The Center for Optics Manufacturing (COM) has developed a line of Opticam precision optics machining centers. Opticam (Optics Automation and Management) is an integral part of a flexible CIM (computer integrated manufacturing) system that includes integrated CAD/CAM, automatic tool changing, on-machine inspection, and SPC capabilities. Opticam is commercially available and can surface, edge, center, and bevel optics to high precision. It is being rapidly implemented in the optics industry. COM is also developing novel finishing techniques to complement the Opticam machining centers. The latest breakthrough in optical finishing is magnetorheological finishing (MRF). The advantages of MRF are that it achieves accurate computer control of final optical figure and surface microroughness and eliminates subsurface damage from grinding.

We have completed a fifteen-year, referenced and documented compilation of more than 15,000 measurements of laser-induced damage thresholds (LIDT) conducted at the Lawrence Livermore National Laboratory. These measurements cover the spectrum from 248 to 1064 nm with pulse durations ranging from < 1 ns to 65 nm and at pulse-repetition frequencies from single shots to 6.3 kHz. We emphasize the changes in LIDTs during the past two years since we last summarized our database. We relate these results to earlier data concentrating on improvements in processing methods, materials, and conditioning techniques. In particular, we highlight the current status of anti-reflective coatings, high reflectors, polarizers, and frequency-conversion crystals used primarily at 355 nm and 1064 nm.

Polymer-filled microporous glass (PFMG) composite materials have been recently proposed as a proper host for dyes to create solid-state dye lasers and laser beam control elements (Q-switchers, etc.) [1,2]. In this paper we report investigation of some laser-related properties of Polymethilmethacrylate (PMAA) - filled porous glass doped with Rhodamine 6G perchiorate (active lasing dye) and 1055 dye (passive bleachable dye): laser induced damage threshold, lasmg efficiency, bleaching efficiency, and microhardness have been measured. All these characteristics have been found to be rather high indicating that PFMG composite materials are perspective hosts for dye impregnation and fabrication highly effective solid-state dye lasers and other laser related elements (Q-switchers, mode-lockers, modeselectors, spatial filters).

Possible mechanisms of formation of interference surface periodical structures (SPS) in the case of optical damage of transparent media are discussed. Such structures were discovered many years ago, when the action ofpulsed laser radiation ofmedium infrared and near infrared on alkali-halide and semiconductor crystals. The period of SPS, for normal incidence of the radiation on dielectrics is equal approximately to light wavelength in the dielectric. In this case the structures are formed on exit surface preferably and their ripples are orientated perpendicular to light field. Limitations of known models of phenomenon are examined (for example, ideas based on either surface quasi-stationary dipoles or surface polaritons on dielectric boundary) when surface-active medium is either a gas damage plasma or an erosion plasma oftarget material. In this work the author proposes a model for SPS formation based on laser generation of waveguide modes in a subsurface layer of dielectric materials. Thermo-optical changes of refraction index due to subsurface heating are considered as the main cause of the induced waveguide. The theoretical analysis takes into account the difference between light field distributions near the entrance and exit surfaces of a sample.

In the present paper an attempt was made to grow crystals with high laser damage threshold. To choose the crystallization conditions, a study was carried out on the correlation between the crystallization conditions, real crystalline structure, absorption coefficient, and the value of the laser damage threshold.

At the 1992 Boulder DAmage Symposium, we reported test results for 6 fused silica glass types exposed to millions of KrF laser pulses at a fluence of 500 mJ/cm² and a pulse repetition rate of 300 Hz. The peculiar results and the big variations between glass types (`slow' relaxing vs. `fast' relaxing glass families) were interpreted as being due to subtle differences in the glass microstructure induced by the homogenization and heat treatments, but no detailed explanation could be offered. As a small step toward improving our understanding, we have expanded our studies to include four additional glass types: Suprasil 300 (S300) and Suprasil 311 (S311) from Heraeus, and conventional 7940 and a new Excimer-grade fused silica from Corning.

We report on picosecond laser-induced damage experiments that were carried out on a natural type-IIa diamond and a thick specimen of high-quality chemically vapor-deposited (CVD) diamond. In conjunction with earlier measurements performed elsewhere on an `optically thick' single crystal, it is shown that for spot sizes (2 (omega) ) ranging from 3 to 60 micrometers , the breakdown field strength (E_BD) at the damage threshold of diamond obeys a pattern best described as follows: E_BD approximately equals A/(root)2(omega) , where A equals 30.7 and 38.7 MV(mu) ^1/2/cm at 532 and 1064 nm, respectively. The case of CVD diamond demonstrates that, if problems arising from localized high absorption at the deposition surface can be avoided, this material should be of much promise for contemplated high-power free-electron laser window applications. We show that corrections for self- focusing in laser damage experiments depend not only on the peak pulse power but also on the position of the diffraction prefocus and the length of the Rayleigh range.

In model wide bandgap materials such as single crystal alkali halides and MgO (nominally transparent), the absorption of laser radiation at 248 nm (5 eV photons) at modest fluences is defect dominated. We describe a technique for imaging the initial defect densities by their luminescence at low laser fluences and show a typical photoluminescence image of cleaved MgO. High defect densities are observed along many cleavage steps, consistent with previous observations of strong point-to-point variations in the ablative response of cleaved MgO surfaces. At fluences below those required for sustained emission, the composition of neutral emissions from the surface can also be strongly influenced by impurity defects, as shown by the intense emission of carbon oxides and the correspondingly weak emissions of atomic and molecular oxygen from arc-fused MgO. We also present evidence for defect-mediated ion emission at these low fluences.

Although sealed, Q-switched Nd:YAG lasers are carefully designed to ensure that the laser intensities in the optical train are well below the intrinsic damage threshold of all components, optical damage remains a frequently encountered long term failure mode. It has been found that during continuous elevated temperature operation (greater than approximately equals 50 degree(s)C), optical damage can occur in a matter of hours. Using a recently developed technique, we have shown that most (if not all) of this damage is due to trace contamination from a variety of sources. In a pure nitrogen environment, even the levels of contamination typical in the output of ultrahigh purity gas bottles is sufficient to induced damage at temperatures greater than approximately equals 60 degree(s)C. This paper describes a method which may be used to identify the types of contaminants most likely to induced optical damage and the levels of contamination at which damage may occur. The application of this method may be extended to provide a broad data base for the use by laser designers in selecting materials and by future researchers in identifying the root causes of contamination-induced damage mechanisms.

Laser damage testing according to ISO 11254 was performed with an automatic testing facility. With a Q-switch Nd:YAG laser up to 700 single `1 on 1' tests were performed for each measurement. A detailed description of the experimental setup is given. Damage was on- line detected by light scatter measurements. Associated problems to this method are discussed here. To evaluate the energy-depended damage frequency values from the measured data, a reliable procedure is needed; different methods are tested. For the linear extrapolation of the damage frequency values to 0% damage frequency, as prescribed by ISO, a certain selection of data points is necessary. We discuss different types of damage statistics and the problems occurring using linear extrapolation.

In the present paper, the experimental results of a 10 ns, 532 nm Q-switched Nd:YAG laser- induced surface and bulk damage of uncoated, polished Ti:sapphire (Ti:³⁺:Al₂O₃) single crystal, grown by the Induction Thermal Field Up-shift Method in our laboratory, are reported. It is found that the measured thresholds of both surface damage and bulk breakdown strongly varied not only with the Ti³⁺ ion doping concentrations of the tested sample but also with the crystallographic direction of the crystal, whose exact nature has not been previously identified. It is also observed that in the same conditions the surface damage threshold is much lower than the bulk damage threshold. The surface damage is the main cause to laser-induced damage of Ti:sapphire single crystal. In addition, the relative damage morphology and the possible explanation for these experimental results are given.

This review discusses three fundamental factors that foster film-bulk differences, namely: (1) unusually varied microstructures produced by serial atomistic deposition and subsequent nucleation and growth processes, (2) the effect of interfaces on either film surface, and in particular, the nature and implications of the film/substrate interface, and (3) arbitrary thinness in one dimension which enables unique size effect phenomena (e.g., optical interference, quantum effects, nonlinear mass transport) to be exhibited in single film or multilayer structures.

Laser induced damage to optical coatings is generally a localized phenomenon associated with coating defects. The most common of the defect types are the well-known nodule defect. This paper reviews the use of experiments and modeling to understand the formation of these defects and their interaction with laser light. Of particular interest are efforts to identify which defects are most susceptible to laser damage. Also discussed are possible methods for stabilizing these defects (laser conditioning) or preventing their initiation (source stabilization, spatter particle trapping).

The response of an optical material to an applied stress (thermal, mechanical, chemical, electromagnetic) is influenced by certain key materials properties which include the resident microstructure, chemical and phase purity, and the magnitude of both interfacial and residual stress. Effective non-destructive methods for evaluating such materials with respect to these parameters involve the use of optical probes. Properties variations as a function of processing conditions, and during and following interaction with a high energy laser pulse can be evaluated. Results of such studies provide insight into the laser damage mechanism and suggest processing changes which might improve materials stability. A brief review of several pertinent optical characterization methods is presented and various examples are discussed which demonstrate the utility of these methods for the characterization of optical materials.

Ion beam sputtering (IBS) is an easily controlled, energetic deposition process. Thin film coatings produced using IBS are superior in terms of scatter, absorption, losses and homogeneous optical properties. The process and properties of coatings produced using IBS will be discussed.

In this paper, the benefits of energetic reactive coating are first briefly introduced. Detailed performance improvement data are supplied for durability, absorption, scatter and mechanical stress. Pictures of the 2-m chambers are presented, an example of a large laser optic is shown, and technical details peculiar to large-area coating are discussed. Finally, laser damage data available to date are discussed, and the challenges of high laser damage resistance over large areas are outlined as a guide to future work.

In this paper the challenges and issues inherent to hitting the moving target of high power laser damage resistance will be discussed from the perspective of one company's view of the industry.

The International Organization for Standardization has published an International Standard entitled `Test Method for Laser Radiation Induced Damage Threshold of Optical Surfaces'. The testing procedure described herein is based on the damage frequency method. The damage threshold is determined from the linear extrapolation of the measured power-density dependent damage probability. A short description of the testing procedure and its theoretical background will be given. Some critical aspects like the beam diagnostics or the damage detection will be discussed more detailed. Unsolved problems of the testing procedure will be illustrated on the basis of selected examples. The measurements presented were made using a Q-switched Nd:YAG-laser with a nominal pulse duration of 15 ns. More than 500 testing sites were used for every measurement. A scatter-probe monitor was used for the damage detection. Besides a lot of encouraging results, it appeared, that some samples have a damage probability, which does not allow a reasonable extrapolation. Thus, a damage threshold cannot be given. Only in some cases this could be explained by the poor homogeneity of the samples.

Thin film optical devices are likely to play an increasingly more important role in the evolution of optical and electro-optical technologies during the next decade. New applications are expected to emphasise a significant stretching of the performance levels currently achievable in coating production, while the continual search for cost reduction will drive the need for more effective material deposition processes as well as the exploitation of more effective optical designs. Coatings for high power laser applications have always been seen as a testing ground for any new deposition technology and indeed the performance levels sought for these applications have played a major role in driving the evolution process.

An investigation into the preparation of sol-gel coatings for high power lasers was started at LLNL in 1983 and AR coatings were successfully developed for use in the Nova laser in 1984. Several other large lasers now use these coatings. Subsequent work on HR coatings resulted in AlOOH/SiO₂ and later ZrO₂ or HfO₂/SiO₂ systems of good optical performance. The use of organic polymer binders gave increased damage threshold and enhanced optical performance. We are in the process of scaling up HR fabrication for substrates approximately 38 cm square. Concurrently we are developing sol-gel random phase plates for laser beam smoothing. These have a patterned surface design of silica which induces phase shifts in the beam by variation in the optical path length. Plates of this type on 80 cm diameter substrates have been used successfully on the Nova.

We are developing a meniscus coating process for manufacturing large-aperture dielectric multilayer high reflectors (HR's) at ambient conditions from liquid suspensions. Using a lab- scale coater capable of coating 150 mm, square substrates, we have produced several HR's which give 99%+ reflection with 24 layers and with edge effects confined to about 10 mm. In calendar 1993 we are taking delivery of an automated meniscus coating machine capable of coating substrates up to 400 mm wide and 600 mm long.

High laser-resistant anti-reflective coatings were made from an amorphous fluoropolymer (Teflon AF2400) material by physical vapor deposition. Single layers of Teflon AF2400 were thermally deposited in a vacuum chamber. The refractive index and adhesion of the coatings were determined as a function of deposition rate (2 to 20 angstroms/s), substrate temperature (20 to 200 degree(s)C), and glow-discharge bias potential (-1500 to 1500 V).

Low absorption coatings were examined using a high repetition rate copper vapor laser to study the surface temperature as a function of incident power. Nonlinear absorption was observed in some of the coatings as a result of increased incident power. A variety of commercial coating vendors using common dielectric oxide material combinations were surveyed. Wavelength, coating material, and coating vendor were varied to study their affects on the linearity of the absorption. The films were deposited by electron beam or ion beam sputtering technologies. Changes in the film characteristics were observed after exposure to high incident power. The nature of these changes and their permanency were also examined.

The visualization of dynamic strain mechanisms in optical materials by the liquid crystal technique is described.

We investigated the relations between damage and laser wavelength, damage and laser energy as well as damage and repetition rate in optical coatings. The wavelength effect and accumulation effect of damage are also reported.

Coated ZnSe optical components are irradiated with high-power, pulsed CO₂ laser radiation ((lambda equals 10.6 micrometers , pulse length approximately 100 ns) at fluences up to 210 J/cm². The components are characterized at various stages of irradiation by thermography, optical microscopy, stylus profilometry, and surface chemical analysis (x-ray photoemission and Auger electron spectroscopy). During irradiation no temperature in the component surface is observed. Two types of coating damage occur within the irradiated area of the component: a breaking apart of the ZnSe overlayer of the coating system over relatively large areas, and the formation of isolate craters of diameter approximately 30 - 50 micrometers extending in depth approximately 3 micrometers through the coating system down to the ZnSe substrate. Chemically, the irradiated area is characterized by an oxidation of both Zn and Se and an increase in the stoichiometric ratio of Zn to Se. These effects are especially pronounced at the crater defects, and are attributed to localized optical absorption, leading to thermal stress and chemical reactions of Zn and Se with atmospheric or adsorbed water and/or oxygen.

A study has been carried out of the design and fabrication of mirrors for Optical Parametric Oscillators (OPOs) operating in the mid-infrared using a variety of coating and substrate materials. The major considerations determining the choice of coating materials are refractive index excursion (determines bandwidth of mirror), optical bandgap (multi-photon effects at the pump wavelength), and porosity (adsorbed water causes absorption features in the tuning range of the OPO). The mirror coatings are mostly of quarter wave type design, and have been fabricated from chalcogenides, fluorides and oxides. The mirrors have been evaluated at repetition rates and pulse lengths similar to those encountered in operation of the OPO, at both the pump (1.064 and 2.1 micrometers ) and typical output wavelengths. Damage data has been gathered for a number of mirrors which form part of the OPO cavity. Second Harmonic Generation was observed at 1.064 micrometers in Cleartran ZnS substrates.

The theory of laser induced damage to an optical single-layer dielectric film (coating) initiated by an absorbing inclusion is presented. The damage model based on the photoionization mechanism due to thermal radiation of the laser heated inclusion is analyzed. Dependences of the laser induced damage threshold upon coating/substrate band-gap ratio and absorption cross-section ratio, and upon coating thickness are derived from a solution of heat and electron diffusion equations. The coating thickness dependence predicted is compared with experimental data.

We have reduced by 50% particulate defect density of hafnia coatings deposited onto silicon substrates through the use of electric fields, physical barriers and deposition rates. In an effort to reduce the number of hafnia particulates deposited onto silicon wafers, parallel plate electrodes were placed on either side of the evaporant plume. The particulate level was determined as the deposition rate was varied from 0.75 angstroms/sec to 12 angstroms/sec. Then, parallel plate electrodes were placed on either side of the plume as a way of electrostatically deflecting hafnia particulates away from the substrates. Later a single plate electrode was used in conjunction with a physical barrier placed over the hearth. The results of our study indicate that minimal defects occur when a parallel plate electric field is applied in conjunction with a fast deposition rate. Using a screen as a physical barrier, and/or a single electrode had little or no effect. This data may be useful in the manufacture of multilayer optical coatings with high laser damage thresholds.

SiO_xN_y thin films were prepared by Ion Beam Sputter Deposition (IBS) and Ion Assisted Deposition (IAD) on polished fused-silica- and BK7-substrates. The influence of process parameters on fundamental film properties was analyzed. Investigated parameters in the IAD process were gas composition, substrate temperature, ion current density, ion energy and neutralization current. The deposition rate and the gas composition were found to be essential parameters of the IBS process. Film characterization was performed by spectrophotometric analysis, laser calorimetry, laser damage testing according to ISO 11254 and X-ray spectroscopy to obtain refractive index, absorption coefficient, damage threshold/morphology and film stoichiometry respectively. Important technical details about both deposition processes are reported.

In the EUREKA EU205 project the target products are industrial excimer lasers in the average power range of one kilowatt or more. The high power optical components and dielectric coatings have to be developed in close adaption to cavity design (optics), beam relay optics, mask imaging optics, and masks. Therefore, we used ultra low loss conventional e-beam evaporation for Al₂O₃/SiO₂ dielectric multilayers. Based on a fundamental coating technique, both multilayer mean background absorption and absorption at localized spikes have been reduced drastically. The resulting KrF laser damage threshold of HR coatings is 16 J/cm² (1-on-1, 30 ns, EMG-202-MSC). Measurements have been performed with an automated damage testing facility, being part of the EUREKA program. Multilayers have been characterized by Atomic Force Microscopy, Photothermal Microscopy, absorption measurements, and Spectroscopy of Sputtered Neutrals.

We discuss the characterization of nonlinear optical processes that give rise to changes in the absorption coefficient and refractive index. We primarily concentrate on methods for determining the dominant nonlinearities present in condensed matter and the responsible physical mechanisms. In extensive studies of a wide variety of materials we have found that there is seldom a single nonlinear process occurring. Often several processes occur simultaneously, sometimes in unison, sometimes competing. It is necessary to experimentally distinguish and separate these processes in order to understand and model the interaction. There are a variety of methods and techniques for determining the nonlinear optical response, each with its own weaknesses and advantages. In general, it is advisable to use as many complementary techniques as possible over a broad spectral range in order to unambiguously determine the active nonlinearities. Here we concentrate on the use of nonlinear transmittance, Z-scan and degenerate four-wave mixing experiments as applied to polycrystalline and single crystal semiconductors and dielectric materials.

To investigate the intrinsic laser induced damage of transparent dielectrics the tight focusing of radiation inside samples bulk is usually used. In this case the threshold electric field strength of light radiation is calculated starting from irradiance, and the customary formulae for non focused radiation are used. At the same time under tight focusing conditions the vectors of electrical field strength of diametrically placed rays are directed under large angles each to another. In this work it is experimentally shown that the calculations performed on the basis of customary formulae can lead to the substantial errors in quantitative estimation of field strength.

Herein is reviewed the utility of scaling relations and pitfalls to be avoided in their application. This is illustrated by recourse to a discussion of selected proposed scaling relationships including their range of validity, experimental foundation and efficacy in determining the basis of fundamental physical interaction processes. The latter is illustrated using the scaling of damage threshold with the duration of an incident laser pulse. It is shown that for a defect dominated pulsed laser interaction mechanism, the pulse length scaling dependence can change over a narrow range due to a variation of the characteristics of the defect which is most sensitive or easiest to damage under the experimental conditions of import even though the gross aspects of the interaction mechanism do not change appreciably.

Revolutionary improvements in optical substrates and coatings over the past 25 years allow the design of efficient lasers with 2 to 3X margins to optical damage in real world applications. Despite this, optics failures are frequently encountered during alignment and use, particularly in systems operating in short-pulse modes under sealed-off conditions. The presence of low-level contaminants, due to assembly processes and/or offgassing, is generally the source of this damage. No existing criteria provide scientifically established guidance in selecting or using optical materials to preclude or eliminate these problems. A critical need exists to develop and compile quantitative data analogous to NASA guides for spacecraft materials, allowing designers to control optics damage in future laser systems.

This paper quantifies the measurement quality, Q, of three test procedures by simulating a series of correlation experiments and employing a Monte Carlo technique. The three methods compared are the ISO standard damage frequency method (DFM), the DFM yielding the highest Q (optimal DFM) and a modified DFM. For each trial, two values of the normalized damage threshold and uncertainty are derived via a PC spreadsheet based Monte Carlo simulation. To simulate various sets of real optics, the normalized results are multiplied by a set of uniformly distributed random numbers which are unique to each trial. The slope of the correlation line for each test procedure is determined via a weighted linear regression, and recorded. The output of the model is a frequency distribution of the slopes of the correlation lines for each procedure. Comparing the distributions of the slopes of the correlations is a direct measure of Q² for each test procedure. It is shown that a revised DFM results in a much higher likelihood of making an accurate measurement with a given precision.

The multimode nonlinear theory of formation of surface periodic point defect-deformational (DD) structures is developed. The general set of coupled nonlinear kinetic equations for DD- gratings Fourier amplitudes is derived and reduced to rate equation with allowance for diffusion and drift in q-space. The conditions of generation of either multimode or single mode DD-structures are cleared out and periods, times of formation and stationary amplitudes of DD-grating are determined. The theoretical results are used for interpretation of previously obtained experimental results on DD-gratings generation in Si under millisecond laser irradiation and under ion implantation.

A novel method for figuring and polishing diamond surfaces is described. It is a three step process, consisting of (1) a diffusion smoothing step using carbon reaction with certain materials at elevated temperatures (such as hot iron, molten rare earth metals, etc.), (2) a laser polishing and figuring step where UV laser ablation actively coupled with in situ interferometry provides the desired diamond figure and (3) an ion beam assisted superpolishing step, where ion beam technology is used to provide the final surface finish.

Laser damage testing of binary phase diffractive-optic components has been carried out at 1064 nm with 0.5 ns pulses. The surface relief components are produced by etching a fused silica substrate. The results show damage thresholds approaching that of polished fused silica. The design and fabrication of the diffractive-optic components for use with the HELEN multi- terrawatt Nd glass laser system at AWE is briefly described. The components under test were focusing beam samplers and harmonic separation filters.

Single shot laser damage studies have been performed using an RF-excited long pulse laser and a TEA-CO₂-laser with pulse durations of 1.2 ms and 100 ns, respectively. Besides bare diamond turned copper mirrors with different metal and dielectric coatings, ZnSe-optics with selected coating types were tested. The temporal damage behavior in the long pulse regime was investigated on the basis of a damage detection system with a time resolution of 10 microsecond(s) . The dependence of the damage threshold on the intensity is discussed in consideration of the integral absorptance of the coatings. The measured damage thresholds of this detection system are compared to those obtained by Nomarski/darkfield microscopy. The local variation of the laser induced damage threshold is correlated to the corresponding photothermal deflection signal, reflectance, and defect density of the coated surfaces.

This paper investigates the laser damage threshold under C.W. CO₂ laser irradiation. It has been already shown that the destruction of each mirror is characterized by a critical temperature: the mirror is destroyed when this temperature is reached. The aim of this paper is to compare the laser damage threshold and the critical temperature.

Scatter in thin film optical coatings may arise from a variety of sources. Our previous investigations have used total internal reflection microscopy (TIRM) to monitor scatter site generation during film growth. These studies have reported the effects of substrate cleaning techniques and certain deposition parameters on scatter site generation. The present investigation using TIRM to monitor the coating process has yielded new insight into defect generating mechanisms for films of HfO₂ and ZrO₂. Of particular interest is surface contamination apparently caused by electrostatic effects. Introduction of high electric potentials in the vacuum chamber has been observed to cause surface contamination prior to deposition, resulting in a significant increase in the number of scatter sites.

A method for injecting a high peak power multimode laser beam into an optical fiber has been developed. The design minimizes the peak irradiance on the fiber's entrance face and reduces its dependence on the laser's mode structure and the system alignment. A simple lens and a specially designed kinoform (or binary optics element) operate together to transform a 5 mm diameter laser beam into two concentric ring foci that fit on the 400 micrometers diameter fiber face.

For several years we have been investigating laser-induced damage mechanisms encountered when transmitting Q-switched Nd/YAG laser pulses through step-index, multimode, fused silica fibers. Previous studies primarily addressed end-face breakdown and damage processes and how corresponding thresholds could be affected by different preparation techniques. However, we frequently encountered two internal mechanisms for damage that influence test procedures and results. An `entry' mechanism is related to the laser mode structure and to the geometry of laser injection into the fiber entrance face. Internal damage is also observed at sites where a fiber is experiencing significant local stresses, either due to fixturing or to severe bends in the fiber path. The present study continued to address these fundamental issues, and began to address additional concerns that may arise in the design of practical high-power fiber transmission systems. End-face preparation issues were examined through a comparison between purely cleaved faces and mechanically polished faces.

We have demonstrated a silver gallium selenide (AgGaSe₂) based optical parametric oscillator (OPO) tunable from 2.75 micrometers to longer than 6 micrometers (limited by the measuring spectrometer) with greater than 1 mJ per pulse output energy in this range. The crystal used was 8 X 8 X 27 mm. We used a 60 mJ, near Gaussian, 2.09 micrometers chromium, thulium, holmium doped YAG (CTH:YAG) laser pump source, Q-switched by an AO modulator to produce approximately 50 ns pulses. As with most OPO's the output energy is limited by damage to the nonlinear crystal. We measured the damage threshold of both coated and uncoated surfaces to be approximately 0.9 J/cm² and 1.2 J/cm² respectively.

Large solid state lasers such as Beamlet and the proposed National Ignition Facility require optical materials with extremely high damage thresholds. Potassium dihydrogen phosphate (KDP) and its deuterated analog (KD*P) both require some form of conditioning to reach the design fluence of these lasers. Both the bulk material and the crystal surfaces must have damage thresholds in excess of 16 J/cm² at 1053 nm and 11 J/cm² at 351 nm for 3- ns pulselengths. The use of ultrafiltration techniques has been demonstrated to produce bulk material with damage thresholds exceeding these requirements with the use of R:1 laser conditioning. More recent results at LLNL using large-area laser conditioning and thermal annealing are described for a variety of state-of-the-art KDP and KD*P crystals. Results on thermally annealed KD*P with a deuteration range of 60% to 80% are also presented, and compared to those of ordinary KDP.

Glass laser is the best one to radiate high-average power used for material processing and X- ray production. However, the thermal conductivity of laser glass is very low compared with other laser crystals. We report newly developed glass slab laser operating at 8 Hz without laser glass breakage, the geometrical shape of the glass slab is different from conventional ones. Our glass slab is composed of small square glasses. Slab laser (10^t mm X 40^w mm X 125^l mm) at pumping power of 1500 W emitted the average output power of 46 W.

Antireflective thin film coated by Teflon^TM AF 2400 amorphous fluoropolymer to improve the pumping efficiency of disk amplifier used for laser fusion is presented. Improvement of pumping efficiency of about 8% can be attained by Teflon^TM AF 2400 coating to the outer surface of Xe flashlamps and the shield glasses set up between Xe flashlamps and disk glasses. Flashlamp irradiation test to the Teflon thin film coated on flashlamp wall was carried out. Flashlamp-induced damage for 100 irradiations at about 15.4 J/cm² was not observed.

Experimental results on the damage of dielectric coatings are considered in the light of an extended mathematical treatment of the thermoelastic material response after nanosecond up to femtosecond UV laser irradiations. The deviation from the r^0.5-law even for the thermal loss mechanisms can be understood, taking into consideration both damage measurements in a vacuum environment and the related laser intensity profile. On the other hand, the calculation and high-resolution measurement of the thermoelastic sample surface response for thermally thin as well as thick optical coatings in the frequency domain demonstrates the potentiality of the photothermal displacement technique with respect to the nondestructive, laterally and depth-resolved characterization of the laser damage resistivity within the films.

The optical absorption coefficient of some polymer materials can be increased by exposure to low fluence UV laser radiation. This phenomenon, known as UV light incubation, has been demonstrated to be a powerful tool for surface patterning of organic polymers. In this paper we report our recent progress in understanding the incubation phenomenon and its application to laser patterning by using various photothermal techniques. The data reported include the in- situ monitored incubation/ablation dynamics and the absolute change in optical absorption and thermal diffusivity of the incubated area. Besides these nondestructive evaluation experiments, some of the incubated sites are exposed to high fluence laser radiation. The results show that fine structures with submicron spatial resolution can be achieved without the necessity to focus tightly the ablation laser beam.

Atomic-force microscopy of pulsed and cw Nd:laser-irradiated Y₂O₃ monolayer coatings reveals that fluences insufficient to eject film-defect nodules are able to prompt formation of structural film features that we characterize and whose formation by linear absorption we establish. These features can be identified as precursors for conventional damage morphologies, i.e., craters.

Water-penetration-induced morphological changes in Y₂O₃ monolayer coatings were studied by means of atomic force microscopy. In a standard laboratory environment, there appears a long-term growth kinetics for these morphological modifications. On a time scale of months, thin films undergo solid-state phase transformations converting the nano-scale columnar, porous film structure to micron-scaled crystallites and islands. We compare these phenomenological long-term observations with accelerated testing results using either a 100% relative humidity environment or artificial seeding of film surfaces by distilled H₂O microdroplets.

The surface microstructure of evaporated single layer and multilayer fluoride coatings for KrF lasers as well as the topography of uncoated fused silica substrates have been investigated with an atomic force microscope (AFM). The fluoride films exhibit a pronounced columnar microstructure that accounts for the typical surface morphology and causes surface roughness the magnitude of which depends on film thickness and substrate temperature. Well polished fused silica substrates show low surface roughness, which has been determined from both AFM and light scattering measurements.

Laser-induced damage in optical coatings is generally associated with micrometer-scale defects. A simple geometric model for nodule-shaped defects is commonly used to describe defects in optical coatings. No systematic study has been done, however, to prove the applicability of that model to standard optical coating deposition. Some defects are known not to have a classical nodule geometry. The present study uses atomic force microscopy (AFM) and scanning electron microscopy to characterize the topography of coatings defects in a HfO₂/SiO₂ multilayer mirror system. Focused ion-beam cross-sectioning is then used to study the underlying defect structure. This work develops a model for defect shape such that the overall geometry of a coating defect, particularly seed size and depth, can be inferred from non-destructive evaluation measurements such as AFM. The relative mechanical stabilities of nodular defects can be deduced based on the nodule's geometry. Auger analysis showed that the seed material that causes nodular defects in HfO₂/SiO₂ multilayers is a hafnia oxide. Such characterization capabilities are needed for understanding the enhanced susceptibility of particular defects to laser damage and for developing improved techniques for depositing low-defect density coatings.

We have studied the changes of dielectric optical coatings after laser conditioning using atomic force microscopy (AFM). Laser coatings is the process which consists of illuminating a film by a laser below damage threshold in order to increase this threshold value. This method is implemented for optics used in high fluence laser beam such as Nd-glass lasers (1064 nm, 3 ns pulse length). We have studied e-beam evaporation deposited highly reflective multilayer ZrO₂/SiO₂ mirrors, and also single layers of SiO₂, HfO₂ and ZrO₂. We have observed the modification of the surface after laser conditioning using the AFM. We find that this process results in localized minimization or elimination of defects (nodules, craters etc...). Furthermore, the origin of the increase in the size of the hillocks observed after laser conditioning and previously reported by other groups, has been experimentally identified as an instrumental artifact.

A series of multilayer mirrors was exposed to a high power laser to measure absorption of the coatings and to test for thermal distortion. A high power chemical oxygen iodine laser with a wavelength of 1.315 micrometers was used to irradiate a variety of high reflectivity mirrors. The mirror coatings were multilayers of Ta₂O₅/SiO₂ and Si₃N₄/SiO₂ as well as aluminum enhanced with Nb₂O₅/SiO₂. The dielectric layers were deposited by modulated reactive-dc-magnetron sputtering on fused silica substrates. The coated samples were placed in a vacuum chamber and monitored with a thermal imaging camera and an interferometer during irradiation. Absorption levels as low as 10 ppm were observed and the maximum distortion of the wave front was less than (lambda) /10 at 0.633 micrometers for the best parts.

In a paper presented at the 1992 Boulder Damage Symposium, we discussed the role of electric field effects, defect type, surface roughness, film thickness and coating absorption on the laser damage thresholds of sinusoidally modulated, plasma deposited, silicon oxy-nitride narrow band reflectors. We concluded that the damage threshold, which was essentially constant at 2 J/cm² at the test wavelength of 0.532 micrometers , was defect dominated. A sizeable fraction of the damage events occurred at a particular type of defect--a hemispherical hillock feature typically 5 micrometers in diameter as identified by SEM and interferometric surface profiling. We postulated that this defect initiated damage because of either a microlensing effect or an enhanced electric field effect. We have since measured the laser damage thresholds of all these samples at 1.064 micrometers , and found significant variations in the damage thresholds, which were a factor of three higher on average than those at 0.532 micrometers . The microlens model presented can explain damage thresholds up to a factor of four higher at the longer wavelength, and predicts a minimum nodule height for increased damage susceptibility. The minimum nodule height is dependent on the wavelength and the coating average index. The wavelength scaling of the fluence enhancement and the minimum nodule height imply that nodule initiated damage will become an even more serious problem as the wavelength approaches the UV.

Films produced by reactive-dc-magnetron sputtering are generally dense and homogeneous. Thus their optical properties are similar to those of ion-beam-sputtered films and distinct from the properties of the more porous electron-beam evaporated films. In this paper, the measured results of the dispersive refractive index n and extinction coefficient k are presented for single- layer films of SiO₂, Al₂O₃, HfO₂, Ta₂O₅, Nb₂O₅, and TiO₂ produced by the three processes. For some of the magnetron-sputtered films, it was necessary to modulate the dc power supply in order to suppress the electrical arcing at the target.

The cw photothermal displacement technique (PDT) has been shown to be a useful tool for the characterization of optical coatings with high lateral resolution combined with an ultrahigh sensitivity. By micrometer resolved PDT-measurements on Al₂O₃/SiO₂ multilayer coatings we found that the non-damaged thin film systems contain a great amount of photothermal inhomogeneities (defects) with lateral sizes ranging from several micrometers to several ten micrometers that are not visible by optical microscopy. In most cases these areas of strongly enhanced displacement response originate from microdelamination, decreased thermal impedance at the film interface or absorption centers. Thermal inhomogeneities in the film normally play a minor role.

Single phase barium titanate thin films prepared by metalorganic deposition and annealed at different temperatures were investigated by using various photothermal and optical methods. The data reported include refractive indices, optical losses, thermal diffusivities, as well as optical and thermal inhomogeneities. Structural analysis by using scanning electron microscopy and x-ray diffraction was carried out to correlate the thin film microstructures with the measured properties, both of which were found strongly dependent on the annealing temperature.

We investigated the damage thresholds and optical stabilities of 193 nm fluoride HR coatings consisting of NdF₃/Na₃AlF₆ and LaF₃/Na₃AlF₃. These coatings were deposited on fused silica substrates by conventional electron beam (EB) and ion assisted deposition process (IAD). Damage thresholds of LaF₃/Na₃AlF₆ HRs were significantly increased by laser conditioning procedure and low index overcoating when they were deposited by EB and low energy IAD process. NdF₃/Na₃AlF₆ HRs showed negligible laser conditioning effect except certain few case, and had considerably lower damage thresholds than LaF₃/Na₃AlF₆ HRs with conditioning (1.8 J/cm²). Optical stabilities of these HRs were significantly improved by low energy IAD process (50 - 100 eV) which had not harmful influence on damage thresholds.

The complex microstructure of dielectric films alters the local electric fields affecting both the strength by which different sites within a film interact, and the spatial extent. Using our self- consistent lattice element model, we determined the site by site interaction of the local electric fields within a defect ridden dielectric film to determine the effects of microstructure on the interaction of defects sites on its surroundings. Local dielectric properties are compared to currently accepted models of dielectric film properties (such as effective medium methods) determine the local field and polarization.

The accumulation effect under multi-photon generation of color centers at 532 nm has been investigated in lead silicate glasses. The mechanism of excitation and color centers formation has been studied. It was founded that a long-wave carriers mobility boundary (minimal energy at which there takes place generation of electron-hole pairs) is disposed much above (> 5.6 eV) a fundamental absorption edge of the glass matrix (approximately 3.5 eV). Excitation occurs through virtual levels located in the fundamental absorption region as a result of the three-photon process. Dependency of the accumulation effect on the color centers generation efficiency and its concentration is studied. It is shown that existing models based on multi- photon accumulation of color centers can not account for the observed regularities. In the work possible mechanisms of under study phenomena are discussed.

In this paper we will address the transient temperature distribution and subsequent optical distortion resulting from an unstable resonator out-coupling a high power Repetitive Pulsed laser beam on optical thin film coated uncooled optical components.

This paper addresses the application of the Reverse Thermal Wave Transform to Transmissive optical components.

This work is devoted to the investigation of questions that can be useful for development of standard for the determination of laser induced damage threshold. It is shown that low- temperature ions exchange is a prospective approach for improving and stabilizing of laser damage thresholds of glasses surfaces. The radiation parameters and exposure conditions which are necessary to obtain the reproducible breakdown thresholds have formulated. The powerful laser system for damage testing designed on the basis of these requirements are described.

Experimental laser damage threshold tests were designed and successfully carried out at the High Energy Laser Systems Test Facility utilizing the Pulsed Laser Vulnerability Test System against optical components from a tactical weapon system in a simulated battlefield environment. The objectives of the experimental tests were to measure laser fluence levels corresponding to minimum damage, maximum functional degradation, and catastrophic damage against the various optical components positioned in a laboratory environment and at a downrange test site (approximate propagation distance of 692 meters). The experimental testing was also designed to investigate laser damage threshold fluence levels over a wide range of laser operating conditions and test parameters. This paper describes in detail the design and experimental configuration of the laser damage threshold tests recently conducted at HELSTF. The results of the experimental tests are not included in this paper.

This paper presents in detail a variant of the damage frequency method for determining laser damage threshold. The procedure includes the definition of an initial search to estimate the location in fluence of the 0%, 60% and 100% damage probability points and a test exposure protocol. The preliminary search yields information that is used to determine both the maximal test fluence and the fluence step size. The fluence range is restricted to the domain of the probability versus fluence curve where the probability of damage is between 0% and approximately 60%. The exposure protocol requires a minimum number of damage events be observed at a given fluence, to reduce statistical error.

The accuracy and precision of a laser damage threshold determination is affected by the uncertainty in the data used. The uncertainty in the data comes from two sources. The first source is imprecise knowledge of the independent variable, the laser fluence. The other source is the uncertainty in the measured damage frequency. The two uncertainties are added in quadrature to yield the final data point uncertainty. Since the uncertainties add in quadrature, it is not advantageous to make one source very small without an effort to lower both. It is shown that the dominant source of uncertainty is in the measurement of the damage frequency.

This paper presents the procedure and apparatus used to laser condition meter-scale HfO₂/SiO₂ multilayer polarizers which will be used in the Beamlet laser system. A study of different conditioning techniques, the effects of conditioning, and the determination of a practical process for conditioning large-area optics is presented.

Thermal optical software has been written and used to reduce surface temperature and optical transmission thermal distortion interferometry data. A high reflectance mirror on a fused silica substrate was irradiated by a high intensity laser beam at 1.3 micrometers . Surface temperature and optical transmission data that anchor the software are presented in this paper. In addition, a novel method of computing the optical transfer function from the interferometer data is discussed.

By properly designing the laser optical resonator, an optimal match between brightness and coherence can be achieved. This paper discusses one such design for an oxygen iodine laser and shows measured beam profiles. The laser mode was shaped and optically relayed to a test specimen. Very uniform beams of high brightness were measured at the plane of the test sample. This paper also presents this data.

The stable parameters laser radiation / TEM_ocm. (m=const.!), τ 7ns, λ=1,06₁ 0,53μm / has been used. The coorelation of N-on-1 bulk damage thresholds for optical glasses KB, STK3, STK13 and its analogies resistive to γ radiation - K1Q8, STK1O3, STK113 were investigated. Results are in good aqreement with the earier proposed model /1/.- the ionization, the color center generation, the change of the material properties, the heatinig and self focusing, the bulk damaqe /1/.

Experimental data of the laser-induced damage thresholds of about 50 samples of NaCl crystals of different optical properties were analyzed. Simultaneous consideration of the damage data, obtained by nanosecond region lasers with wavelengths 10.6; 2.94; 2.76; 1.06; 0.26 micrometers permit to find, the threshold magnitude is a function of a dimensionless product of laser radiation frequency and a parameter of the sample having the dimension of time. The recommended empirical equation enables to explain many experimental data obtained earlier, to predict the laser induced damage threshold magnitude in the wide frequency range, and also the variation of this threshold as a function of temperature.

The amounts of 4 micron pulsed laser fluence necessary to induce one and two orders of magnitude degradation in the R₀A value of Hg_0.7Cd_0.3Te at 100 K have been calculated. The R₀A values used in this calculation were obtained by simultaneously including generation-recombination, diffusion and tunneling mechanisms.

Rare earth fluorides have been investigated as possible substitute materials for standard thorium-fluoride layers in CO₂-laser optic components.

The surface periodic structures induced by interference of surface plasmon-polaritons and waveguide modes with laser radiation are discussed.