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High power Nd:YAG lasers operating at 1.3 μm wave band
Infrared Physics & Technology 51 (2007) 91–94 www.elsevier.com/locate/infrared
High power Nd:YAG lasers operating at 1.3 lm wave band Wei Yong, Zhang Ge *, Huang Chenghui, Huang Lingxiong, Shen Hongyuan Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou Fujian 350002, People’s Republic of China Received 17 May 2006 Available online 26 May 2007
Abstract The laser properties of 1.3 lm spectral region in Nd:YAG crystal and their simultaneous dual wavelength threshold condition are investigated. Three types of high power 1.3-lm Nd:YAG quasi continuous wave (QCW) lasers, which operate at 1.319 lm or 1.338 lm single wavelength, 1.319 lm and 1.338 lm simultaneous dual wavelength, are achieved with a maximum average output power of 138 W, 132 W and 120 W, respectively. Ó 2007 Elsevier B.V. All rights reserved. Keywords: 1.319 lm; 1.338 lm; High power; Nd:YAG
1. Introduction High power lasers in the 1.3 lm spectral region are of great interest in the fields of medical applications and fiber optics, their advantages are not only low loss and dispersion in the quartz fiber, but also good absorption of water molecules and very good capability of blood hemostasis [1,2]. On the other hand, the frequency doubling of a 1.3 lm laser is also an attractive alternative for generating a red light or pumping tunable lasers such as Cr:LiSAF [3]. In addition, 1.3-lm multi-wavelength lasers are useful for the newly developed Thz wave generation based on nonlinear optical difference frequency method [2]. The laser emissions at 1.3 lm wave band come from the 4 F3/2–4I13/2 transitions of Nd3+ ion mainly, and it is well known that Nd:YAG crystal is the most common laser gain medium for its excellent laser characteristics physical, and chemical properties so far. The ratio of simulatedemission cross sections between 1.319 lm and 1.338 lm transitions is approximately unit as well as their branching ratios. As the strongest emission line of Nd3+ ion is 1.064 lm, it is rather difficult for both 1.319 lm and *
Corresponding author. Tel.: +86 591 83714648; fax: +86 591 83714648. E-mail address: [email protected] (G. Zhang). 1350-4495/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.infrared.2007.05.005
1.338 lm wavelengths to obtain high power coherent radiation at single wavelength or simultaneous dual wavelength. Many previous works were investigated on this field. A 122 W of CW output power at 1.319 lm from a diodeside-pumped Nd:YAG laser was reported in Ref. [3], transition lines other than 1.319 lm were suppressed by using a solid etalon. In Ref. [4], a diode-end-pumped simultaneous CW dual wavelength laser operating at 1.319 lm and 1.338 lm in a Nd:YAG crystal has been demonstrated, which achieved a total output power of 6.3 W at an absorbed pump power of 15 W with a slope efficiency of 43.5%. Additionally, in our previous work [5], a single wavelength 1338 nm Nd:YAG laser pumped with a Krlamp achieved a 102 W of average output power. In Ref. [6], a Nd:YAG rod was pumped by a laser diode-sidepumping module, and as high as 131 W and 109 W CW lasers at 1319 nm single wavelength and 1319 nm and 1338 nm simultaneous dual wavelength, respectively, were achieved at the pumping power of 555 W. Flash-lamppumped or diode-pumped, pulsed or CW multi-wavelength laser operations in Nd3+ doped materials, such as Nd:YAG [4,6–8], Nd:YLF [9], Nd:YVO4 [10,11], (Er, Nd):YAG [12], (Ho, Nd):YAG [13], Nd:GdVO4 [14], and Nd:YAP [15,16], have been previously reported. In this paper, through calculating the simultaneous dual wavelength threshold
Y. Wei et al. / Infrared Physics & Technology 51 (2007) 91–94
condition, coating the laser cavity at different wavelengths precisely and increasing Nd3+ ions doping level and the length of Nd:YAG rod, we successfully developed three types of high power 1.3 lm wave band Nd:YAG quasi continuous wave (QCW) lasers pumped with a Kr-lamp. Among these lasers, 1.319 lm and 1.338 lm simultaneous dual wavelength lasers achieved an average output power of 120 W, and 1.319 lm together with 1.338 lm single wavelength lasers achieved 138 W and 132 W, respectively.
1.0
1 2
0.8 0.6
R1
92
0.4 0.2 0.0
2. Analysis of dual wavelength threshold condition
0.0
In Ref. [15], the possibilities of simultaneous multiple wavelength lasing in various Nd host crystals have been analyzed first, and the simultaneous multiple wavelength lasing in a CW Nd:YAP laser at both 1.079 lm and 1.341 lm has been achieved for the first time. Further, Shen studied the operating condition of continuous wave simultaneous dual wavelength laser (SDWL) in neodymium host crystal based on the single longitudinal mode rat equation after considering the spatial hole-burning effects, and came to a conclusion that the thresholds of both lasers with different wavelengths are required to satisfy the following inequality in order to realize SDWL operation [16]: r 2 m1 1 1 ln þ 2aL 6 ln þ 2aL 1 þ P in =P th1 r1 m2 R1 R2 pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 þ 8P in =P th1 þ 1 r2 m1 1 ln 6 þ 2aL ; R1 4 r1 m2 2
ð1Þ
where Pin, Pth1, r, m, R, a and L are the pumping power, the threshold power of the laser at k1, the stimulated-mission cross section, the frequency of photo, reflectivity of laser cavity, the cavity loss and the length of the cavity, respectively, the subscripts 1 and 2 are used to denoted the qualities at k1 and k2, respectively. If all conditions given in Eq. (1) are satisfied, the simultaneous dual wavelength laser will be achieved, otherwise, only k1 or k2 will lase if only the left- or right-hand side of Eq. (1) is satisfied. As for Nd:YAG crystal, the strongest emission line of Nd3+ ion is 1.064 lm, the values of 1.319 lm and 1.338 lm stimulated-mission cross section are very close to each other and only 1/5 of that of 1.064 lm line. Some basic parameters of Nd:YAG crystal are listed in Table 1 [18–20].
0.2
1.0
Shen et al. considered the situation of Pin = 1.3 Pth1 for operating condition of continuous wave SDWL [16], but the pump energy was set to be nearly twice that of the threshold energy in the computational model of Q-switch Nd:YAlO3 dual wavelength laser in Ref. [17]. When focused on 1.3 lm Nd:YAG lasers operating in the state of quasi continuous wave (QCW), Pin/Pth1 is set to 2 in this work. According to Eq. (1) and Table 1, the reflectivity conditions for achieving single line or simultaneous dualline laser of 1.319 lm and 1.338 lm can be calculated after restraining the 1.064 lm strong line. The calculated results are shown in Fig. 1. When the reflectivity conditions are set above Curve 1 or below Curve 2 in Fig. 1, the 1.319 lm or the 1.338 lm single line will lase, respectively. If the region of the selected reflectivity values locates between Curve 1 and Curve 2, the 1.319 lm and 1.338 lm dual wavelength lasing will appear simultaneously, which makes an important indication for the design of coatings. 3. Experiments and results The experimental sketch of the 1.3 lm wave band Nd:YAG laser pumped with a Kr-lamp is shown in Fig. 2. The laser cavity consists of two plane mirrors, allreflective mirror M1 and output mirror M2. The length of the cavity is 30 cm. The all-reflective mirror M1 was coated Ge diode detector
µA meter Grating spectrometer
Kr-lamp
1.319 F/3/2–4I13/2 (R2–X1) 0.92 2.27
0.8
Fig. 1. The calculated corresponding reflectivities in Nd:YAG crystal according to Eq. (1), R1 for 1.319 lm reflectivity and R2 for 1.338 lm reflectivity.
Table 1 The basic parameters of Nd:YAG crystal 4
0.6
R2
Power supply
Wavelength k (lm) Energy level Simulated-mission cross section r (1019 cm2) Frequency m (1014 Hz) Cavity loss
0.4
1.338 4 F/3/2–4I13/2 (R2–X3) 0.9
2.24 0.151
M3
Nd:YAG rod M1
Power meter
M2
Fig. 2. Experimental sketch of 1.3 lm wave band Nd:YAG lasers pumped with a Kr-lamp.
Y. Wei et al. / Infrared Physics & Technology 51 (2007) 91–94 Table 2 Reflectivity values of M2 for 1.3 lm wave band Nd:YAG lasers Lasers
Reflectivity values (%)
1.319 lm 1.338 lm 1.319 lm and 1.338 lm dual line
At 1.064 lm
At 1.319 lm
At 1.338 lm
<40 <40 <40
91.5 <85 93.45
<85 92.3 93.32
140
Out power/W
120 100 80
y=-0.96+0.02x
60 40 20 0 0
1000
2000
3000
4000
5000
6000
7000
8000
7000
8000
Pumping power/W 140
Out power/W
120 100 80 60
y=-4.54+0.02x
40 20 0 0
1000
2000
3000
4000
5000
6000
Pumping power/W 120
93
with high reflectivity (HR, R > 99.6%) coatings at 1.319 lm and 1.338 lm wavelengths and assumed the reflectivity of 100%, hence the laser cavity reflectivities, which are the products of reflectivity values of M1 and M2 at different wavelengths, are actually those of output mirror M2. Based on the results depicted in Fig. 1, the output mirror M2 was coated with different reflectivity coatings at corresponding wavelengths (1.064 lm, 1.319 lm and 1.338 lm) in order to obtain the corresponding single lines and simultaneous dual wavelength Nd:YAG lasers at 1.3 lm wave band, whose reflectivity values are tabulated in Table 2. The Nd:YAG rod, with 1.1 at.% Nd3+ ions doping level and coated with a broadband antireflective film at both of end surfaces, is 6 mm in diameter and 120 mm in length. The Kr-lamp ignited by a power source with the pumping repetition rate of 100 Hz is 8 mm in diameter and 100 mm in the distance between the electrodes. The output power was measured by LPM-100 power meter. In order to detect the wavelength of output lasers, the lasing beam was reflected by a beam splitter M3 and absorbed by a Ge diode detector, which was set at the output end of the grating monochromator (Model 44W) for the determination of the laser wavelength. The relationships between pumping power and output power of 1.3-lm Nd:YAG lasers are described in Fig. 3, and the experimental results are listed in Table 3. The output pulses captured by TDS3052B (500 MHz) oscilloscope at pumping power of 2630 W are shown in Fig. 4. It can be known that the full width at half maximum (FWHM) of each pulse are about 0.75 and 0.76 ms, respectively, in Fig. 4a and b. The spectrum of generation with 1.319 lm and 1.338 lm was detected by using the Model 44W grating monochromator sensitive in the IR region (above 1000 nm) at the maximum pumping power of 7243 W. The measured results are depicted in Fig. 5, in which the intension ratio of 1.319 lm and 1.338 lm wavelength is 41:37, and the center wavelength is 1318.8 nm for 1.319 lm wavelength, however the value changes to 1338.2 nm for 1.338 lm wavelength.
Out power/'W
100
4. Conclusion 80
Based on the calculated results of the simultaneous dual wavelength threshold condition, three types of high power Nd:YAG QCW lasers operating at 1.319 lm or 1.338 lm
y=7.02+0.016x
60
40
20
Table 3 Experimental results of 1.3 lm wave band Nd:YAG lasers
0 0
1000
2000
3000
4000
5000
6000
7000
8000
Lasers
Maximum output power
Overall efficiency (%)
Slope efficiency (%)
Instability of output power (%)
1.319 lm 1.338 lm 1.319 lm and 1.338 lm dual line
138 W 132 W 120 W
1.90 1.83 1.64
1.98 2.04 1.61
65 65 65
Pumping power/W Fig. 3. The relationships between the pumping power and output power of 1.3 lm wave band Nd:YAG lasers. (a) Output power of 1.319 lm laser versus pumping power. (b) Output power of 1.338 lm laser versus pumping power. (c) Output power of 1.319 lm and 1.338 lm dual wavelength laser versus pumping power.
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Y. Wei et al. / Infrared Physics & Technology 51 (2007) 91–94
Acknowledgements Intensity (a.u.)
0.10
The authors would like to acknowledge the financial aid from Fujian Science and Project (No. 2002H005) and the Natural Science Foundation of China (60208001).
0.05
References 0.00
0.00
0.01
0.02
0.03
t/s
Intensity/ (a.u.)
0.04
0.02
0.00
0.00
0.02
0.04
t/s Fig. 4. The measured pulse shape with a pump power of 2630 W (a) for 1.319 lm single wavelength laser and (b) for 1.338 lm single wavelength laser.
Intensity/ (a.u.)
40
Center: 1318.8nm FWHM: 0.407nm
Center: 1338.2nm FWHM: 0.376nm 20
0 1320
1330
1340
Wavelength/nm Fig. 5. Measured spectrum of 1.319 lm and 1.338 lm dual wavelength laser.
single wavelength, 1.319 lm and 1.338 lm simultaneous dual wavelength are developed, and have achieved a maximum average output power of 138 W, 132 W and 120 W, respectively. The experimental results show good agreements with those of theoretical analysis.
[1] J.P. Boquillon, O. Musset, H. Guillet et al., High efficiency flashlamppumped lasers at 1.3 lm with Nd-doped crystals-scientific and medical applications, in: CLEO’99, pp. 126–127. [2] Jan Fanta, Va´clav Mandys, Ladislav Hora´k, Lesser curve photoseromyolysis with the Nd-YAG laser, Laser Med. Sci. 5 (3) (1990) 317– 322. [3] Yoko Inoue, Shuichi Fujikawa, Diode-pumped Nd YAG laser producing 122-W CW power at 1.319 lm, IEEE J. Quantum Electron. 36 (6) (2000) 751–756. [4] Rui Zhou, Wulin Wen, et al., Efficient stable simultaneous CW dual wavelength diode-end-pumped Nd:YAG laser operating at 1319 and 1338 lm, Chin. Opt. Lett. (China) 3 (10) (2005) 597–599. [5] Y. Wei, G. Zhang, et al., High power single wavelength 1338 nm Nd:YAG laser, Opt. Laser Technol. 38 (2006) 173–176. [6] Z. Huiyong, Z. Ge, H. Chenghui, et al., 131 W diode-side-pumped 1319 nm single wavelength CW Nd:YAG laser, Appl. Opt. 46 (3) (2006) 384–388. [7] Yu.-E. Hou, Ya-Xian Fan, et al., High-efficiency continuous-wave and Q-switched diode-end-pumped multi-wavelength Nd:YAG lasers, Opt. Commun. 265 (1) (2006) 301–305. [8] Pingxue Li, Dehua Li, et al., Simultaneous dual-wavelength continuous wave laser operation at 1.06 lm and 946 nm in Nd:YAG and their frequency doubling, Opt. Commun. 235 (1–3) (2004) 169–174. [9] W. Vollmer, M.G. Knight, G.A. Rines, J.C. MeCarthy, E.P. Chicklis, in: Digest of Conference on Lasers and Electro-Optics, Paper THM 2, Optical Society of America, Washington, DC, 1983, p. 188. [10] Y.F. Chen, cw dual-wavelength operation of a diode-end-pumped Nd:YVO4 laser, Appl. Phys. B 70 (2000) 475–478. [11] Rui Zhou, Enbang Li, et al., Simultaneous dual-wavelength CW operation using 4F3/2–4I13/2 transitions in Nd:YVO4 crystal, Opt. Commun. 260 (6) (2006) 641–644. [12] W.Q. Shi, R. Kurtz, et al., Simultaneous, multiple wavelength lasing of (Er, Nd):Y3Al5O12, Appl. Phys. Lett. 51 (1987) 1218–1220. [13] J. Machan, R. Kurtz, M. Bass, M. Birnbaum, Simultaneous, multiple wavelength lasing of (Ho, Nd):Y3Al5O12, Appl. Phys. Lett. 51 (17) (1987) 1313–1315. [14] J.L. He, J. Du, et al., High efficiency single- and dual-wavelength Nd:GdVO4 lasers pumped by a fiber-coupled diode, Appl. Phys. B 79 (2004) 301–304. [15] H.Y. Shen, R.R. Zeng, et al., Comparison of simultaneous multiple wavelength lasing in various neodymium host crystals at transitions from 4F3/2–4I11/2 and 4F3/2–4I13/2, Appl. Phys. Lett. 56 (20) (1990) 1937–1938. [16] H.Y. Shen, H. Su, Operating conditions of continuous wave simultaneous dual wavelength laser in neodymium host crystals, J. Appl. Phys. 86 (12) (1999) 6647–6651. [17] H. Su, H.Y. Shen, W.X. Lin, et al., Computational model of Qswitch Nd:YALO3 dual wavelength laser, J. Appl. Phys. 84 (12) (1998) 6519–6522. [18] Walter Koechner, Solid-state Laser Engineering, Science Press, Beijing, 2002, 45. [19] S. Singh, R.G. Smith, L.G. Van Vitert, Stimulated emission cross section and fluorescent quantum efficiency of Nd3+ in yttrium aluminum garnet at room temperature, Phys. Rev. B 10 (1974) 2566. [20] A.A. Kaminskii, Laser Crystals, second ed., Springer Verlag, Berlin, Germany, 1990, p. 332.
High power Nd:YAG lasers operating at 1.3 lm wave band Wei Yong, Zhang Ge *, Huang Chenghui, Huang Lingxiong, Shen Hongyuan Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou Fujian 350002, People’s Republic of China Received 17 May 2006 Available online 26 May 2007
Abstract The laser properties of 1.3 lm spectral region in Nd:YAG crystal and their simultaneous dual wavelength threshold condition are investigated. Three types of high power 1.3-lm Nd:YAG quasi continuous wave (QCW) lasers, which operate at 1.319 lm or 1.338 lm single wavelength, 1.319 lm and 1.338 lm simultaneous dual wavelength, are achieved with a maximum average output power of 138 W, 132 W and 120 W, respectively. Ó 2007 Elsevier B.V. All rights reserved. Keywords: 1.319 lm; 1.338 lm; High power; Nd:YAG
1. Introduction High power lasers in the 1.3 lm spectral region are of great interest in the fields of medical applications and fiber optics, their advantages are not only low loss and dispersion in the quartz fiber, but also good absorption of water molecules and very good capability of blood hemostasis [1,2]. On the other hand, the frequency doubling of a 1.3 lm laser is also an attractive alternative for generating a red light or pumping tunable lasers such as Cr:LiSAF [3]. In addition, 1.3-lm multi-wavelength lasers are useful for the newly developed Thz wave generation based on nonlinear optical difference frequency method [2]. The laser emissions at 1.3 lm wave band come from the 4 F3/2–4I13/2 transitions of Nd3+ ion mainly, and it is well known that Nd:YAG crystal is the most common laser gain medium for its excellent laser characteristics physical, and chemical properties so far. The ratio of simulatedemission cross sections between 1.319 lm and 1.338 lm transitions is approximately unit as well as their branching ratios. As the strongest emission line of Nd3+ ion is 1.064 lm, it is rather difficult for both 1.319 lm and *
Corresponding author. Tel.: +86 591 83714648; fax: +86 591 83714648. E-mail address: [email protected] (G. Zhang). 1350-4495/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.infrared.2007.05.005
1.338 lm wavelengths to obtain high power coherent radiation at single wavelength or simultaneous dual wavelength. Many previous works were investigated on this field. A 122 W of CW output power at 1.319 lm from a diodeside-pumped Nd:YAG laser was reported in Ref. [3], transition lines other than 1.319 lm were suppressed by using a solid etalon. In Ref. [4], a diode-end-pumped simultaneous CW dual wavelength laser operating at 1.319 lm and 1.338 lm in a Nd:YAG crystal has been demonstrated, which achieved a total output power of 6.3 W at an absorbed pump power of 15 W with a slope efficiency of 43.5%. Additionally, in our previous work [5], a single wavelength 1338 nm Nd:YAG laser pumped with a Krlamp achieved a 102 W of average output power. In Ref. [6], a Nd:YAG rod was pumped by a laser diode-sidepumping module, and as high as 131 W and 109 W CW lasers at 1319 nm single wavelength and 1319 nm and 1338 nm simultaneous dual wavelength, respectively, were achieved at the pumping power of 555 W. Flash-lamppumped or diode-pumped, pulsed or CW multi-wavelength laser operations in Nd3+ doped materials, such as Nd:YAG [4,6–8], Nd:YLF [9], Nd:YVO4 [10,11], (Er, Nd):YAG [12], (Ho, Nd):YAG [13], Nd:GdVO4 [14], and Nd:YAP [15,16], have been previously reported. In this paper, through calculating the simultaneous dual wavelength threshold
Y. Wei et al. / Infrared Physics & Technology 51 (2007) 91–94
condition, coating the laser cavity at different wavelengths precisely and increasing Nd3+ ions doping level and the length of Nd:YAG rod, we successfully developed three types of high power 1.3 lm wave band Nd:YAG quasi continuous wave (QCW) lasers pumped with a Kr-lamp. Among these lasers, 1.319 lm and 1.338 lm simultaneous dual wavelength lasers achieved an average output power of 120 W, and 1.319 lm together with 1.338 lm single wavelength lasers achieved 138 W and 132 W, respectively.
1.0
1 2
0.8 0.6
R1
92
0.4 0.2 0.0
2. Analysis of dual wavelength threshold condition
0.0
In Ref. [15], the possibilities of simultaneous multiple wavelength lasing in various Nd host crystals have been analyzed first, and the simultaneous multiple wavelength lasing in a CW Nd:YAP laser at both 1.079 lm and 1.341 lm has been achieved for the first time. Further, Shen studied the operating condition of continuous wave simultaneous dual wavelength laser (SDWL) in neodymium host crystal based on the single longitudinal mode rat equation after considering the spatial hole-burning effects, and came to a conclusion that the thresholds of both lasers with different wavelengths are required to satisfy the following inequality in order to realize SDWL operation [16]: r 2 m1 1 1 ln þ 2aL 6 ln þ 2aL 1 þ P in =P th1 r1 m2 R1 R2 pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 1 þ 8P in =P th1 þ 1 r2 m1 1 ln 6 þ 2aL ; R1 4 r1 m2 2
ð1Þ
where Pin, Pth1, r, m, R, a and L are the pumping power, the threshold power of the laser at k1, the stimulated-mission cross section, the frequency of photo, reflectivity of laser cavity, the cavity loss and the length of the cavity, respectively, the subscripts 1 and 2 are used to denoted the qualities at k1 and k2, respectively. If all conditions given in Eq. (1) are satisfied, the simultaneous dual wavelength laser will be achieved, otherwise, only k1 or k2 will lase if only the left- or right-hand side of Eq. (1) is satisfied. As for Nd:YAG crystal, the strongest emission line of Nd3+ ion is 1.064 lm, the values of 1.319 lm and 1.338 lm stimulated-mission cross section are very close to each other and only 1/5 of that of 1.064 lm line. Some basic parameters of Nd:YAG crystal are listed in Table 1 [18–20].
0.2
1.0
Shen et al. considered the situation of Pin = 1.3 Pth1 for operating condition of continuous wave SDWL [16], but the pump energy was set to be nearly twice that of the threshold energy in the computational model of Q-switch Nd:YAlO3 dual wavelength laser in Ref. [17]. When focused on 1.3 lm Nd:YAG lasers operating in the state of quasi continuous wave (QCW), Pin/Pth1 is set to 2 in this work. According to Eq. (1) and Table 1, the reflectivity conditions for achieving single line or simultaneous dualline laser of 1.319 lm and 1.338 lm can be calculated after restraining the 1.064 lm strong line. The calculated results are shown in Fig. 1. When the reflectivity conditions are set above Curve 1 or below Curve 2 in Fig. 1, the 1.319 lm or the 1.338 lm single line will lase, respectively. If the region of the selected reflectivity values locates between Curve 1 and Curve 2, the 1.319 lm and 1.338 lm dual wavelength lasing will appear simultaneously, which makes an important indication for the design of coatings. 3. Experiments and results The experimental sketch of the 1.3 lm wave band Nd:YAG laser pumped with a Kr-lamp is shown in Fig. 2. The laser cavity consists of two plane mirrors, allreflective mirror M1 and output mirror M2. The length of the cavity is 30 cm. The all-reflective mirror M1 was coated Ge diode detector
µA meter Grating spectrometer
Kr-lamp
1.319 F/3/2–4I13/2 (R2–X1) 0.92 2.27
0.8
Fig. 1. The calculated corresponding reflectivities in Nd:YAG crystal according to Eq. (1), R1 for 1.319 lm reflectivity and R2 for 1.338 lm reflectivity.
Table 1 The basic parameters of Nd:YAG crystal 4
0.6
R2
Power supply
Wavelength k (lm) Energy level Simulated-mission cross section r (1019 cm2) Frequency m (1014 Hz) Cavity loss
0.4
1.338 4 F/3/2–4I13/2 (R2–X3) 0.9
2.24 0.151
M3
Nd:YAG rod M1
Power meter
M2
Fig. 2. Experimental sketch of 1.3 lm wave band Nd:YAG lasers pumped with a Kr-lamp.
Y. Wei et al. / Infrared Physics & Technology 51 (2007) 91–94 Table 2 Reflectivity values of M2 for 1.3 lm wave band Nd:YAG lasers Lasers
Reflectivity values (%)
1.319 lm 1.338 lm 1.319 lm and 1.338 lm dual line
At 1.064 lm
At 1.319 lm
At 1.338 lm
<40 <40 <40
91.5 <85 93.45
<85 92.3 93.32
140
Out power/W
120 100 80
y=-0.96+0.02x
60 40 20 0 0
1000
2000
3000
4000
5000
6000
7000
8000
7000
8000
Pumping power/W 140
Out power/W
120 100 80 60
y=-4.54+0.02x
40 20 0 0
1000
2000
3000
4000
5000
6000
Pumping power/W 120
93
with high reflectivity (HR, R > 99.6%) coatings at 1.319 lm and 1.338 lm wavelengths and assumed the reflectivity of 100%, hence the laser cavity reflectivities, which are the products of reflectivity values of M1 and M2 at different wavelengths, are actually those of output mirror M2. Based on the results depicted in Fig. 1, the output mirror M2 was coated with different reflectivity coatings at corresponding wavelengths (1.064 lm, 1.319 lm and 1.338 lm) in order to obtain the corresponding single lines and simultaneous dual wavelength Nd:YAG lasers at 1.3 lm wave band, whose reflectivity values are tabulated in Table 2. The Nd:YAG rod, with 1.1 at.% Nd3+ ions doping level and coated with a broadband antireflective film at both of end surfaces, is 6 mm in diameter and 120 mm in length. The Kr-lamp ignited by a power source with the pumping repetition rate of 100 Hz is 8 mm in diameter and 100 mm in the distance between the electrodes. The output power was measured by LPM-100 power meter. In order to detect the wavelength of output lasers, the lasing beam was reflected by a beam splitter M3 and absorbed by a Ge diode detector, which was set at the output end of the grating monochromator (Model 44W) for the determination of the laser wavelength. The relationships between pumping power and output power of 1.3-lm Nd:YAG lasers are described in Fig. 3, and the experimental results are listed in Table 3. The output pulses captured by TDS3052B (500 MHz) oscilloscope at pumping power of 2630 W are shown in Fig. 4. It can be known that the full width at half maximum (FWHM) of each pulse are about 0.75 and 0.76 ms, respectively, in Fig. 4a and b. The spectrum of generation with 1.319 lm and 1.338 lm was detected by using the Model 44W grating monochromator sensitive in the IR region (above 1000 nm) at the maximum pumping power of 7243 W. The measured results are depicted in Fig. 5, in which the intension ratio of 1.319 lm and 1.338 lm wavelength is 41:37, and the center wavelength is 1318.8 nm for 1.319 lm wavelength, however the value changes to 1338.2 nm for 1.338 lm wavelength.
Out power/'W
100
4. Conclusion 80
Based on the calculated results of the simultaneous dual wavelength threshold condition, three types of high power Nd:YAG QCW lasers operating at 1.319 lm or 1.338 lm
y=7.02+0.016x
60
40
20
Table 3 Experimental results of 1.3 lm wave band Nd:YAG lasers
0 0
1000
2000
3000
4000
5000
6000
7000
8000
Lasers
Maximum output power
Overall efficiency (%)
Slope efficiency (%)
Instability of output power (%)
1.319 lm 1.338 lm 1.319 lm and 1.338 lm dual line
138 W 132 W 120 W
1.90 1.83 1.64
1.98 2.04 1.61
65 65 65
Pumping power/W Fig. 3. The relationships between the pumping power and output power of 1.3 lm wave band Nd:YAG lasers. (a) Output power of 1.319 lm laser versus pumping power. (b) Output power of 1.338 lm laser versus pumping power. (c) Output power of 1.319 lm and 1.338 lm dual wavelength laser versus pumping power.
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Y. Wei et al. / Infrared Physics & Technology 51 (2007) 91–94
Acknowledgements Intensity (a.u.)
0.10
The authors would like to acknowledge the financial aid from Fujian Science and Project (No. 2002H005) and the Natural Science Foundation of China (60208001).
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References 0.00
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t/s
Intensity/ (a.u.)
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t/s Fig. 4. The measured pulse shape with a pump power of 2630 W (a) for 1.319 lm single wavelength laser and (b) for 1.338 lm single wavelength laser.
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Center: 1318.8nm FWHM: 0.407nm
Center: 1338.2nm FWHM: 0.376nm 20
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Wavelength/nm Fig. 5. Measured spectrum of 1.319 lm and 1.338 lm dual wavelength laser.
single wavelength, 1.319 lm and 1.338 lm simultaneous dual wavelength are developed, and have achieved a maximum average output power of 138 W, 132 W and 120 W, respectively. The experimental results show good agreements with those of theoretical analysis.
[1] J.P. Boquillon, O. Musset, H. Guillet et al., High efficiency flashlamppumped lasers at 1.3 lm with Nd-doped crystals-scientific and medical applications, in: CLEO’99, pp. 126–127. [2] Jan Fanta, Va´clav Mandys, Ladislav Hora´k, Lesser curve photoseromyolysis with the Nd-YAG laser, Laser Med. Sci. 5 (3) (1990) 317– 322. [3] Yoko Inoue, Shuichi Fujikawa, Diode-pumped Nd YAG laser producing 122-W CW power at 1.319 lm, IEEE J. Quantum Electron. 36 (6) (2000) 751–756. [4] Rui Zhou, Wulin Wen, et al., Efficient stable simultaneous CW dual wavelength diode-end-pumped Nd:YAG laser operating at 1319 and 1338 lm, Chin. Opt. Lett. (China) 3 (10) (2005) 597–599. [5] Y. Wei, G. Zhang, et al., High power single wavelength 1338 nm Nd:YAG laser, Opt. Laser Technol. 38 (2006) 173–176. [6] Z. Huiyong, Z. Ge, H. Chenghui, et al., 131 W diode-side-pumped 1319 nm single wavelength CW Nd:YAG laser, Appl. Opt. 46 (3) (2006) 384–388. [7] Yu.-E. Hou, Ya-Xian Fan, et al., High-efficiency continuous-wave and Q-switched diode-end-pumped multi-wavelength Nd:YAG lasers, Opt. Commun. 265 (1) (2006) 301–305. [8] Pingxue Li, Dehua Li, et al., Simultaneous dual-wavelength continuous wave laser operation at 1.06 lm and 946 nm in Nd:YAG and their frequency doubling, Opt. Commun. 235 (1–3) (2004) 169–174. [9] W. Vollmer, M.G. Knight, G.A. Rines, J.C. MeCarthy, E.P. Chicklis, in: Digest of Conference on Lasers and Electro-Optics, Paper THM 2, Optical Society of America, Washington, DC, 1983, p. 188. [10] Y.F. Chen, cw dual-wavelength operation of a diode-end-pumped Nd:YVO4 laser, Appl. Phys. B 70 (2000) 475–478. [11] Rui Zhou, Enbang Li, et al., Simultaneous dual-wavelength CW operation using 4F3/2–4I13/2 transitions in Nd:YVO4 crystal, Opt. Commun. 260 (6) (2006) 641–644. [12] W.Q. Shi, R. Kurtz, et al., Simultaneous, multiple wavelength lasing of (Er, Nd):Y3Al5O12, Appl. Phys. Lett. 51 (1987) 1218–1220. [13] J. Machan, R. Kurtz, M. Bass, M. Birnbaum, Simultaneous, multiple wavelength lasing of (Ho, Nd):Y3Al5O12, Appl. Phys. Lett. 51 (17) (1987) 1313–1315. [14] J.L. He, J. Du, et al., High efficiency single- and dual-wavelength Nd:GdVO4 lasers pumped by a fiber-coupled diode, Appl. Phys. B 79 (2004) 301–304. [15] H.Y. Shen, R.R. Zeng, et al., Comparison of simultaneous multiple wavelength lasing in various neodymium host crystals at transitions from 4F3/2–4I11/2 and 4F3/2–4I13/2, Appl. Phys. Lett. 56 (20) (1990) 1937–1938. [16] H.Y. Shen, H. Su, Operating conditions of continuous wave simultaneous dual wavelength laser in neodymium host crystals, J. Appl. Phys. 86 (12) (1999) 6647–6651. [17] H. Su, H.Y. Shen, W.X. Lin, et al., Computational model of Qswitch Nd:YALO3 dual wavelength laser, J. Appl. Phys. 84 (12) (1998) 6519–6522. [18] Walter Koechner, Solid-state Laser Engineering, Science Press, Beijing, 2002, 45. [19] S. Singh, R.G. Smith, L.G. Van Vitert, Stimulated emission cross section and fluorescent quantum efficiency of Nd3+ in yttrium aluminum garnet at room temperature, Phys. Rev. B 10 (1974) 2566. [20] A.A. Kaminskii, Laser Crystals, second ed., Springer Verlag, Berlin, Germany, 1990, p. 332.