Browsing by Author "Tai, PT"

Now showing 1 - 6 of 6

Bottle beam from a bare laser for single-beam trapping
(2004-11-10)
Chen, CH
;
Tai, PT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We demonstrate that a laser beam converging from a specific transverse mode is a bottle beam, as described in J. Opt. Soc. Am. B 20, 1220 (2003). To our knowledge, this is the first time that a bottle beam has been generated directly from a laser. By calculating the radiation forces on a dielectric Rayleigh sphere in the bottle beam, we show that the single beam can trap high-refractive-index particles at the multiple axial sites of intensity maxima, and it can confine low-index particles on a transverse plane within the bottle regions. Such a novel laser beam may have other applications. (C) 2004 Optical Society of America.
Cavity-configuration-dependent instability in a tightly focused end-pumped solid-state laser
(2004-11-01)
Chen, CH
;
Tai, PT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
We experimentally studied the cavity-configuration-dependent instability in an end-pumped Nd:YVO4 laser in the vicinity of the degenerate resonator configuration Of g(1)g(2) = 1/4 with small pump size. We found that the laser instability occurs in a narrow range of cavity tuning on each side of the degeneracy, which shows periodic, period-doubling, and chaotic time evolutions. By using Collin's integral together with rate equations and taking into account the thermal lens effect, we show that the simulation is consistent with the experiments. The observed instabilities are new and, as far as we know, this is the first report that discusses the relationship between the instability and the thermal lens effect. (C) 2004 Elsevier B.V. All rights reserved.
Direct generation of optical bottle beams from a tightly focused end-pumped solid-state laser
(2004-11-29)
Tai, PT
;
Hsieh, WF
;
Chen, CH
;
光電工程學系
;
Department of Photonics
We demonstrate that various optical bottle beams can be directly generated from a tightly focused end-pumped Nd:YVO4 laser. By controlling the size of pump beam and intracavity aperture in a planoconcave cavity, we obtain well contrasting optical bottles with semiconfocal, 1/3-, and 1/5-degenerate cavity configurations. These beams result, respectively, from the superposition of the fundamental mode and the corresponding lowest degenerate transverse eigenmode, which is in-phase at their beam waists. Unlike that of our previous simulation model, this new observation is universal; it is suitable for any kind of gain media in tightly end-pumped lasers. (C) 2004 Optical Society of America.
Multibeam-waist modes in an end-pumped Nd : YVO4 laser
(2003-06-01)
Chen, CH
;
Tai, PT
;
Hsieh, WF
;
Wei, MD
;
光電工程學系
We studied both numerically and experimentally the transverse modes near degenerate resonator configurations such as g(1)g(2) = 1/4, 1/2, 3/4 in a simple plano-concave Nd:YVO4 laser with a small pump size. We found that there are stationary modes that show an additional beam waist besides the well-known waist on the flat mirror end near 9 19 2 = 1/4, 3/4. When the specific modes of the three degeneracies propagate through a lens, they are capable of exhibiting multiple beam waists. The multibeam-waist mode possesses a small waist size without a ring structure in the near field on the flat mirror end; nevertheless, it has a far-field pattern with many concentric rings. The numerical results show good agreement with the experimental observations. Furthermore, by simultaneously considering the wavelike and the raylike character of the multibeam-waist mode, we found that it can be represented as a superposition of N consecutive round-trip electric fields of period-N solution in the degenerate empty cavity, where N = 2 for g(1)g(2) = 1/2 and N = 3 for g(1)g(2) 1/4, 3/4. (C) 2003 Optical Society of America.
Suppression of spatial hole burning in a solid-state laser with the degenerate resonator configuration
(2005-03-07)
Tai, PT
;
Hsieh, WF
;
光電工程學系
;
Department of Photonics
Under degenerate resonator configuration and tightly focused pump beam in a linear-cavity solid-state laser, the spatial hole-burning effect can be suppressed. This laser can attain very high intensity in the gain medium due to shrinkage of its beam waist to match the pump beam and therefore most of its gain is depleted even by a standing wave. This was demonstrated by a simulation with spatial dependent rate equations and experiment results of a plano-concave Nd: YVO4 laser. The suppression effect was observed up to 20 times the pump threshold. (C) 2005 Optical Society of America.
Transverse excess noise factor and transverse mode locking in a gain-guided laser
(2005-01-17)
Chen, CH
;
Tai, PT
;
Chiu, WH
;
Hsieh, WF
;
光電工程學系
We use the Collins integral together with a rate equation to calculate the transverse mode profiles near g(1)g(2) = 1/4 in a tightly focused end-pumped Nd:YVO4 laser. The transverse mode locking is confirmed from the mode decomposition into the degenerate empty-cavity eigenmodes and from the observation of beam profile variation along the propagation distance. We obtain that the calculated transverse excess noise factor without considering the thermal effect is consistent with the previous research and it depends on the pump size. We further study the influence of the thermal lens effect on the K factor and discuss how to suppress the laser instabilities that occur near the degeneracy. (C) 2004 Elsevier B.V. All rights reserved.