Multipulse laser damage in potassiumtitanyl phosphate: statisticalinterpretation of measurements and thedamage initiation mechanism
Frank R. WagnerAnne HildenbrandHassan AkhouayriCéline GouldieffLaurent GallaisMireille CommandréJean-Yves Natoli
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Multipulse laser damage in potassium titanyl phosphate:statistical interpretation of measurements and thedamage initiation mechanism
Frank R. WagnerAnne HildenbrandHassan AkhouayriCéline GouldieffLaurent GallaisMireille CommandréJean-Yves NatoliAix-Marseille UniversitéInstitut Fresnel, CNRS, Ecole Centrale Marseille,
Campus de St Jérôme13013 Marseille, FranceE-mail: [email protected]
Abstract. Multipulse laser-induced damage is an important topic for manyapplications of nonlinear crystals. We studied multipulse damage in X-cutKTiOPO4. Using a 6-ns Nd:YAG laser with a weakly focused beam, a fati-gue phenomenon was observed. We addressed whether this phenom-enon necessarily implies material modifications. Two possible modelswere tested, both of them predicting increasing damage probability withincreasing pulse number while all material properties are kept constant.The first model, pulse energy fluctuations and depointing, increases theprobed volume during multiple pulse experiments. The probability tocause damage thus increases with increasing pulse number; however,this effect is too small to explain the observed fatigue. The secondmodel assumes a constant single-shot damage probability p1, so a multi-pulse experiment can be described by statistically independent resam-pling of the material. Very good agreement was found between the2000-on-1 volume damage data and this statistical multipulse model.Additionally, the spot size dependency of the damage probability is welldescribed by a precursor presence model. Supposing that laser damageprecursors are transient, the presented data explain the experimentalresults without supposing material modifications. © 2012 Society of Photo-OpticalInstrumentation Engineers (SPIE). [DOI: 10.1117/1.OE.51.12.121806]
Subject terms: potassium titanyl phosphate; laser-induced damage; multipulsedamage; fatigue; material modification; statistical multipulse model; laser stabilityinfluence.
Paper 120382SSP received Mar. 13, 2012; revised manuscript received Jun. 19,2012; accepted for publication Jun. 19, 2012; published online Jul. 13, 2012.
1 IntroductionMultiple-pulse laser-induced damage of optical materials isof high practical importance for the design of optical sys-tems. The laser damage test closest to the operating condi-tions of an optical system is the S-on-1 test, which measuresthe laser damage probability of the material under irradiationof S successive pulses of constant fluence.1
The topic of multipulse laser–induced damage has beenaddressed since the early days of laser damage measurementsin the 1970s2,3 (see also the review paper4). Generally speak-ing, we observe in many materials a so-called fatigue effect,meaning that the measured damage threshold decreases withincreasing pulse number.5 The damage threshold is usuallydefined by the highest fluence for which the damageprobability during the experiment is zero.
The discussion of these S-on-1 data started from astatistical point of view,2,3 which was replaced later on bya material modification point of view.4,6,7 This change ininterpretation of the fatigue effect was triggered by theunderstanding of another fundamental feature of laser-induced damage: the spot size dependency of the 1-on-1damage probability.
As long as laser-induced damage is extrinsic (i.e., causedby defects and impurities), the damage probability can beunderstood by the probability for the high fluence regionof the beam to encounter at least one of the coarsely spaced
damage precursors.8,9 Statistical considerations then allowone to theoretically describe the measured 1-on-1 damageprobability P as function of the applied peak fluence F.The extrinsic damage precursors are supposed to determinis-tically cause damage upon irradiation at a fluence levelexceeding their threshold T0. By supposing a certain distri-bution of the precursor thresholds, fitting the PðFÞ curvesallows one to extract the parameters of the damage precursorpopulation, in particular the volume density d of the damageprecursors. In the following, we use the notations defined inRef. 10 and write: PðFÞ ¼ 1 − exp½−∫ F
0 gðTÞVFðTÞdT� inthe general case, and
PðFÞ ¼ 1 − exp½−dVFðT0Þ�; (1)
in the simplest case of the degenerate model, where all pre-cursors fail at the same fluence.
Here gðTÞ describes the threshold distribution of thedamage precursor ensemble, and VFðTÞ is the volume ofthe material where the local fluence is higher than the thresh-old T, with F being the peak fluence of the beam. Severalpossibilities have been proposed for the precursor thresholddistribution function gðTÞ. The simplest one is the degener-ate model [gðTÞ ¼ dδðT − T0Þ], where all precursorsdamage at the same fluence T0 and their volume densityis d.8,9 This simple model describes volume damage ratherwell. Other models, such as the power-law model8 and theGaussian law model,10 have been proposed to better describesurface damage data or damage in thin films.0091-3286/2012/$25.00 © 2012 SPIE
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If laser damage is precursor induced, one can imaginetypes of precursors that can evolve during a multipulseexperiment due to irradiation by the pulses preceding thedamaging pulse. As an example, we may quote a thermalmodel for nanometric metallic inclusions11 that evolve dueto enhanced diffusion of metal atoms into the host materialat subcritical temperatures. However, considering the precur-sor number densities deduced from damage curve fits12 and areasonable size for metallic inclusions,11 the atomic concen-tration of the inclusion atoms compared to the host atomsreaches the ppm range only in low-quality materials [thinfilms, fast-grown potassium dihydrogen phosphate crystals(KDP)13]. The physicochemical nature of the precursors isthus impossible to prove in high-quality materials. To thebest of our knowledge, no clear evidence exists about thephysicochemical nature of the bulk damage precursors inhigh-quality materials such as certain crystals and fusedsilica. We may thus ask whether the damage precursors ofthese materials really evolve in multipulse experiments.Usually fatigue data, as we present in this article, is takenas evidence for material modifications. We show, however,that another explanation of the fatigue effect exists.
We analyze two possibilities to explain S-on-1 data withevident fatigue by models that assume constant materialproperties. Section 2 gives experimental details, Sec. 3 pre-sents the 2000-on-1 bulk damage data in potassium titanylphosphate (KTP), Sec. 4 evaluates the influence of pulse-to-pulse laser fluctuations on this data, and Sec. 5 gives anew formulation of the statistical S-on-1 model. Section 6describes the spot size dependency of the 1-on-1 damageprobability in KTP, and we finally discuss in Sec. 7 the impli-cations of the preceding for the damage initiation mechan-isms in materials with fatigue.
2 Experimental DetailsDamage probability data were acquired using the setupdescribed previously.14 Only volume (bulk) damage was con-sidered, and the setup was calibrated for different laser spotdiameters using a fused-silica substrate for which the volumedamage threshold is 100 J∕cm2. We used a Q-switched Nd:YAG laser (Quantel Ultra GRM, FWHM pulse duration6� 1 ns, λ ¼ 1064 nm) with a near-Gaussian beam profilein the high-intensity region of the focus.15 We used 1∕e2focal spot diameters of 24, 75, and 155 μm. In situ damagedetection was performed by imaging the irradiated zone ofthe sample and using automated image processing to stop thelaser upon damage detection.
During the S-on-1 tests, for each site the number of pulsesreceived before damage occurred was recorded. From thisdata, it was thus possible to extract any S-on-1 curve withS ranging from 1 to the maximum pulse number used.The number of tested sites per fluence varied from sampleto sample and is indicated in the corresponding sections.
Fitting of the damage probabilities was performed using astandard χ2 minimization fitting tool. For the higher flu-ences, where all sites are damaged after N1 < 1000 pulses,we only considered the first 2N1 pulses for the fit, to decreasethe importance of the unity probabilities that do not containany additional information.
Laser-damage testing of nonlinear optical crystals such asKTP (KTiOPO4) requires special care concerning the orien-tation of the crystal, the polarization of the test beam, and the
convergence angle of the test beam.16 We irradiated the crys-tals in Y-direction using X-polarized light (Sec. 3), or weused X-direction and Y-polarization. Here X and Y referto the principal axes of the crystal named in order of increas-ing refractive index (nX < nY < nZ). Both combinations ofirradiation direction and polarization have been chosen toavoid frequency doubling, as SHG strongly influences thedamage threshold.17
3 Damage Data in 2000-on-1 Mode in KTPThe experiment was carried out with a maximum number of2000 shots per site at a pulse repetition rate of 10 Hz. Wetested 13 fluences and 20 sites per fluence with a paralleltest beam (diameter 75 μm).
Different representations of the damage probability datacan be found in Fig. 1. Panel 1(a) shows the classic repre-sentation as S-on-1 damage probability curves PSðFÞ with Sranging from 1 to 2000. Some of the 2000 curves are high-lighted to illustrate the evolution of damage probability withincreasing pulse number. In 1(b), the extracted damagethresholds T are plotted as a function of the used pulsesS. In this representation, it becomes clear why the name fati-gue was chosen to describe the phenomenon, but the repre-sentation does not contain the full set of data. Representation1(c) was chosen by Bass and Bassett2,3 in the early papers onmultipulse damage. For curve fitting in Secs. 4 and 5. how-ever, we use the PFðSÞ curves shown on a logarithmic pulsenumber scale in Fig. 1(d). These curves also represent thewhole data set [like the PSðFÞ curves in Fig. 1(a)], butthe data set consists of only some curves (one for eachfluence) with 2000 data points each.
Number of pulses per site S1 10 100 1000
1 10 100 1000
(a) (b)
(c) (d)
Fluence F (J/cm )20 10
10 25Fluence F (J/cm )2
Pul
ses
until
dam
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1
10
104
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102
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esho
ldT
(J/c
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0
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20
0
10
11.5 J/cm2
13.7 J/cm2
15.8 J/cm2
24.1J/cm2
20
15 20Number of pulses per site S
S-on-1
Fig. 1 2000-on-1 data of bulk damage in Y-cut KTP caused by 6 nsX-polarized 1064 nm irradiation. Twenty sites were used for eachfluence. (a) S-on-1 damage probability curves PSðF Þ. Most of the2000 curves are plotted in gray; the curves corresponding toS ¼ 1, 3, 10, 200, and 2000 are highlighted. (b) Experimental damagethresholds T as a function of used pulse number S. The experimentaldamage threshold T is the highest fluence where no damage hasbeen observed. Dashed lines are guides to the eye. (c) Scatterplot of the damaging pulse number as a function of the fluence forall damaged sites. This kind of representation is also used in theearly papers by Bass and Barrett2,3 and the ISO norm.1 (d) Plot ofthe damage probability as a function of the number of pulses PF ðSÞ.Like representation (a), this plot contains the full data set but is moreadapted to fitting.
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4 Influence of Laser Fluctuations on PF �S� CurvesThe data in Fig. 1(d) shows that at constant fluence thedamage probability systematically increases with increasingpulse number. Applying Eq. (1) to a multipulse situation,VFðT0Þ is then the volume in which, at least during onepulse, the fluence exceeds the precursor threshold. For a per-fectly stable laser, size and position of the single-pulseVFðTÞ are constant, and thus the multipulse VFðTÞ is con-stant for any number of pulses too. In consequence, theincrease in PFðSÞ has to be attributed to changing materialparameters [gðTÞ, or simply d and T0 in Eq. (1)].
In reality, however, the multipulse irradiated volume,VF;TðSÞ, increases with increasing pulse number owing tothe laser fluctuations [like pulse energy variations, changingthe size of the single-pulse VFðTÞ] and depointing [changingthe position of the single-pulse VFðTÞ]. In this section, weevaluate if the fatigue effect evidenced in Fig. 1 can entirelybe explained by the laser probing an increasing volumeduring multipulse experiments. For this purpose, 2000 beamprofile images were acquired with a 14-bit CCD-camera afterthe damage experiment. Because of the parallel test beam,the high-intensity surfaces AFðTÞ of the beam profile imageswere proportional to the high-intensity volume VFðTÞ duringthe damage test. These images allowed us to determine themultipulse irradiated volume VF;TðSÞ. We might furthermention that the measured VF;TðSÞ values were in goodagreement with Monte Carlo simulations.18
If only laser fluctuations cause the observed damage prob-ability increase PFðSÞ, the material parameters d and T0
should stay constant when fitting the PðSÞ data of anyfluence with the simple version of Eq. (1), where VFðT0Þhas been replaced by the multipulse version VF;T0
ðSÞ.Figure 2(a) shows the fits corresponding to the two lowest
fluences where damage has been observed. Figure 2(b) sum-marizes the main fit results for all fluences. As a first obser-vation, we state that the model describes the low-fluence datavery well (0.9 < R2 < 1), whereas the high-fluence data ismore difficult to describe (0.65 < R2 < 0.8). Figure 2(b)also shows the threshold values that were necessary to obtainthe best agreement between the model and the PðSÞ data.
The threshold values are not constant but increase withincreasing fluence. This indicates that the probed volumeincrease cannot solely explain the fatigue effect. In fact, itis only possible to describe the PðSÞ data using VF;T0
ðSÞfor threshold T0 and test fluence F being very close to
each other, as shown in Fig. 2(b) by the small deviationof the fitted thresholds from the dashed line representingthe test fluences. Thus, the influence of the increasing probedvolume is too small to explain the measured fatigue effect.
5 Statistical InterpretationAs mentioned before, early papers2,3 proposed a statisticalinterpretation of the fatigue effect. The model is based onconstant material properties causing a constant single-shotdamage probability p1. As in this model, preceding pulsesdo not influence the material response upon irradiation; mul-tipulse damage is caused by statistically independent resam-pling of the material at each pulse. The damage probabilityfor S pulses is then
PðSÞ ¼ 1 − ð1 − p1ÞS: (2)
Figure 3 shows fits of the PðSÞ data using this model. Theonly fit parameter is the single-pulse damage probability p1.
Figure 3(a) shows the fits corresponding to the two lowestfluences where damage was observed, and Fig. 3(b) sum-marizes the fit results for all fluences. We see that the modelwell describes the experimental data over the whole fluencerange (0.89 < R2 < 1). For the higher fluences, the fit qualityslightlydecreases,whichmaybeattributed toasmallernumberof data different from 1 [PðSÞ < 1]. Figure 3(b) also showsthe p1 values that were found by the fits and the experimental1-on-1 data with 95% confidence error bars.16
In fact, for an ideal 1-on-1 measurement with an infinitenumber of tested sites (and thus negligible error bars), themeasured 1-on-1 damage probability Pð1; FÞ should equalthe fitted single-shot damage probability p1ðFÞ, if the mate-rial under test is described by the statistical resamplingmodel. Within the limits of the error bars, this is the casefor our 2000-on-1 data in KTP.
In summary, the statistical-independent resampling modelvery well describes the measurement (as visible by the verygood agreement between experimental data and the fits).
6 Spot Size Dependency and theStatistical S-on-1 Model
Before discussing the result of Sec. 5 in more detail, it isinteresting to look at the spot size dependency of the damageprobabilities for a material where the statistical S-on-1 modelapplies.
Number of pulses per site S
Dam
age
prob
abili
tyP 1
0
0.5
(b)(a)
Fluence F (J/cm )210 15 200 500 1000 1500
11.5 J/cm2
13.7 J/cm2
25
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20
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/cm
)0
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Fit
qual
ity R
2
0.6
0.7
0.8
0.9
1
T0
R2
Fig. 2 (a), Fit to the low-fluence PðSÞ data using the equationPðF Þ ¼ 1 − exp½−dVF;T 0
ðSÞ�. Here VF;T 0ðSÞ has been calculated
from 2000 beam profile images, and the fit parameters are d andT 0. (b), Summary of the fit results for all fluences. The fit quality interms of R2 (squares) and the fitted thresholds T 0 (triangles) areshown. Reasonable fits can be obtained, but only by varying thematerial parameters T 0 and d significantly.
Number of pulses per site S
Dam
age
prob
abili
tyP 1
0
0.5
(a)
0 500 1000 1500Fluence F (J/cm )2
10 15 20 25
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2
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1
Dam
age
prob
abili
ties 0.3
0
0.1
0.2
(b)
p = 0.00041
1-on-1fitted p1
Fig. 3 (a), Fit to the low-fluence PðSÞ data using Eq. (2). p1 is the onlyfit parameter. No assumption is made concerning the fluence depen-dency of p1. (b), Summary of the fit results for all fluences. The fitquality in terms of R2 (full squares) is reported on the right axis;the fitted p1 values (full circles) and the measured 1-on-1 damageprobabilities (open squares) with 95% confidence error bars arereported on the left axis. Good fits can be obtained for all fluencesusing a single fit parameter, and the p1 values are close to the1-on-1 damage probabilities.
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Figure 4 shows damage probabilities acquired with differ-ent spot sizes in the volume of KTP. The experimental 1-on-1data are shown in Fig. 4(a), and the p1 data, deduced from a200-on-1 measurement, are shown in Fig. 4(b). For both datasets, the curves for the three spot sizes are fitted simulta-neously with Eq. (1) using common material parametersd and T0, but the three different beam diameters in theVFðT0Þ expressions for Gaussian beams.9
Based on the partially reduced quality of the fits (seefigure caption), we may note that 200 pulses per site seemto be too few for checking whether the statistical multipulsemodel applies; 1000 or more pulses per site are required.
Together with Fig. 3, the data shown in Fig. 4 show thatKTP can be well described by the statistical multipulsemodel and at the same time by a defect presence model.
7 DiscussionThe results of Sec. 4 roughly allow us to consider the influ-ence of the fluence fluctuations and the limited pointingstability of the laser to be negligible in view of the followingdiscussion. The only remaining fluctuation in the laserparameters that might influence the presented measurementsare intensity modulations because the laser is not singlelongitudinal mode.
Two points indicate that the longitudinal multimodeoperation does not influence the important aspects of the pre-sented observations. First, the fatigue effect has also beenreported using single longitudinal mode lasers (Refs. 2and 3 and Refs. 21 and 44 in Ref. 4). Second, we alsohave performed measurements at the second and third har-monics of the same laser as used in this study on KTP17 andLBO.19 Although the intensity modulations caused by modebeating are increased after extracavity SHG and even moreafter extracavity THG, the fatigue effect decreases withincreasing photon energy. We are thus confident that thedata reported here give information on the light–materialinteraction and not on the laser stability.
We showed in Sec. 5 that the model of statistically inde-pendent resampling well describes the multipulse damagedata in KTP bulk. Section 6 showed that the spot size depen-dency of the 1-on-1 bulk damage data is well described by aprecursor presence model (degenerate population). However,these two models are contradictory under often-usedassumptions. If the damage precursors used in the presencemodel are spatially stable and permanently present (impuri-ties, etc.), the same precursors will be activated by any of the
succeeding pulses. If, additionally, an activation of a precur-sor always causes damage,8 a certain test site would alwaysdamage on the first pulse, or would not damage even aftermany pulses.
When developing a model that describes laser-inducedbulk damage in KTP, we should thus question these assump-tions. The simplest case that is compatible with both thepresence models and the statistical multipulse model is tran-sient damage precursors that always cause damage. Recentlya model has been published for nanosecond laser-induceddamage in KTP which uses transient damage precursors.20
This model not only agrees with the data presented in thisarticle, but it also describes quantitatively the effect of wave-length mixtures on the laser-damage threshold of KTP.
Fitting a laser-damage curve with the degenerate pre-cursor population model yields the volume density d. In thepast, this density has often been considered as a density of aspecies in the material (the damage precursors), such asinclusions or particular defect clusters, and in consequencepeople pointed out the enormous difficulty of detectingnanometric defects of such small volume densities in a sam-ple. In light of the validity of the statistical multipulse model,one has to consider d as the volume density of the damagingprecursors, but not the volume density of the species thatmay give rise to the creation of a damage precursor. Forexample, in KTP, the possibility to create transient laser-damage precursors by laser irradiation is intrinsic to thematerial (see references in Ref. 20).
As a final remark, we may note that our data is contra-dictory to part of a review article.4 Searching for a reasonwhy the p1 model has been abandoned in the early daysof laser damage research, the author of Ref. 4. suggestedthat the statistical multipulse model only describes data forwhich the single-pulse damage probability p1 is quite high(p1 > 0.055). This idea was logical at the time the reviewarticle was written, because the measurement that put a (pre-liminary) end to the application of the statistical multipulsemodel had been performed at an experimental p1 of 0.055,whereas former measurements that supported the statisticalmodel were performed at experimental p1 values of up to0.38. However, we found very good agreement with thestatistical model for p1 values as small as 0.0004.
8 Summary and ConclusionsWe studied multipulse laser–induced damage in KTiOPO4.The fatigue phenomenon was described in detail, and wetried to clarify whether an observed fatigue effect necessarilyimplies material modifications at sub–single-pulse-thresholdfluences. For this purpose, we checked two possible modelsthat cause an increase of the damage probabilitywith the num-ber of pulses while all material properties are kept constant.
Laser fluctuations in terms of pulse energy and depointingincrease the probed volume upon multiple-pulse experi-ments. The increase in the probed volume leads for allprecursor presence models to an increase in the damageprobability. For our setup, however, the laser fluctuationeffect turned out to be too small to explain the observedfatigue effect without changing material parameters.
Assuming constant material properties means in factassuming a constant single-shot damage probability p1.A multipulse experiment can then be described by statisti-cally independent resampling of the material, and the
(a) (b)
Fluence F (J/cm )210 20
Dam
age
prob
abili
ty0.6
0
0.3
30Fluence F (J/cm )2
10 20
Dam
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30
155 µm75 µm24 µm
Beamdiameters
fit
155 µm75 µm24 µm
Beamdiameters
fit
1-on-1 p from200-on-1
1
Fig. 4 (a) Spot size dependent 1-on-1 data for KTP. (b) Spot sizedependent p1 data deduced from a 200-on-1 measurement in KTP.The full p1 points are deduced from good fits (0.9 < R2 < 1), the halfp1 points correspond to 0.8 < R2 < 0.9, and the open p1 points toR2 < 0.8 In both graphs, the solid lines are fits to the data usingEq. (1) obtained by fitting the three spot sizes simultaneously.
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damage probability after S pulses can be deduced from thesingle-pulse damage probability [Eq. (2)]. The same modelhas already been used before in a slightly different formu-lation.2–4 The agreement between the 2000-on-1 volumedamage data and the statistical multipulse model was foundto be very good.
Further, it has been shown that Eq. (1), using a pulse num-ber–independent probed volume VFðTÞ, well describes thespot size dependency of volume damage data. The laserdamage behavior of KTP is thus described by the statisticalmultipulse model and a presence model simultaneously.
In consequence, laser damage precursors in KTP neces-sarily have to be transient. Thus the species that may give riseto the creation of light-induced precursors may be abundantin the material. The volume density d extracted from PðFÞcurves using Eq. (1) has to be regarded as the volume densityof the actually damaging precursors and contains little infor-mation on the species at the origin of laser-damage initiation.In particular, the recently proposed laser-damage model forKTP,20 which is in agreement with the data presented in thisarticle, supposes an intrinsic reason for initiation of laserdamage.
The observation of the so-called fatigue effect is thus notnecessarily linked to material modifications by subthresholdlaser pulses.
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Frank Wagner obtained his MSc degree in physics from the GeorgAugust University (Göttingen, Germany) in 1997. From 1997 to 2000,he prepared a PhD thesis at the Swiss Federal Institute of TechnologyLausanne, Switzerland, working on excimer laser ablation of polymersand concentrating on surface modifications and debris effects in viewof applications in electroosmosis. From 2000 to 2004, he worked asR&D manager of Synova SA (Ecublens, Switzerland) developing thewater-jet guided laser cutting technique. He then joined the HighPower Photonics and Random Media group of the Fresnel Instituteat the University Paul Cézanne in Marseille, France, as an assistantprofessor. His main research topic is the physics of laser-induceddamage in optical components, in particular nonlinear crystals.
Anne Hildenbrand obtained her engineering degree in physics spe-cializing in Optics in 2005 from the Ecole Centrale Marseille in France.She passed her PhD thesis on laser-induced damage in nonlinearoptical crystals at the Fresnel Institute in Marseille. She has workedsince 2009 on laser development in the infrared domain at the French-German Research Institute of Saint-Louis (ISL).
Hassan Akhouayri is a professor at Ecole Centrale Marseille andreceived his PhD in 1981 on condensed matter from Université deProvence; the thesis was on ”Transport properties of disorderedferromagnetic thin films at low temperatures.” In 1991, he receivedthe PhD (Thèse d'état) on nonlinear electromagnetic optics with thesubject: ”Enhancement of nonlinear phenomena by resonant excita-tion of surface waves in corrugated devices and applications to opticalbistability and second harmonic generation.” His main research islinked to linear and nonlinear characterization of optical devices andimaging modalities including electromagnetic modeling.
Céline Gouldieff obtained her Master’s degree in engineering fromthe Ecole Centrale Marseille in 2010 and her Research Master’sdegree in optics 2010 from the Aix-Marseille University. Since Octo-ber 2010, she completes her PhD thesis at the Institut Fresnelon experimental and theoretical aspects of laser damage in opticalmaterials.
Laurent Gallais received his Master’s degree in engineering from theEcole Nationale Supérieure de Physique in 1999 and a ResearchMaster’s degree in optics 1999 from the Aix-Marseille University.He obtained his PhD degree in physics in 2002, after a work onlaser damage in optical components. Since 2003, he has been assis-tant professor at the Ecole Centrale Marseille where he teaches in thefield of Optics and Project Management. His research activities, con-ducted at the Institut Fresnel, deal with high-power laser/optical mate-rials interactions. At the moment his research interests concern laserdamage of optical interference coatings in the femto to nanosecondrange, and the development of processes to “repair” laser-damagedoptics.
Mireille Commandré graduated from the Ecole Nationale Supérieured’Ingénieurs Electriciens de Grenoble (Institut National Polytechniquede Grenoble) in 1979 and received a PhD in materials for micro-electronics in 1981. She is currently a professor at the Ecole CentraleMarseille. She received her “Docteur d’Etat” degree in 1992 with adissertation on photothermal characterization of optical coatings. Atthe Fresnel Institute, Mireille Commandré is currently head ofresearch team “High Power Photonics and Random Media.” Herresearch interests include laser damage, thermal properties, opticalcharacterization, and optical thin film deposition techniques. Shehas published a hundred papers.
Jean-Yves Natoli is a professor at the Institut Fresnel in Marseille,where he is in charge of laser damage activity. He teaches at theUniversity Paul Cézanne—Marseille, in the field of optics, materialsciences, and electronics. He obtained his PhD in material sciencein 1994 and his Habilitus degree in the field of laser damage in 2003.
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