Fabrication and analysis of a directional coupler written in glass by nanojoule femtosecond laser pulses.

A directional coupler written in a glass sample by the focused 400-nm output from a 25-fs oscillator is reported. The coupler is single mode; the splitting ratio is 1.9 dB at 633 nm. A refractive-index profile of the waveguide with a magnitude of Dn = 4.5 x 10(-3) was retrieved from a near-field mode pattern.

Femtosecond ultraviolet autocorrelation measurements based on two-photon conductivity in fused silica.

We utilize the two-photon conductivity of a fused-silica substrate to produce a photoconductive switch for use in an intensity autocorrelator for ultraviolet ultrashort pulses. We perform measurements at 267 nm with pulse durations in the range of 110-330 fs and with energies as weak as 10 nJ. Based on the bandgap of fused silica, this device can potentially operate in the wavelength range of 140-280 nm.

Femtosecond kinetics of electron transfer in the bacteriochlorophyll(M)-modified reaction centers from Rhodobacter sphaeroides (R-26).

Formation of the vibronic wavepacket by 90-fs excitation of the primary electron donor P in bacteriochlorophyll(M)-modified reaction centers is shown to induce nuclear motions accompanied by (1) oscillation of the stimulated emission from excited primary electron donor P* and (2) wavepacket motions leading to electron transfer at 293 K from P* to bacteriochlorophyll (B(L)) and then to bacteriopheophytin (H(L)). The latter motions have low frequency (about 15 cm-1) and are related to protein-nuclear motions which are along the reaction coordinate. When the wavepacket approaches the intersection of the reactant (P*B(L)) and product (P+B(L)-) potential energy surfaces (approximately 1.5 ps delay), about 60% of P* is converted to the P+B(L)- state. The P+H(L)- state formation is delayed by approximately 2 ps with respect to that of P+B(L)-. It is suggested that the wavepacket is transferred to and moves also slowly on the P+B(L)- potential energy surface and approaches the intersection of the surfaces of P+B(L)- and P+H(L)- within approximately 2 ps (approximately 8 cm-1), indicating the electron transfer to H(L).

Dynamic hole burning within special pair absorption band of Rhodobacter sphaeroides (R-26) reaction center at room temperature.

The absorbance spectrum of reaction centers of Rhodobacter sphaeroides at room temperature consists of relatively narrow spectral components which are moving in the femtosecond time scale and can be bleached by femtosecond laser pulses in the short wavelength region with a subsequent broadening and red shift of the bleaching (time constant approximately 250 fs). These data are discussed in terms of the population of the vibronic wave packets in the ground state by the interaction with phonons at 293K. The motion of these packets is probably responsible for the absorbance spectrum of the primary electron donor P at 293K with enhanced short wavelength components and with suppressed Stokes components.