I. Long-term stability examination in the UV and DUV regimes
For our developed UV and DUV lasers to be used in commercial applications, a stable long-term operation is necessary. We have packaged a prototypical UV laser at 355 nm which can be operated at a pulse repetition rate of 30-100 kHz. Under a pulse repetition rate of 40 kHz, the maximum output power at 355 nm can be rated to be 2.5 W at an incident pump power of 22 W. We have performed some primary examinations and found that the key to accomplish a reliable long-term stability for the UV laser is that the avoidance of the humidity and airborne contamination. In addition, the high power density of the focused beams into the nonlinear crystal brings in a large risk of causing the surface damage of the crystal for the configuration of the extracavity harmonic generations. This would eventually render the crystal useless at the impact location, especially for the THG crystal. Such practical issue is also observed by the research group from Coherent Inc. They have proposed a solution that relies on the discrete motion to a fresh spot if significant degradation is seen on the old spot of the THG crystal, where the period of the movement is around 300 hours [1]. As a result, they expect the lifetime of their UV laser can be over 20000 hours with the guaranty of the laser performance to be comfortable within the specification. In the future, we will try to move the THG crystal continuously rather then the discrete motion and slightly alleviate the tight focusing inside the THG crystal to examine the reliability of our UV laser. With this prospect, long-term stability without considerable degradation at least 10000 hours can be expected. Similar consideration may also be usefully applied for the long-term operation of the 266-nm laser.
II. Improvement of transverse distribution at 266 nm
Although we have achieved a high-power DUV laser at 266 nm with the maximum output power of up to 1.67 W, the relatively large walk-off angle of the BBO crystal leads the output transverse distribution to behave a rice kernel shape. Recently, a multi-reflected cavity without tightly focusing was proposed to improve the output beam to be circular shape [2]. However, the conversion efficiency from 532 to 266 nm is only 11.9 %, which is significantly lower than our achievement where the conversion efficiency as high as 37.1 % is obtained. Comparative speaking, using the external optics to modify the astigmatism of the 266-nm beam in the EFHG configuration may be a more practical solution to fulfill the circular output profile while preserving the high conversion efficiency thanks to the tightly focused configuration. This idea will be attempted in the future.
To obtain the efficient DUV laser 266 nm via EFHG scheme, the CLBO crystal is another suitable candidate. Compared with the BBO crystal, it is featured by the relatively small walk-off angle, moderate nonlinear coefficient, large angular bandwidth, and high damage threshold. Nevertheless, the main drawback of the CLBO crystal is the highly hygroscopic property, which needs specially designed protected mechanism to be employed for the commercial product with a long-term stability. As long as the hygroscopic issue can be suitably treated, using the CLBO crystal to perform EFHG presents a promising way to obtain high-efficiency 266-nm laser with the circular output profile. This prospect is under preparation.
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III. Power scaling with multi-segmented Nd:YVO4 crystal
In this thesis, we have constructed a novel dual-end-pumped Nd:YVO4 laser at 1064 nm to efficiently generate the UV radiation with the output power as high as 6.65 W. To further scale up the UV output power, more powerful fundamental IR laser is required. The critical issue for power scaling is the thermal management; that is, the thermally induced fracture is the main limiting factor for power scale-up in the end-pumped solid-state laser. Although the composite crystal, which means the active medium is thermally diffusion-bonded by an undoped part to reduce the thermal effect, was recently proposed [3-6], the exponential decay of the pump radiation due to the homogeneous dopant concentration of the active medium results in high temperature gradient and mechanical stress peaks restricting the maximum incident pump power.
More recently, 407-W diode-end-pumped laser has been successfully demonstrated by applying multiple segments with increasing dopant concentrations for the Nd:YAG crystal [7,8]. This multi-segmented concept enable the power scaling of the end-pumped configuration comparable with the side-pumped systems while keeping the advantages of better beam quality factors and conversion efficiency.
The most promising property of the Nd:YVO4 crystal over the Nd:YAG crystal is the constantly polarized emission due to the natural birefringence, which is essentially beneficial for efficient extracavity harmonic generations. To our knowledge, the multi-segmented Nd:YVO4 crystal has not been realized and applied in the nonlinear frequency conversion. We have fabricated a set of the multi-segmented Nd:YVO4
crystals that consist of undoped part, 0.1 at. % active region, and followed by 0.3 at. % active region. We have also prepared the high-power laser diode that can nominally deliver the maximum output power of 70 W around 808 nm. The large potential for power scaling with the multi-segmented Nd:YVO4 crystal is highly expected and is under development.
IV. Energy scaling of Nd:YLF laser with unstable Cavity
As discussed in Sec. 2.7, the larger output energy can be obtained when the cavity mode area inside the gain medium is increased for a given laser crystal. Unstable cavity has been adopted in a number of literatures for the accomplishment of a good laser performance [9-14]. Recently, side-pumped ultra-low-magnification unstable resonators with the Nd:YLF and Nd:YAG crystals have been built in our group. Several tens of millijoule of output energy are accomplished and the developed lasers have been employed to efficiently pump a monolithic OPO for confirming the applicability in nonlinear frequency conversions. Consequently, the energy scaling in the end-pumped Nd:YLF laser with the nearly diffraction-limited output is greatly expected by using the configuration of the unstable cavity. This is another future work to be studied.
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References
[1] C. X. Wang, G. Y. Wang, A. V. Hicks, D. R. Dudley, H. Y. Pang, and N.
Hodgson, “High power Q-switched TEM00 mode diode-pumped solid state lasers with > 30 W output power at 355 nm,” Proc. SPIE 6100, 610019 (2006).
[2] F. Zhuang, N. Ye, C. Huang, H. Zhu, Y. Wei, Z. Chen, H. Wang, and G. Zhang,
“Multi-reflected enhancement of fourth harmonic DUV laser generation at 266 nm,” Opt. Express 18, 25339-25345 (2010).
[3] F. Hanson, “Improved laser performance at 946 and 473 nm from a composite Nd:Y3Al5O12 rod,” Appl. Phys. Lett. 66, 3549-3551 (1995).
[4] M. Tsunekane, N. Taguchi, T. Kasamastu, and H. Inaba, “Analytical and experimental studies on the characteristics of composite solid-state laser rods in diode-end-pumped geometry,” IEEE J. Sel. Top. Quantum Electron. 3, 9-18 (1997).
[5] Z. Zhuo, T. Li, X. Li, and H. Yang, “Investigation of Nd:YVO4/YVO4
composite crystal and its laser performance pumped by a fiber coupled diode laser,” Opt. Commun. 274, 176-181 (2007).
[6] Y. T. Chang, Y. P. Huang, K. W. Su, and Y. F. Chen, “Comparison of thermal lensing effects between single-end and double-end diffusion-bonded Nd:YVO4
crystals for 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions,” Opt. Express 16, 21155-21160 (2008).
[7] D. Kracht, R. Wilhelm, and M. Frede, “407 W end-pumped multi-segmented Nd:YAG laser,” Opt. Express 13, 10140-10144 (2005).
[8] R. Wilhelm, M. Frede, and D. Kracht, “Power scaling of end-pumped solid-state rod lasers by longitudinal dopant concentration gradients,” IEEE J. Quantum Electron. 44, 232-244 (2008).
[9] R. L. Herbst, H. Komine, and R. L. Byer, “A 200 mJ unstable resonator Nd:YAG oscillator,” Opt. Commun. 21, 5-7 (1977).
[10] A. E. Siegman, “Unstable optical resonators,” Appl. Opt. 13, 353-367 (1974).
[11] V. Magni, G. Valentini, and S. De Silverstri, “Recent developments in laser resonator design,” Opt. Quantum Electron. 23, 1105-1134 (1991).
[12] T. Debuisschért, D. Mathieu, J. Raffy, L. Becouarn, E. Lallier, and J. P.
Pocholle, “High beam quality unstable cavity infrared optical parametric
oscillator,” Proc. SPIE 3267, 170-180 (1998).
[13] M. Morin, “Graded reflectivity mirror unstable laser resonators,” Opt. Quantum Electron. 29, 819-866 (1997).
[14] E. Armandillo, C. Norrie, A. Cosentino, P. Laporta, P. Wazen, and P. Maine,
“Diode-pumped high-efficiency high-brightness Q-switched Nd:YAG slab laser,” Opt. Lett. 22, 1168-1170 (1997).
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171
Curriculum Vitae
Personal Data
Name: Yu-Jen Huang
Nationality: Taiwan (R.O.C.) Birthplace: Hualien
Sex: Male
Birthday: Mar. 11, 1987
Telephone (M): 886-910-535385 E-mail: [email protected]
Education
2009~2013 Ph. D. in Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2005~2009 B. S. in Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan
2002~2005 National Hualien Senior High School, Hualien, Taiwan
Work Experience
2012~2013 Research Methods for Applied Science 2011~2012 Computer Simulation and Analysis (I) & (II) 2010~2011 Physics (I) & (II)
Computer Simulation and Analysis (I) & (II) Research Methods for Applied Science 2009~2010 Physics (I) & (II)
Computer Simulation and Analysis (I) & (II)
Specialty
Physics and technology of solid-state laser Optical physcis
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List of Publication
International journal paper:
[1] Y. P. Huang, Y. J. Huang, C. Y. Cho and Y. F. Chen*, “Influence of output coupling on the performance of a passively Q-switched Nd:YAG laser with intracavity optical parametric oscillator,” Opt. Express 21, 7583-7589 (2013). (IF:
3.587)
[2] Y. J. Huang, C. Y. Tang, Y. S. Tzeng, K. W. Su, and Y. F. Chen*, “Efficient high-energy passively Q-switched Nd:YLF/Cr4+:YAG UV laser at 351 nm with pulsed pumping in a hemispherical cavity,” Opt. Lett. 38, 519-521 (2013). (IF:
3.399)
[3] C. Y. Cho, Y. P. Huang, Y. J. Huang, Y. C. Chen, K. W. Su, and Y. F. Chen*,
“Compact high-pulse-energy passively Q-switched Nd:YLF laser with an ultra-low-magnification unstable resonator: application for efficient optical parametric oscillator,” Opt. Express 21, 1489-1495 (2013). (IF: 3.587)
[4] Y. J. Huang, C. Y. Tang, W. L. Lee, Y. P. Huang, S. C. Huang, and Y. F. Chen*,
“Efficient passively Q-switched Nd:YLF TEM00-mode laser at 1053 nm:
selection of polarization with birefringence,” Appl. Phys. B. 108, 313-317 (2012).
(IF: 2.189)
[5] Y. J. Huang, Y. S. Tzeng, C. Y. Tang, Y. P. Huang, and Y. F. Chen*, “Tunable GHz pulse repetition rate operation in high-power TEM00-mode Nd:YLF lasers at 1047 nm and 1053 nm with self mode locking,” Opt. Express 20, 18230-18237 (2012). (IF: 3.587)
[6] Y. J. Huang, Y. P. Huang, P. Y. Chiang, H. C. Liang, K. W. Su, and Y. F. Chen*,
“High-power passively Q-switched Nd:YVO4 UV laser at 355 nm,” Appl. Phys.
B 106, 893-898 (2012). (IF: 2.189)
[7] Y. P. Huang, C. Y. Cho, Y. J. Huang, and Y. F. Chen*, “Orthogonally polarized dual-wavelength Nd:LuVO4 laser at 1086 nm and 1089 nm,” Opt. Express 20, 5644-5651 (2012). (IF: 3.587)
[8] Y. J. Huang, C. Y. Tang, Y. P. Huang, C. Y. Cho, K. W. Su, and Y. F. Chen*,
“Efficient high-pulse-energy eye-safe laser generated by an intracavity Nd:YLF/KTP optical parametric oscillator: role of thermally induced polarization switching,” Laser Phys. Lett. 9, 709-715 (2012). (IF: 9.97)
[9] Y. J. Huang, C. Y. Tang, Y. P. Huang, S. C. Huang, K. W. Su, and Y. F. Chen*,
“Power scale-up of high-pulse-energy passively Q-switched Nd:YLF laser:
influence of negative thermal lens enhanced by upconversion,” Laser Phys. Lett.
9, 625-630 (2012). (IF: 9.97)
[10] J. Y. Huang, W. Z. Zhuang, Y. P. Huang, Y. J. Huang, K. W. Su, and Y. F.
Chen*, “Improvement of stability and efficiency in diode-pumped passively Q-switched intracavity optical parametric oscillator with a monolithic cavity,”
Laser Phys. Lett. 9, 485-490 (2012). (IF: 9.97)
[11] Y. J. Huang, P. Y. Chiang, H. C. Liang, K. W. Su, and Y. F. Chen*, “Efficient high-power UV laser generated by an optimized flat-flat actively Q-switched laser with extra-cavity harmonic generations,” Opt. Commun. 285, 59-63 (2012).
(IF: 1.486)
[12] Y. J. Huang, P. Y. Chiang, H. C. Liang, K. W. Su, and Y. F. Chen*,
“High-power Q-switched laser with high-order Laguerre-Gaussian modes:
application for extra-cavity harmonic generations,” Appl. Phys. B 105, 385-390 (2011). (IF: 2.189)
[13] Y. J. Huang, H. C. Liang, Y. F. Chen*, H. J. Zhang, J. Y. Wang, and M. H. Jiang,
“High-power 10-GHz self-mode-locked Nd:LuVO4 laser,” Laser Phys. 21, 1750-1754 (2011). (IF: 3.605)
[14] Y. T. Yu, Y. J. Huang, P. Y. Chiang, Y. C. Lin, K. F. Huang, and Y. F. Chen*,
“Non-paraxial contributions to the far-field pattern of surface-emitting lasers: a manifestation of the momentum-space wavefunctions of quantum billiards,” J.
Opt. 13, 075705 (2011). (IF: 1.573)
[15] Y. F. Chen*, Y. J. Huang, P. Y. Chiang, Y. C. Lin, and H. C. Liang, “Controlling number of lasing modes for designing short-cavity self-mode-locked Nd-doped vanadate lasers,” Appl. Phys. B 103, 841-846 (2011). (IF: 2.189)
[16] H. C. Liang, Y. J. Huang, P. Y. Chiang, and Y. F. Chen*, “Highly efficient Nd:Gd0.6Y0.4VO4 laser by direct in-band pumping at 914 nm and observation of self-mode-locked operation,” Appl. Phys. B 103, 637-641 (2011). (IF: 2.189) [17] Y. P. Huang, P. Y. Chiang, Y. J. Huang, K. W. Su, Y. F. Chen*, and K. F. Huang,
“High-repetition-rate megawatt millijoule pulses from a Nd:YVO4 laser passively Q-switched by a semiconductor saturable absorber,” Appl. Phys. B 103, 291-294 (2011). (IF: 2.189)
[18] H. C. Liang, P. Y. Chiang, Y. J. Huang, Y. C. Lin, and Y. F. Chen*,