Laser Damage Measurements Research Articles

Electric Field Enhancement Effect of Aluminum Grating With Nanosecond Pulsed Laser Irradiation

Aluminum grating has wide applications in laser systems and photoelectric equipment. Research on the laser damage characteristics of aluminum grating has guiding significance and application value for improving the laser damage resistance. The aim of this study is to investigate the characteristics of damage induced by nanosecond pulsed lasers on the aluminum grating. To better understand the laser damage characteristics of aluminum grating, herein, Maxwell’s equations were numerically solved according to the finite difference time-domain method, and the electric field model of 1,064 nm Gaussian laser damage aluminum grating was established. The simulation results showed that the light field is modulated by the grating; furthermore, the maximum value of the electric field occurred at the ridge of the grating when the laser is irradiated vertically. Analysis suggested that the electric field distribution is in accordance with the laser energy distribution, and the distribution region of the maximum electric field is a vulnerable location. To further verify the local electric field enhancement effect, based on the 1-on-1 laser damage measurement method, an experimental study of the nanosecond laser (@1,064 nm, 6.5 ns) damage to the aluminum grating was carried out. Moreover, the damage morphology was analyzed using a scanning electron microscope (SEM), and the simulation results showed good agreement with the experimental results.

Large optics metrology for high-power lasers.

The Laser MégaJoule (LMJ) is a high-power laser dedicated to laser-plasma experiments. At the beginning of the project in the mid-1990s, an optical metrology laboratory was created at CEA to help accomplish all the steps in the construction of this laser. This paper proposes an overview of the capabilities of this metrology laboratory in four main fields: surface imperfections, photometry, laser damage measurement, and wavefront measurement. The specificities for high-power laser optics in each domain are highlighted as well as the specific features that make our instruments unique.

Discussing defects related to nanosecond fatigue laser damage: a short review

Laser damage measurements with multiple pulses at constant fluence (S-on-1 measurements) are of high practical importance for design and validation of high-power photonic instruments. Using nanosecond lasers, it was recognized long ago that single-pulse laser damage is linked to fabrication-related defects. Models describing the laser damage probability as the probability of encounter between the high fluence region of the laser beam and the fabrication-related defects are thus widely used. Nanosecond S-on-1 tests often reveal the “fatigue effect,” i.e., a decrease of the laser damage threshold with increasing pulse number. Most authors attribute this effect to cumulative material modifications operated by the incubation pulses. We discuss the different situations that are observed upon nanosecond S-on-1 measurements that are reported in literature and speak in particular about the defects involved in the laser damage mechanism. These defects may be fabrication related or laser induced, stable or evolutive, cumulative or of short lifetime.

Special Section Guest Editorial:Laser Damage III

Laser damage of optical materials, first reported in 1964, continues to limit the output energy and power of pulsed and continuous-wave laser systems. In spite of some 48 years of research in this area, interest from the international laser community to laser damage issues remains at a very high level and does not show any sign of decreasing. Moreover, it grows with the development of novel laser systems, for example, ultrafast and short-wavelength lasers that involve new damage effects and specific mechanisms not studied before. This interest is evident from the high level of attendance and presentations at the annual SPIE Laser Damage Symposium (aka, Boulder Damage Symposium) that has been held in Boulder, Colorado, since 1969. This special section of Optical Engineering is the first one devoted to the entire field of laser damage rather than to a specific part. It is prepared in response to growing interest from the international laser-damage community. Some papers in this special section were presented at the Laser Damage Symposium; others were submitted in response to the general call for papers for this special section. The 18 papers compiled into this special section represent many sides of the broad field of laser-damage research.more » They consider theoretical studies of the fundamental mechanisms of laser damage including laser-driven electron dynamics in solids (O. Brenk and B. Rethfeld; A. Nikiforov, A. Epifanov, and S. Garnov; T. Apostolova et al.), modeling of propagation effects for ultrashort high-intensity laser pulses (J. Gulley), an overview of mechanisms of inclusion-induced damage (M. Koldunov and A. Manenkov), the formation of specific periodic ripples on a metal surface by femtosecond laser pulses (M. Ahsan and M. Lee), and the laser-plasma effects on damage in glass (Y. Li et al). Material characterization is represented by the papers devoted to accurate and reliable measurements of absorption with special emphasis on thin films (C. Muhlig and S. Bublitz; B. Cho, E. Danielewicz, and J. Rudisill; W. Palm et al; and J. Lu et al.). Statistical treatment of measurements of the laser-damage threshold (J. Arenberg) and the relationship to damage mechanisms (F. Wagner et al.) represent the large subfield of laser-damage measurements. Various aspects of multilayer coating and thin-film characterization are considered in papers by B. Cho, J. Rudisill, and E. Danielewicz (spectral shift in multilayer mirrors) and R. Weber et al. (novel approach to damage studies based on third-harmonic generation microscopy). Of special interest for readers is the paper by C. Stolz that summarizes the results of four “thin-film damage competitions” organized as a part of the Laser Damage Symposium. Another paper is devoted to thermal annealing of damage precursors (N. Shen et al.). Finally, the influence of nano-size contamination on initiation of laser damage by ultrashort pulses is considered in paper of V. Komolov et al.« less

Sensitivity test method for the characterization of laser damage behavior

This paper introduces a sensitivity test for characterizing the laser damage behavior of a sample. A sensitivity test analyzes unbinned laser damage test data to estimate the damage probability curve. The means of estimation is by employing a parametric model of the probability of damage and identifying the parameters most likely to produce the observed results using the maximum-likelihood (ML) method. The ML method applied to laser damage measurements is reviewed. The sensitivity test is analyzed for its performance using Monte Carlo methods. A series of laser damage tests are simulated on a test of a hypothetical test optic. A Weibull distribution is selected for the damage probability model, while the virtual test optic was chosen to have a non-Weibull shaped damage probability curve. Damage measurements for varying the number of sites exposed are modeled to show the convergence of the Weibull parameters. This paper concludes by showing how the underlying defect distribution is calculated from results of the sensitivity test.

(Invited) Glass-Glass Direct Bonding

Glass-glass direct bonding is closely rated to proven processes in Si-Si wafer bonding. We describe plasma-assisted hydrophilic direct bonding of different glass materials for various applications in optical and high precision engineering. Dedicated “zero-expansion” glass has been used in constructive type “sandwich” bonding of stiff platforms and mirrors as required in space or lithography applications. For transmissive optical applications in the visual and near infra-red spectral range, fused silica is the material of choice and the technology of direct bonding allows to join optical surfaces without an interlayer in a perfectly materials adapted manner. Binary gratings were fabricated and successfully encapsulated in this way for pulse shaping in high power laser devices. The corresponding activities at Fraunhofer IOF are presented and results of supportive laser damage and transmission efficiency measurements for optical characterization are outlined.

Accurate metrology for laser damage measurements in nonlinear crystals

Accurate laser damage measurements are more difficult to perform in nonlinear optical crystals than in glasses due to several effects proper to these materials or greatly enhanced in these materials. Before discussing these effects, we address the topic of error bar determination for probability measurements. Error bars for the measured damage probabilities are especially important when testing small and expensive samples like nonlinear crystals, where only few sites are used for each measurement. The mathematical basics for the numerical calculation of probability error bars corresponding to a chosen confidence level are presented. Effects that possibly modify the maximum light intensity obtained by focusing into a biaxial nonlinear crystal are mainly the focusing aberrations and self-focusing. Depending on focusing conditions, position of the focal point in the crystal, beam propagation direction, and polarization, strong aberrations may change the beam profile and drastically decrease the maximum intensity in the crystal. A correction factor based on former theoretical work is proposed for this effect. The characteristics of self-focusing are quickly reviewed for the sake of completeness, and a note on parasitic second harmonic generation is added at the end.

Influence of polishing and cleaning on the laser-induced damage threshold of substrates and coatings at <inline-formula><math altimg="none" display="inline" overflow="scroll"><mrow><mn>1064</mn><mspace width="0.3em" /><mi>nm</mi></mrow></math></inline-formula>

Laser-induced damage threshold LIDT results on silica sub- strates and coatings are presented for near-infrared applications. Differ- ent polishing and cleaning processes are evaluated. In particular, we investigate the influence of polishing and cleaning on the LIDT of silica substrates and optical coatings deposited by dual-ion-beam sputtering. Laser damage tests were performed at 1064 nm with a 5-ns-pulse Nd:YAG laser, and experiments were made on surfaces of optical com- ponents using a 12-m-diameter focused beam. Accurate damage prob- ability curves are plotted thanks to a reliable statistical measurement of laser damage. Use of a statistical model permits us to deduce the den- sities of laser damage precursors. We find a significant improvement of the LIDT of our coatings on choosing the appropriate cleaning and pol- ishing process.

Detection and characterization of absorption heterogeneities in KH2PO4 crystals

The SOCRATE facility is used for the detection of heterogeneous absorption in large and rapidly grown KH2PO4 (KDP) crystals. The different regions are subsequently characterized by spectrophotometry and laser-damage measurement. In accordance with previous results from the literature we found that, by using the SOCRATE damage measurement set-up with a large beam (300∗600μm2), the absorption level does not play a major role in the damage mechanism at 355nm. However, by testing the damage resistance of the same KDP component with a focused beam (9μm diameter) at 355nm, we highlight for the first time significantly different damage resistances between highly and weakly absorbing regions from a KDP crystal. Indeed, with a focused beam, we demonstrate that the laser-damage threshold may be lower in some sectors cut in the pyramidal part than in sectors from the prismatic part. This means that the absorbing defects at high concentration are not the predominant damage precursors at 355nm.

Integrated photothermal microscope and laser damage test facility for in-situ investigation of nanodefect induced damage

An integrated setup allowing high resolution photothermal microscopy and laser damage measurements at the same wavelength has been implemented. The microscope is based on photothermal deflection of a transmitted probe beam : the probe beam (633 nm wavelength) and the CW pump beam (1.06 microm wavelength) are collinear and focused through the same objective. In-situ laser irradiation tests are performed thanks to a pulsed beam (1.06 microm wavelength and 6 nanosecond pulse). We describe this new facility and show that it is well adapted to the detection of sub-micronic absorbing defects, that, once located, can be precisely aimed and irradiated. Photothermal mappings are performed before and after shot, on metallic inclusions in dielectric. Results obtained on gold inclusions of about 600 nm in diameter embedded in silica are presented.

Optimized metrology for laser-damage measurement: application to multiparameter study.

An automatic test apparatus for refined testing of laser damage is presented that permits an in situ analysis of the tested area before, during, and after pulsed irradiation. Spatial and temporal beam profiling are performed in real time and give access to the localized fluence for each shot. Furthermore, an optimization of the initiation of damage detection is undertaken by use of image processing and yields a resolution better than 1 microm. Through several examples, these conditions are demonstrated to be useful for reaching an understanding of the laser-damage process. A complete study is undertaken of different kinds of glass that permits the main influence of test parameters (shot frequency, shot number, beam profile variation, temporal and spatial meshing, ...) on the damage procees to be shown. The study was made for different test procedures (1:1, S:1, R:1) and completed by atomic-force microscope analysis. Evidence indicates that the upgrading of metrology associated with an automatic process offers new opportunities for understanding laser-induced damage mechanisms and for emphasizing specific effects such as damage initiation, damage growth, and conditioning for repetitive shots.

Comparison of laser performance of dye molecules in sol-gel, polycom, ormosil, and poly(methyl methacrylate) host media

Laser performance is described for Rhodamine 590, Pyrromethene 567, Perylene red, and Perylene orange in inorganic porous sol-gel glass, poly(methyl methacrylate)(PMMA), a composite of porous sol-gel glass with PMMA and organically modified silicate ormosil glass. Lasers were excited with a flash-lamp-pumped dye laser in the long-pulse-length regime (3 µs, 506 nm, 300 mJ) and a second-harmonic Nd:YAG laser in the short-pulse-length regime (6 or 15 ns, 532 nm, 60 mJ). The feasibility of long-pulse-length operation is demonstrated, detailed characteristics of short-pulse operation are described, and laser damage measurements are given. The nonpolar perylene dyes had better performance in partially organic hosts, and the ionic rhodamine and pyrromethene dyes performed best in the inorganic sol-gel glass host.

Increasing the accuracy of laser beam diameter measurement

A procedure for determining the diameter of a focused laser beam based on the measurement of laser damage to a thin film is described. This method has several advantages over the spatial methods of using calibrated diaphragms and the measurement of relative power density distribution with subapertures.

Acoustic measurement of progressive laser damage in composite material

An acoustic instrumentation system has been developed for continuously monitoring and measuring physical “damage” occurring at a laser-irradiated site of a composite material. With either continuous or pulsed laser radiation of fixed intensity, the thermoelastic response of the material at the beam impact point is recorded during the time of exposure. Simultaneously, sound waves are transmitted through the laser impact region and the modulated signal is measured beyond. Such ultrasonic data reveal the “onset” of internal microstructural damage and provide a temporal history of cumulative damage effects. Also, the spectral composition of the acoustic signals is seen to change as a function of damage evolution. As an example of laser damage assessment, measurement of the progressive depth and volume of pyrolysis at a laser-exposed site on a graphite-epoxy composite will be discussed based on through-transmission acoustic signal-amplitude data.

Defect Characteristics Of Optical Surfaces Using Pulsed Laser Damage Methods

Laser damage to optical surfaces, particularly coated surfaces, is typically initiated by material defects that couple strongly to the laser radiation. Knowledge of damage-related defect characteristics is therefore essential to optical material development efforts and to quality control. Such characteristics include individual defect failure levels, defect densities, and content of optically absorbing impurities. Defect failure distributions containing defect density information can be inferred from properly designed laser damage measurements. The data also permit distinctions among different damage mechanisms, including non-defectrelated mechanisms involving the substrate. Inclusions containing volatile, optically absorbing impurities can be detected by mass analysis of laser-desorbed vapors. These methods are described, and examples of results are presented.

Total internal reflection microscopy: a surface inspection technique

Structure at and near the surface of a transparent sample or in a film on a transparent substrate can be observed by illuminating the sample from within using a well-collimated polarized laser beam incident at an angle equal to or greater than the critical angle of the sample material and examining the air side of the surface using an optical microscope. Although the technique is similar to dark-field microscopy, additional information can be obtained here concerning the size and depth of scattering sites on or near the surface. This technique, total internal reflection microscopy (TIRM), is complementary to phase contrast (Nomarski) microscopy. Two TIRM microscopes are shown, one of which is used as an attachment to a commercial Nomarski microscope and the second of which is used in laser damage measurements. This surface inspection technique had been used to study surface polishing and cleaning methods, laser damage nucleation sites, ion milling of optical surfaces, and thin film inclusions. A biological application for liquid medium studies is suggested. A description of the electric fields present at and near the air sample interface is given.