Laser-induced damage growth of fused silica optics near growth threshold at 351 nm.

Laser-induced damage growth on the exit surface of fused silica optics triggered by nanosecond pulses at 351 nm is widely described with exponential dynamics. In this Letter, a particular experimental setup allowed us to study damage growth with a large beam and fluences near damage growth threshold for a high number of shots. This allowed us to observe and characterize a regime with a slow and linear growth dynamic not documented in the literature and yet fundamental for the operation of high-power laser installations.

Pulse duration dependent optical nonlinearities of BiSe thin films.

Topological insulators, such as the BiSe material, exhibit significant optical nonlinearities. This work investigates the impact of the pulse duration on the nonlinear optical responses of BiSe layers. Scanning electron microscopy studies have been performed to reveal the crystalline structure of the samples.

Parametric study of laser-induced damage growth in fused silica optics with large beams at 351 nm. Part 2: fractal analysis.

The impact of laser fluence and pulse duration on both the rate and probability of growth of laser-induced damage sites has been reported and analyzed statistically in a companion paper. In this paper, we report and analyze the volume morphology of damage sites during the growth process in fused silica optical components, at 351 nm, under various laser fluence and pulse durations. Fractal analysis has been used to quantify the bulk damage morphology.

Parametric study of laser-induced damage growth in fused silica optics with large beams at 351 nm. Part 1: stochastic approach.

Both the rate and probability of the growth of laser-induced damage sites in fused silica depend on several parameters. In this two-part paper, we investigate the impact of the laser parameters on damage growth. In Part I, we present statistical measurements of damage growth at different energy densities, pulse durations, and initial damage sizes.

Giant ultrafast optical nonlinearities of annealed SbTe layers.

The optimization of thin SbTe films in order to obtain giant ultrafast optical nonlinearities is reported. The ultrafast nonlinearities of the thin film layers are studied by the Z-scan technique. Giant saturable absorption is obtained, which is the highest ever reported, by means of the Z-scan technique.

Quantification of laser-induced damage growth using fractal analysis.

Lateral and longitudinal laser damage growth under subsequent irradiations at 351 nm in the nanosecond range from micrometric to millimetric scales is presented herein. Atypical behavior has been observed, showing the growth in the longitudinal direction, whereas the lateral growth does not evolve. We propose the use of fractal analysis to describe the evolution of the bulk damage morphology.

Investigations on laser damage growth in fused silica with simultaneous wavelength irradiation.

The laser-induced damage growth phenomenon is experimentally studied for damage sites on the exit surface of fused silica. The sites are irradiated by nanosecond laser pulses at 1064 and 355 nm separately and also simultaneously. The results in the single wavelength configurations are expressed in terms of the probability of growth and growth coefficient.

Nanosecond UV laser-induced fatigue effects in the bulk of synthetic fused silica: a multi-parameter study.

Multiple-pulse S-on-1 laser damage experiments were carried out in the bulk of synthetic fused silica at 355 nm and 266 nm. Two beam sizes were used for each wavelength and the pulse duration was 8 ns. The results showed a fatigue effect that is due to cumulative material modifications.

Photoluminescence characterization of KH₂PO₄ crystal: application to three-dimensional growth-sector identification.

In this work, rapidly grown KH2PO4 (KDP) crystals extracted from the prismatic and the pyramidal growth sectors of crystal boules were analyzed using photoluminescence measurements. From the spectra, we deduced a robust criterion to discriminate between both growth sectors in an unknown KDP plate. Moreover, spatially resolved photoluminescence was shown to enable a local probing of different planes in the bulk of the material leading to accurate and nondestructive three-dimensional mapping of the sector boundary, which is often the weakest point in terms of laser-damage resistance in rapidly grown KDP crystals.

Contrasted material responses to nanosecond multiple-pulse laser damage: from statistical behavior to material modification.

This work is dedicated to the study of so-called fatigue effects upon nanosecond laser-induced damage of several crystalline materials and synthetic fused silica irradiated by multiple pulses. The obtained damage probability versus fluence and pulse number data are exploited to determine if the observed fatigue is due to statistics (the more often the material is irradiated, the higher the probability for it to be damaged) or to material modification under irradiation. Whereas 1064 nm irradiation seems to be responsible for statistic behavior, 355 nm irradiation generates material modifications in the case of synthetic fused silica.

Nanosecond-laser-induced damage in potassium titanyl phosphate: pure 532 nm pumping and frequency conversion situations.

Nanosecond-laser-induced damage measurements in the bulk of KTiOPO4 (KTP) crystals are reported using incident 532 nm light or using incident 1064 nm light, which pumps more or less efficient second harmonic generation. No damage threshold fatigue effect is observed with pure 532 nm irradiation. The damage threshold of Z-polarized light is higher than the one for X- or Y-polarized light.

Multiple pulse nanosecond laser induced damage study in LiB3O5 crystals.

Multiple pulse nanosecond laser induced damage in the bulk of LiB3O5 (LBO) crystals was investigated at 1064 nm, 532 nm and 355 nm. Scanning electron microscopy of cleaved damage sites confirmed the presence of different zones that have already been reported in the case of KH2PO4 (KDP). Multi pulse measurements reveal a strong decrease of the damage threshold with increasing pulse number at 1064 nm (fatigue effect).

Laser-induced damage of KDP crystals by 1omega nanosecond pulses: influence of crystal orientation.

We investigate the influence of THG-cut KDP crystal orientation on laser damage at 1064 nm under nanosecond pulses. Since laser damage is now assumed to initiate on precursor defects, this study makes a connection between these nanodefects (throughout a mesoscopic description) and the influence of their orientation on laser damage. Some investigations have already been carried out in various crystals and particularly for KDP, indicating propagation direction and polarization dependences.

Nanosecond laser induced damage in RbTiOPO4: the missing influence of crystal quality.

Nanosecond laser induced damage in RbTiOPO(4) (RTP) an isomorphic material to the more widely known KTiOPO(4) (KTP) is studied in crystals with varying properties. The ionic conductivity along the z-axes of the tested crystals ranged from 1.5 10(-9) S/cm to 1.

Multiscale analysis of the laser-induced damage threshold in optical coatings.

We have investigated the influence of laser beam size on laser-induced damage threshold (LIDT) in the case of single- and multiple-shot irradiation. The study was performed on hafnia thin films deposited with various technologies (evaporation, sputtering, with or without ion assistance). LIDT measurements were carried out at 1064 nm and 12 ns with a spot size ranging from a few tens to a few hundreds of micrometers, in 1-on-1 and R-on-1 modes.

Laser damage resistance of hafnia thin films deposited by electron beam deposition, reactive low voltage ion plating, and dual ion beam sputtering.

A comparative study is made of the laser damage resistance of hafnia coatings deposited on fused silica substrates with different technologies: electron beam deposition (from Hf or HfO(2) starting material), reactive low voltage ion plating, and dual ion beam sputtering. The laser damage thresholds of these coatings are determined at 1064 and 355 nm using a nanosecond pulsed YAG laser and a one-on-one test procedure. The results are associated with a complete characterization of the samples: refractive index n measured by spectrophotometry, extinction coefficient k measured by photothermal deflection, and roughness measured by atomic force microscopy.

Effect of laser irradiation on silica substrate contaminated by aluminum particles.

A major issue in the use of high-power lasers, such as the Laser Megajoule (LMJ), is laser-induced damage of optical components. One potential damage initiator is particulate contamination, but its effect is hard to distinguish from that of other damage precursors. To do so, we introduced artificial contaminants typical of metallic pollution likely to be present on the optical components of the LMJ chains.

High-resolution photothermal microscope: a sensitive tool for the detection of isolated absorbing defects in optical coatings.

The photothermal deflection technique allows us to highlight the presence of inhomogeneities of absorption in optical components. This nondestructive tool is of great interest to the study of the role of contaminants, inclusions, and impurities in the laser-induced damage process. We show that the detection of nanometer-sized isolated absorbing defects requires the development of an adapted photothermal setup with high detectivity and high spatial resolution.

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.

Localized pulsed laser interaction with submicronic gold particles embedded in silica: a method for investigating laser damage initiation.

Laser damage phenomena in fused silica are currently under study because of numerous related high power laser applications. Nanosized defects are believed to be responsible for some laser damage initiation. In order to predict and to quantify this initiation process, engineered submicronic gold defects were embedded in silica.

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.

Laser-induced damage of materials in bulk, thin-film, and liquid forms.

Accurate threshold curves of laser-induced damage (7-ns single shot at 1.064 microm) are measured in bulk and at the surfaces of optical components such as substrates, thin films, multilayers, and liquids. The shapes and the slopes of the curves are related to the spot size and to the densities of the nanodefects that are responsible for damage.