Browsing by Author "Liang, H. C."

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A high-power harmonically self- mode-locked Nd:YVO4 1.34-mu m laser with repetition rate up to 32.1 GHz
(2014-04-01)
Wu, T. W.
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Tsou, C. H.
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Tang, C. Y.
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Liang, H. C.
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Chen, Y. F.
We develop a practical method to achieve harmonically self-mode-locked operation in a Nd:YVO4 1.34-mu m laser for the generation of high-repetition-rate pulse trains. We exploit a gain medium with partial-reflection coating at the lasing wavelength to introduce effective mode selection. We numerically demonstrate that the coated gain medium can effectively modify the mode spacing of the laser cavity to be the harmonics of the free spectral range of the gain medium when the optical cavity length is adjusted to be commensurate with the optical length of the gain medium. We further employ a coated Nd: YVO4 crystal to realize harmonically mode-locked operation with a highest repetition rate of up to 32.1 GHz. At a pump power of 11.5 W, the average output power of 2.3 W is generated with a pulse duration as short as 5.7 ps. The locking range for the cavity length is also experimentally explored.
Analytical model for optimizing the parameters of an external passive Q-switch in a fiber laser
(2008-05-01)
Huang, J. Y.
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Liang, H. C.
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Su, K. W.
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Chen, Y. F.
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電子物理學系
An analytical model is developed for optimizing two key parameters of an external passive Q-switch in a fiber laser from the criterion of the minimum average mode area inside the saturable absorber. One parameter is the optimum focal position that is analytically derived to be a function of the thickness and initial transmission of the saturable absorber. The other parameter is the optimum magnification of the reimaging optics that is analytically derived to be in terms of the numerical aperture and core radius of the laser fiber as well as the thickness and initial transmission of the saturable absorber. To demonstrate the utilization of the present model, an experiment on the subject of the passively Q-switched fiber laser is performed and optimized. (C) 2008 Optical Society of America.
Analytical model for the design of external-cavity passively Q-switched fiber lasers
(2008)
Huang, J. Y.
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Liang, H. C.
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Su, K. W.
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Chen, Y. F.
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電子物理學系
An analytical model has been developed to minimize the effective mode area in a saturable absorber for an external-cavity passively Q-switched fiber laser. Under the condition of minimum effective mode size inside the saturable absorber, the analytical expressions for two key parameters of an optimum system have been derived. One parameter is the optimum focal position that is analytically derived to be a function of the thickness and initial transmission of the saturable absorber. The other parameter is the optimum magnification of the re-imaging optics that is analytically derived to be in terms of the numerical aperture and core radius of the laser fiber as well as the thickness and initial transmission of the saturable absorber. The present model provides a straightforward procedure to adopt a focusing system for the output performance. A diode-pumped ytterbium-doped fiber lasers with a Cr:YAG crystal as a saturable absorber is considered to illustrate the utility of the present model.
Analytical representation for structured light generated by astigmatic transformation of Hermite-Gaussian beams
(2018-01-01)
Hsieh, Y. H.
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Tuan, P. H.
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Tung, J. C.
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Liang, H. C.
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Su, K. W.
Theoretical wave functions are analytically derived to formulate the propagation evolution of the Hermite-Gaussian (HG) beams transformed by single lens astigmatic mode converter with arbitrary angle. The derived wave functions are associated with the combination of the rotation transform and the antisymmetric fractional Fourier transform. The derived formula are validated by the mode conversions of high-order HG beams generated by an off-axis diode-pumped solid-state laser. In addition to validation, the creation and evolution of vortex structures in the transformed HG beams are numerically manifested. The present theoretical model can be applied not only to characterize the evolution of the transformed beams but to design the optical vortex beams with various forms.
Astigmatism inducing the degenerate effect in nearly hemispherical cavities: Generation of three-dimensional structured light
(2017-01-01)
Tung, J. C.
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Hsieh, Y. H.
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Liang, H. C.
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Su, K. W.
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Huang, K. F.
We originally perform an analytical form to explore the influence of the astigmatism on the degenerate effect in nearly hemispherical cavities. The frequency spectrum near hemispherical cavities clearly reveals that not only the difference of cavity lengths between each degeneracies but also frequency gaps have significant difference from non-hemispherical cavities. We further thoroughly demonstrate the laser experiment under the condition of nearly hemispherical cavities to confirm the theoretical exploration that the transverse topology of three-dimensional (3D) structured light in the degenerate cavities is well localized on the Lissajous curves.
Broad expansion of optical frequency combs by self-Raman scattering in coupled-cavity self-mode-locked monolithic lasers
(2017-04-03)
Chang, M. T.
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Huang, T. L.
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Liang, H. C.
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Su, K. W.
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Chen, Y. F.
Broad expansion of optical frequency comb (OFC) by the self-Raman scattering is numerically analyzed and experimentally accomplished in a coupled-cavity self-mode-locked (SML) monolithic Yb:KGW laser. The gain medium is coated to achieve the monolithic SML operation and a partially reflective mirror is further exploited to form the coupled cavity and to multiply the repetition rate up to 128.9 GHz. With a coupled reflectivity of 95%, it is experimentally found that not only the first-order but also second-order stimulated Raman scattering (SRS) can be efficiently generated. The mode-locked OFC can be consequently expanded to reach approximately 8.4 THz, leading the pulse width to be as narrow as 53 fs. At the pump power of 8.7 W, the total output power for the fundamental and the first-and second-Stokes waves can be maintained at 1.6 W. The present exploration provides a promising way to generate the ultrahigh-repetition-rate broadband OFC via the simultaneous SML and SRS processes. (C) 2017 Optical Society of America
Characterizing classical periodic orbits from quantum Green's functions in two-dimensional integrable systems: Harmonic oscillators and quantum billiards
(2017-01-30)
Chen, Y. F.
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Tung, J. C.
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Tuan, P. H.
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Yu, Y. T.
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Liang, H. C.
A general method is developed to characterize the family of classical periodic orbits from the quantum Green's function for the two-dimensional (2D) integrable systems. A decomposing formula related to the beta function is derived to link the quantum Green's function with the individual classical periodic orbits. The practicality of the developed formula is demonstrated by numerically analyzing the 2D commensurate harmonic oscillators and integrable quantum billiards. Numerical analyses reveal that the emergence of the classical features in quantum Green's functions principally comes from the superposition of the degenerate states for 2D harmonic oscillators. On the other hand, the damping factor in quantum Green's functions plays a critical role to display the classical features in mesoscopic regime for integrable quantum billiards, where the physical function of the damping factor is to lead to the coherent superposition of the nearly degenerate eigenstates.
Characterizing the propagation evolution of wave patterns and vortex structures in astigmatic transformations of Hermite-Gaussian beams
(2018-01-01)
Chen, Y. F.
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Chang, C. C.
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Lee, C. Y.
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Tung, J. C.
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Liang, H. C.
Theoretical wave functions are analytically derived to characterize the propagation evolution of the Hermite-Gaussian (HG) beams transformed by a single-lens astigmatic mode converter with arbitrary angle. The derived wave functions are related to the combination of the rotation transform and the antisymmetric fractional Fourier transform. The derived formula is systematically validated by using an off-axis diode-pumped solid-state laser to generate various high-order HG beams for mode conversions. In addition to validation, the creation and evolution of vortex structures in the transformed HG beams are numerically manifested. The present theoretical analyses can be used not only to characterize the evolution of the transformed beams but to design the optical vortex beams with various forms.
Compact efficient high-power triple-color Nd:YVO4 yellow-lime-green self-Raman lasers
(2020-03-01)
Liu, Y. C.
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Chen, C. M.
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Hsiao, J. Q.
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Pan, Y. Y.
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Tsou, C. H.
A novel, to the best of our knowledge, approach is developed to realize a high-power compact efficient yellow-lime-green triple-color Nd : YVO4 self-Raman laser. The 588 nm yellow laser, the 559 nm lime laser, and the 532 nm green laser are converted from the 1064 nm fundamental wave and the 1176 nm Stokes Raman field. The simultaneous three-color operation is accomplished with three stages to step-by-step generate the 588 nm, 559 nm, and 532 nm lasers by using three different lithium triborate (LBO) crystals. By tuning the temperature of each individual LBO crystal, the 588 nm, 559 nm, and 532 nm output powers can be nearly the same and concurrently up to 2.4W at the incident pump power of 30 W, corresponding to a conversion efficiency of 24% for the total output power. (C) 2020 Optical Society of America
Compact efficient multi-GHz Kerr-lens mode-locked diode-pumped Nd:YVO(4) laser
(2008-12-08)
Liang, H. C.
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Chen, Ross C. C.
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Huang, Y. J.
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Su, K. W.
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Chen, Y. F.
We demonstrate the compact efficient multi-GHz Kerr-lens mode locking in a diode-pumped Nd:YVO(4) laser with a simple linear cavity without the need of any additional components. Experimental results reveal that the laser system can be characterized in stable single-pulse and multiple-pulse mode-locked operations. With a pump power of 2.5 W, the compact laser cavity produces average output powers greater than 0.8 W with a pulse width less than 10 ps in the range of 2-6 GHz. (C) 2008 Optical Society of America
Comparative study between conventional and diffusion-bonded Nd-doped vanadate crystals in the passively mode-locked operation
(2010-04-26)
Huang, Y. J.
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Huang, Y. P.
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Liang, H. C.
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Su, K. W.
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Chen, Y. F.
We design a reliable linear three-element cavity to make a comparative study between the conventional and diffusion-bonded Nd:GdVO(4) crystals in the passively mode-locked operation. Experimental investigations reveal that the mode-locked pulse width obtained with the diffusion-bonded crystal is considerably broader than that obtained with the conventional crystal, even though the diffusion-bonded crystal can significantly reduce the thermal effects. The pulse broadening is experimentally verified to come from the length of the undoped part that brings in a reduction of the spatial-hole-burning (SHB) effect. (C) 2010 Optical Society of America
Controlling number of lasing modes for designing short-cavity self-mode-locked Nd-doped vanadate lasers
(2011-06-01)
Chen, Y. F.
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Huang, Y. J.
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Chiang, P. Y.
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Lin, Y. C.
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Liang, H. C.
A short-cavity Nd:YVO(4) laser is employed to confirm that a spontaneous mode locking (SML) typically occurs without employing an extra nonlinearity. We further experimentally demonstrate that reducing the number of longitudinal lasing modes can diminish the phase fluctuation and effectively improve the SML pulse stability. Considering the spatial hole-burning (SHB) effect, an analytical expression is derived to accurately estimate the number of longitudinal lasing modes for a practical design guideline.
Criterion for optimizing high-power acousto-optically Q-switched self-Raman yellow lasers with repetition rates up to 500 kHz
(2020-04-01)
Chen, Y. F.
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Chen, K. Y.
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Liu, Y. C.
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Chen, C. M.
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Tsou, C. H.
The criterion for optimizing the high-power acousto-optically Q-switched self-Raman yellow laser is originally explored for the repetition rate within 100-500 kHz. The minimum allowed value for the gate-open time is experimentally verified to be determined by the pulse buildup time. By using the minimum allowed gate-open time, the highest conversion efficiency can be achieved to raise the output power by approximately 20% in comparison with the conventional results. At a repetition rate of 200 kHz, the maximum output power at 588 nm can be up to 8.8 W at an incident pump power of 26 W. Furthermore, a practical formula is developed to accurately calculate the threshold pump power as a function of the gate-open time for a given repetition rate. (C) 2020 Optical Society of America
Dual-central-wavelength passively mode-locked diffusion-bonded Nd:YVO4/Nd:GdVO4 laser with a semiconductor saturable absorber mirror
(2017-08-01)
Chang, F. L.
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Sung, C. L.
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Huang, T. L.
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Wu, T. W.
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Cho, H. H.
A dual-central-wavelength passively mode-locked laser with full modulation in the 0.31 THz optical beating is achieved by using a diffusion-bonded Nd:YVO4/Nd:GdVO4 crystal and a semiconductor saturable absorber mirror. The output power of the dual-band emission is well balanced by tuning the focal position of the pump waist. At a pump power of 13 W, the total output power is up to 2.7 W with a repetition rate of 297.9 MHz. The autocorrelation traces clearly reveal the synchronization of the dual-band emission. Moreover, an analytical model is developed to manifest the multi-pulse structure caused by the etalon effect of the gain medium. More important, we experimentally verify that the etalon effect can be completely eliminated by using the wedge-cut diffusion-bonded Nd:YVO4/Nd:GdVO4 crystal.
Dual-comb self-mode-locked monolithic Yb:KGW laser with orthogonal polarizations
(2015-04-20)
Chang, M. T.
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Liang, H. C.
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Su, K. W.
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Chen, Y. F.
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電子物理學系
The dependence of lasing threshold on the output transmission is numerically analyzed to find the condition for the gain-to-loss balance for the orthogonal N-p and N-m polarizations with a N-g-cut Yb: KGW laser crystal. With the numerical analysis, an orthogonally polarized dual-comb self-mode- locked operation is experimentally achieved with a coated Yb: KGW crystal to form a monolithic cavity. At a pump power of 5.2 W, the average output power, the pulse repetition rate, and the pulse duration are measured to be 0.24 (0.6) W, 25.8 (25.3) GHz, and 1.06 (1.12) ps for the output along the N-p (N-m) polarization. (C)2015 Optical Society of America
Efficient dual-wavelength diode-end-pumped laser with a diffusion-bonded Nd:YVO4/Nd:GdVO4 crystal
(2015-10-01)
Huang, Y. J.
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Cho, H. H.
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Tzeng, Y. S.
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Liang, H. C.
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Su, K. W.
A new type of diffusion-bonded Nd:YVO4/Nd:GdVO4 hetero-composite crystal is originally designed and applied to diode-end-pumped laser for achieving an efficient dual-comb picosecond operation with self-mode locking for the first time. As high as 1.1 W of the total average output power at 1063.18 and 1064.37 nm is generated under an incident pump power of 5.1 W. The corresponding mode-locked pulse width is 42 ps at a pulse repetition rate of 3.82 GHz. Through the optical beating between two carrier frequencies of each spectral component, a train of ultrashort pulses with sub-terahertz repetition rate is further generated with the effective duration of down to 1.6 ps. (C) 2015 Optical Society of America.
Efficient high-power continuous-wave lasers at green-lime-yellow wavelengths by using a Nd:YVO4 self-Raman crystal
(2019-02-04)
Chen, Y. F.
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Pan, Y. Y.
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Liu, Y. C.
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Cheng, H. P.
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Tsou, C. H.
Efficient high-power continuous-wave Nd:YVO4 visible lasers at versatile wavelengths of 532 (green). 559 (lime). and 588 nm (yellow) are demonstrated to be achieved by using the identical cavity mirrors and gain medium. A dichroic coating is deposited on one end surface of the gain medium to gather the backward green-yellow emission. The green. lime. and yellow outputs are individually optimized by using different phase-matched lithium triborate (LBO) crystals for second harmonic generation (SHG) of the fundamental field, sum frequency generation (SFG) of the fundamental and the stimulated Raman fields. and SHG of the stimulated Raman field, respectively. At a pump power of 31.6 W, the output powers at 532, 559, and 588 nm can be up to 6.8. 5.4. and 3.1 W. The high efficient and compact Nd:YVO4 lasers at green-lime-yellow wavelengths can be potentially beneficial to future applications in retinal photocoagulation. (C) 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
Efficient high-power dual-wavelength lime-green Nd:YVO4 lasers
(2019-03-15)
Chen, Y. F.
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Liu, Y. C.
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Pan, Y. Y.
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Gu, D. Y.
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Cheng, H. P.
An efficient high-power dual-wavelength lime-green Nd:YVO4 self-Raman laser is inventively developed by using two different lithium triborate (LBO) crystals. The first and second LBO crystals are employed to generate the 559 nm lime and 532 nm green lasers, respectively. The temperature of the first LBO crystal is fixed at the optimal phase matching, whereas the temperature of the second LBO crystal is tuned to flexibly control the relative strengths between the 532 and 559 nm waves. When the temperature of the second LBO crystal is set for the maximal total output power, the 532 and 559 nm output powers, respectively, are 7.1 and 2.9 W at a pump power of 31.6 W, corresponding to a conversion efficiency of 31.6%. When the temperature is controlled for the balanced output, the 532 and 559 nm powers, respectively, are 4.3 and 4.2 W at a pump power of 31.6 W, corresponding to a conversion efficiency of 26.9%. (C) 2019 Optical Society of America
Efficient high-power terahertz beating in a dual-wavelength synchronously mode-locked laser with dual gain media
(2014-03-15)
Huang, Y. J.
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Tzeng, Y. S.
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Tang, C. Y.
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Chiang, S. Y.
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Liang, H. C.
We originally present a novel tactic to accomplish a compact efficient dual-wavelength synchronously mode-locked laser by physically combining the Nd:YVO4 crystal to the Nd: GdVO4 crystal as a composite gain medium. With the developed method, the total output power at 1.06 mu m could be effectually produced to reach 1.3 W under the optimally balanced two-color intensities. The corresponding mode-locked pulse width and repetition rate are measured to be 47 ps and 2.86 GHz, respectively. Through the optical beating between two carrier frequencies of dual-color synchronous pulses, a train of 0.32 THz ultrashort pulses is further generated with the effective duration of down to 1.6 ps. (C) 2014 Optical Society of America
Efficient high-power UV laser generated by an optimized flat-flat actively Q-switched laser with extra-cavity harmonic generations
(2012-01-01)
Huang, Y. J.
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Chiang, P. Y.
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Liang, H. C.
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Su, K. W.
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Chen, Y. F.
We investigate the parasitic lasing effect in the high-power actively Q-switched laser with a flat-flat resonator. The parasitic lasing effect in the low-Q stage is found to lead to long tails in the output pulses, corresponding to the peak-power reduction. We experimentally determine the shortest cavity length without the parasitic lasing effect to optimize the performance of the high-power actively Q-switched laser with a flat-flat cavity. We further use the optimized fundamental laser to generate green and UV lasers by extra-cavity harmonic generations. At a pump power of 44 W, the output powers at 355 nm and 532 nm as high as 6.65 W and 8.38 W are obtained at a pulse repetition rate of 40 kHz. (C) 2011 Elsevier B.V. All rights reserved.