multiwavelength imaging of defects in ultraviolet optical materials

Multiwavelength imaging of defects inultraviolet optical materials

Annelise During, Caroline Fossati, and Mireille Commandre

Laser-induced damage in bare glass substrates and thin films has long been widely acknowledged as alocalized phenomenon associated with the presence of micrometer and submicrometer scale defects. Thescanning of both optical absorption and scattering allows us to discriminate between absorbing andnonabsorbing defects and can give specific information about the origin of the defects. We investigatethe spectral properties of defects in thin films and fused-silica surfaces. Absorbing and scatteringdefects are studied at different wavelengths in the ultraviolet, visible, and infrared ranges. Absorbingdefects are shown to be highly wavelength dependent, whereas we have observed significant correlationbetween scattering defects. © 2002 Optical Society of America

OCIS codes: 240.6490, 240.0310, 310.3840.

1. Introduction

Extensive use of high-power laser radiation in suchareas as military and civilian optical communica-tions, laser processing of materials, and photolithog-raphy attracts more and more attention with regardto the question of behavior of optical materials anddevices under intensive optical illumination. Theproblem of interaction between high-power opticalradiation and matter is usually connected with linearand nonlinear optical absorption, different thermaleffects, photoinduced phenomena, and photoioniza-tion processes. In this context much interest hasbeen focused on radiation damage resistance of opti-cal materials. Laser-induced damage in bare glasssubstrates and thin films has long been widely ac-knowledged as a localized phenomenon associatedwith the presence of micrometer and submicrometerscale defects.1–5 These defects can be surface imper-fections such as scratches, steps, polishing or clean-ing residue, and, more generally, impurities andcontaminants or bulk inhomogeneities with differentstructural and�or chemical origins. All these de-

A. During �[email protected]�, C. Fossati �[email protected]�, and M. Commandre �[email protected]� are with the Institut Fresnel, Unite Mixte de Recherche6133, Centre National de la Recherche Scientifique, Ecole Natio-nale Superieure de Physique de Marseille, 13397 Marseille Cedex20, France.

Received 3 October 2001; revised manuscript received 16 Janu-ary 2002.

0003-6935�02�163118-09$15.00�0© 2002 Optical Society of America

3118 APPLIED OPTICS � Vol. 41, No. 16 � 1 June 2002

fects could be responsible for local variations ofoptical, thermal, or thermo-optical properties. De-pending on their nature they could be absorbing only,scattering only, or both absorbing and scattering.Absorbing defects can induce thermal effects thatlead to damage. In the case of nonabsorbing defects,they can cause field enhancement or reduction inheat conduction. Ultimately, each can lead to dam-age to the material. Under these conditions a num-ber of techniques have been introduced to investigatelocalized defects in optical materials. Among thesetechniques are dark-field and Nomarski micro-scopy, total internal reflection microscopy,6–8 scatter-ing measurements,9–11 atomic force microscopy�AFM�,12,13 and near-field scanning optical micros-copy �NSOM�.14 These techniques are sensitivemainly to structural inhomogeneities and refractive-index variations. They can detect many kinds ofdefect, but they do not directly address absorptionand thermophysical phenomena involved in laserdamage.

In contrast, the photothermal deflection �PD� tech-nique is based on measurement of probe-beam deflec-tion that is due to optical absorption and is related tolocal heating. During the last ten years, photother-mal techniques have been widely used to characterizeabsorption losses in optical coatings with highsensitivity15–19 to map absorbing defects with highspatial resolution20–22 and to detect thermal inhomo-geneities. The defect-induced laser damage was in-vestigated especially in the UV range.23,24 Itappeared useful to combine absorption and scatteringmeasurements in the same experimental setup.

Thus we performed absorption and scattering map-pings simultaneously and in the same experimentalconditions.17,18 The study of both optical absorptionand scattering allowed us to discriminate betweenabsorbing and nonabsorbing defects and gave specificinformation about the origin of the defects that canplay an important role in laser damage.

Spectral properties of absorption in oxide glassesare well-known from earlier publications and havebeen described in many articles and books; see, forexample, Refs. 25 and 26. The main absorbing com-ponents in the infrared, visible, and ultraviolet spec-tral regions are iron and water. Determination ofabsolute concentrations of ferric, ferrous, and hy-droxyl ions and separation from intrinsic absorptionhas not been made before now, especially because ofthe strong overlap of absorption spectra of differentspecies. Absorption spectra of materials in thin-filmform have also been widely investigated, but the ac-curacy of absorption measurements by spectropho-tometry is not sufficient because of the low level ofabsorption especially in the visible range. We arenot aware of any study on the spectral properties ofdefects. Here we are interested in the study of ab-sorbing and scattering defects performed on the samearea at different wavelengths in the ultraviolet, vis-ible, and infrared ranges. In Section 2 we presentthe experimental setup used to map absorption andpartial scattering simultaneously. Our main inter-ests with this technique are high sensitivity to smalldefects and precise positioning of the sample thatallows comparison between mappings at differentwavelengths. In Section 3 we specify the correlationtools that we used for this study. We present anddiscuss our experimental results in Section 4.

2. Experiments

Low-absorption measurements are performed withthe PD technique.17 An intensity-modulated laser

pump beam illuminates the sample. The absorptionof the sample induces periodic local heating thatbrings about the expansion of materials and causesrefractive-index gradients to appear. A second laserbeam, called the probe beam, passes through theheated area and is then deflected by the modulatedrefractive-index gradient and�or by the bumped sur-faces. The resulting deflection measured by a posi-tion sensor is directly dependent on the opticalabsorption. Calibration is needed to obtain the ab-sorption value from the measured deflection of theprobe beam. We performed the calibration by com-paring the deflection caused by the absorption of thesample to be measured with that of a sample of well-known absorption �measured, for example, with aspectrophotometer�. This problem of calibrationand associated procedures has been widelydiscussed15–17 and calibration is the main limitationof accuracy of absolute absorption measurements byPD. Because PD is governed not only by optical ab-sorption but also by the conversion of radiative en-ergy to heat and by thermal diffusion, PD depends onthe thermal and the thermo-optical properties of thefilm. When various calibration samples with simi-lar characteristics are used, the dispersion of mea-sured calibration coefficients is 20%.17 Of course thesame calibration sample has been used for measure-ments presented in this paper. In these conditions,the accuracy of PD measurement of absorption isrelated to the relative uncertainty of the photother-mal signal. Furthermore the absolute value of ab-sorption is not essential here because we focused ondefects and absorption variations at the sample sur-face.

The experimental setup is presented in Fig. 1.The pump beam �an argon laser in the visible and UVranges� was focused on the sample through lenses ofvarious focal lengths. Its Gaussian beam diameteron the sample surface lies between 3 and 100 �m

Fig. 1. Experimental setup.

1 June 2002 � Vol. 41, No. 16 � APPLIED OPTICS 3119

�diameter at 1�e2�, depending on the desired applica-tion. We chose a 25-�m-diameter pump beam and aHe–Ne laser as the probe beam. The probe beamtravels through the sample �collinear PD or trans-mission configuration� and is deflected by the modu-lated refractive-index gradient induced by opticalabsorption in the three media: air, thin film, andsubstrate. We measured the deflection of the trans-mitted probe beam. Other configurations are possi-ble with our experimental setup but are not used inthis paper. The diameters of the pump and probebeams were controlled by the classical knife-edgetest. The diameter of the probe beam used for thesemeasurements is 28 �m. The relative position of thetwo beams on the sample surface was adjusted to findthe maximum probe-beam deflection. The pumpbeam was modulated at a low frequency �a few tens ofhertz�. The choice of frequency was made to obtainthe best signal-to-noise ratio for the photothermalmeasurement of absorption. The entire experimen-tal setup is computer assisted. Stepping motors al-lowed us to move the sample so that we could takemeasurements at different points on the surface. Inour experimental conditions and for conventionalpump-beam power, the lowest absorptance that wecould detect was 10�7.

For scattering measurements, a low f-number lenscollects part of the pump light scattered in a 20° coneout of the specular direction. An iris diaphragm isused to select the spot related to the front-surfacescattering. In the mappings we represent a partialscattering coefficient defined as the ratio of scatteredlight power in the 20° cone over measured power ofthe incident pump beam. We measured the incidentpower under the same conditions and obtained thescattering calibration. This ratio between two pow-ers is difficult to relate to total scattering, which isusually measured and for which several standardmeasurement procedures exist.27–29 Comparativemeasurements of some samples have shown that par-tial scattering was lower than total scattering but isof the same order of magnitude.17 We have a specialinterest in defects and the absolute value of scatter-ing is not essential. The lowest partial scatteringthat we can detect is limited by the noise and is 10�8

when the usual pump-beam power is applied. Weperformed absorption and scattering mappings withthe same pump beam in exactly the same experimen-tal conditions and at the same time. Thus we ob-tained, the so-called paired mappings of absorptionand scattering. The surfaces of both glasses and op-tical coatings can be characterized.

For mappings at different wavelengths the posi-tioning of the sample is crucial. We must know tohigh precision the relative position of the pump beamon the sample and be able to find this position again.In collinear PD the probe beam can be used as thereference position. By using a specific procedure anda centering tool as a sample we reached a precision of2 �m for sample position. Thus, recurrent map-pings of the same area, detailed studies of a selected

area, or successive mappings at different wave-lengths are possible.

We have studied the repeatability of the mappingsand also the noise to confirm the validity of measure-ments. Absorption and scattering mappings of con-ventional samples are repeatable whatever thewavelength. The noise has to be studied in the fol-lowing manner: we performed a mapping with acutoff pump beam and with the sample placed intothe sample holder, which results in a noise mappingfor this sample and these measurement conditions.In the case of absorption this method takes into ac-count all the noise that can occur during the map-ping: conventional noise in the photothermal signal,noise associated with the moving of the sample, andnoise associated with the sample defects �including,for example, defects on the rear surface�. For scat-tering the noise mapping is associated mainly withdetection system noise �photodiode and amplifica-tion�. To continue and to quantify the repeatabilityof mappings in terms of defects, we need to choosesome correlation tools.

3. Correlation Tools

We must define correlation tools to perform a quan-titative study of defect occurrence in the mappings atdifferent wavelengths. In fact each mapping �ab-sorption A or scattering S� is a two-dimensional ma-trix �N � P�, A�i, j� or S�i, j�, associated with asampled function A�x, y� or S�x, y�, where N and P arethe number of measurement points along the x and yaxes. From this matrix we calculate a new matrix,a�i, j� or s�i, j�, centered and normalized:

a�i, j� �A�i, j� � Amean

��k�

l� A�k, l � � Amean�

2�1�2 ,

where

Amean �

�m�

nA�m, n�

NP.

The most conventional approach is based on the cor-relation function. If F and G are two sampled func-tions centered and normalized, the correlationfunction Cor�F, G� �i, j� is defined as

CorF, G�i, j� � �k�

lF�k, l �G�k � i, l � j�.

When mappings display only a few defects that arewell defined and have a high absorption �or scatter-ing� value compared with background, correlationquantification is easy. If these defects are visible inthe two studied mappings, the maximum of the cor-relation function is high and, of course, the position ofthis maximum provides information about an even-tual shift in mappings. This maximum is generallysituated at or near �0, 0� because the position of thesample is relatively precise. The height of this max-


imum is a classical correlation coefficient CORF,G orCOR given as

CORF, G � maxi0, j0�CorF, G�i, j�� .

When mappings are characterized by many defects orsmooth signal variations, the correlation function canhave several local maximums and its values far fromthese maximums are not negligible. The height ofthe main maximum is not necessarily significant toevaluate correlation. Furthermore, the position ofmaximums of the correlation function �i0, j0� is some-times far from �0, 0�. Such shifts in mappings �i0 orj0 3� are not realistic in our experimental conditions�taking into account the accuracy of the positioning ofthe sample�. For these reasons we used another cor-relation coefficient, the peak-to-correlation energy�PCE� to take into account the relative importance ofenergy at the peak and total energy. PCEF, G isgiven as

PCEF, G �maxi0, j0��CorF, G�i, j��2�

�i�

j��

k�

lF�k, l �G�k � i, l � j��2 .

To obtain a correlation coefficient that varies between0 and 1, we define a normalized PCE given as

PCE �

max��CorF, G�i, j��2�

�i�

j��

k�

lF�k, l �G�k � i, l � j��2

max��CorF, F�i, j��2�

�i�

j��

k�

lF�k, l � F�k � i, l � j��2

.

We have used this expression as the correlation co-efficient for the results presented in this paper. In-deed it is more selective than the COR. We havecompared the COR and the PCE in different experi-mental cases: for two successive absorption �or scat-tering� mappings performed in the same conditions,for paired absorption and scattering mappings, fortwo absorption �or scattering� noise mappings, andalso for two random matrices created by a computer.In the case of high correlation, the values of both CORand PCE are high and the value of PCE can be higheror lower than that of COR, depending on the shape ofthe correlation function. For example, for two ab-sorption mappings performed successively withoutany change on a fused-silica substrate, we obtained a99% COR and a 95% PCE. These values allow us toquantify the repeatability of mappings. For low cor-relation, especially for successive absorption noisemappings �16% COR and 4% PCE� and for two ran-dom matrices created by computer �6% COR, 0.3%PCE at �i0 0, j0 0� and 14% COR, 4.5% PCE at�i0 10, j0 2��, the PCE is significantly lower thanthe COR. Accordingly we used the PCE to quantifycorrelation between mappings. A value lower than

5% for the PCE means that there is no correlation.Nevertheless both the PCE and the COR can be usedin this study and both lead to the same conclusions.

4. Results and Discussion

With regard to multiwavelength mappings of defects,we first studied substrates and thin films at wave-lengths of 514 nm and 1.06 �m.30 The pump-beamlasers were installed in the same experimental setup,and we compared the absorption and scattering map-pings. An example of results for a fused-silica sub-strate was given in the abstract of a presentationgiven at the Optical Interference Coatings TopicalMeeting in Banff.31 These previous studies haveshown that no correlation exists between absorptionmappings at these wavelengths. Generally correla-tion between scattering mappings in the visible andIR ranges is low, however it is better than correlationbetween absorption mappings. The following re-sults concern comparisons of absorption and scatter-ing defects at wavelengths of 351, 363, and 514 nmand 1.06 �m.

A. Bare Substrates

In Fig. 2 we show an example of two-wavelengthmappings performed on a fused-silica substrate �Su-prasil�. Absorbing as well as scattering defects ob-served in these mappings are localized on or near thefront surface of the substrate. The wavelengths are363 nm in �a� and 514 nm in �b�. The experimentalconditions are a pump-beam diameter of 25 �m witha �30° incident angle and s polarization�; a samplingstep of 25 �m; and a mapped area of 500 �m � 500�m with 21 � 21 points. Absorption and scatteringmappings are shown as both a top view and a per-spective. The mean value and standard deviationare listed in Table 1 for each mapping, with differentcorrelation coefficient values. The mean absorptionvalue increases at shorter wavelengths: 10 ppm �1ppm 10�6� at 363 nm and 0.6 ppm at 514 nm.This is not surprising because the wavelength iscloser to the intrinsic UV absorption edge. Thereare also more defects in the UV absorption mappings.In contrast, scattering is somewhat lower at shorterwavelengths �0.6 ppm at 363 nm and 1.6 ppm at 1064nm�. We observed a significant correlation betweenscattering mappings at different wavelengths: thecorrelation function has a maximum in �0, 2� and aPCE of 25.2% at this point. However the two ab-sorption mappings at 514 and 363 nm are not corre-lated; the correlation function is uniform and thePCE calculated at the maximum correlation of thetwo scattering mappings �0, 2� is 2.7%. We also notethat at both wavelengths the correlation between ab-sorption and scattering mappings is equal to zero�0.47% and 0.16%�.

B. Thin Films

Similar results have been obtained for thin films. InFig. 3 we show only top view mappings for a HfO2 film�sample 1� deposited on a Herasil 1 fused-silica sub-strate by electron-beam evaporation. Similar com-


Table 1. Absorption, Scattering and Correlation Values from Fig. 2 for a Fused-Silica Bare Substrate

ParameterMeasurement

at 363 nm PCE �%�Measurement

at 514 nm

Absorption �ppm� Amean 10 N Amean 0.6� 5 2.7 calculated in �0, 2� � 0.5

PCE �%� ) 0.47 ) 0.16Scattering �ppm� Smean 0.6 N Smean 1.6

� 0.5 25.2 max in �0, 2� � 2.6

Fig. 2. Absorption and scattering mappings at wavelengths of 363 514 nm on a fused-silica substrate. Both the top view and theperspective are given for each wavelength in this example. The experimental conditions are a 25-�m pump-beam diameter with anincident angle of 30° and s polarization, a 25-�m sampling step, and a mapped area of 500 �m � 500 �m �21 � 21 points�.

Fig. 3. Absorption and scattering mappings at wavelengths of363 and 514 nm for a HfO2 film deposited by electron-beam evap-oration on a fused-silica substrate. The experimental conditionsare the same as in Fig. 2. A gray-level scale is given for eachmapping.

Fig. 4. Absorption and scattering mappings at wavelengths of363 and 514 nm for MgF2 deposited by electron-beam evaporationon a fused-silica substrate. The experimental conditions are thesame as in Fig. 2.


ments can be made about the associated absorption,scattering, and PCE values listed in Table 2. In thiscase, mean values of both absorption and scatteringincrease at shorter wavelengths. We observed goodcorrelation between scattering mappings at the dif-ferent wavelengths: the correlation function has amaximum at �3, 0� and the PCE at this point is 98.2%.In contrast, the correlation function of A mappings atthe two wavelengths has no well-defined maximum;the PCE, calculated at the maximum of scatteringcorrelation function �3, 0�, is 0.58%. With regard tothe correlation between absorption and scattering atthe same wavelength, it is negligible at 363 nm �PCEof 1.3%�. It is somewhat higher at 514 nm �PCE of6.6%�.

The following example �Fig. 4� is a film of MgF2deposited by electron-beam evaporation at low sub-strate temperature �30 °C� on a Herasil 1 fused-silicasubstrate. The related absorption, scattering, andPCE values are listed in Table 3. If we consider onlythese mappings we can make similar comments.

The mean absorption value is higher at 363 nm thanat 514 nm whereas the mean scattering is the same atthe two wavelengths �approximately 1 ppm�. Corre-lation between scattering mappings at 363 and 514nm find a maximum in �0, 0� but the PCE is some-what low, only 14.5%. Furthermore, correlation be-tween absorption at 363 and 514 nm is againnegligible; the PCE is 0.12% at �0, 0�. On top of that,correlation between absorption and scattering at thesame wavelength is negligible at both 363 and 514nm �the PCE is approximately 0.1%�. Neverthelessthe behavior of this sample is different, and we ob-served a photoinduced effect during scanning at 363nm. Absorption decreases during UV irradiationand the kinetics of this evolution is quick at least atthe beginning of irradiation �only a few tens of sec-onds are necessary to divide absorption by five�. Theirradiance of the sample was approximately 1 kW�cm2 and the absorptance is 10�4 at maximum. Thusthe total absorbed power is approximately 100 mW�cm2, and we cannot justify this decrease of absorption

Table 2. Absorption, Scattering, and Correlation Values from Fig. 3 for HfO2 Film Sample 1



at 514 nm

Absorption �ppm� Amean 21.4 N Amean 1.6� 11.2 0.58 calculated in �3, 0� � 0.7

PCE �%� ) 1.3 ) 6.6Scattering �ppm� Smean 5.5 N Smean 2.6

� 1.5 98.2 max in �3, 0� � 2.4

Table 3. Absorption, Scattering, and Correlation Values from Fig. 4 for MgF2 Film



at 514 nm

Absorption �ppm� Amean 46 N Amean 11.9� 17 0.12 calculated in �0, 0� � 1.6

PCE �%� ) 0.14 ) 0.1Scattering �ppm� Smean 1 N Smean 0.8

� 0.1 14.5 max in �0, 0� � 0.2

Fig. 5. Absorption and scattering mappings at 514-nm wavelength centered on the same point as the mappings in Fig. 4, but the mappedfield is now 750 �m � 750 �m �31 � 31 points�. Other experimental conditions are the same as in Fig. 4. With absorption mapping wecan observe the imprint of UV scanning.


by a thermal effect. We have already observed sucha photoinduced decrease of absorption in TiO2 andTa2O5 films deposited by electron-beam evaporationand for irradiation in the visible range �600 nm�.32,33

This photoinduced decrease was only partially re-versible when irradiation was stopped and was at-tributed to electronic transitions in low-density thinfilms. A similar effect is possible for this MgF2 filmbecause of the low substrate temperature during dep-osition. We note that for this MgF2 film the decreasein absorption during UV irradiation is not limited tothe UV range and can also be observed at 514 nm.In Fig. 5 we show a larger mapping of absorption andscattering centered on the same point as the map-pings in Fig. 4. In this absorption mapping at 514nm we observe the square imprint of the UV scan-ning. This imprint is not apparent in scatteringmappings. This kind of photoinduced effect compli-cates the interpretation of correlation between map-pings. It would be interesting to test suchinstability under UV irradiation for MgF2 films pre-pared at higher substrate temperatures.

Table 4. Absorption, Scattering, and Correlation Values from Fig. 6 for Sc2O3 Film



at 514 nm

Absorption �ppm� Amean 129 N Amean 22� 189 90.8 max in �0, 0� � 34

PCE �%� ) 0.41 ) 0.57Scattering �ppm� Smean 188 N Smean 198

� 43 21.2 max in �1, �2� � 1070.007 calculated in �0, 0�

Fig. 6. Rare case of correlation between absorption mappings.Absorption and scattering mappings at wavelengths of 363 and514 nm for a Sc2O3 film deposited by electron-beam evaporation ona fused-silica substrate. The experimental conditions are thesame as in Fig. 2.

Fig. 7. Absorption and scattering mappings at wavelengths of 363, 514, and 1.06 �m for a HfO2 film deposited by electron-beamevaporation on a fused-silica substrate. The experimental conditions are the same as in Fig. 2 for the UV and visible ranges. For � 1064 nm, the pump beam is focused at normal incidence on the sample surface.


In some rare cases it is possible to observe corre-lation between absorption mappings at differentwavelengths. In Fig. 6 we show the example of aSc2O3 film deposited on a fused-silica substrate.The related absorption, scattering, and PCE valuesare listed in Table 4. This sample had a high level ofsurface contamination because of multiple handlingand measurements. For this reason, the mean val-ues of absorption and scattering are high. We didobserve that the correlation between absorption map-pings at 363 and 514 nm has a maximum in �0, 0�with a PCE of 90.8%. Similarly correlation betweenabsorption mappings at 363 and 351 nm is very high�94.4%� �this last mapping is not given here becauseit is similar to the 363-nm mapping�. In contrast, inthe case of scattering, correlation at different wave-lengths is not so high. Correlation between scatter-ing mappings at 351 and 363 nm is rather good �PCEof 78.3%� but correlation between scattering map-pings at 363 and 514 nm is low the PCE is only 21.2%and the correlation maximum was found in �1, �2�.

A final example allows us to compare mappings atwavelengths of 363, 514, and 1064 nm. These map-pings are shown in Fig. 7 and the related absorption,scattering, and PCE values are listed in Table 5.For mappings at 363 and 514 nm, we again had thesame results: a good correlation between scatteringmappings but no correlation between absorptionmappings. Even when the mappings at 1064 nmwere not performed with the same experimentalsetup and under the same conditions �normal inci-dence for 1064 nm and incident angle of 30°, s polar-ization for 363 and 514 nm� we obtained a goodcorrelation between scattering mappings �PCE of86.2% between 514 and 1064 nm� and no correlationbetween absorption mappings �PCE of 0.3% between514 and 1064 nm�.

5. Conclusion

We have studied the spectral properties of absorbingand scattering defects in thin films and on substratesurfaces. For this kind of study a precise positioningof the pump beam on the sample surface is necessary.To compare mappings at different wavelengths weperformed correlation calculations. Similar resultswere obtained for thin films and substrates. Themean absorption value generally increased when thewavelength decreased. Absorption mappings at363, 514, and 1064 nm are generally not correlated.In most cases, the correlation coefficient is less than5%, which is considered as the limit of correlation.

Our results show that damage studies and absorptionmeasurements must be made at the same wave-length. Some rare cases of correlation have beenobserved, but they are associated with the presence ofsurface contamination. With regard to correlationbetween scattering mappings at different wave-lengths, in most cases it is better than correlationbetween absorption mappings. In addition, wefound no correlation between absorption and scatter-ing mappings at the same wavelength.

We thank Herve Bercegol of the Commissariat al’Energie atomique, Centre d’Etudes Scientifiques etTechniques d’aquitaine, Laboratoire Endommage-ment Laser for the loan of the UV laser. We alsothank Mireille Guillaume of the Institut Fresnel inMarseille for helping us with the correlation study.

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Table 5. Absorption, Scattering, and Correlation Values from Fig. 7 for HfO2 Film Sample 2



at 514 nm PCE �%�Measurementat 1064 nm

Absorption �ppm� Amean 132 N Amean 102 N Amean 6� 43 0.08 calculated in �1, 2� � 33 0.3 calculated in �0, 0� � 8

PCE �%� ) 0.04 ) 0.4 ) 2.1Scattering �ppm� Smean 11.5 N Smean 17 N Smean 5.6

� 21 82.1 max in �1, 2� � 18 86.2 max in �0, 0� � 2


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multiwavelength imaging of defects in ultraviolet optical materials

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