Zhang Guang-Yin

All-optical logic-gates based on bacteriorhodopsin film

Based on self-diffraction in bacteriorhodopsin (bR) film, we propose all-optical NOT, XOR, half adder and XNOR logic operations. Using the relation between diffraction light and the polarization states of recording beams, we demonstrate NOT and XNOR logic operations. Studying the relation of polarization states among the diffracting, recording and reading beams, we implement XOR logic and half adder operations with three inputs. The methods are simple and practicable.

Photorefractive Spatial Dark-Soliton Stripes in LiNbO3:Fe Crystal and Their Application

We observed the photorefractive spatial dark-soliton stripes in LiNbO3:Fe crystal, and demonstrate the planar waveguide property of refractive index profile induced by these spatial dark-soliton stripes. We suggest a new mothed to form the planar waveguide utilizing the grating fixing technique.

Light-climbing effect in LiNbO(3):Fe crystal.

The light-climbing effect in a LiNbO(3):Fe crystal sheet was experimentally studied, and the mechanism for light climbing proposed was proved to be correct. The relevant optical properties were investigated.

Theoretical and experimental study of the intensity distribution in biological tissues

Based on the diffusion approximate theory (DA), a theoretical model about the distribution of the intensity of a narrow collimation beam illuminating on a semi-infinite biological tissue is developed. In order to verify the correctness of the model, a novel method of measuring the distributions of the intensity of light in Intralipid-10% suspension at 650 nm is presented and measurements of the distributions of the distance-dependent intensity of scattering light in different directions are made. The investigations show that the results from our diffusion model are in good agreement with the experimental results beyond and in the areas around the light source and the distance-dependent intensity in the incident direction attenuates approximately in the exponential form. Furthermore, our theoretic results indicate the anisotropic characteristics of the intensity in different directions of scattering light inside the biological tissue.

Influence of nonlinear absorption on Z-scan measurements of nonlinear refraction

A simple division of close-aperture Z-scan curve by open-aperture Z-scan is conveniently used to obtain the nonlinear refractive index. It usually causes an error, which even reaches up to over 50% for Z-scan measurements with a pinhole or a medium with a high nonlinear absorption. Here the influence of nonlinear absorption on the determination of nonlinear refraction by Z-scan is analysed. We suggest that the error can be reduced greatly by a simple analysis of the symmetric features (symmetric method) of Z-scan curves from the closed-aperture Z-scan curve. As an example, experiments were carried out on CS2 solution of C60 derivative, symmetric method agrees well with exact simulation.

Analysis of the Influence of Thermal Effect on Z-Scan Measurements with a Nanosecond Pulse Laser

The influence of thermally induced optical nonlinearities on Z-scan measurements with a nanosecond pulse laser is investigated theoretically. The results demonstrate that thermal effect plays an important role in certain circumstance. As an example, the optical nonlinearities of CS2 with an adjustable linear absorption coefficient which is used to alter the magnitude of thermally induced optical nonlinearities are analysed, and the results show that thermal effect even makes the change of the sign of optical nonlinearities.

A Passive Q-Switched Microchip Er/Yb Glass Laser Pumped by Laser Diode

A laser-diode-pumped 1.54-μm passive Q-switched erbium doped glass laser was reported. We utilize a laser diode with wavelength of 973 nm to pump a 1-mm Er/Yb co-doped phosphate glass with the erbium and ytterbium concentrations of 1 wt.% and 21 wt.%, respectively. A Co2+:MgAl2O4 slab crystal was used as a passive Q-switcher. Q-switched pulses with repetition frequency of 800 Hz, width of 7.4 ns, peak power of 2.2 kW and average power of 13.3 mW were obtained when absorbed pump power was 475 mW. A sandwich structure of the Q-switched microchip Er/Yb glass laser was demonstrated, which shows shorter pulse width of 6.8 ns. Dependences of pulse duration and repetition frequency on pump power were also investigated.

Laser Diode Pumped 1.54 µm Er:Yb:Phosphate Glass Continuous Wave Compact Laser

We report a cw Er3+:Yb3+ co-doped phosphate glass laser pumped by a laser diode. The maximum output power of 78.3 mW and a slope efficiency of 15.25% were achieved. The laser spectral region was from 1532 nm to 1535 nm, with the peak laser wavelength at 1534 nm. The laser modes and time stability were also measured. The thermal effect had little influence on the output in our experiment.

Determination of the absolute fluorescence quantum yields of laser dyes using photoacoustic spectroscopy

A new technique of photoacoustic spectroscopy measurements of the absolute fluorescence quantum yields has been investigated and used in laser dye solutions. The fluorescence quenchers is used in the experiment. Five home-made dyes, Rhodamine 6G, Disodium Fluorescein, Eosin Y, Cuomarin 1 and Quinine Bisulphate, have been measured. The results are in excellent agreement with those reported.

Monte Carlo Simulation of Light Transport in Five-Layered Skin Tissue

The light propagation and distribution in skin tissue is studied by using Monte Carlo technique. The radially resolved diffuse reflectance R and transmittance T vs radius r, angularly resolved R and T vs the exiting angle of the photon, absorption energy density A and internal fluence F vs r and z are simulated. Our results reveal that the light distribution for Gaussian beam is more centralized and its change is more rapid than those of circularly flat beam under the same incident energy and radius, no matter what R and T or A and F are. In addition, except that R(r) for circularly flat beam needs to be fitted by 15-order curve, the others can be fitted by 5-order or 6-order curve.