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Diode-pumped passively Q-switched c-cut Nd:GdVO4 laser
Optics Communications 219 (2003) 317–321 www.elsevier.com/locate/optcom
Diode-pumped passively Q-switched c-cut Nd:GdVO4 laser Jie Liu *, Jimin Yang, Jingliang He Laboratory of Modern Optics, Shandong Normal University, Jinan 250014, PR China Received 5 November 2002; received in revised form 7 February 2003; accepted 12 February 2003
Abstract We demonstrate a passively Q-switched operation of c-cut Nd:GdVO4 laser in which a Cr4þ :YAG crystal was used as the saturable absorber for the first time as far as we know. Stable laser pulses 9 ns with 65 lJ energy can be generated with this laser. Compared with a-cut Nd:GdVO4 crystal, c-cut crystal can produce a peak power much higher than a-cut crystal. Ó 2003 Elsevier Science B.V. All rights reserved. PACS: 42.55.Xi; 42.55.Rz; 42.60.Gd Keywords: Diode-pumped; Cr4þ :YAG; Passive Q-switch; c-cut Nd:GdVO4 laser
1. Introduction All solid-state Q-switched lasers are of potential interest for numerous applications, such as micromachining, ranging, remote sensing, and microsurgery. Compared with active Q-switching, passive Q-switching is simple and inexpensive without the need for high-voltage or RF drivers. Recently, Cr4þ :YAG crystals have been successfully used as passively Q-switched for a variety of gain media such as Nd:YAG [1–3], Nd:YVO4 [4–6], and a-cut Nd:GdVO4 [7–9] crystals. Passively Q-switched Nd:YAG=Cr4þ :YAG lasers can generate extremely short high-peak-power pulses. The
*
Corresponding author. Tel.: +86-531-618-6736; fax: +86531-655-3334. E-mail address: [email protected] (J. Liu).
relatively narrow absorption band of a Nd:YAG crystal, however, sets stringent requirements on the spectrum of the pump diodes. Very recently, a diode-pumped passively Q-switched c-cut Nd:YVO4 microchip laser [10] demonstrated short-pulse (subnanosecond) and high-peak-power lasers. The main advantages of the c-cut Nd:YVO4 crystal are the combination of its high-absorption cross-section, wide absorption bandwidth, and low intrinsic losses. GdVO4 and YVO4 crystals belong to the group of oxide compounds crystallizing in a Zircon structure with a tetragonal space group [11,12]. Compared with Nd:YVO4 , Nd:GdVO4 crystals have almost entirely similar lasing properties, but much higher absorption coefficient and larger absorption cross-section. Besides these, most importantly, Nd:GdVO4 crystal is characterized by its unexpectedly high-thermal conductivity along the h1 1 0i directions, which was measured to be
0030-4018/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0030-4018(03)01284-7
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ð1Þ
cross-section (rg ), and the lifetime (s) of the laser medium. c is the inversion reduction factor with a value between 0 and 2 [13]. b is the ratio of the excited-state absorption cross-section to that of the ground-state absorption in the saturable absorber with a value of 0:09 0:28. Since the rg1 value of the Nd:GdVO4 crystal is comparable to the ra value of the Cr4þ :YAG crystal (3:6 1019 cm2 –7 1018 cm2 ), using a Cr4þ :YAG crystal as a saturable absorber in a-cut Nd:GdVO4 laser generally produces a longer pulse width and lower peak power [7]. Because the effective stimulated emission cross-section of the c-cut crystal (rg2 ) is much smaller than that of the a-cut crystal (rg1 ), so the c-cut Nd:GdVO4 crystals may be more appropriate than the a-cut crystal with a Cr4þ :YAG crystal as a saturable absorber, as indicated in the criterion of Eq. (1). In our experiment, we make a comparison between c-cut and a-cut Nd:GdVO4 lasers passively Q-switched with a Cr4þ :YAG saturable absorber. The laser arrangement is shown schematically in Fig. 1. The length of the flat–flat cavity is approximately 50 mm. A piece of Cr4þ :YAG crystal was used to test the properties of the passively Q-switched Nd:GdVO4 lasers. It was 0.4 mm thick with an initial transmission of 85% at 1.06 lm. Two pieces of 1.3% Nd3þ -doped Nd:GdVO4 crystals with dimensions of 3 3 4 mm3 were used in the experiment, one was c-cut, the other was a-cut. The Nd:GdVO4 crystal was pumped by a fibre coupled semiconductor laser at a wavelength of 808 nm with the maximum output power of 10 W and a numerical aperture of 0.12. The output from the semiconductor laser is focused with a coupling optics system onto the Nd:GdVO4
where aa , La and ra are the small-signal absorption coefficient, the thickness, and the absorption crosssection of the saturable absorber. Aa is the laser beam area in the saturable absorber. ag , Lg and rg are the small-signal gain coefficient, the thickness, and the emission cross-section of the laser medium. Ag is the laser beam area in the laser medium. According to the theory of laser oscillation, ag equals to DN rg for typical four-level systems. DN is the inversion population density, which depends on the dopant concentration, the emission
Fig. 1. Schematics for passively Q-switched Nd:GdVO4 =Cr4þ : YAG lasers.
comparable to that of Nd:YAG. Thus Nd:GdVO4 crystals are promising substitutes for Nd:YVO4 and Nd:YAG in diode-pumped laser products. It is a very efficient laser material for diode pumping and has been receiving considerable attention in recent years. Since the early work on a-cut Nd:GdVO4 lasers, passively Q-switching operation has been realized with Cr4þ :YAG in a diodepumped a-cut Nd:GdVO4 laser [7–9]. The conventional a-cut Nd:GdVO4 have a large emission cross-section (rg1 ¼ 7:6 1019 cm2 ). When a Nd: GdVO4 crystal is cut along the c axis, i.e., c-cut, the effective stimulated emission cross-section is dominated by rg2 ¼ 1:2 1019 cm2 . In this paper, we demonstrated, for the first time as far as we know, a passively Q-switched c-cut Nd:GdVO4 lasers at 1.06 lm with Cr4þ :YAG crystal as the saturable absorber in a simple flat–flat resonator.
2. Experimental laser setup Diode-pumped passively Q-switched Nd:Gd VO4 lasers using Cr4þ :YAG crystal as the saturable absorber are not easy to operate successfully. The main difficulties stem from the fact that the conventional a-cut Nd:GdVO4 , having a large emission cross-section, thus need a cavity to produce a large beam area in Nd:GdVO4 crystal and a small beam area in Cr4þ :YAG crystal so that they can satisfy the passively Q-switching criteria. From the analysis of the coupled rate equations, the criterion for good passive Q-switching is given by [4,7]: 2aa La ra Ag c ; > 2ag Lg rg Aa 1 b
J. Liu et al. / Optics Communications 219 (2003) 317–321
crystal. The left side of the Nd:GdVO4 crystal is coated to be highly reflecting (HR) at 1.06 lm, and anti-reflecting (AR) at 808 nm pumping wavelength. It also acts as the input mirror M1 . The other side of the crystal is coated for AR at 1.06 lm. M2 was a flat mirror with transmission at 1.06 lm of 10% served as output coupler. The pulse temporal behavior was recorded by a PIN (NEW FOUCS 1623) and oscilloscope (TeKtronix TDS620A). In such a configuration, the diameters of the TEM00 laser mode in the Nd:GdVO4 and Cr4þ :YAG crystals were calculated as about 700 and 320 lm, respectively. We found in our experiments that such a flat–flat cavity could satisfy the Q-switching criteria and mode-matching condition.
319
Fig. 2 shows the CW output power (without the Cr4þ :YAG crystal) of a-cut and c-cut Nd:GdVO4 lasers as a function of incident pump power. Because of the c-cut Nd:GdVO4 crystal has a lower stimulated emission cross-section compared with the a-cut crystal, a higher threshold was expected. As is seen, thresholds of 0.4 and 1.5 W, slop efficiencies of 48% and 50% were obtained for the a-cut and c-cut Nd:GdVO4 crystals, respectively. The higher slop efficiency for the c-cut Nd:GdVO4 crystal is because that its intrinsic loss is smaller than that of the a-cut Nd:GdVO4 crystal. The
conversion efficiency of the pump power into the output power for a-cut and c-cut Nd:GdVO4 crystals were about 47% and 41%, respectively. When the incident pump power was 8 W, we obtained 3.75 W (a-cut) and 3.25 W (c-cut) output power at the wavelength of 1.06 lm. Fig. 3 shows the average output power of a-cut and c-cut Nd:GdVO4 passively Q-switched lasers as function of incident pump power with a saturable absorber of T0 ¼ 85%. The threshold and the slop efficiency are 1.8 W and 14% for a-cut crystal, respectively. The threshold for the c-cut crystal was 3.3 W. Although the threshold of the c-cut crystal is higher, the corresponding slop efficiency of 20% was obtained. For the passively Q-switched operation, the conversion efficiency of the pump power into the average output power for a-cut and c-cut Nd:GdVO4 crystals were about 10.8% and 12.5%, respectively. When the incident pump power was 8 W, The average output power at the wavelength of 1.06 lm was measured to be about 870 and 996 mW for a-cut and c-cut Nd:GdVO4 crystals, respectively. Figs. 4 and 5 show the pulse width and the pulse-repetition rate, respectively, versus the incident pump power for both lasers. It can be seen that the pulse width is insensitive to the pump power in the c-cut Nd:GdVO4 =Cr4þ :YAG passively Q-switched laser. At the incident pump power of 8 W, the pulse width for a-cut and c-cut crystals were 30 and 9 ns, and the pulse-repetition rate for a-cut and c-cut crystals were 76 and 15.3
Fig. 2. The CW output power of a-cut and c-cut Nd:GdVO4 lasers as a function of incident pump power.
Fig. 3. The average output power of a-cut and c-cut Nd:GdVO4 passively Q-switched lasers as a function of incident pump power with a saturable absorber of T0 ¼ 85%.
3. Results and discussion
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Fig. 4. The pulse width versus the incident pump power for a-cut and c-cut Nd:GdVO4 passively Q-switched lasers.
Fig. 6. The pulse peak power versus the incident pump power for a-cut and c-cut Nd:GdVO4 passively Q-switched lasers.
effect to produce much higher peak power just like Nd:YVO4 lasers [10]. It is inferred that a decrease in the initial transmission of the saturable absorber will result an increase of the pulse energy and a decrease of the pulse width for the c-cut Nd:GdVO4 crystal. Therefore, a much higher peak power will be obtained if we used a lower transmission of the saturable absorber. 4. Conclusions
Fig. 5. The pulse-repetition rate versus the incident pump power for a-cut and c-cut Nd:GdVO4 passively Q-switched lasers.
kHz, respectively. At the same pump power, the peak power and pulse energy for c-cut crystal were 7.23 kW and 65 lJ, respectively, which are much higher than the a-cut crystal of 382 W and 11.4 lJ. Fig. 6 illustrate the pulse peak power of a-cut and c-cut lasers as a function of incident pump power. The pulse-to-pulse amplitude fluctuations were measured to be less than 5% for c-cut Nd:GdVO4 laser. In the a-cut Nd:GdVO4 =Cr4þ :YAG passively Q-switched laser, a decrease in the initial transmission of the absorber resulted in an increase of the pulse energy and a decrease of the pulse width, thus leading to a higher peak power [7]. Compared with the a-cut Nd:GdVO4 =Cr4þ :YAG lasers, a c-cut Nd:GdVO4 can enhance the passive Q-switching
In summary, we have demonstrated a passively Q-switched c-cut Nd:GdVO4 =Cr4þ :YAG lasers firstly as far as we know. When a Cr4þ :YAG crystal with an initial transmission of 85% was used, we obtained 996 mW average output power at the incident pump power of 8 W, the corresponding pulse width and repetition frequency were 9 ns and 15.3 kHz, respectively. The pulse energy and peak power were 65 lJ and 7.23 kW, respectively. This result confirms that in order to obtain narrow pulse duration and high-peak power the c-cut Nd:GdVO4 crystal is more appropriate than the acut crystal for the passively Q-switched laser with a Cr4þ :YAG saturable absorber.
Acknowledgements This work was supported by the National Natural Science Foundation of China under Grant No. 60078011.
J. Liu et al. / Optics Communications 219 (2003) 317–321
References [1] Y. Shimony, Z. Burshtein, A. Ben-Amar Baranga, et al., IEEE J. Quant. Electron. 32 (1996) 305. [2] R.S. Afzal, A.W. Yu, J.J. Zayhowski, T.Y. Fan, Opt. Lett. 22 (1997) 1314. [3] J. Song, C. Li, N.S. Kim, Appl. Opt. 39 (2000) 4954. [4] Y. Bai, N. Wu, J. Zhang, J. Li, S. Li, P. Deng, Appl. Opt. 36 (1997) 2468. [5] J.L. He, W. Hou, H.L. Zhang, et al., Chin. Phys. Lett. 15 (1998) 883. [6] C. Li, J. Song, D.Y. Shen, J.Q. Xu, Opt. Commun. 186 (2000) 245.
321
[7] C. Li, J. Song, D.Y. Shen, N.S. Kim, J. Lu, Appl. Phys. B 70 (2000) 471. [8] I.V. Klimov, V.B. Tsvetkov, I.A. Shcherbakov, et al., OSA TOPS Adv. Solid-State Lasers 1 (1996) 438. [9] C. Du, J. Liu, Z. Wang, et al., Opt. Laser Technol. 34 (2002) 699. [10] Y.F. Chen, Y.P. Lan, Appl. Phys. B 74 (2002) 415. [11] H.D. Jiang, H.J. Zhang, J.Y. Wang, et al., Opt. Commun. 198 (2001) 447. [12] H.J. Zhang, J.H. Liu, J.Y. Wang, et al., J. Opt. Soc. Am. B 19 (2002) 18. [13] J.J. Degnan, D.B. Coyle, R.B. Kay, IEEE J. Quant. Electron. QE-34 (1998) 887.
Diode-pumped passively Q-switched c-cut Nd:GdVO4 laser Jie Liu *, Jimin Yang, Jingliang He Laboratory of Modern Optics, Shandong Normal University, Jinan 250014, PR China Received 5 November 2002; received in revised form 7 February 2003; accepted 12 February 2003
Abstract We demonstrate a passively Q-switched operation of c-cut Nd:GdVO4 laser in which a Cr4þ :YAG crystal was used as the saturable absorber for the first time as far as we know. Stable laser pulses 9 ns with 65 lJ energy can be generated with this laser. Compared with a-cut Nd:GdVO4 crystal, c-cut crystal can produce a peak power much higher than a-cut crystal. Ó 2003 Elsevier Science B.V. All rights reserved. PACS: 42.55.Xi; 42.55.Rz; 42.60.Gd Keywords: Diode-pumped; Cr4þ :YAG; Passive Q-switch; c-cut Nd:GdVO4 laser
1. Introduction All solid-state Q-switched lasers are of potential interest for numerous applications, such as micromachining, ranging, remote sensing, and microsurgery. Compared with active Q-switching, passive Q-switching is simple and inexpensive without the need for high-voltage or RF drivers. Recently, Cr4þ :YAG crystals have been successfully used as passively Q-switched for a variety of gain media such as Nd:YAG [1–3], Nd:YVO4 [4–6], and a-cut Nd:GdVO4 [7–9] crystals. Passively Q-switched Nd:YAG=Cr4þ :YAG lasers can generate extremely short high-peak-power pulses. The
*
Corresponding author. Tel.: +86-531-618-6736; fax: +86531-655-3334. E-mail address: [email protected] (J. Liu).
relatively narrow absorption band of a Nd:YAG crystal, however, sets stringent requirements on the spectrum of the pump diodes. Very recently, a diode-pumped passively Q-switched c-cut Nd:YVO4 microchip laser [10] demonstrated short-pulse (subnanosecond) and high-peak-power lasers. The main advantages of the c-cut Nd:YVO4 crystal are the combination of its high-absorption cross-section, wide absorption bandwidth, and low intrinsic losses. GdVO4 and YVO4 crystals belong to the group of oxide compounds crystallizing in a Zircon structure with a tetragonal space group [11,12]. Compared with Nd:YVO4 , Nd:GdVO4 crystals have almost entirely similar lasing properties, but much higher absorption coefficient and larger absorption cross-section. Besides these, most importantly, Nd:GdVO4 crystal is characterized by its unexpectedly high-thermal conductivity along the h1 1 0i directions, which was measured to be
0030-4018/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0030-4018(03)01284-7
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J. Liu et al. / Optics Communications 219 (2003) 317–321
ð1Þ
cross-section (rg ), and the lifetime (s) of the laser medium. c is the inversion reduction factor with a value between 0 and 2 [13]. b is the ratio of the excited-state absorption cross-section to that of the ground-state absorption in the saturable absorber with a value of 0:09 0:28. Since the rg1 value of the Nd:GdVO4 crystal is comparable to the ra value of the Cr4þ :YAG crystal (3:6 1019 cm2 –7 1018 cm2 ), using a Cr4þ :YAG crystal as a saturable absorber in a-cut Nd:GdVO4 laser generally produces a longer pulse width and lower peak power [7]. Because the effective stimulated emission cross-section of the c-cut crystal (rg2 ) is much smaller than that of the a-cut crystal (rg1 ), so the c-cut Nd:GdVO4 crystals may be more appropriate than the a-cut crystal with a Cr4þ :YAG crystal as a saturable absorber, as indicated in the criterion of Eq. (1). In our experiment, we make a comparison between c-cut and a-cut Nd:GdVO4 lasers passively Q-switched with a Cr4þ :YAG saturable absorber. The laser arrangement is shown schematically in Fig. 1. The length of the flat–flat cavity is approximately 50 mm. A piece of Cr4þ :YAG crystal was used to test the properties of the passively Q-switched Nd:GdVO4 lasers. It was 0.4 mm thick with an initial transmission of 85% at 1.06 lm. Two pieces of 1.3% Nd3þ -doped Nd:GdVO4 crystals with dimensions of 3 3 4 mm3 were used in the experiment, one was c-cut, the other was a-cut. The Nd:GdVO4 crystal was pumped by a fibre coupled semiconductor laser at a wavelength of 808 nm with the maximum output power of 10 W and a numerical aperture of 0.12. The output from the semiconductor laser is focused with a coupling optics system onto the Nd:GdVO4
where aa , La and ra are the small-signal absorption coefficient, the thickness, and the absorption crosssection of the saturable absorber. Aa is the laser beam area in the saturable absorber. ag , Lg and rg are the small-signal gain coefficient, the thickness, and the emission cross-section of the laser medium. Ag is the laser beam area in the laser medium. According to the theory of laser oscillation, ag equals to DN rg for typical four-level systems. DN is the inversion population density, which depends on the dopant concentration, the emission
Fig. 1. Schematics for passively Q-switched Nd:GdVO4 =Cr4þ : YAG lasers.
comparable to that of Nd:YAG. Thus Nd:GdVO4 crystals are promising substitutes for Nd:YVO4 and Nd:YAG in diode-pumped laser products. It is a very efficient laser material for diode pumping and has been receiving considerable attention in recent years. Since the early work on a-cut Nd:GdVO4 lasers, passively Q-switching operation has been realized with Cr4þ :YAG in a diodepumped a-cut Nd:GdVO4 laser [7–9]. The conventional a-cut Nd:GdVO4 have a large emission cross-section (rg1 ¼ 7:6 1019 cm2 ). When a Nd: GdVO4 crystal is cut along the c axis, i.e., c-cut, the effective stimulated emission cross-section is dominated by rg2 ¼ 1:2 1019 cm2 . In this paper, we demonstrated, for the first time as far as we know, a passively Q-switched c-cut Nd:GdVO4 lasers at 1.06 lm with Cr4þ :YAG crystal as the saturable absorber in a simple flat–flat resonator.
2. Experimental laser setup Diode-pumped passively Q-switched Nd:Gd VO4 lasers using Cr4þ :YAG crystal as the saturable absorber are not easy to operate successfully. The main difficulties stem from the fact that the conventional a-cut Nd:GdVO4 , having a large emission cross-section, thus need a cavity to produce a large beam area in Nd:GdVO4 crystal and a small beam area in Cr4þ :YAG crystal so that they can satisfy the passively Q-switching criteria. From the analysis of the coupled rate equations, the criterion for good passive Q-switching is given by [4,7]: 2aa La ra Ag c ; > 2ag Lg rg Aa 1 b
J. Liu et al. / Optics Communications 219 (2003) 317–321
crystal. The left side of the Nd:GdVO4 crystal is coated to be highly reflecting (HR) at 1.06 lm, and anti-reflecting (AR) at 808 nm pumping wavelength. It also acts as the input mirror M1 . The other side of the crystal is coated for AR at 1.06 lm. M2 was a flat mirror with transmission at 1.06 lm of 10% served as output coupler. The pulse temporal behavior was recorded by a PIN (NEW FOUCS 1623) and oscilloscope (TeKtronix TDS620A). In such a configuration, the diameters of the TEM00 laser mode in the Nd:GdVO4 and Cr4þ :YAG crystals were calculated as about 700 and 320 lm, respectively. We found in our experiments that such a flat–flat cavity could satisfy the Q-switching criteria and mode-matching condition.
319
Fig. 2 shows the CW output power (without the Cr4þ :YAG crystal) of a-cut and c-cut Nd:GdVO4 lasers as a function of incident pump power. Because of the c-cut Nd:GdVO4 crystal has a lower stimulated emission cross-section compared with the a-cut crystal, a higher threshold was expected. As is seen, thresholds of 0.4 and 1.5 W, slop efficiencies of 48% and 50% were obtained for the a-cut and c-cut Nd:GdVO4 crystals, respectively. The higher slop efficiency for the c-cut Nd:GdVO4 crystal is because that its intrinsic loss is smaller than that of the a-cut Nd:GdVO4 crystal. The
conversion efficiency of the pump power into the output power for a-cut and c-cut Nd:GdVO4 crystals were about 47% and 41%, respectively. When the incident pump power was 8 W, we obtained 3.75 W (a-cut) and 3.25 W (c-cut) output power at the wavelength of 1.06 lm. Fig. 3 shows the average output power of a-cut and c-cut Nd:GdVO4 passively Q-switched lasers as function of incident pump power with a saturable absorber of T0 ¼ 85%. The threshold and the slop efficiency are 1.8 W and 14% for a-cut crystal, respectively. The threshold for the c-cut crystal was 3.3 W. Although the threshold of the c-cut crystal is higher, the corresponding slop efficiency of 20% was obtained. For the passively Q-switched operation, the conversion efficiency of the pump power into the average output power for a-cut and c-cut Nd:GdVO4 crystals were about 10.8% and 12.5%, respectively. When the incident pump power was 8 W, The average output power at the wavelength of 1.06 lm was measured to be about 870 and 996 mW for a-cut and c-cut Nd:GdVO4 crystals, respectively. Figs. 4 and 5 show the pulse width and the pulse-repetition rate, respectively, versus the incident pump power for both lasers. It can be seen that the pulse width is insensitive to the pump power in the c-cut Nd:GdVO4 =Cr4þ :YAG passively Q-switched laser. At the incident pump power of 8 W, the pulse width for a-cut and c-cut crystals were 30 and 9 ns, and the pulse-repetition rate for a-cut and c-cut crystals were 76 and 15.3
Fig. 2. The CW output power of a-cut and c-cut Nd:GdVO4 lasers as a function of incident pump power.
Fig. 3. The average output power of a-cut and c-cut Nd:GdVO4 passively Q-switched lasers as a function of incident pump power with a saturable absorber of T0 ¼ 85%.
3. Results and discussion
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Fig. 4. The pulse width versus the incident pump power for a-cut and c-cut Nd:GdVO4 passively Q-switched lasers.
Fig. 6. The pulse peak power versus the incident pump power for a-cut and c-cut Nd:GdVO4 passively Q-switched lasers.
effect to produce much higher peak power just like Nd:YVO4 lasers [10]. It is inferred that a decrease in the initial transmission of the saturable absorber will result an increase of the pulse energy and a decrease of the pulse width for the c-cut Nd:GdVO4 crystal. Therefore, a much higher peak power will be obtained if we used a lower transmission of the saturable absorber. 4. Conclusions
Fig. 5. The pulse-repetition rate versus the incident pump power for a-cut and c-cut Nd:GdVO4 passively Q-switched lasers.
kHz, respectively. At the same pump power, the peak power and pulse energy for c-cut crystal were 7.23 kW and 65 lJ, respectively, which are much higher than the a-cut crystal of 382 W and 11.4 lJ. Fig. 6 illustrate the pulse peak power of a-cut and c-cut lasers as a function of incident pump power. The pulse-to-pulse amplitude fluctuations were measured to be less than 5% for c-cut Nd:GdVO4 laser. In the a-cut Nd:GdVO4 =Cr4þ :YAG passively Q-switched laser, a decrease in the initial transmission of the absorber resulted in an increase of the pulse energy and a decrease of the pulse width, thus leading to a higher peak power [7]. Compared with the a-cut Nd:GdVO4 =Cr4þ :YAG lasers, a c-cut Nd:GdVO4 can enhance the passive Q-switching
In summary, we have demonstrated a passively Q-switched c-cut Nd:GdVO4 =Cr4þ :YAG lasers firstly as far as we know. When a Cr4þ :YAG crystal with an initial transmission of 85% was used, we obtained 996 mW average output power at the incident pump power of 8 W, the corresponding pulse width and repetition frequency were 9 ns and 15.3 kHz, respectively. The pulse energy and peak power were 65 lJ and 7.23 kW, respectively. This result confirms that in order to obtain narrow pulse duration and high-peak power the c-cut Nd:GdVO4 crystal is more appropriate than the acut crystal for the passively Q-switched laser with a Cr4þ :YAG saturable absorber.
Acknowledgements This work was supported by the National Natural Science Foundation of China under Grant No. 60078011.
J. Liu et al. / Optics Communications 219 (2003) 317–321
References [1] Y. Shimony, Z. Burshtein, A. Ben-Amar Baranga, et al., IEEE J. Quant. Electron. 32 (1996) 305. [2] R.S. Afzal, A.W. Yu, J.J. Zayhowski, T.Y. Fan, Opt. Lett. 22 (1997) 1314. [3] J. Song, C. Li, N.S. Kim, Appl. Opt. 39 (2000) 4954. [4] Y. Bai, N. Wu, J. Zhang, J. Li, S. Li, P. Deng, Appl. Opt. 36 (1997) 2468. [5] J.L. He, W. Hou, H.L. Zhang, et al., Chin. Phys. Lett. 15 (1998) 883. [6] C. Li, J. Song, D.Y. Shen, J.Q. Xu, Opt. Commun. 186 (2000) 245.
321
[7] C. Li, J. Song, D.Y. Shen, N.S. Kim, J. Lu, Appl. Phys. B 70 (2000) 471. [8] I.V. Klimov, V.B. Tsvetkov, I.A. Shcherbakov, et al., OSA TOPS Adv. Solid-State Lasers 1 (1996) 438. [9] C. Du, J. Liu, Z. Wang, et al., Opt. Laser Technol. 34 (2002) 699. [10] Y.F. Chen, Y.P. Lan, Appl. Phys. B 74 (2002) 415. [11] H.D. Jiang, H.J. Zhang, J.Y. Wang, et al., Opt. Commun. 198 (2001) 447. [12] H.J. Zhang, J.H. Liu, J.Y. Wang, et al., J. Opt. Soc. Am. B 19 (2002) 18. [13] J.J. Degnan, D.B. Coyle, R.B. Kay, IEEE J. Quant. Electron. QE-34 (1998) 887.