- Email: [email protected]
Electro-optical detection of THz radiation in Fe implanted LiNbO3
Optical Materials 35 (2013) 596–599
Contents lists available at SciVerse ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Electro-optical detection of THz radiation in Fe implanted LiNbO3 Yuhua Wang a,⇑, Hongwei Ni b, Weiting Zhan b, Jie Yuan a, Ruwu Wang a a b
Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Wuhan University of Science and Technology, Wuhan 430081, China Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China
a r t i c l e
i n f o
Article history: Received 6 July 2012 Received in revised form 24 September 2012 Accepted 18 October 2012 Available online 24 November 2012 Keywords: Ion implantation Fe nanoclusters LiNbO3 Terahertz
a b s t r a c t In this letter, the authors present first observation of terahertz generation from Fe implantation of LiNbO3 crystal substrate. LiNbO3 single crystal is grown by Czochralski method. Metal nanoparticles synthesized by Fe ion implantation were implanted into LiNbO3 single crystal using metal vapor vacuum arc (MEVVA) ion source. 1 kHz, 35 fs laser pulsed centered at 800 nm were focused onto the samples. Terahertz was generated via optical rectification. The findings suggest that under the investigated implantation parameter, a spectral component in excess of 0.44 THz emission were found from Fe ion implantation of LiNbO3. Published by Elsevier B.V.
1. Introduction In the past few years, applications of terahertz (THz) wave have been exploited in various fields. It plays an important role in applied physics, sensing, communications, and life sciences [1]. Efficient and compact sources of THz wave are of great importance. It is well known that the LiNbO3 crystal has large second-order nonlinear optical susceptibility [2]. The optical rectification in nonlinear optic (NLO) crystals is one of the most promising techniques, and several demonstrations have been made by using LiNbO3 [3– 5]. In these experiments, the pump light in the infrared region was launched into the NLO crystal, and the THz wave was generated through the second-order nonlinearity. It is well known ion implantation produces a high density of metal colloids in crystals and other materials. The high-precipitate volume fraction and small size of nanoclusters lead to values for the nonlinear susceptibility are greater than those for metal doped solids [6]. This has stimulated the interest in using ion implantation to make nonlinear optical materials. LiNbO3 crystal has proved to be a good material for nonlinear optical devices [7,8]. After it produced by ion implantation, in some case, light confinement in LiNbO3 is achieved with an optical isolation barrier with low refractive index in the nuclear stopping region of the ions. On the other side, ion implantation can undermine the lattice structure of single crystal. Hence, to get information about implantation of metal ions in LiNbO3 is of interest because of its potential interest in a variety of device applications [9].
⇑ Corresponding author. E-mail address: [email protected] (Y. Wang). 0925-3467/$ - see front matter Published by Elsevier B.V. http://dx.doi.org/10.1016/j.optmat.2012.10.034
In this letter, we report on, for the first time to our knowledge, terahertz emission from LiNbO3 with Fe ion implantation. We use Czochralski technique [10] to grow the LiNbO3 single crystal. Fe nanoparticles under crystal face were synthesized by ion implantation. The pump light of 800 nm was launched into the crystal, and the THz wave was generated through the second-order nonlinearity. We focus our interesting on get the THz wave information from this kind of sample.
2. Experiment LiNbO3 single crystal is grown by Czochralski method. The starting materials prepared for crystal were Li2CO3 (4 N purity), Nb2O5 (4 N purity), K2CO3 (spectrum purity). The crystals were grown under the optimum conditions: the temperature gradient above melt was 25 °C mm1, pull speed was 0.2 mm h1, and seed rotation rate was 15 rpm. It was Cut and polished at the room temperature to form a plate with polar faces perpendicular to the Z axis. The size of the plates was 20 20 1 mm3. LiNbO3 crystal was implanted with Fe using a using metal vapor vacuum arc (MEVVA) ion source implanter at room temperature. The acceleration voltage was 35 kV and flux densities was 25 lA/cm2. The dose for the sample is 1.2 1017 ions/cm2. Optical absorption spectrum of the sample was recorded at room temperature by using a UV–VIS dual-beam spectrophotometer with wavelengths from 1100 to 190 nm. The terahertz generated from the sample is investigated using the electro-optical sampling technique (EOS) [11]. The schematic diagram of the experimental arrangement is shown in Fig. 1. The laser source in our experiment is a 1 kHz, 35 fs Ti-Sapphire laser. As in a standard pump–probe experiment, the beam is separated
597
Y. Wang et al. / Optical Materials 35 (2013) 596–599
Fig. 1. Schematics of the experimental setup.
1 Pump LiNbO3:Fe
Intensity (a.u.)
into pump and probe arm by a beam splitter. The pump beam is focused onto the sample by a 15 cm focal length lens. Terahertz generated by the sample is collimated and refocus onto the EOS crystal by a set of off-axis parabolic mirrors. In this experiment, pulse energy of the laser is about 0.4 mJ, power of the pump beam incident on the sample is about 400 mW. The polarization of the laser beam is perpendicular to the C-axis of the crystal. Spot size of the pump beam on the sample is about 4 mm in diameter. A balanced photodetector used in the EOS detection. The terahertz radiation was detected by EOS in a 0.5-mm-thick 110-oriented ZnTe crystal. The experiment done in atmosphere. The remaining of near infrared pump is block by high resistivity silicon after the first off-axis parabolic mirror. The probe beam goes through a hole in the second off-axis mirror and incident on the EOS crystal collinearly with the THz beam.
0.1
0.01
1E-3 600
700
800
900
1000
Wavelength (nm) 3. Results and discussion +
Fig. 2 is the Vis-T spectra of the Fe implanted LiNbO3 sample. The spectra range from 200 to 1100 nm. There are about three parts from this figure. Under 315 nm wavelength, the sample absorbed all the lights. From 315 nm to 390 nm, the transmission of the sample increased fast from 0% to 50%. From 390 nm to 1100 nm, the transmission increase slowly. In pump beam of 800 nm, the transmittance of the sample is 64.5%. To further show the large n2 (second-order nonlinear refractive index of the medium) of ion implanted LiNbO3 crystal, the supercontinuum spectra of sample is obtained and shown in Fig. 3. The beam propagates along the C-axis. The frequency deviation
Fig. 3. Supercontinuum spectra of Fe implanted LiNbO3 crystal sample compare to pump laser.
100 90
Transmission (%)
80 70 60 50 40 30
Fig. 4. Profile of the beam through the Fe implanted sample in the far field.
20 10
resulting from the Self-phase modulation (SPM) effect can be described in the form [12]:
pump beam
0 200
400
600
800
1000
Wavelength (nm) Fig. 2. Optical transmittance spectra of Fe implanted LiNbO3 with dose of 1.2 1017 ions/cm2.
xðtÞ ¼ x0 þ
2 4pLn2 I0 t t exp k0 s2 s2
ð1Þ
where x0 and k0 are the carrier frequency and wavelength of the pulse, and L is the distance the pulse has propagated. I0 is the peak
Y. Wang et al. / Optical Materials 35 (2013) 596–599
signal (µV)
598
25 20 15 10 5 0 -5 -10 -15 -20 -6
-4
-2
0
2
4
6
4
5
6
delay (ps)
FFT (a.u.)
2.0x10-6 1.5x10-6 1.0x10-6 5.0x10-7 0.0 0
1
2
3
frequency (THz) Fig. 5. (a) Electro-optical Sampling time trace of the generated terahertz. (b) The corresponding spectrum.
intensity, and s is half the pulse duration. Plotting x(t) shows the frequency shift of each part of the pulse. The leading edge shifts to lower frequencies (‘‘redder’’ wavelengths), trailing edge to higher frequencies (‘‘bluer’’). For the centre portion of the pulse (between t = ±s/2), there is an approximately linear frequency shift given by:
xðtÞ ¼ x0 þ a t
ð2Þ
where a is:
a¼
dx 4pLn2 I0 ¼ dt 0 k0 s2
ð3Þ
It is clear that the frequency deviation is proportional to n2 when other conditions are identical. That means larger n2 will lead to wider supercontinuum spectrum. As it is illustrated in Fig. 3, the spectrum of the Fe implanted LiNbO3 crystal sample show a wider spectrum than that of pump laser, and it demonstrates that this kind of sample has secondorder nonlinear optical properties of n2. This is a necessary condition for terahertz emission. Supercontinuum radiation combines high spatial coherence and spectral brightness. Its high peak intensity and average power enables strong light-matter interactions in the nonlinear regime [13,14]. We think that interplay of light scattering from the sample and nonlinear selfaction allows one to separate selectively or combine different spectral components. Small refractive-index changes lead to strong beam reshaping and spectral filtering. Since the mode profile and confinement depend on the wavelength, the discrete diffraction exhibits spectral dispersion. As for implanted LiNbO3 sample, it show spatial redistribution of the colors of the supercontinuum radiation is red.1 See Fig. 4. The Electro-Optical Sampling data is shown in Fig. 5, the terahertz generated from our sample is centered at 0.44 THz. The bandwidth from the sample is 1 THz. Meserole et al. [15] discovered a novel application for thin Fe films. The bandwidth from the Fe (0 0 1) samples is 0.5 THz. They believe that the narrow THz pulse is due to a very rapid demagnetization of the Fe film. The Fe films
are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Wu et al. [10] investigated the frequency dependence of dielectric spectra of iron doped lithium niobate single crystal. They found the variation of refractive index has a linear relationship on scale with the applied light intensity accompanied with a steplike decrease. This relationship were attributed to the internal space charge field of photorefraction and the light-induced domain reversal in the crystal. At this study, we compared THz emission from Fe-implanted LiNbO3 and blank LiNbO3 crystal. We find they have similar center position. The effect of the increased second order nonlinear index of refraction in LiNbO3 crystal is not shown in experimental results. The implanted sample show a little weak signal compare to LiNbO3 crystal. Hence, we think in progress of ion implantation, the formed Fe naoparticles undermine the lattice structure of the crystal. In terms of terahertz generation, the influence of nonlinear susceptibility generated by implanted Fe nanoparticles is small compare to that of the undermined lattice structure of the LiNbO3 crystal. 4. Conclusion In summary, LiNbO3 doped Fe nanoclusters have been formed by the ion implantation of Fe+ ions using MEVVA ion source. We have demonstrated, for the first time, the terahertz generated through optical rectification process of this kind of sample, which presents a strong spectral component in excess of 0.44 THz. The results indicated that this new structure of LiNbO3 crystal with metal nanoclusters inside gives a new circumstance in the study of the nonlinear optical response. The further studies are in progress. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 10805035). References
1
For interpretation of color in Fig. 4, the reader is referred to the web version of this article.
[1] Y. Takushima, S.Y. Shin, Y.C. Chung, Opt. Express 15 (2007) 14783–14792.
Y. Wang et al. / Optical Materials 35 (2013) 596–599 [2] Q. Wang, S. Wang, W. Huang, Q. Gong, B. Yang, J. Shi, J. Phys. D: Appl. Phys. 35 (2002) 430–432. [3] K. Kawase, H. Minamide, K. Imai, J. Shikata, H. Ito, Appl. Phys. Lett. 80 (2002) 195–198. [4] A.C. Chiang, T.D. Wang, Y.Y. Lin, S.T. Lin, H.H. Lee, Y.C. Huang, Opt. Lett. 30 (2005) 3392–3394. [5] T. Ikari, X. Zhang, H. Minamide, H. Ito, Opt. Express 14 (2006) 1604–1610. [6] S.S. Sarkisov, M.J. Ferley, E.K. Williams, D. Ila, V.L. Svetchnikov, H.W. Zandbergen, G.A. Zykov, C. Banks, J.C. Wang, D.B. Poker, D.K. Hensley, Nucl. Instrum. Methods B 166 (2000) 750–757. [7] J. Chen, X. Chen, Y. Ma, Y. Zheng, A. Wu, H. Li, L. Jiang, J. Xu, J. Opt. Soc. Am. B 29 (2012) 665–668. [8] H. Li, F. Zhou, X. Zhang, Wei. Ji, Appl. Phys. B 64 (1997) 659–662.
599
[9] J.J. Ju, T.Y. Kwon, S.I. Yun, M. Cha, H.J. Seo, Appl. Phys. Lett. 69 (1996) 1358– 1360. [10] L. Wu, F. Ling, X. Tian, H. Zhao, J. Liu, J. Yao, Opt. Mater. 33 (2011) 1737–1740. [11] Q. Wu, X.-C. Zhang, Appl. Phys. Lett. 67 (24) (1995) 3523–3525. [12] V.P. Kandidov, O.G. Kosareva, I.S. Golubtsov, W. Liu, A. Becker, N. Akozbek, C.M. Bowden, S.L. Chin, Appl. Phys. B 77 (2003) 149–165. [13] D.N. Neshev, A.A. Sukhorukov, A. Dreischuh, R. Fischer, S. Ha, J. Bolger, L. Bui, W. Krolikowski, B.J. Eggleton, A. Mitchell, M.W. Austin, Y.S. Kivshar, Phys. Rev. Lett. 99 (2007) 123901.1–123901.4. [14] M. Balu, J. Hales, D.J. Hagan, E.W. Van Stryland, Opt. Express 13 (2005) 3594– 3599. [15] C.A. Meserole, G.L. Fisher, D.J. Hilton, R.D. Averitt, D.J. Funk, A.J. Taylor, Appl. Surf. Sci. 253 (2007) 6992–7003.
Contents lists available at SciVerse ScienceDirect
Optical Materials journal homepage: www.elsevier.com/locate/optmat
Electro-optical detection of THz radiation in Fe implanted LiNbO3 Yuhua Wang a,⇑, Hongwei Ni b, Weiting Zhan b, Jie Yuan a, Ruwu Wang a a b
Hubei Province Key Laboratory of Systems Science in Metallurgical Process, Wuhan University of Science and Technology, Wuhan 430081, China Key Laboratory for Ferrous Metallurgy and Resources Utilization of Ministry of Education, Wuhan University of Science and Technology, Wuhan 430081, China
a r t i c l e
i n f o
Article history: Received 6 July 2012 Received in revised form 24 September 2012 Accepted 18 October 2012 Available online 24 November 2012 Keywords: Ion implantation Fe nanoclusters LiNbO3 Terahertz
a b s t r a c t In this letter, the authors present first observation of terahertz generation from Fe implantation of LiNbO3 crystal substrate. LiNbO3 single crystal is grown by Czochralski method. Metal nanoparticles synthesized by Fe ion implantation were implanted into LiNbO3 single crystal using metal vapor vacuum arc (MEVVA) ion source. 1 kHz, 35 fs laser pulsed centered at 800 nm were focused onto the samples. Terahertz was generated via optical rectification. The findings suggest that under the investigated implantation parameter, a spectral component in excess of 0.44 THz emission were found from Fe ion implantation of LiNbO3. Published by Elsevier B.V.
1. Introduction In the past few years, applications of terahertz (THz) wave have been exploited in various fields. It plays an important role in applied physics, sensing, communications, and life sciences [1]. Efficient and compact sources of THz wave are of great importance. It is well known that the LiNbO3 crystal has large second-order nonlinear optical susceptibility [2]. The optical rectification in nonlinear optic (NLO) crystals is one of the most promising techniques, and several demonstrations have been made by using LiNbO3 [3– 5]. In these experiments, the pump light in the infrared region was launched into the NLO crystal, and the THz wave was generated through the second-order nonlinearity. It is well known ion implantation produces a high density of metal colloids in crystals and other materials. The high-precipitate volume fraction and small size of nanoclusters lead to values for the nonlinear susceptibility are greater than those for metal doped solids [6]. This has stimulated the interest in using ion implantation to make nonlinear optical materials. LiNbO3 crystal has proved to be a good material for nonlinear optical devices [7,8]. After it produced by ion implantation, in some case, light confinement in LiNbO3 is achieved with an optical isolation barrier with low refractive index in the nuclear stopping region of the ions. On the other side, ion implantation can undermine the lattice structure of single crystal. Hence, to get information about implantation of metal ions in LiNbO3 is of interest because of its potential interest in a variety of device applications [9].
⇑ Corresponding author. E-mail address: [email protected] (Y. Wang). 0925-3467/$ - see front matter Published by Elsevier B.V. http://dx.doi.org/10.1016/j.optmat.2012.10.034
In this letter, we report on, for the first time to our knowledge, terahertz emission from LiNbO3 with Fe ion implantation. We use Czochralski technique [10] to grow the LiNbO3 single crystal. Fe nanoparticles under crystal face were synthesized by ion implantation. The pump light of 800 nm was launched into the crystal, and the THz wave was generated through the second-order nonlinearity. We focus our interesting on get the THz wave information from this kind of sample.
2. Experiment LiNbO3 single crystal is grown by Czochralski method. The starting materials prepared for crystal were Li2CO3 (4 N purity), Nb2O5 (4 N purity), K2CO3 (spectrum purity). The crystals were grown under the optimum conditions: the temperature gradient above melt was 25 °C mm1, pull speed was 0.2 mm h1, and seed rotation rate was 15 rpm. It was Cut and polished at the room temperature to form a plate with polar faces perpendicular to the Z axis. The size of the plates was 20 20 1 mm3. LiNbO3 crystal was implanted with Fe using a using metal vapor vacuum arc (MEVVA) ion source implanter at room temperature. The acceleration voltage was 35 kV and flux densities was 25 lA/cm2. The dose for the sample is 1.2 1017 ions/cm2. Optical absorption spectrum of the sample was recorded at room temperature by using a UV–VIS dual-beam spectrophotometer with wavelengths from 1100 to 190 nm. The terahertz generated from the sample is investigated using the electro-optical sampling technique (EOS) [11]. The schematic diagram of the experimental arrangement is shown in Fig. 1. The laser source in our experiment is a 1 kHz, 35 fs Ti-Sapphire laser. As in a standard pump–probe experiment, the beam is separated
597
Y. Wang et al. / Optical Materials 35 (2013) 596–599
Fig. 1. Schematics of the experimental setup.
1 Pump LiNbO3:Fe
Intensity (a.u.)
into pump and probe arm by a beam splitter. The pump beam is focused onto the sample by a 15 cm focal length lens. Terahertz generated by the sample is collimated and refocus onto the EOS crystal by a set of off-axis parabolic mirrors. In this experiment, pulse energy of the laser is about 0.4 mJ, power of the pump beam incident on the sample is about 400 mW. The polarization of the laser beam is perpendicular to the C-axis of the crystal. Spot size of the pump beam on the sample is about 4 mm in diameter. A balanced photodetector used in the EOS detection. The terahertz radiation was detected by EOS in a 0.5-mm-thick 110-oriented ZnTe crystal. The experiment done in atmosphere. The remaining of near infrared pump is block by high resistivity silicon after the first off-axis parabolic mirror. The probe beam goes through a hole in the second off-axis mirror and incident on the EOS crystal collinearly with the THz beam.
0.1
0.01
1E-3 600
700
800
900
1000
Wavelength (nm) 3. Results and discussion +
Fig. 2 is the Vis-T spectra of the Fe implanted LiNbO3 sample. The spectra range from 200 to 1100 nm. There are about three parts from this figure. Under 315 nm wavelength, the sample absorbed all the lights. From 315 nm to 390 nm, the transmission of the sample increased fast from 0% to 50%. From 390 nm to 1100 nm, the transmission increase slowly. In pump beam of 800 nm, the transmittance of the sample is 64.5%. To further show the large n2 (second-order nonlinear refractive index of the medium) of ion implanted LiNbO3 crystal, the supercontinuum spectra of sample is obtained and shown in Fig. 3. The beam propagates along the C-axis. The frequency deviation
Fig. 3. Supercontinuum spectra of Fe implanted LiNbO3 crystal sample compare to pump laser.
100 90
Transmission (%)
80 70 60 50 40 30
Fig. 4. Profile of the beam through the Fe implanted sample in the far field.
20 10
resulting from the Self-phase modulation (SPM) effect can be described in the form [12]:
pump beam
0 200
400
600
800
1000
Wavelength (nm) Fig. 2. Optical transmittance spectra of Fe implanted LiNbO3 with dose of 1.2 1017 ions/cm2.
xðtÞ ¼ x0 þ
2 4pLn2 I0 t t exp k0 s2 s2
ð1Þ
where x0 and k0 are the carrier frequency and wavelength of the pulse, and L is the distance the pulse has propagated. I0 is the peak
Y. Wang et al. / Optical Materials 35 (2013) 596–599
signal (µV)
598
25 20 15 10 5 0 -5 -10 -15 -20 -6
-4
-2
0
2
4
6
4
5
6
delay (ps)
FFT (a.u.)
2.0x10-6 1.5x10-6 1.0x10-6 5.0x10-7 0.0 0
1
2
3
frequency (THz) Fig. 5. (a) Electro-optical Sampling time trace of the generated terahertz. (b) The corresponding spectrum.
intensity, and s is half the pulse duration. Plotting x(t) shows the frequency shift of each part of the pulse. The leading edge shifts to lower frequencies (‘‘redder’’ wavelengths), trailing edge to higher frequencies (‘‘bluer’’). For the centre portion of the pulse (between t = ±s/2), there is an approximately linear frequency shift given by:
xðtÞ ¼ x0 þ a t
ð2Þ
where a is:
a¼
dx 4pLn2 I0 ¼ dt 0 k0 s2
ð3Þ
It is clear that the frequency deviation is proportional to n2 when other conditions are identical. That means larger n2 will lead to wider supercontinuum spectrum. As it is illustrated in Fig. 3, the spectrum of the Fe implanted LiNbO3 crystal sample show a wider spectrum than that of pump laser, and it demonstrates that this kind of sample has secondorder nonlinear optical properties of n2. This is a necessary condition for terahertz emission. Supercontinuum radiation combines high spatial coherence and spectral brightness. Its high peak intensity and average power enables strong light-matter interactions in the nonlinear regime [13,14]. We think that interplay of light scattering from the sample and nonlinear selfaction allows one to separate selectively or combine different spectral components. Small refractive-index changes lead to strong beam reshaping and spectral filtering. Since the mode profile and confinement depend on the wavelength, the discrete diffraction exhibits spectral dispersion. As for implanted LiNbO3 sample, it show spatial redistribution of the colors of the supercontinuum radiation is red.1 See Fig. 4. The Electro-Optical Sampling data is shown in Fig. 5, the terahertz generated from our sample is centered at 0.44 THz. The bandwidth from the sample is 1 THz. Meserole et al. [15] discovered a novel application for thin Fe films. The bandwidth from the Fe (0 0 1) samples is 0.5 THz. They believe that the narrow THz pulse is due to a very rapid demagnetization of the Fe film. The Fe films
are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Wu et al. [10] investigated the frequency dependence of dielectric spectra of iron doped lithium niobate single crystal. They found the variation of refractive index has a linear relationship on scale with the applied light intensity accompanied with a steplike decrease. This relationship were attributed to the internal space charge field of photorefraction and the light-induced domain reversal in the crystal. At this study, we compared THz emission from Fe-implanted LiNbO3 and blank LiNbO3 crystal. We find they have similar center position. The effect of the increased second order nonlinear index of refraction in LiNbO3 crystal is not shown in experimental results. The implanted sample show a little weak signal compare to LiNbO3 crystal. Hence, we think in progress of ion implantation, the formed Fe naoparticles undermine the lattice structure of the crystal. In terms of terahertz generation, the influence of nonlinear susceptibility generated by implanted Fe nanoparticles is small compare to that of the undermined lattice structure of the LiNbO3 crystal. 4. Conclusion In summary, LiNbO3 doped Fe nanoclusters have been formed by the ion implantation of Fe+ ions using MEVVA ion source. We have demonstrated, for the first time, the terahertz generated through optical rectification process of this kind of sample, which presents a strong spectral component in excess of 0.44 THz. The results indicated that this new structure of LiNbO3 crystal with metal nanoclusters inside gives a new circumstance in the study of the nonlinear optical response. The further studies are in progress. Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 10805035). References
1
For interpretation of color in Fig. 4, the reader is referred to the web version of this article.
[1] Y. Takushima, S.Y. Shin, Y.C. Chung, Opt. Express 15 (2007) 14783–14792.
Y. Wang et al. / Optical Materials 35 (2013) 596–599 [2] Q. Wang, S. Wang, W. Huang, Q. Gong, B. Yang, J. Shi, J. Phys. D: Appl. Phys. 35 (2002) 430–432. [3] K. Kawase, H. Minamide, K. Imai, J. Shikata, H. Ito, Appl. Phys. Lett. 80 (2002) 195–198. [4] A.C. Chiang, T.D. Wang, Y.Y. Lin, S.T. Lin, H.H. Lee, Y.C. Huang, Opt. Lett. 30 (2005) 3392–3394. [5] T. Ikari, X. Zhang, H. Minamide, H. Ito, Opt. Express 14 (2006) 1604–1610. [6] S.S. Sarkisov, M.J. Ferley, E.K. Williams, D. Ila, V.L. Svetchnikov, H.W. Zandbergen, G.A. Zykov, C. Banks, J.C. Wang, D.B. Poker, D.K. Hensley, Nucl. Instrum. Methods B 166 (2000) 750–757. [7] J. Chen, X. Chen, Y. Ma, Y. Zheng, A. Wu, H. Li, L. Jiang, J. Xu, J. Opt. Soc. Am. B 29 (2012) 665–668. [8] H. Li, F. Zhou, X. Zhang, Wei. Ji, Appl. Phys. B 64 (1997) 659–662.
599
[9] J.J. Ju, T.Y. Kwon, S.I. Yun, M. Cha, H.J. Seo, Appl. Phys. Lett. 69 (1996) 1358– 1360. [10] L. Wu, F. Ling, X. Tian, H. Zhao, J. Liu, J. Yao, Opt. Mater. 33 (2011) 1737–1740. [11] Q. Wu, X.-C. Zhang, Appl. Phys. Lett. 67 (24) (1995) 3523–3525. [12] V.P. Kandidov, O.G. Kosareva, I.S. Golubtsov, W. Liu, A. Becker, N. Akozbek, C.M. Bowden, S.L. Chin, Appl. Phys. B 77 (2003) 149–165. [13] D.N. Neshev, A.A. Sukhorukov, A. Dreischuh, R. Fischer, S. Ha, J. Bolger, L. Bui, W. Krolikowski, B.J. Eggleton, A. Mitchell, M.W. Austin, Y.S. Kivshar, Phys. Rev. Lett. 99 (2007) 123901.1–123901.4. [14] M. Balu, J. Hales, D.J. Hagan, E.W. Van Stryland, Opt. Express 13 (2005) 3594– 3599. [15] C.A. Meserole, G.L. Fisher, D.J. Hilton, R.D. Averitt, D.J. Funk, A.J. Taylor, Appl. Surf. Sci. 253 (2007) 6992–7003.