Plasma-assisted coherent backscattering for standoff spectroscopy

We show that an intense coherent backward signal can be generated through a Raman-type four-wave-mixing process using forward propagating fields only. Phase matching for this process is achieved through a plasma modulation of the refractive index. Applications to standoff spectroscopy are discussed.     

Variable spectral filter based on optically saturated selective reflection

We have studied the selective reflection from glass-rubidium vapor interface at a large incidence angle in pump-probe experiment. The linear reflectivity can be more than 0.9 in a narrow spectral range (several GHz) at the blue side of the atomic resonance. The effect can be called the reduced total selective reflection. The reflectivity has been decreased two times due to the optical saturation. The obtained results can be used to develop a variable optical filter or optical switcher. Our estimations show that switching time can be less than the natural lifetime of the excited state. We suggested a multi-reflection scheme to increase the contrast of the variable spectral filter.     

Sensitive femtosecond coherent anti-Stokes Raman spectroscopy discrimination between dipicolinic acid and dinicotinic acid

We demonstrate that femtosecond ultraviolet and visible coherent anti-Stokes Raman spectroscopy provides the sensitivity and specificity needed to distinguish between two similar molecules of pyridinedicarboxylic acid. The Fourier transforms of the temporal measurements provide the energy difference between the ground state vibrational modes. Quantum chemical calculations provide theoretical predictions that agree well with the measurements. The present technique allows us to distinguish 10 cm(-1) frequency shifts by using pulses ten times broader than the shifts.     

Development of a laser-based fluorescence microscope with subnanosecond time resolution

This report describes the development of a fluorescence microscope based on a standard inverted optical microscope which incorporates a pulsed picosecond dye laser excitation source and a detector consisting of a gated image intensifier coupled to a CCD camera. Fluorescence images have been obtained using gate durations of 0.5 ns from this apparatus, representing a reduction in gate duration of an order of magnitude compared with similar instruments reported by others recently. Subnanosecond gated fluorescence images of V79-4 Chinese hamster lung fibroblasts stained with a phthalocyanine photosensitizer used in photodynamic therapy are presented. The results of these measurements are discussed in terms of the intracellular distribution of the sensitizer. Other potential applications and limitations of this technique are also outlined.     

Time-bandwidth problem in room temperature slow light

For many applications of slow or stopped light, the delay-time-bandwidth product is a fundamental issue. So far, however, slow-light demonstrations do not show a large delay-time-bandwidth product, especially in room temperature solids. Here we demonstrate that the use of artificial inhomogeneous broadening has the potential to solve this problem. A proof-of-principle experiment is done using slow light produced by two-beam coupling in a photorefractive crystal Ce:BaTiO3 where Bragg selection is used to provide the artificial inhomogeneity. Examples of how to generalize this concept for use with other room temperature slow-light solids are also given.     

Pair transfer in the absence of phase coherence

In his thesis, Josephson asserts that pair transfer accompanied by spontaneous photon emission does not demand the existence of a definite phase relationship between the two superconductors. In this letter we demonstrate the validity of this statement.     

Laser Line-Scanning Confocal Fluorescence Imaging of the Photodynamic Action of Aluminum and Zinc Phthalocyanines in V79–4Chinese Hamster Fibroblasts

Confocal fluorescence microscopy, using a newly constructed laser line-scanning confocal microscope, was applied to an investigation of the early stages of photoinduced destruction of V79–4Chinese hamster fibroblasts using aluminum and zinc phthalocyanines as photosensitize. Results obtained in this work show that aluminum and zinc phthalocyanines, once internalized, localize in perinuclear sites that are disrupted upon light exposure resulting in fluorescence redistribution. The combination of laser-line scanning with charge-coupled device detection used in the confocal microscope developed in this work can enable rapid high-resolution sequential imaging, which is ideal for studying photoinduced intracellular fluorescence dynamics.