A comparison of the pentaammine(pyridyl)ruthenium(II) and 4-(dimethylamino)phenyl groups as electron donors for quadratic non-linear optics.

Hyper-Rayleigh scattering and Stark spectroscopic studies show that the complex salts [1-4]PF6 have larger static first hyperpolarizabilities beta 0 than [5-8]PF6, because the higher HOMO energy of a (RuII(NH3)5)2+ centre more than offsets the superior pi-orbital overlap in the purely organic chromophores.

Tracking novelty filter at 780 nm based on a photorefractive polymer in a two-beam coupling geometry.

We have constructed an all-optical tracking novelty filter based on the dynamic holographic properties of an efficient and fast infrared-sensitive photorefractive polymer. The photorefractive polymer was used in a two-beam coupling geometry. The polymer had a gain coefficient of 175 cm(-1) at a wavelength of 780 nm and an applied field of 72 V/microm. In contrast to what has been observed in photorefractive crystals, the gain coefficient and the filter contrast are largely independent of the writing beam's intensity ratio. We show images of a swinging pendulum observed through the novelty filter.

Quasi-phase-matching in chiral materials

The second-order nonlinear optical coefficients associated with chirality differ in sign for the two mirror-image forms (enantiomers) of a chiral material. Structures comprised of alternating stacks of the enantiomers can therefore be used for quasi-phase-matched frequency conversion, as we demonstrate here by second-harmonic generation from Langmuir-Blodgett films of a helicenebisquinone. Such structures could lead to new types of frequency converters in which both the second-order nonlinear response and quasi-phase-matching arise from the chirality of a material rather than its polar order.

Bacteriorhodopsin: a natural (nonlinear) photonic bandgap material.

The angular dependence of the hyper-Rayleigh scattered light intensity from a suspension of bacteriorhodopsin has been analyzed. The observation calls for combination of the second-order nonlinear hyperpolarizability of the retinal chromophore with the linear refractive index of the apo-protein matrix. The structuring of the small nonlinear chromophore in the large linear matrix imparts properties of a photonic bandgap to bacteriorhodopsin.

High-frequency demodulation of multiphoton fluorescence in long-wavelength hyper-Rayleigh scattering.

Suppression of the multiphoton fluorescence contribution to the hyper-Rayleigh (second-order nonlinear optical) scattering signal was recently achieved by intrinsic demodulation of the fluorescence at high amplitude-modulation (AM) frequencies [Olbrechts et al., Rev. Sci. Instrum. 69, 2233 (1998)]. These high AM frequencies were obtained from the high harmonic content in the Fourier spectrum of a repetitive train of femtosecond pulses from a Ti:sapphire laser emitting at 800 nm. We have used a femtosecond parametric oscillator to shift the fundamental wavelength to 1.3 mum . By further improving the detection electronics, we can now obtain fluorescence suppression at AM frequencies up to 600 MHz. Fluorescence-free hyperpolarizability values were obtained for fluorescent dipolar compounds as well as for an ionic fluorophore. The results also indicate that shifting the fundamental wavelength to the near infrared only is not a general solution to the multiphoton fluorescence problem in hyper-Rayleigh scattering.

Strong enhancement of nonlinear optical properties through supramolecular chirality

A new approach to second-order nonlinear optical (NLO) materials is reported, in which chirality and supramolecular organization play key roles. Langmuir-Blodgett films of a chiral helicene are composed of supramolecular arrays of the molecules. The chiral supramolecular organization makes the second-order NLO susceptibility about 30 times larger for the nonracemic material than for the racemic material with the same chemical structure. The susceptibility of the nonracemic films is a respectable 50 picometers per volt, even though the helicene structure lacks features commonly associated with high nonlinearity. Susceptibility components that are allowed only by chirality dominate the second-order NLO response.

Determination of resonant and nonresonant third-order nonlinearities of organic molecules by phase-conjugate interferometry.

We have used a phase-conjugate interferometer to determine the real and imaginary parts of the third-order hyperpolarizability of 3,3'-diethyloxadicarbocyanine iodide (DODCI) and 4-methoxy-4'-nitrostilbene (MONS) at 1064 nm. For DODCI the values are enhanced by a two-photon resonance, and the two-photon extinction coefficient is determined. However, the nonlinear loss of DODCI is dominated by linear absorption from the two-photon excited state. We could not observe linear or nonlinear absorption for the MONS solutions, and we have determined the nonresonant third-order hyperpolarizability for this molecule.

Nonlinear optical properties of proteins measured by hyper-rayleigh scattering in solution.

Hyper-Rayleigh scattering has been used to determine the nonlinear optical properties of a chromophore-containing protein in solution. Because the technique of hyper-Rayleigh scattering allows the measurement of hyperpolarizabilities in an isotropic solution without the application of an electric field, this method is ideally suited for the study of proteins that carry a net charge. The observed orientational correlation between the nonlinear optical chromophores in incompletely solubilized protein molecules suggests that guidelines from protein structures can be used for the engineering of supramolecular structures with high optical nonlinearity.

Determination of the hyperpolarizability of an octopolar molecular ion by hyper-Rayleigh scattering.

The first observation to our knowledge of a second-order nonlinear optical effect in a nonpolar molecular ion is reported. Hyper-Rayleigh scattering was observed from aqueous and organic solutions of the tricyanomethanide ion [C(CN)(3)](-). Because of the absence of a dipole moment and the presence of a charge in this planar, nonpolar, but highly polarizable molecular anion with D(3h) symmetry, no electric-field-induced second-harmonic-generation experiments are possible. The experimental values for the first hyperpolarizability beta(xxx) [(7 +/- 1.5) x 10(-30) esu, independent of the solvent] are in good agreement with the results from quantum-chemical calculations.

A fluorescence lifetime study of virginiamycin S using multifrequency phase fluorometry.

Using multifrequency phase fluorometry, fluorescence lifetimes have been assigned to the different protolytic forms of the antibiotic virginiamycin S. These lifetimes are 0.476 +/- 0.005 ns for the uncharged form, 1.28 +/- 0.2 and 7.4 +/- 0.2 ns for the zwitterionic form, 1.19 +/- 0.01 ns for the negatively charged form, and 1.9 +/- 0.1 ns for the double negatively charged form. The assignments are based on lifetime measurements as a function of pH, volume percent ethanol, and excitation wavelength. Excited-state proton transfer is taken into account. It is complete at pH values lower than 1, and no fluorescence of the fully protonated charged form is observed. At pH 8, an excited-state pK* increase is calculated, but proton association is too slow to cause excited-state proton transfer. The addition of divalent cations, at pH 9.4, increases the lifetime of the negatively charged form to a value dependent upon the specific nature of the cation (7.58 +/- 0.06 ns for Mg2+, 6.54 +/- 0.02 ns for Ca2+, and 3.74 +/- 0.05 ns for Ba2+). Monovalent cations do not influence the lifetimes, indicating that their binding to the macrocycle does not influence the fluorescent moiety. The model compound 3-hydroxypicolinamide shows an analogous behavior, but the retrieved lifetime can differ significantly.

Large-bowel perforation. A rare complication of intravesical Nd-YAG laser irradiation of bladder tumors.

A case report of large-bowel perforation after intravesical neodymium-yttrium aluminum garnet laser irradiation is presented. Recommendations to prevent bowel injury are discussed.

A diffusion-adsorption model for the computation of the amount of hormone around a secreting cell, detected by the reverse hemolytic plaque assay.

The reverse hemolytic plaque assay enables the detection of secretion products from individual cells in cultures by visualizing the plaques formed after complement-mediated hemolysis around the secreting cells. However, the precise quantitation of the amount of secretion remains problematic. In this study we propose a computation model for estimating the spreading of the secreted molecules, based on the underlying processes of diffusion and antigen adsorption by immobilized antibodies. The translational diffusion coefficient of rat prolactin at 37 degrees C, determined by laser light scattering, was 9.89 x 10(-7) cm2/s. The time-dependent concentration distribution around a constantly secreting cell in a flat quasi infinite layer, was derived from the diffusion equation, using an analytical approach based on Laplace transformation. The relations between plaque size, incubation time and secretion level were expressed as a function of the threshold concentration of secretion product that can be detected and the effective diffusion coefficient, taking antigen adsorption into account. We obtained very good agreement between observed and predicted results for plaque formation by dispersed prolactin secreting cells of 14-day-old female rat pituitaries. This study confirms the validity of the assumptions underlying the reverse hemolytic plaque assay, provided that the cell density is low, the incubation time is moderately long and the concentration of specific antiserum is sufficiently high.

Reduction of phase instability in a mode-locked argon laser.

Timing fluctuations in a mode-locked laser cause phase noise sidebands on the carrier and its harmonics in the frequency spectrum of the output of the laser. We reduced the phase noise of the output of a mode-locked argon laser by 40 dB, 80 Hz away from the carrier, as measured on its twentieth harmonic by simply replacing the commonly supplied rf synthesizer by a higher performance frequency generator. Applications demanding reduced timing fluctuations or reduced phase noise include synchronization of lasers and cross-correlation detection as in phase fluorometry.

New electric field methods in chemical relaxation spectrometry.

New stationary relaxation methods for the investigation of ionic and dipolar equilibria are presented. The methods are based on the measurement of non-linearities in conductance and permittivity under high electric field conditions. The chemical contributions to the nonlinear effects are discussed in their static as well as their dynamic behavior. A sampling of experimental results shows the potential and range of possible applications of the new techniques. It is shown that these methods will become useful in the study of nonlinear responses to perturbation, in view of the general applicability of the experimental principles involved.