Dye-doped Films Research Articles

Photoluminescence properties of dye-doped polymer multilayer films with periodic structure

We report the photoluminescence properties of polymer alternating multilayer films containing a fluorescent dye in one component. The alternating multilayer film with periodicity in both refractive indices and dye distribution showed 6 times higher intensity of amplified spontaneous emission than the multilayer film with periodicity in dye distribution only. Multilayer films that have a structure of Fabry–Perot resonator showed a lasing threshold of approximately 1.7 mJ cm − 2 .

Metal-induced photoluminescence quenching in thin organic films originating from noncontact energy transfer between single molecule and atom

Severe quenching of photoluminescence in dye-doped organic thin films is observed after submonolayer metal (metal atoms) deposition. Insertion of a spacer layer between the organic film and metal atoms has minor effect on eliminating the quenching, indicating that it is a long-range noncontact interaction. The phenomenon is regarded as a result of Förster energy transfer between organic molecules and metal atoms. The origin of the transfer is the coupling between dipoles in excited organic molecules and electron transitions in isolated atoms. Atoms among most elements rather than metals are capable of being involved in such a noncontact energy transfer process.

OPTICAL DATA STORAGE IN ACID RED DYES

High-density optical data storage is a current field gaining importance where research work is done in abundance to bring about holographic CDs to light. Dye-doped gelatin films are promising candidates as recording materials for holographic data storage because of the ease of preparation and low cost. In this report we suggest some acid red dyes as useful recording materials for optical data storage. Acid red dyes namely Acid Red 73 and Acid Red 114 that are completely water-soluble are used to sensitize gelatin thin films for data storage. These dyes have their absorption peak around 514 nm. Two coherent beams of Argon ion laser (514.5 nm) are used to form the grating in the dye-sensitized gelatin films. The grating formed is found to be permanent. The diffraction efficiency of each material as a function of different parameters like dye concentration, writing beam intensities and their ratios and spatial frequency has been studied and presented. An attempt to store data in the sample has been made.

Enhanced laser emission in opposite handedness using a cholesteric polymer film stack

We demonstrate an enhanced circularly polarized laser emission whose handedness is opposite to the cholesteric helix by the stacked cholesteric polymeric films. The dye-doped right-handed cholesteric polymer film is sandwiched between a mirror and a cholesteric polymer reflector. Due to the stimulated amplification and light recycling effects, the original laser emission from the middle active layer is not only dramatically enhanced but also converted to a left-handed circularly polarized emission with high purity. Moreover, a single 15 mum dye-doped cholesteric film is found to lase more efficiently when the top side faces the pump source than when the bottom side does. This phenomenon is attributed to the band gap broadening of the bottom side.

Distributed feedback sol-gel zirconia waveguide lasers based on surface relief gratings

Distributed feedback waveguide lasers based on dye-doped sol-gel zirconia films with permanent grating structures were demonstrated. The permanent grating was realized by employing a novel epoxy-based azo-polymer that generates a surface relief grating by a photo-isomerization process induced by two interfering writing beams. When employing the rhodamine 6G dye, tuning of the output wavelength of the distributed feedback waveguide laser from around 575 nm to 610 nm can be achieved by adjusting the tilting angle between the orientation of the grating and the pump beam.

Effect of dye doping and multilayer structures in polyurethane waveguides

The effect of dye doping and four-layer structuring in polyurethane-based waveguides is presented. The waveguides were fabricated using a dip coating method and characterized by the prism coupling technique. It was found that using these two effects, the various optical parameters of polyurethane waveguides, e.g. refractive index, birefringence, propagation losses, number of modes, can be suitably controlled. Polyurethane films are highly transparent (above 90%) in the UV-VIS region and this high transparency was found to be present in dye-doped polyurethane films.

Amplified Spontaneous Emissions from -Conjugated Dye Doped Polymer Film and Silicate Optical Fiber

We prepared transparent polymer films doped with n-conjugated organic dyes around a multimode silica fiber and observed very narrow fluorescence peaks as compared with the fluorescence in solution. The peak position showed no dependence on the excitation wavelength, indicating that it could not be explained by a whispering gallery mode in a medium with broad optical gain. The peaks can be explained by amplified spontaneous emissions (ASE) because the intensity depended linearly on the excitation intensity with a threshold. When the dye-doped film was formed on the portion of a fiber with the clad etched out and was excited by the polarized laser propagating inside the fiber core, we observed ASE peaks not of the dyes but of the optical fiber itself, suggesting the possibility that the dyes were oriented with their transition moment pointing parallel to the film surface. These fiber ASE peaks shifted to longer wavelength when we varied the excitation wavelength to shorter wavelength, which clearly ruled out the possibility of silicate Raman scattering as the origin.

Optical phase conjugation by degenerate four-wave mixing in basic green 1 dye-doped gelatin film using He–Ne laser

Optical phase conjugation in gelatin film doped with basic green 1 has been measured using CW laser radiation ( λ=632.8 nm) generated by He–Ne laser of total power 35 mW. The degenerate four-wave mixing (DFWM) experiment allowed for measurement of phase conjugate reflectivity as a function of dye concentration, backward beam intensity, forward beam intensity, probe beam intensity, mean pumping beam intensity and angle between the forward pumping beam and probe beam. For 1 mM concentration of basic green 1-doped gelatin film, 0.1% phase conjugate reflectivity has been observed.

Polarization characteristics of diffracted beams from twisted nematic gratings fabricated by the photoalignment effect in dye-doped liquid-crystal films

The polarization characteristics of diffracted beams from twisted nematic (TN) gratings are investigated. The TN grating is fabricated by exploiting the photoalignment effect in a dye-doped homogeneous liquid-crystal film. Experimental results indicate that the irradiation of an azo-dye-doped liquid-crystal film with appropriate light can induce dye adsorption on a glass substrate. The adsorbed dyes then reorient the liquid-crystal director perpendicular to the pump-beam polarization. The polarizations of the diffracted beams from such a TN grating are systematically studied. The experimental results correlate well with theory. Additionally, the TN grating can be used as a polarization beam splitter.

The Dependence of Orientational Optical Nonlinearity in Dye-Doped Liquid-Crystal Films on the Polarization Direction of the Recording Beams

We study, both experimentally and theoretically, the dependence of the absorbance and the two-beam coupling diffraction efficiency of dye-doped liquid-crystal films on the angle between the director vector of the liquid-crystal molecules and the polarization direction of the recording beams, which is shifted continuously from parallel to antiparallel corresponding to the director vector of the liquid-crystal molecules. The sample used in our experiment is the nematic liquid-crystal 5CB-doped with Disperse Red 1 (DR1). Also, there is no electronic field applied to it. The diffraction efficiency of the probe beam increases with the increase of the recording light absorption. Coupled-wave equations are developed to describe the laser-induced refractive index change, grating formation, and coherent wave-mixing effect. The analytical solutions of the recorded holographic grating and the diffraction efficiency of the probe beam are obtained for the case of taking losses into account. The results show that the diffraction efficiency can be improved by choosing suitable material parameters and recording parameters

Photoluminescence and Possible Amplified Spontaneous Emission from π-Conjugated Dye-Doped Thin Film

We prepared transparent polymer films doped with π-conjugated organic dyes around a multimode silica fiber and observed very narrow fluorescence peaks as compared with the fluorescence in solution. The peak position showed no dependence on the excitation wavelength, indicating that it could not be explained by a whispering gallery mode. The peaks can be explained by amplified spontaneous emissions (ASEs) because the intensity depended linearly on the excitation intensity with a threshold. When the excitation laser was directly coupled to the fiber core, we observed ASE peaks of the optical fiber itself. These fiber ASE peaks shifted to longer wavelength when we varied the excitation to shorter wavelength, which clearly ruled out the possibility of silicate Raman scattering as the origin.

Optical properties of dye-doped zirconia films by spectroscopic ellipsometry

The optical properties of zirconia films doped with rhodamine 6G and oxazine 725 by the sol–gel process were investigated using spectroscopic ellipsometry (SE). Accurate refractive index n and the extinction coefficient k were determined using a three-oscillator classical Lorentz model in the wavelength range of 300–800 nm. The derived refractive index of dye-doped films exhibited anomalous dispersion in the absorption region. Wavelength tunable output lasing action yellow and near-infrared wavelength region was achieved by DFB configuration using zirconia films doped with R6G and oxazine 725.

Optical phase-conjugation studies in Acid blue 9 dye-doped gelatin film using low-power He–Ne laser

We report on the observation of optical phase-conjugation (OPC) in Acid blue 9 dye-doped gelatin film using a low-power continuous-wave (He–Ne, 633 nm, 35 mW) laser by the degenerate four-wave mixing (DFWM) method. The intensity of the phase-conjugate signal was measured as a function of time of exposure. The phase-conjugate signal contributions from induced transmission and reflection gratings were measured. The fringe spacing (Λ) of the transmission and reflection gratings formed in the Acid blue 9 dye film were calculated as 5.12 and 0.32 µm respectively.

Optical phase-conjugation in erioglaucine dye-doped thin film

Optical phase-conjugation (OPC) has been demonstrated in erioglaucine (acid blue 9) dye-doped gelatin films via continuous-wave degenerate four-wave mixing (DFWM) using a low-power He-Ne laser at 633 nm. DFWM and holographic processes are found to contribute to the observed phase-conjugate signal. A maximum phase-conjugate beam reflectivity of about 0.24% has been observed in these dye-doped gelatin films.

Micro-ring cavity mode of dye-doped thin film: Dependence on the excitation energy

We have prepared π-conjugated organic dye specimens embedded in a transparent polymer film and observed a characteristic photoluminescence peak, having very narrow peak width as compared with the fluorescence in solution, when we prepared the film around the perimeter of a multimode silica fiber. The peak position showed no dependence on the excitation wavelength, indicating that it could not be explained by a whispering gallery mode. The peaks can be explained by amplified spontaneous emissions (ASE) because the intensity depended linearly on the excitation intensity with some threshold. When the excitation laser was directly coupled to the fiber core, we observed ASE peaks of the optical fiber itself. These fiber ASE peaks shifted to longer wavelength when we varied the excitation to shorter wavelength, which clearly ruled out the possibility of silicate Raman scattering as the origin.

Laser emission from transversely pumped dye-doped free-standing polymer film

We present a compact solid-state laser based on leaky mode propagation from a dye-doped polymer free-standing film waveguide. The edge emitted spectrum clearly indicated the existence of periodic resonant modes. The reflections from the lateral faces of the free-standing film provided the optical feedback thus giving rise to a Fabry?Perot like optical cavity. This together with the guidance through the gain medium gave rise to intense narrow emission lines. For a pump energy of 1.82?mJ/pulse, an intense line with FWHM ~0.4?nm was observed at 576.5?nm.

Highly efficient UV-absorbing thin-film coatings for protection of organic materials against photodegradation

UV-protective coatings have been prepared by the sol–gel method, to reduce the destructive effects of UV radiation on easily photodegradable devices, i.e. those containing organic compounds, such as dyes and pigments or plastic materials to be used in outdoor applications. A benzophenone derivative (2,2-dihydroxy, 4-methoxybenzophenone), showing high photostability and strong absorption in the UV range, was embedded in an ormosil matrix. The usage of an organically modified silica matrix enhances the solubility of the UV absorber in the matrix allowing the preparation of highly loaded coatings. The protective coatings, prepared at room temperature, require no thermal treatment after deposition, allowing therefore their application on temperature sensitive materials. The resulting films have a strong absorption in the UV range with a thickness of only 1.0 µm. In addition, the UV-absorbing coatings are transparent, colourless, and exhibit high optical quality. The UV-protective coatings offer an easy method to prevent the photodegradation of organic materials without altering their optical properties in the visible region. Fluorescent rhodamine dye-doped thin ormosil films were coated with a UV-protective layer in order to study their effectiveness in the reduction of the photodegradation of the dye upon irradiation with UV light. The degradation of 20% of the molecules in coated samples was 14 times slower than that of the uncoated samples. The effective temperature range of the UV-protective coatings was established by measuring the photodegradation of the samples at different temperatures.

Optical phase conjugation and double-exposure phase-conjugate interferometry in dye-doped thin film using He–Ne laser

We have experimentally demonstrated optical phase conjugation and double-exposure phase-conjugate interferometry in a methyl green dye-doped gelatin film via degenerate four-wave mixing using a low-power He–Ne laser for the first time. The origin of phase conjugation associated with this dye-doped film is discussed. A phase-conjugate reflectivity of 0.13% is obtained with a He–Ne laser of total power 35 mW.

Degenerate four-wave mixing experiments in Methyl green dye-doped gelatin film

Degenerate four-wave mixing (DFWM) was performed in Methyl green dye-doped gelatin films using continuous-wave laser radiation ( λ = 633 nm ) generated by a He–Ne laser of total power 35 mW. Various parameters which influence the phase-conjugate (PC) signal during the DFWM process were studied. The PC signal contributions from induced holographic transmission and reflection gratings were measured. We observed a maximum PC beam reflectivity of 0.13% in these dye-doped gelatin films.

Demonstration of Optical Phase-conjugation in Methyl Green Dye-doped Thin Film

Optical Phase-Conjugation (OPC) has been observed in Methyl Green (MG) dye sensitized gelatin films in Degenerate Four-Wave Mixing (DFWM) configuration at 633 nm radiation from a He-Ne laser of total power 35 mW. The mechanism of Phase-Conjugate (PC) wave generation associated with this dye-doped system was discussed. The dependence of the PC wave generation on the incident angle between the forward-pump and the probe beams and time of evolution were also studied. A maximum phase-conjugate beam reflectivity of about 0.13% has been observed in this dye-doped gelatin films.