August 15, 2014 / Vol. 39, No. 16 / OPTICS LETTERS
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Efficient Q-switched Ho:GdVO4 laser resonantly pumped at 1942 nm B. Q. Yao,1 Y. Ding,1 X. M. Duan,1,* T. Y. Dai,1 Y. L. Ju,1 L. J. Li,2 and W. J. He3 1
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China 2 Institute of Optoelectronic Technology, Heilongjiang Institute of Technology, Harbin 150001, China 3
Sichuan Wisepride Industry Co., LTD, Chengdu 610000, China *Corresponding author: [email protected]
Received June 4, 2014; revised July 10, 2014; accepted July 13, 2014; posted July 14, 2014 (Doc. ID 213472); published August 7, 2014 An efficient 2 μm room-temperature Q-switched Ho:GdVO4 laser end-pumped by a 1942 nm Tm-fiber laser is demonstrated. To our knowledge, this is the first report of Q-switched performance of Ho:GdVO4 crystal. A maximum CW output power of 6.85 W under the absorbed pump power of 24.1 W was obtained with a slope efficiency of 39.5% at a temperature of 17°C. With the same absorbed pump power, a maximum output energy per pulse of about 0.9 mJ and minimum pulse width of 4.7 ns were obtained at the pulsed repetition frequency (PRF) of 5 kHz, corresponding to a peak power of approximately 187.2 kW. © 2014 Optical Society of America OCIS codes: (140.3540) Lasers, Q-switched; (140.3580) Lasers, solid-state; (140.5680) Rare earth and transition metal solid-state lasers. http://dx.doi.org/10.1364/OL.39.004755
Solid-state lasers emitting in the 2 μm spectral region are very attractive for a number of possible applications [1–3], such as atmospheric sensing, wind lidar, medical testing, and molecular spectroscopy. Among various laser crystals, gadolinium vanadate (GdVO4 ) crystals doped with various ions represent a promising new material for diode-pumped lasers and thus have been of interest for some time. The tetragonal uniaxial gadolinium vanadate crystal belongs to the space group of I 41 ∕amd [4]. It was previously shown to be a promising laser host material for Ho3 ions [4]. The GdVO4 crystal has a large thermal conductivity (11.7 W/mK), which makes it favorable to cool the crystal efficiently [5]. The thermal conductivity of GdVO4 is more than a factor of two higher than that of YVO4 and is comparable to YAG. As the laser medium in the 2 μm spectral region, laser performances of Tm:GdVO4 and Tm, Ho:GdVO4 crystals have been widely investigated [6–8]. However, these lasers rely on up-conversion and energy-transfer processes. Consequently, more channels for radiative and nonradiative losses are present, which will result in large heat loading of the laser crystal for room-temperature operation [9]. Singly Ho-doped crystals resonantly pumped at 1.9 μm avoid these problems. The low quantum defect enables high laser efficiencies for various Ho lasers [10–12]. However, there is little report on singly Ho-doped GdVO4 lasers. In 2007, using a Tm:YAP laser as a pump source, a continuous wave (CW) output power of greater than 0.2 W at 2.05 μm was achieved with a slope efficiency of 9% from a Ho:GdVO4 laser operating at room temperature [13]. At the temperature of 7°C, a Ho:GdVO4 laser with output power of 2.03 W was reported [14]. In this Letter, to the best of our knowledge, a roomtemperature acousto-optical (AO) Q-switched Ho:GdVO4 laser end-pumped by a 1942 nm Tm-fiber laser is reported for the first time. A maximum CW output power of 6.85 W under the absorbed pump power of 24.1 W with slope efficiency of 39.5% was obtained at a temperature of 17°C. With the same absorbed pump power, a maximum 0146-9592/14/164755-03$15.00/0
output energy per pulse of about 0.9 mJ and minimum pulse width of 4.7 ns were obtained at a pulse repetition frequency (PRF) of 5 kHz, corresponding to a peak power of approximately 187.2 kW. The output-beamquality factor of M 2x and M 2y was 1.14 and 1.08 at maximum output level, respectively. The experimental setup is schematically shown in Fig. 1. A 50 W FBG-locked Tm-fiber laser was used as the pump source. The output spectrum of the Tm-fiber laser was measured by an EXFO WA-650 spectrum analyzer combined with an EXFO WA-1500 wave meter (0.7 pm spectral resolution). The central wavelength of the Tm-fiber laser was 1942 nm. The absorption spectrum of the Ho:GdVO4 crystal was measured with a JASCO V-570 type ultraviolet/visible/near-IR spectrophotometer with a resolution of 0.4 nm. Thus, an absorption peak of the Ho:GdVO4 crystal is addressed for high pump powers (see Fig. 2). The full unpolarized pump light was collimated and sent through a telescope consisting of two focusing lenses (antireflection, T 99.8%) with respective focal lengths of 8 and 150 mm. The beam-quality factor M 2 of the fiber laser was about 1.8. The spot radius of the pump beam was measured to be 256 μm, resulting in a Rayleigh length (zr πω2 n∕λM 2 ) of about 64 mm with refraction index of n 1.96 inside the crystal. The 4 mm × 4 mm × 20 mm with 1.0 at.% Ho3 active Ho:GdVO4 crystal was grown by the Czochralski method and a-cut along the growth direction. The two end faces of the crystal were antireflection coated at both 1.94 μm
Fig. 1. Experimental setup of the Ho:GdVO4 laser. © 2014 Optical Society of America
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Fig. 2. Absorption spectrum of Ho:GdVO4 crystal.
R=200mm, T=50%, Slope=38.9% R=200mm, T=40%, Slope=39.5% R=200mm, T=2.5%, Slope=10.7% R=150mm, T=30%, Slope=29.1% R=150mm, T=10%, Slope=21.9%
Output power (W)
7 6 5 4 3 2 1 0
efficiency of 39.5%. To the best of our knowledge, this is the highest output power obtained from a roomtemperature Ho:GdVO4 laser pumped by a Tm-fiber laser. By using the above EXFO wavemeter, the output spectrum of the Ho:GdVO4 laser was measured, as shown in Fig. 4. For the transmission of 10%, the output wavelength was centered at 2048.2 nm with full width at half-maximum (FWHM) of 0.2 nm. For the transmission of 2.5%, the output wavelength was centered at 2049.2 nm with FWHM of 1.2 nm. For the transmission of 30% output coupler, the output wavelength was centered at 2047.9 nm with FWHM of 0.2 nm. For the output coupler with T 40% and T 50%, the output wavelength similar to the T 30% was not shown. No visible wavelength shifts were observed under different pump power levels with the five output couplers used in the experiment. Based on the above investigation, the output performance of the Q-switched Ho:GdVO4 laser were demonstrated by using the 200 mm output coupler with a transmission of 40%. The Q-switched laser pulse was detected by an InGaAs photodiode and recorded by a 350 MHz digital oscilloscope. With a PRF of 5, 10, 20, and 30 kHz, the average output power of the Q-switched Ho:GdVO4 laser as a function of the absorbed pump power is shown in Fig. 5. At a PRF of 5 kHz, a maximum output energy per pulse of about 0.9 mJ and a minimum pulse width of 4.7 ns were achieved under the absorbed pump power of 24.1 W, corresponding to a peak power of approximately 187.2 kW. At a PRF of 30 kHz, we obtained a maximum average output power of 6.8 W,
Average output power (W)
(T 99.7%) and 2 μm (T 99.8%). The crystal wrapped in 0.1-mm-thick indium foil was sandwiched between two water-cooled copper heat sinks. The temperature of the cooling water for the laser crystal is controlled at 17°C. A simple L-shaped resonator was used for the Ho:GdVO4 laser with total physical length of about 105 mm. The cavity mirror M1 was flat with high reflectivity at 2 μm and high transmission at 1.94 μm. The flat 45° dichroic mirror M2 had high transmission (T 99.7%) for the pump light and high reflectivity (R 99.8%) at 2 μm. The output coupling M3 was plane-concave mirror. A 35-mm-long quartz acousto-optic Q-switch with an acoustic aperture of 1.1 mm was inserted for Q-switched operation. The radio frequency (RF) was 41 MHz and the RF power was 20 W. In the first experiment, we investigated the CW output performance of the laser. The influence on the output performance of the Ho:GdVO4 laser with several different transmissions and two kinds of curvature (R 150 mm and R 200 mm) output couplers was investigated, as shown in Fig. 3. Without considering thermal lensing, the calculated TEM00 beam radius in the GdVO4 crystal was 230 and 250 μm at the radius of curvature of 150 and 200 mm, respectively. The pump radiation is focused to fill the mode volume of the Ho:GdVO4 resonator. Thus, good overlap of the pump-to-Ho-resonator mode is achieved. Considering the slope efficiency and the stability of output power, the best performance came from the 200 mm curvature output coupler with a transmission of 40%. The threshold absorbed pump power was 7.1 W with a single-pass absorption of 73.6%. Up to 6.85 W output power under 24.1 W total absorbed pump power at the temperature of 17°C was achieved, corresponding to an optical-to-optical efficiency of 28.4% and a slope
Fig. 4. Output spectra of the Ho:GdVO4 laser with different output transmissions.
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PRF= 5kHz, Slope=27.1% PRF= 10kHz, Slope=36.1% PRF= 20kHz, Slope=37.3% PRF= 30kHz, Slope=38.7%
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Fig. 3. CW output power of Ho:GdVO4 laser with different output couplers.
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Fig. 5. Average output power of Q-switched Ho:GdVO4 laser versus absorbed pump power.
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Fig. 6. Pulse width of Q-switched Ho:GdVO4 laser versus absorbed pump power.
My=1.08 0.5 0.4 0.3 0.2 0.1 200
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Fig. 8. Beam radius of the Ho:GdVO4 laser. Inset is the typical 2D beam profiles.
efficiency of 39.5% under the absorbed pump power of 24.1 W was obtained with a maximum CW output power of 6.85 W at 17°C. With the same absorbed pump power, a maximum output energy per pulse of about 0.9 mJ and minimum pulse width of 4.7 ns were obtained at the PRF of 5 kHz, corresponding to a peak power of approximately 187.2 kW. In addition, the output-beam-quality factor of M 2x and M 2y was 1.14 and 1.08 at maximum output level, respectively.
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Fig. 7. Dependence of pulse width on different PRF at an absorbed pump power of 24.1 W.
corresponding to a slope efficiency of 38.7% with respect to the absorbed pump power. Pulse-to-pulse stability was measured at approximately 7% about the mean at 30 kHz. The pulse widths of the Q-switched Ho:GdVO4 laser as a function of the absorbed pump power are shown in Fig. 6, for a PRF of 5, 10, 20, and 30 kHz. In addition, we measured the dependence of laser-pulse widths on different repetition rates when absorbed pump power was 24.1 W, as shown in Fig. 7. The pulse width increased greatly from 4.7 to 29.9 ns as the repetition rate was tuned from 5 to 60 kHz. Correspondingly, the peak power of the laser output decreased from 187.2 to 3.8 kW. To determine the beam quality of the Q-switched Ho:GdVO4 laser, we measured the 1∕e2 beam radius along the propagation direction after passing through a 150 mm focal length lens. Under the maximum absorbed pump power and PRF of 5 kHz, beam radiuses were measured by a 90/10 knife-edge technique at several positions, as shown in Fig. 8. By fitting Gaussian beam standard expression to these data, the beam-quality factor was determined to be 1.14 for M 2x and 1.08 for M 2y . The inset of Fig. 8 is the measured beam-intensity distribution by the, Spiricon’s Pyrocam III pyroelectric array camera. In conclusion, we have demonstrated a roomtemperature AO Q-switched Ho: GdVO4 laser at 2 μm operation pumped by a 1942 nm Tm-fiber laser. A slope
This work is supported by National Natural Science Foundation of China (No. 61308009), China Postdoctoral Science Foundation funded project (No. 2013M540288), and Science Fund for Outstanding Youths of Heilongjiang Province (No. JQ201310). References 1. T. M. Taczak and D. K. Killinger, Appl. Opt. 37, 8460 (1998). 2. S. M. Hannon and J. A. Thomson, J. Mod. Opt. 41, 2175 (1994). 3. J. Yang, Y. Tang, and J. Xu, Photon. Res. 1, 52 (2013). 4. W. Xu, X. Xu, J. Wang, F. Wu, L. Su, G. Zhao, Z. Zhao, G. Zhou, and J. Xu, J. Alloys Compd. 440, 319 (2007). 5. P. A. Studenikin, A. I. Zagumennyi, Y. D. Zavartsev, P. A. Popov, and I. A. Shcherbakov, IEEE J. Quantum Electron. 25, 1162 (1995). 6. M. J. D. Esser, D. Preussler, E. H. Bernhardi, C. Bollig, and M. Posewang, Appl. Phys. B 97, 351 (2009). 7. L. J. Li, B. Q. Yao, Y. F. Bai, Y. W. Liu, Z. L. He, S. Zhou, J. Wang, and M. N. Xing, Laser Phys. 23, 025802 (2013). 8. Y. Du, B. Yao, X. Duan, Z. Cui, Y. Ding, Y. Ju, and Z. Shen, Opt. Express 21, 26506 (2013). 9. B. M. Walsh, Laser Phys. 19, 855 (2009). 10. X. Yang, B. Yao, Y. Ding, X. Li, G. Aka, L. Zheng, and J. Xu, Opt. Express 21, 32566 (2013). 11. Y. Shen, B. Yao, X. Duan, G. Zhu, W. Wang, Y. Ju, and Y. Wang, Opt. Lett. 37, 3558 (2012). 12. M. Schellhorn, in Advances in Optical Materials, OSA Technical Digest (CD) (Optical Society of America, 2011), paper AWA8. 13. B. Q. Yao, Y. F. Li, Y. Z. Wang, X. M. Duan, G. J. Zhao, Y. H. Zong, and J. Xu, Chin. Phys. Lett. 24, 2594 (2007). 14. X. T. Yang and B. Y. Yao, Optik 125, 2484 (2014).
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Efficient Q-switched Ho:GdVO4 laser resonantly pumped at 1942 nm B. Q. Yao,1 Y. Ding,1 X. M. Duan,1,* T. Y. Dai,1 Y. L. Ju,1 L. J. Li,2 and W. J. He3 1
National Key Laboratory of Tunable Laser Technology, Harbin Institute of Technology, Harbin 150001, China 2 Institute of Optoelectronic Technology, Heilongjiang Institute of Technology, Harbin 150001, China 3
Sichuan Wisepride Industry Co., LTD, Chengdu 610000, China *Corresponding author: [email protected]
Received June 4, 2014; revised July 10, 2014; accepted July 13, 2014; posted July 14, 2014 (Doc. ID 213472); published August 7, 2014 An efficient 2 μm room-temperature Q-switched Ho:GdVO4 laser end-pumped by a 1942 nm Tm-fiber laser is demonstrated. To our knowledge, this is the first report of Q-switched performance of Ho:GdVO4 crystal. A maximum CW output power of 6.85 W under the absorbed pump power of 24.1 W was obtained with a slope efficiency of 39.5% at a temperature of 17°C. With the same absorbed pump power, a maximum output energy per pulse of about 0.9 mJ and minimum pulse width of 4.7 ns were obtained at the pulsed repetition frequency (PRF) of 5 kHz, corresponding to a peak power of approximately 187.2 kW. © 2014 Optical Society of America OCIS codes: (140.3540) Lasers, Q-switched; (140.3580) Lasers, solid-state; (140.5680) Rare earth and transition metal solid-state lasers. http://dx.doi.org/10.1364/OL.39.004755
Solid-state lasers emitting in the 2 μm spectral region are very attractive for a number of possible applications [1–3], such as atmospheric sensing, wind lidar, medical testing, and molecular spectroscopy. Among various laser crystals, gadolinium vanadate (GdVO4 ) crystals doped with various ions represent a promising new material for diode-pumped lasers and thus have been of interest for some time. The tetragonal uniaxial gadolinium vanadate crystal belongs to the space group of I 41 ∕amd [4]. It was previously shown to be a promising laser host material for Ho3 ions [4]. The GdVO4 crystal has a large thermal conductivity (11.7 W/mK), which makes it favorable to cool the crystal efficiently [5]. The thermal conductivity of GdVO4 is more than a factor of two higher than that of YVO4 and is comparable to YAG. As the laser medium in the 2 μm spectral region, laser performances of Tm:GdVO4 and Tm, Ho:GdVO4 crystals have been widely investigated [6–8]. However, these lasers rely on up-conversion and energy-transfer processes. Consequently, more channels for radiative and nonradiative losses are present, which will result in large heat loading of the laser crystal for room-temperature operation [9]. Singly Ho-doped crystals resonantly pumped at 1.9 μm avoid these problems. The low quantum defect enables high laser efficiencies for various Ho lasers [10–12]. However, there is little report on singly Ho-doped GdVO4 lasers. In 2007, using a Tm:YAP laser as a pump source, a continuous wave (CW) output power of greater than 0.2 W at 2.05 μm was achieved with a slope efficiency of 9% from a Ho:GdVO4 laser operating at room temperature [13]. At the temperature of 7°C, a Ho:GdVO4 laser with output power of 2.03 W was reported [14]. In this Letter, to the best of our knowledge, a roomtemperature acousto-optical (AO) Q-switched Ho:GdVO4 laser end-pumped by a 1942 nm Tm-fiber laser is reported for the first time. A maximum CW output power of 6.85 W under the absorbed pump power of 24.1 W with slope efficiency of 39.5% was obtained at a temperature of 17°C. With the same absorbed pump power, a maximum 0146-9592/14/164755-03$15.00/0
output energy per pulse of about 0.9 mJ and minimum pulse width of 4.7 ns were obtained at a pulse repetition frequency (PRF) of 5 kHz, corresponding to a peak power of approximately 187.2 kW. The output-beamquality factor of M 2x and M 2y was 1.14 and 1.08 at maximum output level, respectively. The experimental setup is schematically shown in Fig. 1. A 50 W FBG-locked Tm-fiber laser was used as the pump source. The output spectrum of the Tm-fiber laser was measured by an EXFO WA-650 spectrum analyzer combined with an EXFO WA-1500 wave meter (0.7 pm spectral resolution). The central wavelength of the Tm-fiber laser was 1942 nm. The absorption spectrum of the Ho:GdVO4 crystal was measured with a JASCO V-570 type ultraviolet/visible/near-IR spectrophotometer with a resolution of 0.4 nm. Thus, an absorption peak of the Ho:GdVO4 crystal is addressed for high pump powers (see Fig. 2). The full unpolarized pump light was collimated and sent through a telescope consisting of two focusing lenses (antireflection, T 99.8%) with respective focal lengths of 8 and 150 mm. The beam-quality factor M 2 of the fiber laser was about 1.8. The spot radius of the pump beam was measured to be 256 μm, resulting in a Rayleigh length (zr πω2 n∕λM 2 ) of about 64 mm with refraction index of n 1.96 inside the crystal. The 4 mm × 4 mm × 20 mm with 1.0 at.% Ho3 active Ho:GdVO4 crystal was grown by the Czochralski method and a-cut along the growth direction. The two end faces of the crystal were antireflection coated at both 1.94 μm
Fig. 1. Experimental setup of the Ho:GdVO4 laser. © 2014 Optical Society of America
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OPTICS LETTERS / Vol. 39, No. 16 / August 15, 2014 1.4
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Fig. 2. Absorption spectrum of Ho:GdVO4 crystal.
R=200mm, T=50%, Slope=38.9% R=200mm, T=40%, Slope=39.5% R=200mm, T=2.5%, Slope=10.7% R=150mm, T=30%, Slope=29.1% R=150mm, T=10%, Slope=21.9%
Output power (W)
7 6 5 4 3 2 1 0
efficiency of 39.5%. To the best of our knowledge, this is the highest output power obtained from a roomtemperature Ho:GdVO4 laser pumped by a Tm-fiber laser. By using the above EXFO wavemeter, the output spectrum of the Ho:GdVO4 laser was measured, as shown in Fig. 4. For the transmission of 10%, the output wavelength was centered at 2048.2 nm with full width at half-maximum (FWHM) of 0.2 nm. For the transmission of 2.5%, the output wavelength was centered at 2049.2 nm with FWHM of 1.2 nm. For the transmission of 30% output coupler, the output wavelength was centered at 2047.9 nm with FWHM of 0.2 nm. For the output coupler with T 40% and T 50%, the output wavelength similar to the T 30% was not shown. No visible wavelength shifts were observed under different pump power levels with the five output couplers used in the experiment. Based on the above investigation, the output performance of the Q-switched Ho:GdVO4 laser were demonstrated by using the 200 mm output coupler with a transmission of 40%. The Q-switched laser pulse was detected by an InGaAs photodiode and recorded by a 350 MHz digital oscilloscope. With a PRF of 5, 10, 20, and 30 kHz, the average output power of the Q-switched Ho:GdVO4 laser as a function of the absorbed pump power is shown in Fig. 5. At a PRF of 5 kHz, a maximum output energy per pulse of about 0.9 mJ and a minimum pulse width of 4.7 ns were achieved under the absorbed pump power of 24.1 W, corresponding to a peak power of approximately 187.2 kW. At a PRF of 30 kHz, we obtained a maximum average output power of 6.8 W,
Average output power (W)
(T 99.7%) and 2 μm (T 99.8%). The crystal wrapped in 0.1-mm-thick indium foil was sandwiched between two water-cooled copper heat sinks. The temperature of the cooling water for the laser crystal is controlled at 17°C. A simple L-shaped resonator was used for the Ho:GdVO4 laser with total physical length of about 105 mm. The cavity mirror M1 was flat with high reflectivity at 2 μm and high transmission at 1.94 μm. The flat 45° dichroic mirror M2 had high transmission (T 99.7%) for the pump light and high reflectivity (R 99.8%) at 2 μm. The output coupling M3 was plane-concave mirror. A 35-mm-long quartz acousto-optic Q-switch with an acoustic aperture of 1.1 mm was inserted for Q-switched operation. The radio frequency (RF) was 41 MHz and the RF power was 20 W. In the first experiment, we investigated the CW output performance of the laser. The influence on the output performance of the Ho:GdVO4 laser with several different transmissions and two kinds of curvature (R 150 mm and R 200 mm) output couplers was investigated, as shown in Fig. 3. Without considering thermal lensing, the calculated TEM00 beam radius in the GdVO4 crystal was 230 and 250 μm at the radius of curvature of 150 and 200 mm, respectively. The pump radiation is focused to fill the mode volume of the Ho:GdVO4 resonator. Thus, good overlap of the pump-to-Ho-resonator mode is achieved. Considering the slope efficiency and the stability of output power, the best performance came from the 200 mm curvature output coupler with a transmission of 40%. The threshold absorbed pump power was 7.1 W with a single-pass absorption of 73.6%. Up to 6.85 W output power under 24.1 W total absorbed pump power at the temperature of 17°C was achieved, corresponding to an optical-to-optical efficiency of 28.4% and a slope
Fig. 4. Output spectra of the Ho:GdVO4 laser with different output transmissions.
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Fig. 3. CW output power of Ho:GdVO4 laser with different output couplers.
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Fig. 5. Average output power of Q-switched Ho:GdVO4 laser versus absorbed pump power.
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Fig. 6. Pulse width of Q-switched Ho:GdVO4 laser versus absorbed pump power.
My=1.08 0.5 0.4 0.3 0.2 0.1 200
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Fig. 8. Beam radius of the Ho:GdVO4 laser. Inset is the typical 2D beam profiles.
efficiency of 39.5% under the absorbed pump power of 24.1 W was obtained with a maximum CW output power of 6.85 W at 17°C. With the same absorbed pump power, a maximum output energy per pulse of about 0.9 mJ and minimum pulse width of 4.7 ns were obtained at the PRF of 5 kHz, corresponding to a peak power of approximately 187.2 kW. In addition, the output-beam-quality factor of M 2x and M 2y was 1.14 and 1.08 at maximum output level, respectively.
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Fig. 7. Dependence of pulse width on different PRF at an absorbed pump power of 24.1 W.
corresponding to a slope efficiency of 38.7% with respect to the absorbed pump power. Pulse-to-pulse stability was measured at approximately 7% about the mean at 30 kHz. The pulse widths of the Q-switched Ho:GdVO4 laser as a function of the absorbed pump power are shown in Fig. 6, for a PRF of 5, 10, 20, and 30 kHz. In addition, we measured the dependence of laser-pulse widths on different repetition rates when absorbed pump power was 24.1 W, as shown in Fig. 7. The pulse width increased greatly from 4.7 to 29.9 ns as the repetition rate was tuned from 5 to 60 kHz. Correspondingly, the peak power of the laser output decreased from 187.2 to 3.8 kW. To determine the beam quality of the Q-switched Ho:GdVO4 laser, we measured the 1∕e2 beam radius along the propagation direction after passing through a 150 mm focal length lens. Under the maximum absorbed pump power and PRF of 5 kHz, beam radiuses were measured by a 90/10 knife-edge technique at several positions, as shown in Fig. 8. By fitting Gaussian beam standard expression to these data, the beam-quality factor was determined to be 1.14 for M 2x and 1.08 for M 2y . The inset of Fig. 8 is the measured beam-intensity distribution by the, Spiricon’s Pyrocam III pyroelectric array camera. In conclusion, we have demonstrated a roomtemperature AO Q-switched Ho: GdVO4 laser at 2 μm operation pumped by a 1942 nm Tm-fiber laser. A slope
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