RESUMEN
We demonstrate theoretically and experimentally that one-, two-, and three-photon excited fluorescence from dye molecules in spherical microcavities has an asymmetrical angular distribution and is enhanced in the backward direction. The enhancement ratios (of intensities at 180 degrees and 90 degrees ) are 9, 5, and 1.8 for three-, two-, and one-photon excitation, respectively. Even larger ratios are expected for microspheres with an index of refraction larger than that used in the experiments. Because of the reciprocity principle and concentration of the incident wave inside particles, the backward enhancement is expected to occur even with nonspherical particles.
RESUMEN
A pump-probe two-photon-excited fluorescence technique deciphers in space and time the propagation of ballistic wave packets sustained by whispering-gallery modes (WGMs) in a spiral-shaped microcavity. Diffraction on the spiral discontinuity does not prevent the WGMs from closing. The resultant average Q of the resonator is 3 x 10(4) +/- 50%. Experimental results are compared with numerical simulations, providing evidence of a new contribution to output coupling: Part of the WGM evanescent wave is reflected at the spiral notch and leads to a propagating wave at an angle that matches the previously observed laser emission direction in 4-dicyanomethylene-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran-doped poly(methyl methacrylate) and InGaN spiral lasers.
RESUMEN
We present what is to our knowledge the first mid-IR lidar system based on a KNbO(3) optical parametric oscillator pumped by a Ti:sapphire laser. The optical parametric oscillator works in a nontracking configuration and provides high-frequency agility from 1 to 4 mum. This system constitutes an extension to the IR of UV lidars described previously [Europhys. J. D 4, 231 (1998); Appl. Opt. 37, 2231 (1998); Atmos. Environ. 32, 2957 (1998)] for the determination of aerosol concentrations in urban atmospheres. As first field tests, measurements at 3.5 mum were performed in fog conditions. Water droplet size and concentration were determined from Mie calculations. Quantitative temporal mappings and angular profiles are presented.
RESUMEN
Resonant two photon ionization (R2PI) technique was used to obtain the excitation spectrum of the Ba2 molecule. A group of 12 vibrational bands was found in the 740-764 nm region. As a result of mass selective detection, they were attributed unambiguously to the Ba2 molecule. By comparison to recent theoretical calculations, those bands were assigned to the (2)1Sigma+u-X(1)1Sigma+g transition; they may be fitted to give the following vibrational constants (in cm-1): omega"e = 33.2 +/- 0.2, omega"ex"e = 0.5 +/- 0.2, omegae = 65.2 +/- 0.2, and omega'ex'e = 0.4 +/- 0.2. Copyright 1998 Academic Press.