Picosecond and Nanosecond Components in Bacteriorhodopsin Light-Induced Electric Response Signal

Numerous investigations on the primary events of the bacteriorhodopsin photocycle indicate that the first steps of the energy transformation process take place in the 500 fs-5 ps region. These processes are known to be followed by others in the μs and ms regions. Recent observations indicate also the existence of nanosecond intermediate(s). Here we are reporting on direct measurements of the light-induced electric response signal of purple membrane carried out in the ps and ns regions. The laser flash-induced electric response of dried oriented purple membrane samples were detected by an ultrafast sampling oscilloscope. The measured kinetic curves were analyzed by exponential fitting and by a simulation-optimization method taking into account the time characteristics of the measuring setup. This analysis revealed a two phase real charge separation process. The first phase (tau = 21±2 ps) coincides well with the overall bR-[unk] K transition. The second phase (tau = 6±0.5 ns) can be correlated with the nanosecond optical transitions reported by several workers, or may be an optically silent charge movement inside the protein moiety or on the surface of the membrane

Spatially-hole-burned distributed feedback dye laser produced tunable single picosecond pulses.

A new type of distributed feedback dye laser is described in which the Bragg grating is formed by spatial hole-burning. With a simple excimer laser pumped arrangement, single high stability 6 ps pulses were generated. The pulses were nearly transformlimited and were 33 times shorter than the rise time of the pulse which created the Bragg grating

Femtosecond Structural Dynamics in VO2 during an Ultrafast Solid-Solid Phase Transition

Femtosecond x-ray and visible pulses were used to probe structural and electronic dynamics during an optically driven, solid-solid phase transition in VO(2). For high interband electronic excitation (approximately 5 x 10(21) cm(-3)), a subpicosecond transformation into the high-T, rutile phase of the material is observed, simultaneous with an insulator-to-metal transition. The fast time scale observed suggests that, in this regime, the structural transition may not be thermally initiated