Inactivation of bacteria in plasma.

The photo-inactivation rate of bacteria by methylene blue, MB, was found to be significantly lower in plasma than in water, saline, and PBS solutions. The spectroscopic data and ultrafast time resolved transient spectra and kinetics presented show that methylene blue photo-bleaches faster and to a larger degree in plasma and the MB excited singlet and triplet state populations in plasma are much lower in plasma than in water and PBS solutions. The optical density, OD, of MB in plasma was found to decrease by ~50% after a minute of illumination with 661 nm light, while under identical conditions the OD in PBS solution decreased by only 1%. Based on these data and the effect of the plasma proteins on MB photochemistry, a mechanism is proposed that accounts for the low inactivation rate of bacteria in plasma.

Advances in picosecond spectroscopy.

Progress in the technology of picosecond spectroscopy in the past few years has made possible the generation of well-characterized pulses emitted by synchronously pumped tunable dye lasers. In addition, the development of sensitive emission and absorption detection methods and the advent of picosecond Raman and coherent anti-Stokes Raman spectroscopy make possible the direct observaton of picosecond transient spectra and lifetimes. The information obtained allows the complete determination of mechanisms through the identification of transient states, radicals, and ions that evolve during the course of a chemical or biological reaction.

Picosecond chemical and biological events.

Picosecond spectroscopy is a relatively new field of science that utilizes ultrashort laser pulses to monitor events taking place in the 10(-12) second regime. The continuing development of picosecond spectroscopy has made possible the detection and measurement of the primary events in many physical and tiological processes. This article describes a currently used picosecond spectroscopy system that is capable of reliably recording picosecond events. Two areas of picosecond research are discussed; one concerns the interaction of electrons in fluids, and the second the primary events in vision.

Picosecond chemistry.

The ability to directly measure and evaluate ultrafast processes with unprecedented time resolution and reliability has greatly extended our knowledge about the kinetics of primary processes in chemistry and allied physical and biological sciences. Improvements in the reliability and versatility of picosecond techniques should lead to an increase in the experimental information about basic interactions in atomic and molecular systems.

Three-dimensional optical storage memory.

A novel three-dimensional (3-D) optical memory device is presented that allows fast random access of the information and extremely high bit densities. This device is based on two-photon writing, reading, and erasing of the information in a photochromic material embedded in a polymer matrix. Absorption and emission data show that two-photon writing and reading of information is feasible. The advantages and properties of such a 3-D optical memory are discussed.

Picosecond kinetics of events leading to reaction center bacteriochlorophyll oxidation.

A transient absorption spectrum has been measured in Rhodopseudomonas spheroides R26 reaction centers. Its salient features indicate that both the bacteriopheophytin and bacteriochlorophyll chromophores play a role in the excited state. Decay of this state yields a rise time for oxidation of the reaction center complex of about 150 picoseconds.

Two-photon three-dimensional optical storage memory.

We describe the design and construction of ultrahigh capacity three-dimensional, 3D, optical storage devices that operate by two-photon absorption. The molecular systems and their properties that are used as two photon media for writing and one photon for accessing the stored information within the volume of the device are presented in some detail and the nonlinear two-photon absorption mechanism is briefly visited. The optical system and its components, which facilitated writing and reading, are also described and the bit density, bit error rate, store and access speeds, cycle times, and stability of the materials under various experimental conditions are also topics addressed in this review. The first ever storage of terabyte data in a removable storage disk is described in detail.

Picosecond kinetics of chlorophyll and chlorophyll/quinone solutions in ethanol.

The mechanism of quenching by quinones of the lowest excited singlet state of chlorophyll has been investigated using picosecond laser spectroscopy. With chlorophyll alone, laser excitation resulted in immediate (less than 10 ps) bleaching of the 665 nm band and production of new absorption bands in the regions 460-550 and 800-830 nm. The lifetimes of these changes were greater than 500 ps. Addition of 2,6-dimethylbenzoquinone caused quenching of these absorbance changes. No indication of chlorophyll cation radical formation was obtained. Thus, the interaction between quinone and the chlorophyll excited singlet state results in energy dissipation without measurable formation of radical species having lifetimes longer than 10 ps. This is in marked contrast to the quenching of the chlorophyll lowest triplet state by quinones, during which easily detectable stable radical formation has been observed.

Photolysis of CBr4 and its transient solvent stabilized (CBr3+//Br-)solv ion pair.

In this paper we describe the mechanism of the photodissociation of CBr4 in various solvents. We have monitored and identified the intermediate species and determined the growth and decay rates of the excited states and metastable species formed during the photodissociation process by means of ultrafast time-resolved spectroscopy. On the basis of the experimental data presented in this paper, the observed transient spectra and species have been assigned to the stabilized solvated ion pair (CBr3+//Br-)solv.

Probing ultrafast biological processes by picosecond spectroscopy.

A brief discussion of the initial events leading to the visual transduction process will be presented to illustrate the capabilities of picosecond spectroscopy.