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Simultaneous irradiation of laser and ion beams on optical materials
Nuclear Instruments and Methods in Physics Research B 210 (2003) 281–284 www.elsevier.com/locate/nimb
Simultaneous irradiation of laser and ion beams on optical materials F. Sato *, T. Tanaka, T. Kagawa, T. Iida Department of Electronic, Information Systems and Energy Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871, Japan
Abstract A simultaneous irradiation system of laser and ion beams has been developed to investigate ion beam induced luminescence and optical absorption of crystalline a-Al2 O3 samples. The luminescence induced by 30 keV Arþ in visible wavelength region had peaks that were attributed to oxygen vacancies. The optical absorption at 633 nm in wavelength was also measured during the ion irradiation. The amount of optical absorption for the irradiated sample with Qswitched Nd:YAG laser pulses was less than that without the laser pulses. The ion irradiation reduced the threshold level of laser damage on the surface region of the sample, and the laser ablation selectively happened on the ion irradiation region. Ó 2003 Elsevier B.V. All rights reserved. PACS: 78.60.H; 79.20.D; 42.88.+h; 41.75.A Keywords: Ionoluminescence; Laser ablation; Radiation effects
1. Introduction Data on radiation effects for optical materials is required for the design of the next fusion device [1]. In the optical spectroscopy such as laser interferometry and LIDAR Thomson scattering [2], the optical windows with hard vacuum seals are required to maintain vacuum integrity and to transmit the light spectrum from the core plasma to the spectrometers without distortion. The nuclear radiation induced luminescence and the optical absorption on the optical materials such
*
Corresponding author. Tel.: +81-6-6879-7909; fax: +81-66879-7363. E-mail address: [email protected] (F. Sato).
as Al2 O3 and SiO2 have been observed in high radiation dose environment [3,4]. However, there is no data on the optical material simultaneously irradiated by nuclear radiation and laser. The ion beam technique may be useful for the investigation of the nuclear radiation effects. The ion beam can be precisely controlled in time and space region. Thus, the simultaneous irradiation system of laser and ion beams has been developed for the study of damage on optical materials. A preliminary experiment of the ion beam induced luminescence and optical absorption for Al2 O3 samples was performed with the simultaneous irradiation system. This paper describes the arrangement of the developed irradiation system and some experimental results obtained with the system.
0168-583X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01033-4
282
F. Sato et al. / Nucl. Instr. and Meth. in Phys. Res. B 210 (2003) 281–284
2. Experimental The configuration of the simultaneous irradiation system of laser and ion beams is shown in Fig. 1. The irradiation system was set in one of the beam lines of a 200 keV ion accelerator [5]. The irradiation system consisted of a target vacuum chamber, deflectors, aperture collimators, a stigmator, an electrostatic lens, laser system and the related optical components. The samples were set in the target vacuum chamber. The Q-switched Nd:YAG laser system with a fourth harmonic generator (k ¼ 266 nm) and a diode laser for probe light (k ¼ 633 nm) were used in the experiment. The laser light was propagated into the target vacuum chamber with a F/100 parabolic mirror and a mirror with a center hole of 1mm in diameter. The laser intensity profile in the focal region was measured with a magnified image of the focal spot on a CCD camera. The measured focal spot size was 200 lm (FWHM of the intensity). The size of the ion beam was adjusted to be 200 lm/ with the aperture collimator and the electrostatic lens. The ion beam profile was measured with the knifeedge method. The positions of the laser and ion focal spots were adjusted by use of a plate with an aperture of 300 lm in diameter placed on the sample stage. The laser pulse intensity and the ion beam current were measured with a photodiode and a Faraday cup respectively. The ion beam induced luminescence was measured by a multi-channel photon spectrometer with an image intensifier (Hamamatsu Photonics,
PMA-10). The spectrometer was calibrated with a calibrated integrating sphere light source (Labsphere, USS-600) and a mercury lamp. The optical absorption measurement was performed with the diode laser during the ion irradiation. For the unirradiated region, an aluminum electrode was made on the surface of the sample by evaporation process. This made it possible to monitor the ion beam current flowing on the sample.
3. Results and discussion Crystalline a-Al2 O3 samples (SA-100, Kyocera Inc.) were irradiated with 30 keV Arþ , with a beam intensity of about 1 1013 ion/cm2 /s. The ion transport code TRIM estimated that the ion range was about 20 nm and the number of the displacement atoms was 500–1000 atoms/ion. Fig. 2 shows an ion beam induced luminescence spectrum for ion fluence of 1 1015 ion/cm2 . The spectrum had large luminescence peaks around 330 and 410 nm. The luminescence peaks around 330 and 410 nm are related to the excitation and relaxation of Fþ - and F-center, i.e. oxygen vacancies with one and two trapped electrons, respectively [6]. Similar luminescence peaks have also been observed with other radiations [7,8]. Fig. 3 shows changes of the intensity of the luminescence around 410 nm and the optical transmittance at 633 nm as a function of the ion fluence. The optical transmittance was measured with and without the Nd:YAG laser irradiation. The
Fig. 1. Configuration of simultaneous laser and ion irradiation system.
F. Sato et al. / Nucl. Instr. and Meth. in Phys. Res. B 210 (2003) 281–284
Fig. 2. Spectrum of photons emitted from Al2 O3 sample during 30 keV Arþ beam irradiation.
irradiation condition of the laser pulse was 10 mJ/ cm2 /10 ns at 10 Hz. The intensity of the luminescence degraded shortly after the start of the ion irradiation. The degradation is considered to be due to the optical absorption related to the highdensity defects formed in the sample. The increase in the loss of the optical transmittance of the sample started from the fluence of about 2 1016 ions/cm2 . However, the loss of the optical transmittance with the laser pulses stopped around 8 1016 ions/cm2 . For the sample with the laser irradiation, it is possible that the recovery of the defects and/or the laser ablation occurred in the irradiated region. Another Al2 O3 sample was irradiated up to the fluence of 1017 ions/cm2 . After the ion irradiation, the sample was irradiated with laser pulses of 10 mJ/cm2 /10 ns in the vacuum. The spot size of the
283
Fig. 3. Intensity of the luminescence around 410 nm and the optical transmittance at 633 nm as a function of the ion beam fluence.
ion beam irradiation was 200 lm in diameter, while the laser irradiation region was 8 mm in diameter. Fig. 4 shows surface images of the laserand ion-irradiated sample observed with an optical microscope. The layer irradiated with the ion beam might be peeled off owing to the laser irradiation. In addition, there was no significant damage in the region where ion beam did not impinge. The threshold level of the laser damage might be reduced owing to the high-density defects formed by ion beam irradiation and also the laser ablation might occur selectively in the ion-irradiated region. Further detailed experiments and discussions are needed for the explanation of the damage mechanism for the simultaneous irradiation of the laser and ion beams on optical materials.
Fig. 4. Surface images of the laser- and ion-irradiated Al2 O3 sample observed with optical microscope.
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F. Sato et al. / Nucl. Instr. and Meth. in Phys. Res. B 210 (2003) 281–284
4. Conclusions
References
The simultaneous irradiation system of laser and ion beams has been developed and the preliminary irradiation experiment on the Al2 O3 sample was carried out. The ion beam induced luminescence of the Al2 O3 samples had some peaks, which were due to F centers. The loss of optical transmittance with the Nd:YAG laser irradiation was less than that without the laser. The simultaneous laser and ion irradiation technique might be useful for the study of the irradiation effects and for the micro processing of optical materials.
[1] T. Nishitani et al., Fusion Eng. Des. 56–57 (2001) 905. [2] C.I. Walker et al., Proc. of the 19th Symposium on Fusion Technology, 849 (1996). [3] T. Tanabe, A. Omori, M. Fujiwara, J. Nucl. Mater. 258–263 (1998) 1914. [4] R.J. Brooks, D.E. Hole, P.D. Townsend, Nucl. Instr. and Meth. B 190 (2002) 136. [5] T. Iida, F. Sato, T. Tanaka, M. Naito, in: Proc. 8th Int. Conf. on Nuclear Microprobe Technology and Applications, P1-05, 2002. [6] T. Tanabe, S. Tanaka, K. Yamaguchi, N. Otsuki, T. Iida, M. Yamawaki, J. Nucl. Mater. 212–215 (1994) 1050. [7] A. Morono, E.R. Hodgson, J. Nucl. Mater. 224 (1995) 216. [8] F. Sato, T. Iida, Y. Oyama, F. Maekawa, Y. Ikeda, J. Nucl. Mater. 258–263 (1998) 1897.
Simultaneous irradiation of laser and ion beams on optical materials F. Sato *, T. Tanaka, T. Kagawa, T. Iida Department of Electronic, Information Systems and Energy Engineering, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita-shi, Osaka 565-0871, Japan
Abstract A simultaneous irradiation system of laser and ion beams has been developed to investigate ion beam induced luminescence and optical absorption of crystalline a-Al2 O3 samples. The luminescence induced by 30 keV Arþ in visible wavelength region had peaks that were attributed to oxygen vacancies. The optical absorption at 633 nm in wavelength was also measured during the ion irradiation. The amount of optical absorption for the irradiated sample with Qswitched Nd:YAG laser pulses was less than that without the laser pulses. The ion irradiation reduced the threshold level of laser damage on the surface region of the sample, and the laser ablation selectively happened on the ion irradiation region. Ó 2003 Elsevier B.V. All rights reserved. PACS: 78.60.H; 79.20.D; 42.88.+h; 41.75.A Keywords: Ionoluminescence; Laser ablation; Radiation effects
1. Introduction Data on radiation effects for optical materials is required for the design of the next fusion device [1]. In the optical spectroscopy such as laser interferometry and LIDAR Thomson scattering [2], the optical windows with hard vacuum seals are required to maintain vacuum integrity and to transmit the light spectrum from the core plasma to the spectrometers without distortion. The nuclear radiation induced luminescence and the optical absorption on the optical materials such
*
Corresponding author. Tel.: +81-6-6879-7909; fax: +81-66879-7363. E-mail address: [email protected] (F. Sato).
as Al2 O3 and SiO2 have been observed in high radiation dose environment [3,4]. However, there is no data on the optical material simultaneously irradiated by nuclear radiation and laser. The ion beam technique may be useful for the investigation of the nuclear radiation effects. The ion beam can be precisely controlled in time and space region. Thus, the simultaneous irradiation system of laser and ion beams has been developed for the study of damage on optical materials. A preliminary experiment of the ion beam induced luminescence and optical absorption for Al2 O3 samples was performed with the simultaneous irradiation system. This paper describes the arrangement of the developed irradiation system and some experimental results obtained with the system.
0168-583X/$ - see front matter Ó 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0168-583X(03)01033-4
282
F. Sato et al. / Nucl. Instr. and Meth. in Phys. Res. B 210 (2003) 281–284
2. Experimental The configuration of the simultaneous irradiation system of laser and ion beams is shown in Fig. 1. The irradiation system was set in one of the beam lines of a 200 keV ion accelerator [5]. The irradiation system consisted of a target vacuum chamber, deflectors, aperture collimators, a stigmator, an electrostatic lens, laser system and the related optical components. The samples were set in the target vacuum chamber. The Q-switched Nd:YAG laser system with a fourth harmonic generator (k ¼ 266 nm) and a diode laser for probe light (k ¼ 633 nm) were used in the experiment. The laser light was propagated into the target vacuum chamber with a F/100 parabolic mirror and a mirror with a center hole of 1mm in diameter. The laser intensity profile in the focal region was measured with a magnified image of the focal spot on a CCD camera. The measured focal spot size was 200 lm (FWHM of the intensity). The size of the ion beam was adjusted to be 200 lm/ with the aperture collimator and the electrostatic lens. The ion beam profile was measured with the knifeedge method. The positions of the laser and ion focal spots were adjusted by use of a plate with an aperture of 300 lm in diameter placed on the sample stage. The laser pulse intensity and the ion beam current were measured with a photodiode and a Faraday cup respectively. The ion beam induced luminescence was measured by a multi-channel photon spectrometer with an image intensifier (Hamamatsu Photonics,
PMA-10). The spectrometer was calibrated with a calibrated integrating sphere light source (Labsphere, USS-600) and a mercury lamp. The optical absorption measurement was performed with the diode laser during the ion irradiation. For the unirradiated region, an aluminum electrode was made on the surface of the sample by evaporation process. This made it possible to monitor the ion beam current flowing on the sample.
3. Results and discussion Crystalline a-Al2 O3 samples (SA-100, Kyocera Inc.) were irradiated with 30 keV Arþ , with a beam intensity of about 1 1013 ion/cm2 /s. The ion transport code TRIM estimated that the ion range was about 20 nm and the number of the displacement atoms was 500–1000 atoms/ion. Fig. 2 shows an ion beam induced luminescence spectrum for ion fluence of 1 1015 ion/cm2 . The spectrum had large luminescence peaks around 330 and 410 nm. The luminescence peaks around 330 and 410 nm are related to the excitation and relaxation of Fþ - and F-center, i.e. oxygen vacancies with one and two trapped electrons, respectively [6]. Similar luminescence peaks have also been observed with other radiations [7,8]. Fig. 3 shows changes of the intensity of the luminescence around 410 nm and the optical transmittance at 633 nm as a function of the ion fluence. The optical transmittance was measured with and without the Nd:YAG laser irradiation. The
Fig. 1. Configuration of simultaneous laser and ion irradiation system.
F. Sato et al. / Nucl. Instr. and Meth. in Phys. Res. B 210 (2003) 281–284
Fig. 2. Spectrum of photons emitted from Al2 O3 sample during 30 keV Arþ beam irradiation.
irradiation condition of the laser pulse was 10 mJ/ cm2 /10 ns at 10 Hz. The intensity of the luminescence degraded shortly after the start of the ion irradiation. The degradation is considered to be due to the optical absorption related to the highdensity defects formed in the sample. The increase in the loss of the optical transmittance of the sample started from the fluence of about 2 1016 ions/cm2 . However, the loss of the optical transmittance with the laser pulses stopped around 8 1016 ions/cm2 . For the sample with the laser irradiation, it is possible that the recovery of the defects and/or the laser ablation occurred in the irradiated region. Another Al2 O3 sample was irradiated up to the fluence of 1017 ions/cm2 . After the ion irradiation, the sample was irradiated with laser pulses of 10 mJ/cm2 /10 ns in the vacuum. The spot size of the
283
Fig. 3. Intensity of the luminescence around 410 nm and the optical transmittance at 633 nm as a function of the ion beam fluence.
ion beam irradiation was 200 lm in diameter, while the laser irradiation region was 8 mm in diameter. Fig. 4 shows surface images of the laserand ion-irradiated sample observed with an optical microscope. The layer irradiated with the ion beam might be peeled off owing to the laser irradiation. In addition, there was no significant damage in the region where ion beam did not impinge. The threshold level of the laser damage might be reduced owing to the high-density defects formed by ion beam irradiation and also the laser ablation might occur selectively in the ion-irradiated region. Further detailed experiments and discussions are needed for the explanation of the damage mechanism for the simultaneous irradiation of the laser and ion beams on optical materials.
Fig. 4. Surface images of the laser- and ion-irradiated Al2 O3 sample observed with optical microscope.
284
F. Sato et al. / Nucl. Instr. and Meth. in Phys. Res. B 210 (2003) 281–284
4. Conclusions
References
The simultaneous irradiation system of laser and ion beams has been developed and the preliminary irradiation experiment on the Al2 O3 sample was carried out. The ion beam induced luminescence of the Al2 O3 samples had some peaks, which were due to F centers. The loss of optical transmittance with the Nd:YAG laser irradiation was less than that without the laser. The simultaneous laser and ion irradiation technique might be useful for the study of the irradiation effects and for the micro processing of optical materials.
[1] T. Nishitani et al., Fusion Eng. Des. 56–57 (2001) 905. [2] C.I. Walker et al., Proc. of the 19th Symposium on Fusion Technology, 849 (1996). [3] T. Tanabe, A. Omori, M. Fujiwara, J. Nucl. Mater. 258–263 (1998) 1914. [4] R.J. Brooks, D.E. Hole, P.D. Townsend, Nucl. Instr. and Meth. B 190 (2002) 136. [5] T. Iida, F. Sato, T. Tanaka, M. Naito, in: Proc. 8th Int. Conf. on Nuclear Microprobe Technology and Applications, P1-05, 2002. [6] T. Tanabe, S. Tanaka, K. Yamaguchi, N. Otsuki, T. Iida, M. Yamawaki, J. Nucl. Mater. 212–215 (1994) 1050. [7] A. Morono, E.R. Hodgson, J. Nucl. Mater. 224 (1995) 216. [8] F. Sato, T. Iida, Y. Oyama, F. Maekawa, Y. Ikeda, J. Nucl. Mater. 258–263 (1998) 1897.