conditions of silica glasses. In this paper, the LIDT of synthetic fused silica which contains 4~1220ppm of OH, 1.7x1018~2x1019 molecules/cm3 of H2, and 100~3700 ppm of fluorine were studied by irradiating the higher harmonics of Nd:YAG laser at 355 and 266 nm with pulse width of 4 ns. Current experimental results show that the improvement of the LIDT with impurity contained silica glass is possible.

The surface-damage resistance of fused silica was enhanced 2.8-fold by removing a subsurface damage. For the conventionally polished fused silica surface, μm-scale subsurface damage and a shallow (20 nm to 100 nm) structurally modified zone produced during grinding and polishing were formed on the top of surface. Several surface etching techniques and super-precise polishing process were used to remove subsurface damage from a fused silica surface. First the conventionally polished surfaces were chemically etched in a buffered HF solution to remove 300μm of surface material, and then super-precise polishing was performed to obtain an optical surface. After that, the polishing compound was removed by using ion-beam etching. The effect of subsurface damage on laser damage resistance was characterized by the measuring of the laser-induced damage threshold (LIDT) for the laser radiations of 1064 nm and 266 nm respectively. For the wavelength of 1064 nm, the effect of the removal of subsurface damage wasn't clearly seen, although the enhancement of surface-damage resistance by the ion-beam etching could be confirmed. However, in the case of 266 nm, enhanced LIDT of 28 J/cm² was obtained from the subsurface damage removed surface. The surface LIDT increased by 2.8 times compared to that of conventionally polished fused silica surfaces.

Ultra-short pulse systems are considered as innovative laser sources for a variety of applications in micro material structuring, medicine and diagnostics. Current commercial systems are still lacking in output power limiting the throughput and the economic efficiency within a production line. In the optimization of ultra short pulse sources of the next generation, special effects in optical components during interaction with ultra-short pulses play a major role. Especially, low damage thresholds and non-linear absorptance have already been observed within the activities of the EUREKA-project CHOCLAB II, which are concentrated on the evaluation of multiple-pulse damage and the absorptance of fs-optical components according to the International Standards ISO 11254-2 and ISO 11551. In this paper, a theoretical model on the basis of photo- and avalanche ionization is presented describing the incidence of damage as a consequence of a sufficient high density of conduction band electrons. Furthermore, the influence of the Kerr-effect and conduction band electrons on the optical properties of dielectrics is investigated theoretically. From our calculations, a significant increase in reflectance due to the dominant Kerr-effect can be deduced as well as a noticeable increase in absorptance induced by free electron heating already at energy density values clearly below the damage threshold. Finally, results of an experimental investigation in the influence of the internal field strength in a dielectric layer stack on the damage threshold are described. The experiments clearly support the assumption already stated in other publications, that the field intensity formed by the optical design plays a key role for damage resistance of optical coatings for ultrashort pulses.

For the development of standard measurement procedures in optics characterization, comparative measurement campaigns (Round-robin experiments) are indispensable. Within the framework of the CHOCLAB project in the mid-90s, several international Round-robins were successfully performed qualifying procedures for e. g. 1 on 1-LIDT, laser-calorimetry and total scattering. During the recent years, the demand for single pulse damage investigations has been overtaken by the more practically relevant S on 1-LIDT. In contrast to the industrial needs, the comparability of the multiple-pulse LIDT has not been proven by Round-robin experiments up to now. As a consequence of the current research activities on the interaction of ultra-short pulses with matter as well as industrial applications, numerous fs-laser systems become available in universities and research institutes. Furthermore, special problems for damage testing may be expected because of the intrinsic effects connected with the interaction of ultrashort pulses with optical materials. Therefore, a Round-robin experiment on S on 1-damage testing utilizing fs-pulses was conducted within the framework of the EUREKA-project CHOCLAB II. For this experiment, seven parties investigated different types of mirrors and windows. Most of the partners were guided by the International Standard ISO 11254-2, but one partner employed his own damage testing technique. In this presentation, the results of this comparative experiment are compiled demonstrating the problems induced by special effects of damage testing in the ultra-short pulse regime.

Femtosecond lasers are very effective tools for three-dimensional micromachining of transparent materials. Nonlinear absorption of tightly focused femtosecond laser pulses allows energy to be deposited in a micrometer-sized volume in the bulk of the sample. If enough energy is deposited, localized changes in the material are produced (a change in refractive index, for example). These localized changes are the building blocks from which three-dimensional structures can be produced. With sufficiently tight focusing, the threshold for producing these changes can be achieved with pulse energies that are available directly from laser oscillators, offering greatly increased machining speeds and simpler, cheaper technology compared to using amplified lasers. In addition, the inter-pulse spacing from a laser oscillator is much shorter than the time required for energy deposited by one pulse to diffuse out of the focal volume. As a result, irradiation with multiple pluses on one spot in the sample leads to an accumulation of heat around the focal region. This localized heating provides another mechanism by which material properties can be altered. We demonstrate the three-dimensional fabrication of optical waveguides and microfluidic channels using pulse energies of only a few nanojoules to tens of nanojoules.

In the framework of the European research project EUFELE, a set of fluoride and oxide single layer coatings was deposited, irradiated with synchrotron radiation, and subsequently thoroughly characterised. The observed coating damage is strongly related to the spatial distribution of the synchrotron radiation. Therefore, characterisation methods have to be adapted to techniques that are capable to reveal the structural and optical behavior with adequate spatial resolution. A summary of the radiation damages of oxide materials (SiO₂, Al₂O₃ and HfO₂) produced by conventional and sputter deposition techniques, and of fluoride single layers (MgF₂, LaF₃, AlF₃) deposited by thermal evaporation is presented. Degradation was observed within the irradiated areas as well as in the not directly exposed area. The observed degradation effects depend on the surface site. Oxide systems show a superior resistance compared to fluoride coatings. The most sensitive material is Lanthanum fluoride.

Magnetorheological finishing (MRF) techniques have been developed to manufacture continuous phase plates (CPPs) and custom phase corrective structures on polished fused silica surfaces. These phase structures are important for laser applications requiring precise manipulation and control of beam-shape, energy distribution, and wavefront profile. The MRF’s unique deterministic-sub-aperture polishing characteristics make it possible to imprint complex topographical information onto optical surfaces at spatial scale-lengths approaching 1 mm. In this study, we present the results of experiments and model calculations that explore imprinting two-dimensional sinusoidal structures. Results show how the MRF removal function impacts and limits imprint fidelity and what must be done to arrive at a high quality surface. We also present several examples of this imprinting technology for fabrication of phase correction plates and CPPs for use at high fluences.

A large aperture, kJ-class, multi-wavelength Nd-glass laser system has been constructed at Lawrence Livermore National Lab which has unique capabilities for studying a wide variety of optical phenomena. The master-oscillator, power-amplifier (MOPA) configuration of this "Optical Sciences Laser" (OSL) produces 1053 nm radiation with shaped pulse lengths which are variable from 0.1 - 100 ns. The output can be frequency doubled or tripled with high conversion efficiency with a resultant 100 cm² high quality output beam. This facility can accommodate prototype hardware for large-scale inertial confinement fusion lasers allowing for investigation of integrated system issues such as optical lifetime at high fluence, optics contamination, compatibility of non-optical materials, and laser diagnostics.

The effective lifetime of optics is limited by both laser-induced damage and the subsequent growth of laser initiated damage sites. We have measured the growth rate of laser-induced damage in fused silica in both air and vacuum at 527 nm. For damage on the exit surface, the data shows exponential growth in the lateral size of the damage site with shot number. The exponential growth coefficient depends linearly on the laser fluence. The behavior at the fluence threshold for growth is contrasted to that observed at 351 nm. The growth rate was not significantly affected by either the wavelength of the initiating fluence or the presence of 10 torr of air as compared to vacuum. When the damage is located on the input surface, it has both a higher threshold for growth and does not grow exponentially.

Femtosecond ablation of both absorbing and transparent materials has several distinct advantages: the threshold energy fluence for the onset of damage and ablation is orders of magnitude less than for traditional nanosecond laser machining, and by virtue of the rapid material removal of approximately an optical penetration depth per pulse, femtosecond machined cuts can be cleaner and more precise than those made with traditional nanosecond or longer pulse lasers. However, in many materials of interest, especially metals, this limits ablation rates to 10 - 100 nm/pulse. We will present the results of using multiple pulse bursts to significantly increase the per-burst ablation rate compared to a single pulse with the same integrated energy, while keeping the peak intensity of each individual pulse below the air ionization limit. Femtosecond ablation using 850-nm single and eight-pulse 30-ns duration bursts with 4-mJ integrated energy was seen to yield a five-fold increase in the copper ablation rate in ambient air.

Various cleaning methods are available depending on the sizes of the parts, mounted or unmounted, and purpose of the cleaning. Dust and other particle contamination affect scattering and act as nuclei for defects in optical coatings. In some cases, these defects can initiate laser damage. Noncontact cleaning methods to eliminate particle contamination include blowing large particles from surfaces with an air bulb, "canned air," or a nitrogen gas jet, for a gentle cleaning and CO₂ snow for more aggressive particle removal. Laser assisted particle removal is a new high tech method. A strip coating material applied to the surface and subsequently removed will remove large fresh particles and often fingerprints. Contamination films affect the quality and adherence of optical coatings. These are usually removed (from unmounted optics) by cleaning the surface in a detergent and water bath followed by extensive rinsing and non-contact drying. Alternate methods when immersion in water is not possible are drag wiping, or spraying or squirting organic solvents over the surface. Before cleaning, surfaces must be visually inspected to determine the type and location of the contamination, to decide if cleaning is necessary, and what type of cleaning technique to use. Finally, bad cleaning is much worse than no cleaning! Illustrations of the cleaning methods described above will be given.

The problem of transmitting light through fibers has been synonymous with the identification of low loss materials, since the transparency of a conventional index-guided fiber cannot exceed that of its constituents. To date, precious few materials have been shown to exhibit high transparency at any wavelength and none have been found to exhibit it over wide wavelength ranges. The focus of our research at MIT has been on the elucidation of strategies for creating optical fibers where transparency is determined by the fiber microstructure, the ultimate goal being to create a fiber that is "more transparent than the materials that it is made from." This talk will present the underlying physics, materials selection and processing methodology which have resulted in the design and draw of hollow fibers lined with an interior omnidirectional dielectric mirror. A pair of glassy materials with substantially different indices of refraction but with similar thermo-mechanical properties was used to construct a fiber with multiple layers of alternating high and low refractive indices surrounded by a tough polymer cladding. Confinement of light in the hollow core is provided by the large photonic bandgaps established by the multiple alternating sub-micrometer-thick layers of a high-refractive-index chalcogenide glass and a low-index polymer. The fundamental and higher order transmission windows are determined by the layer thicknesses and can be scaled from 0.75 to 10.6 microns in wavelength. Recent transmission loss measurements were found to be orders of magnitude lower than those of the intrinsic fiber material, thus demonstrating that low attenuation can be achieved by structural design rather than high-transparency material selection. Scaling laws as well as device applications will be surveyed, recent results pertaining to CO₂ laser transmission will be presented, and future directions will be discussed.

This review is devoted to a long-term investigation into the nature of the laser-induced damage of silciate glasses. As an important result, we show that the threshold power density of the intrinsic damage of the boro-silicate glass at ~1 μm wavelength does not depend on pulse duration from 2 x 10^-13 to 3 x 10^-8s as long as self-focusing is avoided. This result cannot be explained by existing theories and indicates that the damage mechanism involves a collective response of a certain volume in the dielectric as a whole, rather than the accumulation of electrons via individual generation processes like multiphoton, tunneling, or avalanche. Special attention in the research was paid to investigation into the processes of multiple pulse damage and subthreshold modification of boro- and lead-silicate glasses.

Because of the unique laser-matter interaction processes involved, femtosecond laser micro-machining and femtosecond laser materials processing techniques are developing rapidly to stages where they may be introduced into manufacturing. Yet in both these areas, some complex interaction phenomena are not fully understood. In this talk we describe two studies of fundamental processes that impact both of these areas. These studies were made in transparent media, but their findings will be applicable to many non-transparent materials. Micro-machining in confined regions can give rise to new physical mechanisms emerging to dominate the machining process. We show this occurs in deep hole drilling of glasses by femtosecond laser pulse, where self-focusing effects takes over in the ablating process. The conditions under which this occurs will be described, and other configurations discussed where these phenomena may be important. At intensities below that required for ablation, structural modification of materials may be effected by femtosecond laser pulses. This has opened pathways towards direct femtosecond laser writing of optical waveguides, micro-fluidic systems and other structures. We will describe the controlled variation of refractive index that can be created in certain types of glasses and there potential for optical waveguides, and active optical elements. The evolution of these techniques will lead to their eventual integration for the fabrication of multi-component systems on a single chip.

We have studied the nonlinear optical properties of a high-index (n = 1.82) glass that is used as the core material in a commercially available fiber optic inverter, which is a coherent fiber bundle twisted 180 degrees to produce an inverted image. We have determined through open aperture Z-scan the two-photon absorption coefficient of the glass to be 0.8 cm/GW using 23 ps pulses (FWHM) at 532 nm, far from the linear absorption edge of 320 nm. For 5 ns (FWHM) pulses the nonlinear absorption is much larger, and is dominated by two-photon induced excited-state absorption. These effects contribute to the nanosecond optical limiting response that we have observed for the inverter using an F/5 focusing geometry.

Photo-thermo-refractive (PTR) glass is a photosensitive silicate glass where high-efficient holographic optical elements are created for visible and near infrared spectral region. Photosensitivity of this glass is ranged down to 350 nm. Induced absorption and refraction in PTR glass were studied under consequent exposing to low power UV and high power laser radiation of second harmonic of Nd:YAG laser at 532 nm (25 mJ, 5 ns). It was found that additional absorption induced in short wavelength region by initial UV irradiation can be partially bleached by consequent irradiation at visible region. Bleaching of additional absorption was observed after high-power irradiation at 532 nm while no effect was observed after low-power illumination with the same dosage. Induced refractive index of PTR glass is higher in the area consequently exposed to UV and high-power radiation at 532 nm compare to that in the area exposed to UV radiation only. The maximal refractive index difference between single-exposed and double-exposed areas was up to 10^-4. Volume Bragg grating and complex hologram were recorded in PTR glass by visible radiation at 532 nm.