Flash-induced absorbance changes in the picosecond and nanosecond time range have been measured in the 'Dl-D2-cyt b-559 complex' isolated from photosystem II membranes. The results indicate the efficient formation of the primary radical pair P680' pheophytin-, which had a lifetime of about 36 ns, and the presence of unconnected chlorophyll in this preparation. It is concluded that the complex contains the active photosystem II reaction center, and that this reaction center contains at most 4 chlorophyll a molecules.
We demonstrate a four-stage optical parametric chirped-pulse amplification system that delivers carrier-envelope phase-stable approximately 1.5 microm pulses with energies up to 12.5 mJ before recompression. The system is based on a fusion of femtosecond diode-pumped solid-state Yb technology and a picosecond 100 mJ Nd:YAG pump laser. Pulses with 62 nm bandwidth are recompressed to a 74.4 fs duration close to the transform limit. To show the way toward a terawatt-peak-power single-cycle IR source, we demonstrate self-compression of 2.2 mJ pulses down to 19.8 fs duration in a single filament in argon with a 1.5 mJ output energy and 66% energy throughput.
The concept of optical parametric chirped-pulse amplification is applied to attain pulses with energies up to 8 mJ and a bandwidth of more than 100 THz. Stretched broadband seed pulses from a Ti:sapphire oscillator are amplified in a multistage noncollinear type I phase-matched beta-barium borate parametric amplifier by use of an independent picosecond laser with lock-to-clock repetition rate synchronization. Partial compression of amplified pulses is demonstrated down to a 10-fs duration with a down-chirped pulse stretcher and a nearly lossless compressor comprising bulk material and positive-dispersion chirped mirrors.
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