Xun Hou

Room-temperature dual-wavelength erbium-doped fibre laser based on a sampled fibre Bragg grating and a photonic Robin Hood

With the assistance of a kind of photonic Robin Hood that is originated from four-wave mixing in a dispersion-flattened high-nonlinearity photonic-crystal fibre, a novel dual-wavelength erbium-doped fibre (EDF) laser is proposed and demonstrated by using a sampled fibre Bragg grating. The experiments show that, due to the contribution of the photonic Robin Hood, the proposed fibre laser has the advantage of excellent uniformity, high stability and stable operation at room temperature. Our dual-wavelength EDF laser has the unique merit that the wavelength spacing remains unchanged when tuning the two wavelengths of laser, and this laser is simpler and more stable than the laser reported by Liu et al. [Opt. Express, 13 142 (2005)].

Kinetics of picosecond laser pulse induced charge separation and proton transfer in bacteriorhodopsin

Bacteriorhodopsin (BR) films oriented by an electrophoretic method are deposited on a transparent conductive ITO glass. A counterelectrode of copper and gelose gel is used to compose a sandwich-type photodetector with the structure of ITO/BR film/gelose gel/Cu. A single 30-ps laser pulse and a mode-locked pulse train are respectively used to excite the BR photodetector. The ultrafast falling edge and the bipolar response signal are measured by the digital oscilloscope under seven different time ranges. Marquardt nonlinear least squares fitting is used to fit all the experimental data and a good fitting equation is found to describe the kinetic process of the photoelectric signal. Data fitting resolves six exponential components that can be assigned to a seven-step BR photocycle model: BR-->K-->KL-->L-->M-->N-->O-->BR. Comparing tests of the BR photodetector with a 100-ps Si PIN photodiode demonstrates that this type of BR photodetector has at least 100-ps response time and can also serve as a fast photoelectric switch.

Multi-peak spectrum of KML Ti: Sapphire pulse

The multi-peak spectrum of Ti:sapphire pulses observed experimentally under ultra-broad bandwidth conditions (< 15 fs pulse length) has been explained theoretically. It is shown that the self-phase-modulation effect is equivalent to the process of degenerate four-wave frequency-mixing. Based on this theoretical underpinning, the presence or absence of a multipeak spectrum provides a practical measure of whether the intracavity group-velocity-dispersion is ideally compensated for or not.

Theoretical analysis of the flash photolysis kinetics of purple membrane

The laser flash excitation and thermal relaxation kinetics of purple membrane is theoretically analyzed using the rate equations of multiple states system. The derived equation indicates that the photoinduced absorbance change is a complex multi-exponential process. This is proved by a flash photolysis experiment using 532 nm, 10 ns laser pulse as pumping source and 632.8 nm CW laser as probing light. Comparison between the experimental fitting result and the theoretical analysis reveals the possibility of the existence of the KL state.

Laser-induced bacteriorhodopsin LB films' fast photoelectric dynamics

Ten layers of oriented bacteriorhodopsin (BR) LB films are prepared on ITO conductive glass to constitute an ITO electrode/BR LB films/KCl solution/Cu electrode wet photocell. A Q-switched double frequency Nd:YAG laser with 10 Hz repetitive rate and 8 ns pulse width is used to excite the BR LB films. The photoelectric signal is directly captured by a 300 MHz digitizing oscilloscope. A theory on the BR photoelectric dynamics is established. By nonlinear least square fitting of the experimental curves acquired at different time bases, the experimental equation corresponding to the theoretical model is obtained, and the charge displacements and the decay time constants for each step in the BR photocycle are calculated.