Zhang Chun-Ping

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.

Measurements of Absorption and Anisotropy Coefficients of the Fat Emulsion Intralipid-10%

The absorption and anisotropy coefficients of the fat emulsion Intralipid-10% were measured. An adding-absorber method was used for measurement of absorption and anisotropy coefficients of the Intralipid-10%. Using the diffusion theory which has been extended to include anisotropy scattering for a point-source in infinite-medium geometry, the standard deviations of multiple measurements for (μa/D)～(1/2) are less than 0.6% and the residuals between the measured data and the fits have rms values of 0.1%, where μa is the absorbing coefficient of the solution in our experiment and D is the diffusion coefficient of the medium. The values of the standard deviations and the residuals demonstrate the high precision of the measurements.

Enhancement of modulation depth of an all-optical switch using an azo dye-ethyl red film

The polymethyl methacrylate (PMMA.) film doped with an azo dye ethyl-red (ER,) film is employed to demonstrate the properties of an all-optical switch by its photoinduced dichroism and birefringence. We show how to enhance remarkably the modulation depth of all-optical switches almost to 100% by using two linear polarization beams: one beam is inclined at 45 degrees with respect to the probing beam and serves as a pumping beam, and the other beam is perpendicular to the probing beam and used as an erasing beam. Furthermore, a maximum-to-minimum output intensity ratio of 2000:1 is achieved in experiment, which is very useful and important for optical storages and image displays.

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.

Dynamic Behaviour of Self-Diffraction in Bacteriorhodopsin Film

We investigate the dependences of the diffraction efficiency of the first order self-diffracted beam in bacteriorhodopsin (bR) films on the illumination time, the intensity and wavelength of the incident light. When the blue light (λ = 488 nm) and low intensity red light (λ = 632.8 nm) are incident on the bR film respectively, the diffraction efficiencies increase from zero to a stable value with the illumination time. When the green light (λ = 533 nm) and high-intensity red light illuminate the bR film respectively, the diffraction efficiencies increase from zero to the maximum and then decrease to a stable value with the illumination time. Rise and decay times are dependent on the intensity and wavelength of the incident light. The maximal diffraction efficiency of the red light is twice as high as that of the green light. The highest diffraction efficiency of 5.4% is obtained at 633 nm. The diffraction efficiency change with the time for the green light is larger than that for the blue and red light.

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.

Calculation and Measurement of the Diffraction Efficiency of a Dilute Developed Silver Halide Holographic Plate

The optical properties of dilute developed silver halide hologram have been analysed using the Maxwell-Garnett effective-medium theory, and its diffraction efficiencies calculated using coupled-wave theory. The calculated and measured results are in agreement.

Highly Directional Emission from a Subwavelength Slit in Metal-Dielectric Layered Films

The directional light emission from a single subwavelength slit surrounded by periodic grooves in layered films consisting of Ag and transparent dielectric is analysed numerically by the finite difference time domain method. The results show that the transmission through this structure is strongly confined by the modulation of the dielectric film with grooves on the output side. The role of evanescent waves in this phenomenon is discussed. It is the re-diffraction of the evanescent waves (that are generated by the diffraction of the subwavelength slit) caused by the grooves on the dielectric film that leads to the directional transmission. Some suggestions are given to obtain beaming light with high transmittance.