The primary, light-induced charge separation in reaction centers of Rhodopseudomonas widis is investigated with femtosecond time resolution. The absorption changes after direct excitation of the primary donor P at 955 nm are investigated in the time range from 100 fs to 600 ps. The experimental data, taken at various probing wavelengths, reveal one subpicosecond and two picosecond time constants: 0.65 k 0.2 ps, 3.5 k 0.4 ps, and 200f 20 ps. The previously undetected 0.65 ps kinetics can be observed clearly in the spectral range of the QX and Qu transitions of the monomeric bacteriochlorophylls. The experimental data support the idea that the accessory bacteriochlorophyll B, participates in the electron-transfer process.

Thin-film superconducting tunnel junctions (SnlSn0,iSn) operated a t a temperature of 0.3 K were irradiated by a 56Fe X-ray source. Pulses due to photo-absorption in the devices were observed and the Mn K,, Kp lines at 5.89 keV and 6.49 keV, respectively, could clearly be resolved by pulse-height analysis. An energy resolution of hE(FWHM) = 250 eV was obtained in the first tests reported here. Improvements may be possible by straightforward techniques.

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