Browsing by Author "Cho, C. Y."

Now showing 1 - 20 of 24

> 100-kW linearly polarized pulse fiber amplifier seeded by a compact efficient passively Q-switched Nd:YVO4 Laser
(2012-11-01)
Zhuang, W. Z.
;
Huang, W. C.
;
Cho, C. Y.
;
Huang, Y. P.
;
Huang, J. Y.
We thoroughly develop compact high-peak-power Nd:YVO4/Cr4+:YAG passively Q-switched lasers (PQS) as the seed source of the fiber amplifier. We exploit a nearly hemispherical cavity to reach the second threshold criterion and systematically consider the thermal lensing effect and the mode-size matching in the overall optimization. Employing a Cr4+:YAG absorber with 70% initial transmission, we obtain a 50-kHz seed pulse train with the pulse duration of 4.8 ns and the pulse energy of 22 mu J at a pump power of 5.4 W. Injecting this seed laser into a polarization maintained Yb-doped fiber, the pulse energy and peak power at a pump power of 16 W are enhanced up to 178 mu J and 37 kW, respectively. We also use an absorber with 40% initial transmission to generate a 25 kHz pulse train with the pulse duration of 1.6 ns and the pulse energy of 36 mu J at a pump power of 5.4 W. With this seed laser, we find that the surface damage of the fiber limits the maximum pulse energy and peak power to be 192 mu J and 120 kW, respectively.
24-W cryogenically cooled Nd:YAG monolithic 946-nm laser with a slope efficiency > 70%
(2015-04-20)
Cho, C. Y.
;
Lee, C. Y.
;
Chang, C. C.
;
Tuan, P. H.
;
Huang, K. F.
A high-power efficient monolithic Nd: YAG 946-nm laser is demonstrated at the cryogenic temperature. By exploring the absorption and the fluorescence spectra of the Nd: YAG crystal, it reveals the fact that the absorption bandwidth at 808 nm is narrowing and the fluorescence intensity at 1061 nm is significant enhanced when the temperature is decreased. The temperature dependence of the lasing threshold at 946 nm is found to display a minimum value near a temperature of 170 K. At an incident pump power of 34.5 W, the local heating leads the optimum temperature to be approximately 120 K and the maximum output power can reach 24.4 W with the conversion efficiency of 71% as well as the slope efficiency up to 75%. (C)2015 Optical Society of America
A cryogenically cooled Nd:YAG monolithic laser for efficient dual-wavelength operation at 1061 and 1064 nm
(2013-04-01)
Cho, C. Y.
;
Tuan, P. H.
;
Yu, Y. T.
;
Huang, K. F.
;
Chen, Y. F.
We experimentally explore the fluorescence spectra of the Nd:YAG (YAG: yttrium aluminum garnet) crystal at cryogenic temperatures to confirm the feasibility of dual-wavelength operation at 1061 and 1064 nm. Furthermore, a cryogenically cooled Nd:YAG crystal with coating to form a monolithic cavity is employed to investigate the performance of the dual-wavelength operation. At an incident pump power of 20 W, the output powers for each wavelength can simultaneously reach 6.0 W at the optimally balanced temperature of 152 K. The optimal temperature for balancing the output powers of the two wavelengths is experimentally determined as a function of the incident pump power intensity.
An energy adjustable linearly polarized passively Q-switched bulk laser with a wedged diffusion-bonded Nd:YAG/Cr4+:YAG crystal
(2015-03-23)
Cho, C. Y.
;
Cheng, H. P.
;
Chang, Y. C.
;
Tang, C. Y.
;
Chen, Y. F.
An energy adjustable passively Q-switched laser is demonstrated with a composite Nd:YAG/Cr4+:YAG crystal by applying a wedged interface inside the crystal. The theoretical model of the monolithic laser resonator is explored to show the energy adjustable feature with different initial transmissions of the saturable absorber at the horizontal axis. By adjusting the pump beam location across the Nd: YAG crystal, the output pulse energy can be flexibly changed from 10.9 mu J to 17.6 mu J while maintaining the same output efficiency. The polarization state of the laser output is found to be along with the polarization of the C-mount pump diode. Finally, the behavior of the multi-transverse-mode oscillation is also discussed for eliminating the instability of the pulse train. (C) 2015 Optical Society of America
Analysis of the optimal temperature for the cryogenic monolithic Nd:YAG laser at 946-nm
(2016-01-11)
Cho, C. Y.
;
Huang, T. L.
;
Cheng, H. P.
;
Huang, K. F.
;
Chen, Y. F.
The optimal temperature for the cryogenic monolithic Nd:YAG laser at 946-nm is theoretically and experimentally analyzed. It is clear that decreasing temperature can considerably eliminate the thermal population at the lower laser level to enhance the quantum efficiency. However, the narrowing of the absorption bandwidth for the gain medium leads to a reduction of the effective absorption efficiency as the temperature is decreased. Consequently, an optimal temperature for the maximum output power is found to be in the range of approximately 120 K to 140 K. It is experimentally verified that employing a pump source with a narrower emission spectrum linewidth contributes a more efficient output for the cryogenic laser. (C) 2016 Optical Society of America
Compact high-pulse-energy passively Q-switched Nd:YLF laser with an ultra-low-magnification unstable resonator: application for efficient optical parametric oscillator
(2013-01-28)
Cho, C. Y.
;
Huang, Y. P.
;
Huang, Y. J.
;
Chen, Y. C.
;
Su, K. W.
We exploit an ultra-low-magnification unstable resonator to develop a high-pulse-energy side-pumped passively Q-switched Nd:YLF/Cr4+:YAG laser with improving beam quality. A wedged laser crystal is employed in the cavity to control the emissions at 1047 nm and 1053 nm independently through the cavity alignment. The pulse energies at 1047 nm and 1053 nm are found to be 19 mJ and 23 mJ, respectively. The peak powers for both wavelengths are higher than 2 MW. Furthermore, the developed Nd:YLF lasers are employed to pump a monolithic optical parametric oscillator for confirming the applicability in nonlinear wavelength conversions. (C) 2013 Optical Society of America
Cryogenically monolithic self-Raman lasers: observation of single-longitudinal-mode operation
(2015-05-01)
Lee, C. Y.
;
Chang, C. C.
;
Tuan, P. H.
;
Cho, C. Y.
;
Huang, K. F.
A cryogenically monolithic Nd:YVO4 self-Raman laser is experimentally explored and theoretically analyzed. The variation of the stimulated Raman scattering (SRS) threshold on the temperature is found to be nonlinear because the reduction of thermal lensing enlarges the cavity mode size. In spite of the nonlinear variation of the SRS threshold on the temperature, the overall SRS output power can be efficiently increased from 0.78 to 1.36 W for temperature decreasing from 285 to 80 K at an absorbed power of 17.2 W. More interestingly, the single-longitudinal-mode operation is experimentally achieved when temperature is lower than 125 K. (C) 2015 Optical Society of America
Diode-end-pumped solid-state lasers with dual gain media for multi-wavelength emission
(2015-01-01)
Cho, C. Y.
;
Chang, C. C.
;
Chen, Y. F.
;
電子物理學系
;
Department of Electrophysics
We develop a theoretical model for designing a compact efficient multi-wavelength laser with dual gain media in a shared resonator. The developed model can be used to analyze the optimal output reflectivity for each wavelength to achieve maximum output power for multi-wavelength emission. We further demonstrate a dual-wavelength laser at 946 nm and 1064 nm with Nd: YAG and Nd: YVO4 crystals to confirm the numerical analysis. Under optimum conditions and at incident pump power of 17 W, output power at 946 nm and 1064 nm was up to 2.51 W and 2.81 W, respectively.
Efficient dual-wavelength laser at 946 and 1064 nm with compactly combined Nd:YAG and Nd:YVO4 crystals
(2013-04-01)
Cho, C. Y.
;
Chang, C. C.
;
Chen, Y. F.
;
電子物理學系
;
Department of Electrophysics
We originally employ a compact combination of a Nd:YAG crystal and a Nd:YVO4 crystal to develop an efficient dual-wavelength laser operating at 946 and 1064 nm. We exploit a short Nd:YAG crystal to generate 946 nm laser by reducing the reabsorption loss and a follow-up Nd:YVO4 crystal to generate a 1064 nm laser by absorbing the residual pump light. The output power ratio between the 946 and 1064 nm emissions can be flexibly adjusted from 0.3 to 0.9 by varying the separation between the two output couplers. At an incident pump power of 17 W, the total output power is generally higher than 5.2 W, with an overall optical-to-optical efficiency greater than 30%.
Efficient high-energy pulse generation from a diode-side-pumped passively Q-switched Nd:YAG laser and application for optical parametric oscillator
(2014-09-01)
Huang, Y. P.
;
Huang, Y. J.
;
Cho, C. Y.
;
電子物理學系
;
Department of Electrophysics
We employ a convex-concave resonator to develop a high-pulse-energy diode-side-pumped passively Q-switched Nd:YAG laser with high extraction efficiency. At a diode pump energy of 227 mJ, the output laser pulse reaches 30 mJ with a pulse width of 6 ns at a repetition rate of 20 Hz. The optical-to-optical conversion efficiency is up to 13.2%. Based on the developed Nd:YAG laser oscillator, we further employ a monolithic KTP crystal to perform the optical parametric oscillator (OPO). With the 1064 nm input energy of 30 mJ, the OPO energy at 1573 nm is found to be 13.3 mJ, corresponding to an OPO conversion efficiency as high as 44.3%.
Efficient high-energy pulse generation from a diode-side-pumped passively Q-switched Nd:YAG laser and application for optical parametric oscillator
(2014-09-01)
Huang, Y. P.
;
Huang, Y. J.
;
Cho, C. Y.
;
電子物理學系
;
Department of Electrophysics
We employ a convex-concave resonator to develop a high-pulse-energy diode-side-pumped passively Q-switched Nd:YAG laser with high extraction efficiency. At a diode pump energy of 227 mJ, the output laser pulse reaches 30 mJ with a pulse width of 6 ns at a repetition rate of 20 Hz. The optical-to-optical conversion efficiency is up to 13.2%. Based on the developed Nd:YAG laser oscillator, we further employ a monolithic KTP crystal to perform the optical parametric oscillator (OPO). With the 1064 nm input energy of 30 mJ, the OPO energy at 1573 nm is found to be 13.3 mJ, corresponding to an OPO conversion efficiency as high as 44.3%.
Efficient high-pulse-energy eye-safe laser generated by an intracavity Nd:YLF/KTP optical parametric oscillator: role of thermally induced polarization switching
(2012)
Huang, Y. J.
;
Tang, C. Y.
;
Huang, Y. P.
;
Cho, C. Y.
;
Su, K. W.
A high-pulse-energy eye-safe laser at 1552 nm is effectually generated by an intracavity Nd:YLF/KTP optical parametric oscillator (OPO) with the help of the thermally induced polarization switching. The polarization characteristics of the c-cut Nd:YLF laser at 1053 nm in the continuous-wave (CW) and Q-switched operation are comprehensively investigated. We experimentally verify the thermally induced birefringence can lead to a polarization switching between the mutually orthogonal components of the fundamental pulses. Consequently, an efficient intracavity nonlinear frequency conversion can be achieved in an optically isotropic laser crystal without any additional polarization control. With this finding, the pulse energy and peak power of the compact Nd: YLF/KTP eye-safe laser under an incident pump power of 12.7 W and a pulse repetition rate of 5 kHz are up to 306 mu J and 4 kW, respectively.
Exploiting concave-convex linear resonators to design end-pumped solid-state lasers with flexible cavity lengths: application for exploring the self-mode-locked operation
(2016-11-14)
Tuan, P. H.
;
Chang, C. C.
;
Lee, C. Y.
;
Cho, C. Y.
;
Liang, H. C.
The characteristics of a convex-concave linear resonator under the thermal lensing effect are theoretically analyzed to find an analytical model for designing end-pumped solid-state lasers with flexible cavity lengths. By exploiting the design model, the power scaling for continuous-wave operation under strong thermal lensing can be easily achieved in the proposed resonator with different cavity lengths. Furthermore, the proposed resonator is applied to explore the exclusive influence of cavity length on the self-mode-locked (SML) operation. It is discovered that the lasing longitudinal modes will split into multiple groups in optical spectrum to lead to a multi-pulse mode-locked temporal state when the cavity length increases. Finally, a theoretical model is derived to reconstruct the experimental results of SML operation to deduce a simple relationship between the group number of lasing modes and the cavity length. (C) 2016 Optical Society of America.
Exploring the self-mode-locked dynamics of cryogenic diode-pumped Nd: YLF lasers: switching of orthogonal polarizations
(2017-08-01)
Huang, T. L.
;
Cho, C. Y.
;
Liang, H. C.
;
Huang, K. F.
;
Chen, Y. F.
The self-mode-locked output for cryogenic Nd:YLF laser at the temperature range of 90 K to 290 K is thoroughly investigated. Linearly polarized self-mode-locked lasing at 1047 nm (053 nm) with a repetition rate up to 1.59 GHz and a pulse width as short as 52 ps can be realized at temperatures above 155 K (below 135 K). Orthogonally polarized self-mode-locked operation can be observed at temperatures near 145 K. During dual-polarization operation, it is found that the polarized component with higher output power is the fundamental transverse mode, whereas the other component with lower output power becomes the high-order transverse mode. The dominant polarized component can be either pi- or sigma-polarization, depending on the fine adjustment of the cavity.
Generation of orthogonally polarized self-mode-locked Nd:YAG lasers with tunable beat frequencies from the thermally induced birefringence
(2016-04-15)
Sung, C. L.
;
Cheng, H. P.
;
Lee, C. Y.
;
Cho, C. Y.
;
Liang, H. C.
The simultaneous self-mode-locking of two orthogonally polarized states in a Nd:YAG laser is demonstrated by using a short linear cavity. A total output power of 3.8 W can be obtained at an incident pump power of 8.2 W. The beat frequency Delta f(c) between two orthogonally polarized mode-locked components is observed and measured precisely. It is found that the beat frequency increases linearly with an increase in the absorbed pump power. The origin of the beat frequency can be utterly manifested by considering the thermally induced birefringence in the Nd: YAG crystal. The present result offers a promising approach to generate orthogonally polarized mode-locked lasers with tunable beat frequency. (C) 2016 Optical Society of America
High-repetition-rate quasi-CW side-pumped mJ eye-safe laser with a monolithic KTP crystal for intracavity optical parametric oscillator
(2014-04-07)
Cho, C. Y.
;
Chen, Y. C.
;
Huang, Y. P.
;
Huang, Y. J.
;
Su, K. W.
We demonstrate a high-repetition-rate millijoule passively Q-switched eye-safe Nd:YVO4 laser pumped by a quasi-CW diode stack. A theoretical analysis has been explored for the design criteria of generating TEMn,0 mode in the diode-stack directly side-pumping configuration. We successfully generate TEMn,0 modes at 1064 nm by adjusting the gain medium with respected to the laser axis. We further observe the spatial cleaning ability for generating an nearly TEM0,0 mode output at 1573 nm with a monolithic OPO cavity. At the repetition rate up to 200 Hz, the output pulse energy reaches 1.21 mJ with the threshold pump energy of 17.9 mJ. (C) 2014 Optical Society of America
Influence of output coupling on the performance of a passively Q-switched Nd:YAG laser with intracavity optical parametric oscillator
(2013-03-25)
Huang, Y. P.
;
Huang, Y. J.
;
Cho, C. Y.
;
Chen, Y. F.
;
電子物理學系
A singly-resonant intracavity optical parametric oscillator (OPO), pumped by a passively Q-switched Nd:YAG laser, is systematically investigated by means of a series of the output mirrors with various reflectivities for the fundamental wavelength at 1064 nm. Experimental results reveal that the output mirror with partial reflectivity instead of high reflection at 1064 nm not only is practicable to avoid the optical coatings damaged, but also enhances the dual-wavelength output efficiency for the OPO signal and fundamental laser waves. The overall optical-to-optical conversion efficiency is enhanced from 6.4% to 8.2% for the reflectivity decreasing from 99.8% to 90%. (C) 2013 Optical Society of America
Modelling end-pumped passively Q-switched Nd-doped crystal lasers: manifestation by a Nd:YVO4/Cr4+:YAG system with a concave-convex resonator
(2017-02-06)
Tuan, P. H.
;
Chang, C. C.
;
Chang, F. L.
;
Lee, C. Y.
;
Sung, C. L.
A theoretical model for the passively Q-switched (PQS) operation which includes the spatial overlapping between the pump and lasing modes under the thermal lensing effect is developed to give a transcendental equation that can directly determine the critical parameters such as pulse energy, pulse repetition rate, and pulse width for the PQS performance. More importantly, an analytical function which gives the approximate solution for the transcendental equation as well as a specific critical criterion for good PQS operation are derived for practical analyses and design. A Nd: YVO4/Cr4+: YAG system with a concave-convex resonator which can achieve fairly stable PQS pulse trains even at a high pump level is further exploited to manifest the proposed spatially dependent model. The good agreement between the experimental results and the theoretical predictions is verified to show the feasibility of the proposed model for designing high-power PQS lasers with high accuracy. (C) 2017 Optical Society of America
Monolithic dual-polarization self-mode-locked Nd: YAG 946-nm lasers: controlling beat frequency and observation of temporal chaos
(2016-10-17)
Cheng, H. P.
;
Huang, T. L.
;
Lee, C. Y.
;
Sung, C. L.
;
Cho, C. Y.
The self-mode-locked (SML) operation at 946 nm can be achieved with a monolithic Nd: YAG crystal when the pump power is above the threshold of the multiple-longitudinal-mode generation. The SML output is further found to include two orthogonal polarization components with a beat frequency coming from the birefringence effect in the laser crystal. The beat frequency can be widely adjusted in the range of 5-220 MHz by controlling the cooling temperature. The present experiment also confirms the theoretical prediction that the two-mode operation generally exhibits the chaotic dynamics when the frequency difference is sufficiently close to the relaxation frequency. (C) 2016 Optical Society of America
Nd:YLF laser at cryogenic temperature with orthogonally polarized simultaneous emission at 1047 nm and 1053 nm
(2014-10-20)
Cho, C. Y.
;
Huang, T. L.
;
Wen, S. M.
;
Huang, Y. J.
;
Huang, K. F.
A Nd:YLF laser at cryogenic temperature is demonstrated for the first time with orthogonally polarized simultaneous emission at 1047 nm and 1053 nm. By exploring the temperature dependence of the fluorescence and the absorption spectra from the Nd: YLF crystal, the feasibility of simultaneous emission at low temperature is achieved. Due to the local heating from the pump absorption, the optimal temperature with respect to the pump power for balancing output powers of simultaneous emission is thoroughly explored. At the optimal temperature of 138 K, the total output power of the simultaneous emission can reach 3.1 W at an incident pump power of 7.9 W, corresponding to the optical to optical slope efficiency up to 43%. (C) 2014 Optical Society of America