Boric Acid Glass Research Articles

PHOTOACOUSTIC SPECTROSCOPIC STUDIES OF POLYCYCLIC AROMATIC HYDROCARBONS: NAPHTHALENE CATION

The photoacoustic (PA) spectrum of naphthalene cation in boric acid glass, in the region 250–400 nm is reported for the first tune and compared with its optical absorption spectrum. The energy levels for the ions are calculated using open shell Wasilewski method with limited configuration interaction and used to interpret the observed PA spectrum.

Photoacoustic spectroscopic studies of polycyclic aromatic hydrocarbons: naphthalene molecule

The photoacoustic spectra of naphthalene in powder form and in boric acid glass are reported in the region 250–400 nm. They show additional bands on the higher-wavelength side when compared with the conventional electronic absorption spectra. The CNDO/S-CI method is used to calculate the electronic transitions of the naphthalene molecule with the optimized geometries. On the basis of these calculations, the additional bands observed on the higher-wavelength side are attributed to singlet—triplet absorptions. Good agreement is found between the experimental and calculated results.

Z-scan studies in fluorescein-doped boric acid glass

The non-linear response of fluorescein-doped boric acid glass was probed using the Z-scan technique. A striking contrast was observed in its non-linear transmission characteristics at different argon-ion laser wavelengths. The non-linear transmission characteristics exhibit strong saturation behaviour at 457.9nm whilst at 476.5nm and 488.0nm the response is dominated by intense excited state absorption. The experimental observations are explained using the four-level saturable absorber model. The excited state absorption cross-section, saturation intensity, light induced absorption and refraction changes have been determined along with the sign of the non-linearity at various argon laser wavelengths. The optical limiting characteristics of fluorescein at 476.5 nm and 457.9 nm are also reported. The behaviour of the sample was in agreement with the Z-scan observations.

Laser-induced darkening in thin films of fluorescein-doped boric acid glass

We report laser-induced permanent darkening in thin films of fluorescein-doped boric acid glass. The photodarkening is accompanied by a substantial increase in the absorption of the irradiated samples. The photoinduced absorption appears to be permanent. Optical and electron paramagnetic resonance measurements suggest the creation of a new photochemical species on irradiation within the absorption band of the fluorescein molecule. A possible mechanism for the photochemical change responsible for the darkening is proposed. Optical storage of information through the formation of permanent holograms is demonstrated.

Dispersion of the induced optical nonlinearity in rhodamine 6G doped boric acid glass

The spectral dispersion of the induced optical nonlinearity has been investigated in an optically thick sample of rhodamine 6G dye doped boric acid glass. The light-induced changes in the absorption coefficient were measured over a wide range of frequencies. The corresponding changes in the phase dispersion were calculated by the Kramers-Kronig transformation. The changes in the complex refractive index so obtained were used to calculate the diffraction efficiency within Kogelnik's model. The results show a good agreement with the measured diffraction efficiency of a nondegenerate probe. The analysis revealed the presence and the significant role of excited state absorption in the dynamic grating diffraction process.

Nature of delayed luminescence and optical nonlinearity in rhodamine 6G doped boric acid glass

The triplet state relaxation dynamics in R6G doped in boric acid glass have been probed using luminescence and transient grating studies. The measured transient grating and luminescence decay signal profiles are explained by excited state relaxation mainly through triplet-triplet annihilation. The observed delayed emission is identified as P-type delayed fluorescence. Our findings support saturable absorption as the mechanism for optical nonlinearity.

Multiwave diffraction in saturable absorbers

We present an analytical description of the degenerate multiwave diffraction of an independent probe beam incident at an arbitrary angle upon a population grating created by two resonant and coherent pump beams in a saturable absorbing medium. We have also undertaken experimental verification of some of the features, using a thin-film sample of Rhodamine 6G-doped boric acid glass. It is found that the three-beam configuration provides a broader angular bandwidth for observing nonlinear effects.

Transient nonlinear optical behavior of fluorescein-doped boric acid glass

The nonlinear optical properties of fluorescein-doped boric acid glass films have been investigated with sub-nanosecond laser pulses. With the use of degenerate four-wave mixing, large third-order susceptibilities of χ(3) ∼ 10−7 esu have been measured, connected to the relatively fast decay of the singlet state S1 (τ = 2.4 ± 0.6 ns). This particular system has a long-lived lowest-lying triplet state (0.1–1 s), and the transient nonlinear-optical and fluorescence properties show a marked dependence on the laser-pulse repetition rate in this time regime.

Polarization dependences of degenerate backward four-wave mixing in dye doped boric acid glass

The three components of third-order nonlinear susceptibilities responsible for degenerate backward four-wave mixing are calculated for an isotropic medium and their dependence with respect to wave-vector difference between the two beams are shown. Comparisons are made with their experimental values in dye doped boric acid glass. The results are in very good agreement with theory.

Optical image subtraction in fluorescein-doped boric acid glass

The interference of two coherent images with a controlled phase difference between them is shown by using four-wave mixing in fluorescein-dye-doped boric acid glass and a liquid-crystal television spatial light modulator. We present results showing the digital optical exclusive OR operation with milliwatt optical power and an output that is compatible with CCD camera sensitivities.

Bistable operation of a phase-conjugate resonator containing an intracavity saturable absorber

We have demonstrated bistability in a phase-conjugate resonator containing an intracavity saturable absorber. The saturable absorber was a film of fluorescein-doped boric acid glass. The state of the resonator is determined by an external control beam incident upon the saturable absorber. When the resonator is switched to the on state by means of the control beam, it remains in that state even with the control beam turned off.

Photon-gated holography: triphenylene in a boric acid glass

The observatiqn of photon-gated hologram formation in a boric acid glass doped with triphenylene is reported. The first photon excites triphenylene to its first singlet excited state and, through intersystem-crossing, populates the first triplet stateTI. The second photon excites TI to T,, where autoionization occurs, leading to the formation of a radical cation. The gatinglight populating TI via SI is spatially uniform, while the light exciting TI to T, is spatially modulated. The long lifetime of the first triplet state allows Recording with low light intensities (mW/cm2). The spatially modulated excitation light forms three gratings (educt, intermediate state, and product). The extent of the interaction between these gratings depends on the overlap between educt, intermediate, and product absorption and refraction spectra as well as on the reading wavelength. The holograms were read at 363.8 and 632.8 nm. When the gating light is blocked, the holographic efficiency stays constant when read at 632.8 nm but increases substantially when read at 363.8 nm.

Continuous-wave self-diffraction in dye-doped glasses

We study self-diffraction of cw Ar laser radiation from thin films of boric acid glass doped with Rhodamine 6G. The observed intensity dependence of the diffraction efficiency in various orders of diffraction is interpreted in terms of a recently proposed nonperturbative theory [ J. Opt. Soc. Am. B4, 1309– 1315 ( 1987)]. The order of the nonlinear polarization that contributes to a particular diffraction order is identified. In addition, the angular dependence of the diffraction efficiency is described. The relevance to the present case of the parameters normally used to demarcate the Raman–Nath and Bragg regimes of diffraction is discussed.

Enhancement of the nonlinear optical properties of fluorescin doped boric-acid glass through cooling

We examine, both theoretically and experimentally, the temperature dependence of the nonlinear optical response of fluorescein doped boric-acid glass. The third-order nonlinear susceptibility is increased by an order of magnitude over its room temperature value to greater than 10 esu by cooling the sample to a temperature below 200 K.

Single-pass imaging through a thick dynamic distorter using four-wave mixing

We have reconstructed images after a single pass through a thick, turbulent aberrator. The reconstructed image's resolution was independent of the presence, severity, and length of a hot-air aberrator (at least 50 times the collecting optics' depth of field). The slowly responding four-wave mixing medium, fluorescein-doped boric acid glass, averaged out rapidly varying intensity apodizations, which would otherwise degrade the reconstructed image quality.

Optical phase conjugation in Rhodamine-6G doped boric acid glass

Optical phase conjugation has been demonstrated in Rhodamine-6G doped boric acid glass using a cw argon ion laser. The dependence of the phase conjugated signal on the intensity and wavelength of the pump beam is studied The role of amplitude and phase grating contributions to the phase conjugated signal is discussed.

Determination of the phase of the complex nonlinear refractive index by transient two-wave mixing in saturable absorbers

The ratio of the imaginary part to the real part of the complex nonlinear refractive index has been measured by transient two-wave mixing in acridine-orange-doped fluorophosphate glass, fluorescein-doped boric-acid glass, and ruby at argon-ion wavelengths. The method enables the individual signs of the components of the nonlinear index to be obtained. A simple theory based on a single homogeneously broadened absorption from the ground state agrees with measurements of the phase of the nonlinear index in acridine but not in fluorescein, where our data suggest that excited-state absorption plays an important role.

Polarization properties of phase conjugation by degenerate four-wave mixing in a medium of rigidly held dye molecules

The saturation properties of dye molecules that are rigidly held in a solid host are qualitatively different from those of molecules that are free to rotate. We have found that these unique saturation characteristics can be exploited to achieve nearly perfect vector phase conjugation for field strengths near the saturation intensity. We have studied these properties experimentally by using fluorescein-doped boric acid glass as the nonlinear-optical material.

Saturable absorbers for low power optical phase conjugation

Properties of a few saturable absorbers as candidates for low power optical phase conjugation (OPC) are examined. The specific systems studied are the dyes eosin, erythrosin B and Rose Bengal, doped in gelatin, polyvinyl alcohol and boric acid glass films. A method for quickly checking saturated absorption is suggested and demonstrated. Examples for OPC with these systems are cited and limitations are briefly discussed.

Optically induced birefringence and dichroism in rigidly held dye molecules

Nonlinear-optical properties of Fluorescein-doped boric acid glass are investigated. By considering a linearly polarized pumping field we were able to obtain a complete expression of the dielectric susceptibility tensor. Utilizing a heterodyne detection polarimeter, we characterized the material at λ = 457.9, 476.5, and 632.8 nm. Large values of the nonlinear susceptibility are observed as well as considerable light-induced changes of the absolute values of the dielectric response. As an example, at λ = 457.9 nm and for a sample thickness d = 100 μm, a concentration C = 1.5 × 10−3 M, and an incident intensity I = 100 mW/cm2, the induced dichroism is Δα/α = 30%, and the birefringence is Δn/n = 3.2 × 10−4.