- Email: [email protected]
A CW blue laser emission by self-sum-frequency-mixing in Nd3+:GdAl3(BO3)4 crystal
1 July 2002
Optics Communications 208 (2002) 163–166 www.elsevier.com/locate/optcom
A CW blue laser emission by self-sum-frequency-mixing in Nd3þ : GdAl3ðBO3Þ4 crystal Miaoliang Huang a,b,c, Yujin Chen a, Xueyuan Chen a, Yidong Huang a,*, Zundu Luo a,1 a
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China b College of Materials Science and Engineering, Huaqiao University, Quanzhou, Fujian 362011, China c The Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Received 28 March 2002; received in revised form 9 May 2002; accepted 15 May 2002
Abstract In this paper, we report a CW blue laser emission by self-sum-frequency-mixing in NGAB crystal. 48 lW of 0.459 lm blue laser output power was obtained with the absorbed pump power of 0.99 W from a CW Ti:sapphire laser, and the threshold power is about 100 mW. The results indicate that the NGAB is also a promising candidate for a blue laser source by self-sum-frequency-mixing. The blue laser efficiency can be further improved by optimizing the device parameters. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 42.55.Rz; 42.70.Hj; 42.70.Mp; 42.65.Ky Keywords: Nd3þ : GdAl3 ðBO3 Þ4 crystal; Blue laser; Self-sum-frequency-mixing
1. Introduction In recent years, rare earth ions doped nonlinear laser crystals such as Nd3þ or Yb3þ doped YAl3 ðBO3 Þ4 (YAB), Ca4 GdOðBO3 Þ3 (GCOB), Ca4 YOðBO3 Þ3 (YCOB), and MgO : LiNbO3 have been paid much attention [1–22], because they combine laser and nonlinear optical functions into *
Corresponding author. Tel.: +86-591-3776990; fax: +86591-3714946. E-mail addresses: [email protected] (Y. Huang), [email protected] (Z. Luo). 1 Also corresponding author. Tel.: +86-591-3713077.
a single crystal, which makes it possible that the red, green and blue lasers can be produced in a crystal via self-frequency-doubling (SDF) of fundamental infrared lasers of the active ions and selfsum-frequency-mixing (SSFM) of fundamental and pump lasers. In particular, blue laser emissions by the SSFM in nonlinear crystals are attracting interest increasingly due to the fact that the device is more compact, reliable, robust, low cost, and provides an excellent visible source for the application in laser printing, display, underwater communication and laser measurement, etc. Jaque et al. [6] first reported the CW blue laser emission by the SSFM in the Nd : YAl3 ðBO3 Þ4
0030-4018/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 0 - 4 0 1 8 ( 0 2 ) 0 1 5 7 5 - 4
164
M. Huang et al. / Optics Communications 208 (2002) 163–166
(NYAB) crystal. Meanwhile, Brenier and Boulon [2] have also realized the pulse blue and ultraviolet (UV) laser operation in the same crystal. Mougel and his co-workers [23] investigated the SSFM process in the Nd3þ : Ca4 GdOðBO3 Þ3 (NGCOB) crystal, and realized about 1.2 mW blue laser output, which indicates that SSFM process provides an effective way to obtain blue laser emission. Recently, pulse blue and UV laser generations by the SSFM in a Nd3þ : GdAl3 ðBO3 Þ4 (NGAB) crystal, which is in the same family as the NYAB crystal, have also been successfully performed and obtained some good results [24,25]. The related theoretical analysis has been made by Chen et al. [26]. In this paper, we are focused on the CW blue laser emission by the SSFM of infrared fundamental laser and pump laser from a tunable Ti:sapphire laser in the Nd3þ : GdAl3 ðBO3 Þ4 crystal.
2. Experiments The NGAB is a negative uniaxial crystal. Its refractive index had been measured and the Sellmeier equations of refractive index are as follows [27]: 0:03079 ; k2 þ 0:03265 0:0242 : n2e ðkÞ ¼ 2:82998 þ 2 k þ 0:03127
n2o ðkÞ ¼ 3:07289 þ
ð1Þ ð2Þ
According to these equations, the phase matching angle for type I ðo þ o ! eÞ SSFM of 1.062 lm fundamental wave and the pump laser can be calculated. The phase matching angle as a function of the pump wavelength is presented in Fig. 1. The phase matching angle of SSFM at 1.062 and 0.807 lm is about 34.06°. The plano-concave cavity is adopted in our experiments. The input mirror is a plane mirror coated with high reflectivity at 1.062 lm (99.5%), with reflectivity of more than 90% at blue band from 0.440 to 0.470 lm, and with transmittance of 90% at 0.807 lm. Output coupler with radius curvature of 98 mm has high reflectivity at 1.062 lm (99.3%) and 85% transmittance at 0.459 lm.
Fig. 1. Phase matching angle for type I self-sum-frequencymixing as a function of pump wavelength.
The cavity length is about 61 mm, and kept unchanged throughout the experiments. The pump source is a CW Ti:sapphire tunable laser (SpectraPhysics Model 3900s) with a tunability from 0.7 to 1.0 lm, and was focused into the cavity through a focal lens with 71 mm focal length, which provided a light waist of 30 lm in the NGAB crystal. The crystal NGAB used in the experiments has a dimension of 3 mm 3 mm 5:5 mm, and was cut in the phase matching angle direction of h ¼ 34:06° for type I SSFM. Its both faces were polished to obtain parallel flat surfaces, but not antireflection (AR) coated. Nd3þ doped concentration in the crystal is about 3.35%. The crystal was placed as close as possible to the input mirror, in which large mode overlap between the pump and the fundamental infrared laser could be obtained and intense laser emission could be realized. 3. Results and discussion The output powers of blue and infrared lasers versus absorbed pump power at 0.807 lm are shown in Fig. 2. The infrared laser output increases linearly with the absorbed pump power, while the blue laser emission has a parabolic relation with the absorbed pump power. The infrared and blue laser output powers are 53 mW and 48 lW with the absorbed pump power of 0.99 W, respectively. The laser threshold power is about 100 mW. In the optimum case, by means of the theoretical model in [26] and Eqs. (1) and (2), the blue laser output is calculated to be about 310 lW
M. Huang et al. / Optics Communications 208 (2002) 163–166
Fig. 2. Infrared and blue laser output power as a function of absorbed pump power. The pump wavelength was 0.807 lm.
and much larger than the value measured in our experiments. This may be attributed to the fact that the laser cavity is not fully optimized and the crystal exists some defects. The output power of the blue laser as a function of the pumping wavelength is given in Fig. 3 where the pump power was kept as a constant of 0.8 W. It should be noted that the corresponding absorbed pump power is different for different wavelength of the pump laser. Although the crystal was cut in the direction of the phase matching angle at 0.807 lm, the blue laser was observed in the range from 0.457 to 0.464 lm when the wavelength of pumping laser was tuned from 0.801 to 0.825 lm. According to the theoretical model proposed in [26], the acceptance wavelength is estimated to be about 4.5 nm and close to the ex-
165
perimental value. On the other hand, the focused pump beam had large divergence, part of the pump laser beam satisfied phase matching condition even if a slight mismatch existed between the pump laser beam and the infrared fundamental laser beam, which also made it possible to realize the blue laser emission in a wide range of pump wavelength. Of course, this resulted in a low conversion efficiency of SSFM as well. We also found that the maximum output of blue laser was not at 0.807 lm where the maximum absorption of 93% happens, but at 0.811 lm with the absorption of 76% and the output power of the blue laser was 32 lW, larger than 24 lW at 0.807 lm with the same pump power of 0.8 W (corresponding absorbed pump powers are 0.669 W at 0.807 lm and 0.55 W at 0.811 lm, respectively). This phenomenon has been predicted and explained in the theoretical model proposed by Brenier [11]. The explanation is as follows: if the absorption of the pump laser is too strong, the pump beam is only intense at the entrance of the crystal, the interaction length between the pump and the infrared fundamental laser is shorter, which results in a lower efficient conversion to the blue laser compared with the weaker absorption which leads to a larger interaction length.
4. Conclusions We have demonstrated the blue laser emission by the SSFM in the NGAB crystal and 48 lW blue light output power was obtained with the absorbed pump power of 0.99 W, and the threshold power is about 100 mW. The results indicate that the NGAB crystal is also a promising candidate for a blue laser source by the SSFM. The blue laser emission can be further improved by optimizing the device parameters. The experiments of diodepumped SSFM are being undertaken.
Acknowledgements
Fig. 3. Blue laser output versus pump wavelength. The pump power was kept as a constant of 0.8 W.
This project has been supported by Fujian Provincial International Cooperation Foundation (No. 99-I-7), Foundation of Chinese Academy of
166
M. Huang et al. / Optics Communications 208 (2002) 163–166
Sciences for Outstanding Returned Scholars and National Natural Science Foundation of China (No. 60088004). The authors also would like to thank Prof. A. D. Jiang, M. W. Qiu, C. Y. Tu and Q. G. Tan for providing crystals and helping in the experiments.
References [1] F. Mougel, G. Aka, A. Kahn-Harari, D. Vivien, Opt. Mater. 13 (1999) 293. [2] A. Brenier, G. Boulon, J. Lumin. 86 (2000) 125. [3] Q. Ye, L. Shah, J. Eichenholz, D. Hammons, R. Peale, M. Richardson, A. Chin, B.H.T. Chai, Opt. Commun. 164 (1999) 33. [4] G. Aka, F. Mougel, F. Auge, A. Kahn-Harari, D. Vivien, J.M. Benitez, F. Salin, D. Pelenc, F. Balembois, P. Georges, A. Brun, N. Le Nain, M. Jacquet, J. Alloys Compd. 303–304 (2000) 401. [5] D. Vivien, F. Mougel, F. Auge, G. Aka, A. Kahn-Harari, F. Balembois, G. Lucas-Leclin, P. Geoges, A. Brun, P. Aschehoug, J.M. Benitz, N. Le Nain, M. Jacquet, Opt. Mater. 16 (2001) 213. [6] D. Jaque, J. Capmany, J. Garcia Sole, Appl. Phys. Lett. 75 (1999) 325. [7] D. Jaque, J. Capmany, F. Molero, J. Garcia Sole, Appl. Phys. Lett. 73 (1998) 3659. [8] T.Y. Fan, A. Cordova-Plaza, M.J.F. Digonnet, R.L. Byer, H.J. Shaw, J. Opt. Soc. Am. B 3 (1986) 140. [9] J.M. Eichenhoiz, D.A. Hammons, L. Shah, Q. Ye, R.E. Peale, M. Richardson, B.H.T. Chai, Appl. Phys. Lett. 74 (1999) 1954. [10] J. Bartschke, R. Knappe, K.J. Boller, R. Wallenstein, IEEE J. Quantum Electron. 33 (1997) 2295.
[11] A. Brenier, J. Lumin. 91 (2000) 121. [12] A. Brenier, Opt. Commun. 141 (1997) 221. [13] D. Jaque, J. Capmany, J. Garcia Sole, Z.D. Luo, A.D. Jiang, J. Opt. Soc. Am. B 15 (1998) 1656. [14] F. Mougel, F. Auge, A. Kahn-Harari, D. Vivien, F. Balembois, P. Georges, A. Brun, Appl. Phys. B 67 (1998) 533. [15] F. Mougel, G. Aka, A. Kahn-Harari, H. Hubert, J.M. Benitez, D. Vivien, Opt. Mater. 8 (1997) 161. [16] J.H. Lu, G.M. Li, J.H. Liu, B. Gong, Y.G. Liu, J.Y. Wang, Z.S. Shao, M.H. Jiang, Chin. J. Laser B 8 (1999) 485. [17] F. Mougel, K. Dardenne, G. Aka, A. Kahn-Harari, D. Vivien, J. Opt. Soc. Am. B 16 (1999) 164. [18] D.A. Hammons, J.M. Eichenholz, Q. Ye, B.H.T. Chai, L. Shah, R.E. Peale, M. Richardson, H. Qiu, Opt. Commun. 156 (1998) 327. [19] F. Auge, F. Druon, F. Balembois, P. Georges, A. Brun, F. Mougel, G. Aka, D. Vivien, IEEE J. Quantum Electron. 36 (2000) 598. [20] X.L. Meng, H.J. Zhang, L. Zhu, L.K. Sun, X.S. Liu, P. Wang, J.M. Dewes, Acta Opt. Sinica 20 (2000) 419. [21] E. Montoya, J. Capmany, L.E. Bause, Appl. Phys. Lett. 75 (1999) 325. [22] P. Wang, P. Dekker, J.M. Dawes, J.A. Piper, Y.G. Liu, J.Y. Wang, Opt. Lett. 25 (2000) 731. [23] F. Mougel, G. Aka, A. Kahn-Harari, D. Vivien, Opt. Mater. 13 (1999) 293. [24] A. Brenier, C. Tu, M. Qiu, A. Jiang, J. Li, B. Wu, J. Opt. Soc. Am. B 18 (2001) 1104. [25] A. Brenier, C. Tu, M. Qiu, A. Jiang, J. Li, B. Wu, Opt. Lett. 27 (2002) 240. [26] X.Y. Chen, Z.D. Luo, Y.D. Huang, J. Opt. Soc. Am. B 18 (2001) 646. [27] C.Y. Tu, M.W. Qiu, Y.C. Huang, X.Y. Chen, A.D. Jiang, Z.D. Luo, J. Cryst. Growth 208 (2000) 487.
Optics Communications 208 (2002) 163–166 www.elsevier.com/locate/optcom
A CW blue laser emission by self-sum-frequency-mixing in Nd3þ : GdAl3ðBO3Þ4 crystal Miaoliang Huang a,b,c, Yujin Chen a, Xueyuan Chen a, Yidong Huang a,*, Zundu Luo a,1 a
Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, China b College of Materials Science and Engineering, Huaqiao University, Quanzhou, Fujian 362011, China c The Graduate School of the Chinese Academy of Sciences, Beijing 100039, China Received 28 March 2002; received in revised form 9 May 2002; accepted 15 May 2002
Abstract In this paper, we report a CW blue laser emission by self-sum-frequency-mixing in NGAB crystal. 48 lW of 0.459 lm blue laser output power was obtained with the absorbed pump power of 0.99 W from a CW Ti:sapphire laser, and the threshold power is about 100 mW. The results indicate that the NGAB is also a promising candidate for a blue laser source by self-sum-frequency-mixing. The blue laser efficiency can be further improved by optimizing the device parameters. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 42.55.Rz; 42.70.Hj; 42.70.Mp; 42.65.Ky Keywords: Nd3þ : GdAl3 ðBO3 Þ4 crystal; Blue laser; Self-sum-frequency-mixing
1. Introduction In recent years, rare earth ions doped nonlinear laser crystals such as Nd3þ or Yb3þ doped YAl3 ðBO3 Þ4 (YAB), Ca4 GdOðBO3 Þ3 (GCOB), Ca4 YOðBO3 Þ3 (YCOB), and MgO : LiNbO3 have been paid much attention [1–22], because they combine laser and nonlinear optical functions into *
Corresponding author. Tel.: +86-591-3776990; fax: +86591-3714946. E-mail addresses: [email protected] (Y. Huang), [email protected] (Z. Luo). 1 Also corresponding author. Tel.: +86-591-3713077.
a single crystal, which makes it possible that the red, green and blue lasers can be produced in a crystal via self-frequency-doubling (SDF) of fundamental infrared lasers of the active ions and selfsum-frequency-mixing (SSFM) of fundamental and pump lasers. In particular, blue laser emissions by the SSFM in nonlinear crystals are attracting interest increasingly due to the fact that the device is more compact, reliable, robust, low cost, and provides an excellent visible source for the application in laser printing, display, underwater communication and laser measurement, etc. Jaque et al. [6] first reported the CW blue laser emission by the SSFM in the Nd : YAl3 ðBO3 Þ4
0030-4018/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII: S 0 0 3 0 - 4 0 1 8 ( 0 2 ) 0 1 5 7 5 - 4
164
M. Huang et al. / Optics Communications 208 (2002) 163–166
(NYAB) crystal. Meanwhile, Brenier and Boulon [2] have also realized the pulse blue and ultraviolet (UV) laser operation in the same crystal. Mougel and his co-workers [23] investigated the SSFM process in the Nd3þ : Ca4 GdOðBO3 Þ3 (NGCOB) crystal, and realized about 1.2 mW blue laser output, which indicates that SSFM process provides an effective way to obtain blue laser emission. Recently, pulse blue and UV laser generations by the SSFM in a Nd3þ : GdAl3 ðBO3 Þ4 (NGAB) crystal, which is in the same family as the NYAB crystal, have also been successfully performed and obtained some good results [24,25]. The related theoretical analysis has been made by Chen et al. [26]. In this paper, we are focused on the CW blue laser emission by the SSFM of infrared fundamental laser and pump laser from a tunable Ti:sapphire laser in the Nd3þ : GdAl3 ðBO3 Þ4 crystal.
2. Experiments The NGAB is a negative uniaxial crystal. Its refractive index had been measured and the Sellmeier equations of refractive index are as follows [27]: 0:03079 ; k2 þ 0:03265 0:0242 : n2e ðkÞ ¼ 2:82998 þ 2 k þ 0:03127
n2o ðkÞ ¼ 3:07289 þ
ð1Þ ð2Þ
According to these equations, the phase matching angle for type I ðo þ o ! eÞ SSFM of 1.062 lm fundamental wave and the pump laser can be calculated. The phase matching angle as a function of the pump wavelength is presented in Fig. 1. The phase matching angle of SSFM at 1.062 and 0.807 lm is about 34.06°. The plano-concave cavity is adopted in our experiments. The input mirror is a plane mirror coated with high reflectivity at 1.062 lm (99.5%), with reflectivity of more than 90% at blue band from 0.440 to 0.470 lm, and with transmittance of 90% at 0.807 lm. Output coupler with radius curvature of 98 mm has high reflectivity at 1.062 lm (99.3%) and 85% transmittance at 0.459 lm.
Fig. 1. Phase matching angle for type I self-sum-frequencymixing as a function of pump wavelength.
The cavity length is about 61 mm, and kept unchanged throughout the experiments. The pump source is a CW Ti:sapphire tunable laser (SpectraPhysics Model 3900s) with a tunability from 0.7 to 1.0 lm, and was focused into the cavity through a focal lens with 71 mm focal length, which provided a light waist of 30 lm in the NGAB crystal. The crystal NGAB used in the experiments has a dimension of 3 mm 3 mm 5:5 mm, and was cut in the phase matching angle direction of h ¼ 34:06° for type I SSFM. Its both faces were polished to obtain parallel flat surfaces, but not antireflection (AR) coated. Nd3þ doped concentration in the crystal is about 3.35%. The crystal was placed as close as possible to the input mirror, in which large mode overlap between the pump and the fundamental infrared laser could be obtained and intense laser emission could be realized. 3. Results and discussion The output powers of blue and infrared lasers versus absorbed pump power at 0.807 lm are shown in Fig. 2. The infrared laser output increases linearly with the absorbed pump power, while the blue laser emission has a parabolic relation with the absorbed pump power. The infrared and blue laser output powers are 53 mW and 48 lW with the absorbed pump power of 0.99 W, respectively. The laser threshold power is about 100 mW. In the optimum case, by means of the theoretical model in [26] and Eqs. (1) and (2), the blue laser output is calculated to be about 310 lW
M. Huang et al. / Optics Communications 208 (2002) 163–166
Fig. 2. Infrared and blue laser output power as a function of absorbed pump power. The pump wavelength was 0.807 lm.
and much larger than the value measured in our experiments. This may be attributed to the fact that the laser cavity is not fully optimized and the crystal exists some defects. The output power of the blue laser as a function of the pumping wavelength is given in Fig. 3 where the pump power was kept as a constant of 0.8 W. It should be noted that the corresponding absorbed pump power is different for different wavelength of the pump laser. Although the crystal was cut in the direction of the phase matching angle at 0.807 lm, the blue laser was observed in the range from 0.457 to 0.464 lm when the wavelength of pumping laser was tuned from 0.801 to 0.825 lm. According to the theoretical model proposed in [26], the acceptance wavelength is estimated to be about 4.5 nm and close to the ex-
165
perimental value. On the other hand, the focused pump beam had large divergence, part of the pump laser beam satisfied phase matching condition even if a slight mismatch existed between the pump laser beam and the infrared fundamental laser beam, which also made it possible to realize the blue laser emission in a wide range of pump wavelength. Of course, this resulted in a low conversion efficiency of SSFM as well. We also found that the maximum output of blue laser was not at 0.807 lm where the maximum absorption of 93% happens, but at 0.811 lm with the absorption of 76% and the output power of the blue laser was 32 lW, larger than 24 lW at 0.807 lm with the same pump power of 0.8 W (corresponding absorbed pump powers are 0.669 W at 0.807 lm and 0.55 W at 0.811 lm, respectively). This phenomenon has been predicted and explained in the theoretical model proposed by Brenier [11]. The explanation is as follows: if the absorption of the pump laser is too strong, the pump beam is only intense at the entrance of the crystal, the interaction length between the pump and the infrared fundamental laser is shorter, which results in a lower efficient conversion to the blue laser compared with the weaker absorption which leads to a larger interaction length.
4. Conclusions We have demonstrated the blue laser emission by the SSFM in the NGAB crystal and 48 lW blue light output power was obtained with the absorbed pump power of 0.99 W, and the threshold power is about 100 mW. The results indicate that the NGAB crystal is also a promising candidate for a blue laser source by the SSFM. The blue laser emission can be further improved by optimizing the device parameters. The experiments of diodepumped SSFM are being undertaken.
Acknowledgements
Fig. 3. Blue laser output versus pump wavelength. The pump power was kept as a constant of 0.8 W.
This project has been supported by Fujian Provincial International Cooperation Foundation (No. 99-I-7), Foundation of Chinese Academy of
166
M. Huang et al. / Optics Communications 208 (2002) 163–166
Sciences for Outstanding Returned Scholars and National Natural Science Foundation of China (No. 60088004). The authors also would like to thank Prof. A. D. Jiang, M. W. Qiu, C. Y. Tu and Q. G. Tan for providing crystals and helping in the experiments.
References [1] F. Mougel, G. Aka, A. Kahn-Harari, D. Vivien, Opt. Mater. 13 (1999) 293. [2] A. Brenier, G. Boulon, J. Lumin. 86 (2000) 125. [3] Q. Ye, L. Shah, J. Eichenholz, D. Hammons, R. Peale, M. Richardson, A. Chin, B.H.T. Chai, Opt. Commun. 164 (1999) 33. [4] G. Aka, F. Mougel, F. Auge, A. Kahn-Harari, D. Vivien, J.M. Benitez, F. Salin, D. Pelenc, F. Balembois, P. Georges, A. Brun, N. Le Nain, M. Jacquet, J. Alloys Compd. 303–304 (2000) 401. [5] D. Vivien, F. Mougel, F. Auge, G. Aka, A. Kahn-Harari, F. Balembois, G. Lucas-Leclin, P. Geoges, A. Brun, P. Aschehoug, J.M. Benitz, N. Le Nain, M. Jacquet, Opt. Mater. 16 (2001) 213. [6] D. Jaque, J. Capmany, J. Garcia Sole, Appl. Phys. Lett. 75 (1999) 325. [7] D. Jaque, J. Capmany, F. Molero, J. Garcia Sole, Appl. Phys. Lett. 73 (1998) 3659. [8] T.Y. Fan, A. Cordova-Plaza, M.J.F. Digonnet, R.L. Byer, H.J. Shaw, J. Opt. Soc. Am. B 3 (1986) 140. [9] J.M. Eichenhoiz, D.A. Hammons, L. Shah, Q. Ye, R.E. Peale, M. Richardson, B.H.T. Chai, Appl. Phys. Lett. 74 (1999) 1954. [10] J. Bartschke, R. Knappe, K.J. Boller, R. Wallenstein, IEEE J. Quantum Electron. 33 (1997) 2295.
[11] A. Brenier, J. Lumin. 91 (2000) 121. [12] A. Brenier, Opt. Commun. 141 (1997) 221. [13] D. Jaque, J. Capmany, J. Garcia Sole, Z.D. Luo, A.D. Jiang, J. Opt. Soc. Am. B 15 (1998) 1656. [14] F. Mougel, F. Auge, A. Kahn-Harari, D. Vivien, F. Balembois, P. Georges, A. Brun, Appl. Phys. B 67 (1998) 533. [15] F. Mougel, G. Aka, A. Kahn-Harari, H. Hubert, J.M. Benitez, D. Vivien, Opt. Mater. 8 (1997) 161. [16] J.H. Lu, G.M. Li, J.H. Liu, B. Gong, Y.G. Liu, J.Y. Wang, Z.S. Shao, M.H. Jiang, Chin. J. Laser B 8 (1999) 485. [17] F. Mougel, K. Dardenne, G. Aka, A. Kahn-Harari, D. Vivien, J. Opt. Soc. Am. B 16 (1999) 164. [18] D.A. Hammons, J.M. Eichenholz, Q. Ye, B.H.T. Chai, L. Shah, R.E. Peale, M. Richardson, H. Qiu, Opt. Commun. 156 (1998) 327. [19] F. Auge, F. Druon, F. Balembois, P. Georges, A. Brun, F. Mougel, G. Aka, D. Vivien, IEEE J. Quantum Electron. 36 (2000) 598. [20] X.L. Meng, H.J. Zhang, L. Zhu, L.K. Sun, X.S. Liu, P. Wang, J.M. Dewes, Acta Opt. Sinica 20 (2000) 419. [21] E. Montoya, J. Capmany, L.E. Bause, Appl. Phys. Lett. 75 (1999) 325. [22] P. Wang, P. Dekker, J.M. Dawes, J.A. Piper, Y.G. Liu, J.Y. Wang, Opt. Lett. 25 (2000) 731. [23] F. Mougel, G. Aka, A. Kahn-Harari, D. Vivien, Opt. Mater. 13 (1999) 293. [24] A. Brenier, C. Tu, M. Qiu, A. Jiang, J. Li, B. Wu, J. Opt. Soc. Am. B 18 (2001) 1104. [25] A. Brenier, C. Tu, M. Qiu, A. Jiang, J. Li, B. Wu, Opt. Lett. 27 (2002) 240. [26] X.Y. Chen, Z.D. Luo, Y.D. Huang, J. Opt. Soc. Am. B 18 (2001) 646. [27] C.Y. Tu, M.W. Qiu, Y.C. Huang, X.Y. Chen, A.D. Jiang, Z.D. Luo, J. Cryst. Growth 208 (2000) 487.