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Citation Luuml Hai-Bing Xu Shi-Zhen Wang Hai-Jun Yuan Xiao-Dong Zhao Chao and Fu Yong Qing (2014) Evolution of Oxygen Deficiency Center on Fused Silica Surface Irradiated by Ultraviolet Laser and Posttreatment Advances in Condensed Matter Physics 2014 p 769059 ISSN 1687-8108

Published by Hindawi

URL httpdxdoiorg1011552014769059 lthttpdxdoiorg1011552014769059gt

This version was downloaded from Northumbria Research Link httpnrlnorthumbriaacuk21735

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Research ArticleEvolution of Oxygen Deficiency Center on Fused Silica SurfaceIrradiated by Ultraviolet Laser and Posttreatment

Hai-Bing Luuml12 Shi-Zhen Xu13 Hai-Jun Wang1 Xiao-Dong Yuan1

Chao Zhao2 and Y Q Fu2

1 Research Center of Laser Fusion China Academy of Engineering Physics (CAEP) PO Box 919-988-5 Mianyang 621900 China2Thin Film Centre Scottish Universities Physics Alliance (SUPA) University of the West of Scotland Paisley PA1 2BE UK3 School of Physical Electronics University of Electronic Science and Technology of China Chengdu Sichuan 610054 China

Correspondence should be addressed to Hai-Bing Lu haibinglv163com and Y Q Fu richardfuuwsacuk

Received 7 February 2014 Accepted 11 May 2014 Published 29 May 2014

Academic Editor Haiyan Xiao

Copyright copy 2014 Hai-Bing Lu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Evolution of oxygen deficiency centers (ODCs) on a fused silica surface irradiated using a 355 nm ultraviolet (UV) laser beamin both vacuum and atmospheric conditions was quantitatively studied using photoluminescence and X-ray photoelectronspectroscopy When the fusedsilica surface was exposed to the UV laser in vacuum the laser damage threshold was decreasedwhereas the concentration of the ODCs was increased For the fuse silica operated under the high power lasers creation of ODCson their surface resulted from the UV laser irradiation and this is more severe in a high vacuum The laser fluence andor laserintensity have significant effects on the increase of the ODCs concentrationTheODCs can be effectively repaired using postoxygenplasma treatment andUV laser irradiation in an excessive oxygen environment Results also demonstrated that the ldquogainrdquo and ldquolossrdquoof oxygen at the silica surface is a reversible and dynamic process

1 Introduction

Silica optics operated in vacuumgenerally show a poor stabil-ity when they are exposed to high-power laser systems Somecommon damage of the silica optics includes (a) thermaldamage when operated using the fundamental harmonic(1120596) laser and (b) photoionization when operated using thethird harmonic (3120596) laser It is generally accepted that thesilica optics can be safely performed below their damagethresholds However surface damage easily occurs when theoptics are operated in vacuum and their damage thresholdsare even lower than those measured at an atmospheric con-ditionThe phenomenon is correlated with oxygen deficiencyand has been widely investigated to elucidate the damagemechanisms [1ndash6]

Some luminescent defects in the fused silica are wellknown for example the oxygen deficiency centers (ODCs)nonbridging oxygen hole centers (NBOHCs) the peroxyradicals (PORs) and the singlet oxygen transition associatedwith interstitial neutral molecular oxygen (O

2) with their

emission bands at 27 eV (454 nm) 19 eV (650 nm) 22 eVand 12 eV respectively [4ndash9]

A few researchers [10 11] experimentally observed degra-dation in performance of the silica optics and found theoxygen deficiency centers (ODCs) on the surface of the silicaoptics using photoluminescence (PL) analysis However theydid not provide the explanation of the detailed formationmechanisms of the ODCs in the fused silica optics So farevolution of the ODCs on the surface of the fused silicairradiated by UV laser has been rarely reported

To reduce the ODCs on the surface of the fused silicahigh temperature annealing of the fused silica for severalhours in oxygen atmosphere has generally been used [1213] Ion beam etching has also been used to remove thesurface layer rich in defects in order to restore the damagethreshold of the fused silica [6] As an important componentfor high-power laser systems the fused silica requires a highquality surface finish thus the heat treatmentmethod at hightemperature is obviously not preferred In this paper twomethods have been applied to decrease the concentration of

Hindawi Publishing CorporationAdvances in Condensed Matter PhysicsVolume 2014 Article ID 769059 4 pageshttpdxdoiorg1011552014769059

2 Advances in Condensed Matter Physics

Nd-YAG laser

Energy meterLens

Collimation laserVacuum chamber

SampleUV laser

CCDBeam splitter

Figure 1 Arrangement of experimental system

ODCs (1) plasma treatment with low temperature oxygenplasma and (2) irradiation using a pulse UV laser in a pureoxygen atmosphere

2 Experimental

The experimental system is schematically shown in Figure 1Laser irradiation experiments were conducted using an Nd-YAG laser beamwith a frequency of 355 nmThe full width athalf maximum (FWHM) of the laser pulse was 75 ns and thelaser repetition rate was 10Hz

The fluence of the laser beam was adjusted by changingthe distance from sample surface to lens Experimental sam-ples of the fused silica (Schott Company) had a diameter of35mm and a thickness of 5mm A laser beamwas introducedinto the chamber with a based vacuum of about 10minus3 Paachieved using a turbo pump and a mechanical roughingpump The surface damage was monitored in situ using aCCD camera mounted on the chamber window Duringlaser irradiation the fluence duration time or laser dosewas changed Some samples preexposed with laser beam invacuum chamber were reirradiated using pulsed UV laseratmospheric conditions to clarify evolution processes of theODCs

The point defects of the ODCs induced by the UVlaser preirradiation in the fused silica were characterizedby measuring the photoluminescence (PL) spectra usinga fluorescent spectrometer (F900 Edinburgh InstrumentsLtd) The PL intensity is corresponding to the concentrationof theODCs Spectra of the Si 2p O 1s andC 1s were obtainedusingX-ray photoelectron spectroscopy (XPS ESCALAB250system)TheX-ray sourcewas amonochromaticMgK

120572beam

with an energy of 12536 eV The Si O ratios on the surfacesof the silica optics under different irradiation conditions wereobtained from analysis of the XPS spectra

Two methods have been proposed in this study to repairpreirradiated ODCs (1) low temperature oxygen plasmatreatment and (2) pulsed UV laser treatment During plasmatreatment the chamber pressure was kept constant at 20 Paand preformed using a Harrick plasma (PDC-001 10W) UVlaser treatment was conducted in atmospheric condition

3 Results and Discussion

31 Effect of Laser Fluence Figure 2 shows the emissionbands of typical PL spectra which are centered at 27 eV(about 452 nm) excited using a laser wavelength of 292 nmA peak centered at sim452 nm is assigned to the ODCs After

400 450 500 550

101

102

103

104

105

PL in

tens

ity (c

ount

s)

Wavelength (nm)

Original2 Jcm2 irradiated4 Jcm2 irradiated

Figure 2 PL intensityof fused silica irradiated with different laserfluences and 30 laser pulses

irradiation using UV laser at the fluences of 2 Jcm2 and4 Jcm2 with 30 pulses the PL peak intensity of theODCswasincreased from 178 to 191 and 311 (times104 counts) respectivelyTheODCsrsquo concentration has been increased after pulsedUVlaser irradiation in the vacuum [4 5] Moreover the O Siratios on the surface of the fused silica obtained from the XPSanalysis decreased after the laser irradiation The O Si ratioof the unirradiated (ie original fused silica sample) 2 Jcm2and 4 Jcm2 irradiated samples with 30 laser pulses obtainedfrom XPS analysis is 151 134 and 132 respectively

After the specimens were long-term (gt20 hrs) irradiatedusing a continuous wave (CW) laser with a wavelength of355 nm and a power of 75mW in vacuum there is littleincrease of the PL peak intensity of the ODCs as shown inFigure 3 Clearly the CW-UV laser irradiation in vacuum haslittle effect on concentration of the ODCs on surface of thefused silica

The ODCs and peroxy radicals (PORs) are the primarydefects on the surface of the fused silica after laser irradiationThe Frenkel-type mechanism has been used to explain thiseffect using the following [14 15]

equivSindashOndashSiequiv 997888rarr equivSindashSiequiv + O2 interstitial

(PORs and O2)

(1)

Advances in Condensed Matter Physics 3

Table 1 Effects of ODCs reduction on silica surface using two treatment methods

Treatment method Original After UV irradiationin vacuum

Repaired with pulse UVlaser in excessive oxygen

Repaired with oxygenplasma

PL peak intensityof ODCscount 455 times 10

4

625 times 104 351 times 104 351 times 104

0 500 1000 1500 2000 2500 3000

1

2

3

4

5

6

7

8

9

10

PL intensity

Pulse number

140

142

144

146

148

150

152

154

156

158

160

PL in

tens

ity (times

104

coun

ts)

Ratio (O Si)

Ratio

(O S

i)

Figure 3 PL intensity and ratio (O Si) of the silica optic samples as afunction of pulse number (with a laser beam intensity of 31 Jcm2)

The generated interstitial O2gas may escape from the

sample surface resulting in oxygen vacancy and substoi-chiometric silica Compared with laser irradiation in theatmospheric condition the reactions (ie (1)) easily occur invacuumAfter the interstitial O

2was escaped from the sample

surface a substoichiometric SiO2 that is SiOx (0 lt 119909 lt

2) would form which showed higher absorption levels andaccounted for the continued degradation of the silica optics[4]

32 Effect of Laser Pulse Number Figure 3 shows the effectof laser pulse number on the PL peak intensity of theODCs With the increase of pulse range from 1 to 1000 thePL intensity increased with the laser doses However theconcentrations of the ODCs did not increase further whenthe number of laser pulses was above 1000 The O Si ratiowas obtained from the XPS data [4 5] and the O Si ratiodecreases with increase of the laser irradiation doses It showsthat the formation rate of the ODCs (or the reaction shownin (1)) decreases due to the increase of the generated defectsand laser irradiation

33 Reduction of ODCs Figure 4 shows the changes of thePL peaks after laser irradiation in vacuum (red shift) andafter plasma treatment respectively compared with thoseof the original sample Table 1 summarizes the results ofreduction of the ODCs using the two methods From Table 1and Figure 4 the PL intensity decreases after the plasmatreatment indicating that the concentration of the ODCs has

400 450 500 550

102

103

104

105

PL in

tens

ity (c

ount

s)

Wavelength (nm)

OriginalBefore plasma repairAfter plasma repair

440 445 450 455

2

4

6

times104

Figure 4 PL spectra of fused silica preirradiated in vacuum beforeand after oxygen plasma treatment

been recovered Clearly both the methods can be successfullyused to repair the defects of the generation of ODCs

For high quality SiO119909thin films a PL peak was reported

to have red shifts with decreasing oxygen concentration [16]andor increasing the annealing temperature [17] Such a redshift was also observed in this study using the silica whenits surface was exposed to nondamaging UV laser fluences ina vacuum environment (as shown in Figures 2 and 4) Theclose relationship between the luminescence signals and lossof oxygen on the surface of the silica can be evidenced fromthe observed back shift of the PL peak when the sample wasilluminated by pulsed or CW-UV laser [18] in the presence ofoxygen

Above results showed that the ldquogainrdquo and ldquolossrdquo of oxygenelements on the silica surface is a reversible and dynamicprocess which could reach a dynamic balance under a givenlaser irradiation condition Oxygen plasma treatment andpulsed UV laser irradiation can decrease the ODCs and otherdefects to recover the performance of the fused silica Usingthese methods the lifetime of the fused silica optics used inhigh-powerUV laser system can be prolongedwhen operatedin an oxygen atmosphere

4 Conclusion

For the fuse silica operated under the high-power laserscreation of ODCs on their surface resulted from the UV laser


irradiation and this is more severe in a high vacuum Thelaser fluence andor laser intensity have significant effects onthe increase of the ODCs concentration The ODCs can beeffectively repaired using postoxygen plasma treatment andUV laser irradiation in an excessive oxygen environmentResults also demonstrated that the ldquogainrdquo and ldquolossrdquo of oxygenat the silica surface is a reversible and dynamic process

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

Financial support from Carnegie Trust Funding RoyalSociety of Edinburgh and Royal Academy of Engineering-Research Exchange with China and India was acknowl-edged This work is also supported by the FundamentalResearch Funds for theCentralUniversities China (Grant noZYGX2012J057)

References

[1] G Pacchioni L Skuja and D L Griscom Eds Defects inSiO2and Related Dielectrics Science and Technology Kluwer

Academic Publishers Norwell Mass USA 2000[2] R A B Devine J P Duraud and E Dooryhee Eds Structure

and Imperfections in Amorphous and Crystalline SiliconDioxideJohn Wiley amp Sons Chichester UK 2000

[3] H S Nalwa Ed Silicon-BasedMaterials andDevices AcademicPress San Diego Calif USA 2001

[4] S-Z Xu H-B Lv X-D Yuan et al ldquoEffects of vacuum on fusedsilicaUVdamagerdquoChinese Physics Letters vol 25 no 1 pp 223ndash226 2008

[5] S Xu X Zu X Jiang et al ldquoThe damage mechanisms offused silica irradiated by 355 nm laser in vacuumrdquo NuclearInstruments and Methods in Physics Research B vol 266 no 12-13 pp 2936ndash2940 2008

[6] S Xu W Zheng X Yuan H Lv and X Zu ldquoRecovery of fusedsilica surface damage resistance by ion beam etchingrdquo NuclearInstruments and Methods in Physics Research B vol 266 no 15pp 3370ndash3374 2008

[7] J Fournier J Neauport P Grua et al ldquoLuminescence studyof defects in silica glasses under near-UV excitationrdquo PhysicsProcedia vol 8 pp 39ndash43 2010

[8] R Salh ldquoDefect related luminescence in silicon dioxide net-work a reviewrdquo in Crystalline SiliconmdashProperties and UsesInTech 2011

[9] A F Zatsepin E A Buntov V A Pustovarov and H-J FittingldquoPhotoluminescence of Se-related oxygen deficient center inion-implanted silica filmsrdquo Journal of Luminescence vol 143 pp498ndash502 2013

[10] T M Stephen B van Zyl and R C Amme ldquoDegradation ofvacuum-exposed SiO

2laser windowsrdquo in 24th Annual Boulder

Damage Symposium ProceedingsmdashLaser-Induced Damage inOptical Materials vol 1848 of Proceedings of SPIE pp 106ndash1091992

[11] A N Trukhin K M Golant Y Maksimov M Kink andR Kink ldquoRecombination luminescence of oxygen-deficient

centers in silicardquo Journal of Non-Crystalline Solids vol 354 no2-9 pp 244ndash248 2008

[12] N Shen M J Matthews S Elhadj P E Miller A J Nelsonand J Hamilton ldquoCorrelating optical damage threshold withintrinsic defect populations in fused silica as a function of heattreatment temperaturerdquo Journal of Physics D Applied Physicsvol 46 no 16 Article ID 165305 2013


[14] T E Tsai and D L Griscom ldquoExperimental evidence forexcitonic mechanism of defect generation in high-purity silicardquoPhysical Review Letters vol 67 no 18 pp 2517ndash2520 1991

[15] H Hosono H Kawazoe and N Matsunami ldquoExperimentalevidence for frenkel defect formation in amorphous SiO

2by

electronic excitationrdquo Physical Review Letters vol 80 no 2 pp317ndash320 1998

[16] T Mohanty N C Mishra S V Bhat P K Basu and D KanjilalldquoDense electronic excitation induced defects in fused silicardquoJournal of Physics D vol 36 no 24 pp 3151ndash3155 2003

[17] S Hayashi T Nagareda Y Kanzawa and K Yamamoto ldquoPho-toluminescence of Si-rich SiO

2films Si clusters as luminescent

centersrdquo Japanese Journal of Applied Physics vol 32 no 9 pp3840ndash3845 1993

[18] S G Demos A Burnham PWegner et al ldquoSurface defect gen-eration in optical materials under high fluence laser irradiationin vacuumrdquo Electronics Letters vol 36 no 6 pp 566ndash567 2000

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Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

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FluidsJournal of

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Advances in Condensed Matter Physics

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Advances in

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International Journal of


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Statistical MechanicsInternational Journal of


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Solid State PhysicsJournal of

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Soft MatterJournal of

Hindawi Publishing Corporationhttpwwwhindawicom

AerodynamicsJournal of

Volume 2014


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ThermodynamicsJournal of

Research ArticleEvolution of Oxygen Deficiency Center on Fused Silica SurfaceIrradiated by Ultraviolet Laser and Posttreatment

Hai-Bing Luuml12 Shi-Zhen Xu13 Hai-Jun Wang1 Xiao-Dong Yuan1

Chao Zhao2 and Y Q Fu2

1 Research Center of Laser Fusion China Academy of Engineering Physics (CAEP) PO Box 919-988-5 Mianyang 621900 China2Thin Film Centre Scottish Universities Physics Alliance (SUPA) University of the West of Scotland Paisley PA1 2BE UK3 School of Physical Electronics University of Electronic Science and Technology of China Chengdu Sichuan 610054 China

Correspondence should be addressed to Hai-Bing Lu haibinglv163com and Y Q Fu richardfuuwsacuk

Received 7 February 2014 Accepted 11 May 2014 Published 29 May 2014

Academic Editor Haiyan Xiao

Copyright copy 2014 Hai-Bing Lu et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Evolution of oxygen deficiency centers (ODCs) on a fused silica surface irradiated using a 355 nm ultraviolet (UV) laser beamin both vacuum and atmospheric conditions was quantitatively studied using photoluminescence and X-ray photoelectronspectroscopy When the fusedsilica surface was exposed to the UV laser in vacuum the laser damage threshold was decreasedwhereas the concentration of the ODCs was increased For the fuse silica operated under the high power lasers creation of ODCson their surface resulted from the UV laser irradiation and this is more severe in a high vacuum The laser fluence andor laserintensity have significant effects on the increase of the ODCs concentrationTheODCs can be effectively repaired using postoxygenplasma treatment andUV laser irradiation in an excessive oxygen environment Results also demonstrated that the ldquogainrdquo and ldquolossrdquoof oxygen at the silica surface is a reversible and dynamic process

1 Introduction

Silica optics operated in vacuumgenerally show a poor stabil-ity when they are exposed to high-power laser systems Somecommon damage of the silica optics includes (a) thermaldamage when operated using the fundamental harmonic(1120596) laser and (b) photoionization when operated using thethird harmonic (3120596) laser It is generally accepted that thesilica optics can be safely performed below their damagethresholds However surface damage easily occurs when theoptics are operated in vacuum and their damage thresholdsare even lower than those measured at an atmospheric con-ditionThe phenomenon is correlated with oxygen deficiencyand has been widely investigated to elucidate the damagemechanisms [1ndash6]

Some luminescent defects in the fused silica are wellknown for example the oxygen deficiency centers (ODCs)nonbridging oxygen hole centers (NBOHCs) the peroxyradicals (PORs) and the singlet oxygen transition associatedwith interstitial neutral molecular oxygen (O

2) with their

emission bands at 27 eV (454 nm) 19 eV (650 nm) 22 eVand 12 eV respectively [4ndash9]

A few researchers [10 11] experimentally observed degra-dation in performance of the silica optics and found theoxygen deficiency centers (ODCs) on the surface of the silicaoptics using photoluminescence (PL) analysis However theydid not provide the explanation of the detailed formationmechanisms of the ODCs in the fused silica optics So farevolution of the ODCs on the surface of the fused silicairradiated by UV laser has been rarely reported

To reduce the ODCs on the surface of the fused silicahigh temperature annealing of the fused silica for severalhours in oxygen atmosphere has generally been used [1213] Ion beam etching has also been used to remove thesurface layer rich in defects in order to restore the damagethreshold of the fused silica [6] As an important componentfor high-power laser systems the fused silica requires a highquality surface finish thus the heat treatmentmethod at hightemperature is obviously not preferred In this paper twomethods have been applied to decrease the concentration of

Hindawi Publishing CorporationAdvances in Condensed Matter PhysicsVolume 2014 Article ID 769059 4 pageshttpdxdoiorg1011552014769059


Nd-YAG laser

Energy meterLens


SampleUV laser

CCDBeam splitter



2 Experimental




120572beam





400 450 500 550

101

102

103

104

105

PL in

tens

ity (c

ount

s)

Wavelength (nm)







(PORs and O2)

(1)







4


0 500 1000 1500 2000 2500 3000

1

2

3

4

5

6

7

8

9

10

PL intensity

Pulse number

140

142

144

146

148

150

152

154

156

158

160

PL in

tens

ity (times

104

coun

ts)

Ratio (O Si)

Ratio

(O S

i)









400 450 500 550

102

103

104

105

PL in

tens

ity (c

ount

s)

Wavelength (nm)


440 445 450 455

2

4

6

times104






4 Conclusion






Acknowledgments


References




















2by












FluidsJournal of


Journal of







Advances in

Astronomy



Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




Nd-YAG laser

Energy meterLens


SampleUV laser

CCDBeam splitter



2 Experimental




120572beam





400 450 500 550

101

102

103

104

105

PL in

tens

ity (c

ount

s)

Wavelength (nm)







(PORs and O2)

(1)







4


0 500 1000 1500 2000 2500 3000

1

2

3

4

5

6

7

8

9

10

PL intensity

Pulse number

140

142

144

146

148

150

152

154

156

158

160

PL in

tens

ity (times

104

coun

ts)

Ratio (O Si)

Ratio

(O S

i)









400 450 500 550

102

103

104

105

PL in

tens

ity (c

ount

s)

Wavelength (nm)


440 445 450 455

2

4

6

times104






4 Conclusion






Acknowledgments


References




















2by












FluidsJournal of


Journal of







Advances in

Astronomy



Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics









4


0 500 1000 1500 2000 2500 3000

1

2

3

4

5

6

7

8

9

10

PL intensity

Pulse number

140

142

144

146

148

150

152

154

156

158

160

PL in

tens

ity (times

104

coun

ts)

Ratio (O Si)

Ratio

(O S

i)









400 450 500 550

102

103

104

105

PL in

tens

ity (c

ount

s)

Wavelength (nm)


440 445 450 455

2

4

6

times104






4 Conclusion






Acknowledgments


References




















2by












FluidsJournal of


Journal of







Advances in

Astronomy



Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics







Acknowledgments


References




















2by












FluidsJournal of


Journal of







Advances in

Astronomy



Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics








FluidsJournal of


Journal of







Advances in

Astronomy



Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



northumbria research linknrl.northumbria.ac.uk/21735/1/769059.pdf · northumbria research link...

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