High-contrast interferometry based on anti-Stokes stimulated Raman scattering with broadband and narrow-band quasi-continuous-wave laser light.

Two versions of an anti-Stokes stimulated Raman scattering (SRS) experiment are presented, one with narrow-band light, the other with broadband light. The interferograms exhibit, at optical periods, alternation between complete signal extinction and high signal intensity with much higher contrast than seen in ordinary linear interferometry. Furthermore, for broadband excitation, the envelope of the high-contrast SRS interferogram is limited to an ultrashort time period. Possible applications of such signals for use as switches or logic gates are discussed.

Femtosecond energy-transfer processes in the B800-850 light-harvesting complex of Rhodobacter sphaeroides 2.4.1.

The B800-to-B850 energy transfer time in the purified B800-850 light-harvesting complex of Rhodobacter sphaeroides 2.4.1 is determined to be 0.7 ps at room temperature. The electronic state dynamics of the principal carotenoid of this species, spheroidene, are examined, both in vivo and in vitro, by direct femtosecond time-resolved experiments and by fluorescence emission yield studies. Evidence is presented which suggests that carotenoid-to-bacteriochlorophyll energy transfer may occur directly from the initially excited carotenoid S2 state, as well as from the carotenoid S1 state. Further support for this conjecture is obtained from calculations of energy transfer rates from the carotenoid S2 state. Previous measurements of in vivo carotenoid and B800 dynamics are discussed in light of the new results, and currently unresolved issues are described.

Femtosecond dynamics of energy transfer in B800-850 light-harvesting complexes of Rhodobacter sphaeroides.

We report femtosecond transient absorption studies of energy transfer dynamics in the B800-850 light-harvesting complex (LHC) of Rhodobacter sphaeroides 2.4.1. For complexes solubilized in lauryldimethylamine-N-oxide (LDAO), the carotenoid to bacteriochlorophyll (Bchl) B800 and carotenoid to Bchl B850 energy transfer times are 0.34 and 0.20 ps, respectively. The B800 to B850 energy transfer time is 2.5 ps. For complexes treated with lithium dodecyl sulfate (LDS), a carotenoid to B850 energy transfer time of less than or equal to 0.2 ps is seen, and a portion of the total carotenoid population is decoupled from Bchl. In both LDAO-solubilized and LDS-treated complexes an intensity-dependent picosecond decay component of the excited B850 population is ascribed to excitation annihilation within minimal units of the LHC.

Thermal lens technique: a new method of absorption spectroscopy.

Both a single beam and a dual beam (with synchronous detection) thermal lens technique have been employed in the measurement of "colorless" organic compounds in the range 15,700 to 17,400 cm-1. Combination overtones of C-H stretching vibrations in benzene have been identified and agree with previous results obtained by conventional spectroscopy with a long optical path. Extinction coefficients as low as 1 X 10(-6) liter mole-1 cm-1 have been accurately determined. The sensitivity of the technique has been further demonstrated by measuring the So leads to T1 absorption of anthracene; the spectrum compares favorably with results obtained by conventional techniques.