Biomedical subjects

Hui-Tian Wang

Publications and source records attributed to Hui-Tian Wang.

8 recordsLinked to original sources

PubMed2006

Saturation effect and forward-dominant second-harmonic generation in single-defect photonic crystals with dual localizations.

We study the forward-dominant output of second-harmonic generation (SHG) in single-defect and dual-localized photonic crystals within the saturation limit. We propose that an asymmetric structure can be used to improve the performance of the enhanced SHG. We get two empirical expressions for the total saturation SHG efficiency and the forward factor and provide a reasonable explanation. The theoretical results predict a nearly 100% conversion efficiency and a nearly 100% forward output. Our work is very valuable for designing nonlinear photonic devices. As a test, a practical asymmetrical structure is presented.

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PubMed2005

Passively mode-locking Nd:Gd0.5Y0.5VO4 laser with an In0.25Ga0.75As absorber grown at low temperature.

We have demonstrated stable self-starting passive mode locking in a diode-end-pumped Nd:Gd0.5Y0.5VO4 laser by using an In0.25Ga0.75As absorber grown at low temperature (LT In0.25Ga0.75As absorber). An In0.25Ga0.75As single-quantum-well absorber, which was grown directly on the GaAs buffer by use of the metal-organic chemical-vapor deposition technique, acts simultaneously as a passive mode-locking device and as an output coupler. Continuous-wave mode-locked pulses were obtained at 1063.5 nm. We achieved a pulse duration of 2.6 ps and an average output power of 2.15 W at a repetition rate of 96.4 MHz.

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PubMed2005

Optimal annular computer-generated holograms for the generation of optical vortices.

We analyze a method for efficiently generating optical vortices by use of annular computer-generated holograms and a spatial light modulator. We found that there exists an optimal annular width by which the reconstructed vortex ring in the focal plane has the steepest gradient and the worthless subbright rings can be largely suppressed. We fitted a general formula for determining the value of this optimal annular width and propose a method for designing a multiring structure of optical vortices and specialized interferometric vortex patterns. Finally, we discuss the situation of a Gaussian beam as illuminated light and find that there exists an optimal beam waist that results in the best energy efficiency.

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PubMed2004

4-ps passively mode-locked Nd:Gd0.5Y0.5VO4 laser with a semiconductor saturable-absorber mirror.

We have demonstrated a passively mode-locked diode end-pumped all-solid-state laser, which is composed of a Nd:Gd0.5Y0.5VO4 crystal and a folded cavity with a semiconductor saturable-absorber mirror grown by metal-organic chemical-vapor deposition. Stable cw mode locking with a 3.8-ps pulse duration at a repetition rate of 112 MHz was obtained. At 13.6 W of the incident pump power, a clean mode-locked fundamental-mode average output power of 3.9 W was achieved with an overall optical-to-optical efficiency of 29.0%, and the slope efficiency was 38.1%.

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PubMed2004

Tunable high-peak-power, high-energy hybrid Q-switched double-clad fiber laser.

A cw laser-diode-pumped Yb-doped double-clad fiber laser operating in a hybrid Q-switched regime was demonstrated. The output pulses had a duration as short as 4.2 ns, a tunable wavelength range from 1080.8 to 1142.7 nm, and a linewidth of less than 0.05 nm. Maximum peak power of approximately 175 kW and single-pulse energy of 1.57 mJ were obtained.

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PubMed2003

Phase-shifting with computer-generated holograms written on a spatial light modulator.

We propose a new computer-controlled phase-shifting method based on computer-generated holograms (CGHs) displayed on a spatial light modulator (SLM). In this method the accurate phase shifts required in phase-shifting digital holography or interferometry are induced by a suitable transformation of the encoding patterns of the CGH displayed on a SLM. Both the theoretical analysis and the experimental results demonstrate the feasibility of this approach. We also discuss possible applications of this method in the field of interferometric null testing of aspheres.

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PubMed2003

Determination of global phase shifts between interferograms by use of an energy-minimum algorithm.

A new algorithm for precise determination of the global phase shift between two interferograms is introduced. First we calculate the frame difference between the first and the second interferogram; the difference is multiplied by a properly chosen test phase factor, and then we implement a two-dimensional Fourier transform of the frame difference and calculate the energy of the first positive (or negative) diffraction order. An iterative approach is used for the test phase to ensure that the minimum energy is obtained, and then the correct phase shift value is found. This method is called the energy-minimum Fourier transform method, which is accurate and noise insensitive compared with the single-point Fourier transform method. Both the theoretical analysis and experimental results are given.

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PubMed2003

Highly efficient direct third-harmonic generation based on control of the electro-optic effect in quasi-periodic optical superlattices.

We present a method for controlling the efficiency of direct third-harmonic generation in quasi-periodic optical superlattices by means of the electro-optic effect. The calculated results manifest that this method is extremely efficient for achieving high efficiency of direct third-harmonic generation in predesigned quasi-phase-matched coupled parametric processes and is feasible at any given fundamental intensity. In addition, we demonstrate that the electro-optic control approach is significantly better than the temperature-control method.

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