A high efficiency dye laser tunable from the UV to the IR

A dye laser has been developed as a source of tunable radiation in the wavelength range 3500–3700 Å. A Variety of dyes and dye mixtures have been used to cover this range. Output powers up to 30 kW are obtained with line-widths less than 1.8 Å. A Fabry-Pérot etalon reduces the output linewidth to 0.1 Å and the peak output power by a factor of three. Second harmonic powers in excess of 2 kW have been generated from the output of this laser.     

Laser emission from mixtures of dipyrromethene dyes in liquid solution and in solid polymeric matrices

Laser emission from binary mixtures of different dyes both in liquid solution and incorporated into solid polymeric matrices, covering the spectral region from green to red, is investigated. Mixtures of two synthesized dyes, analogs of the commercial dye Pyrromethene 567 (PM567), allowed covering the spectral range from green to orange. Tuning ranges in solid state of up to 42 nm with good photostabilities were demonstrated. To extend the tuning range to the red, binary mixtures of the dyes Pyrromethene 597 (PM597)/Pyrromethene 650 (PM650), PM567/DCM, and PM597/DCM were also studied. In liquid solution, a mixture of dyes PM567 and DCM allowed for narrow-linewidth laser emission continuously tunable over a range of 85 nm. In solid-state, mixtures of dyes PM597 and PM650 allowed laser emission tunable over two separate spectral regions up to a wavelength of 619 nm.     

Laser properties of fluorescent brightening agents

The laser properties of 19 dyes commonly used as fluorescent brightening agents (FBA) have been studied. A nitrogen laser served as the pumping source. The absorption spectra and the relationship between laser power and wavelength was determined for these dyes. Since several of these compounds have an efficiency comparable to that of the POPOP scintillator commonly used in this part of the spectrum, and since they are easily soluble in alcohols and furthermore, are very inexpensive, they may be competitive with other dyes hitherto used in the violet-blue region.     

Multi-component chemical analysis of gas mixtures using a continuously tuneable lidar system

Differential absorption lidar (DIAL) measurements are usually made on single compounds by alternately switching the wavelength between on and off a resonance line. The selection of more than two wavelengths is a mathematical necessity for simultaneous measurement of multiple species or for resolving interference effects between a compound of interest and a background gas such as water vapour or carbon dioxide. This is especially true in the mid-IR region, where many hydrocarbon compounds have important spectral features. We present a method for remote measurement of gas mixtures in the mid-IR region based on a newly developed fast-switching, frequency-agile optical parametric oscillator lidar transmitter. A multivariate statistical procedure has also been applied for this system, which combines a genetic algorithm for wavelength selection with a partial least squares method for identifying individual compounds from their combined absorption spectrum. A calibration transfer is performed for compounds of interest using reference spectra from an absorption spectra database. Both indoor absorption cell measurements and outdoor remote range resolved measurements of hydrocarbon mixtures were performed to explore the performance of the method. PACS 42.62 Fi; 42.79 Qx; 02.50 Sk     

Photoacoustic studies on excitation transfer in Rh6G and RhB dye mixture

The photoacoustic spectra of Rhodamine 6G (Rh6G), Rhodamine B (RhB) dyes and their mixtures were recorded at different concentrations. It is observed that in the mixture the photoacoustic signal increases due to excitation transfer from Rh6G to RhB in the wavelength region 480–530 nm. The excitation transfer rate estimated from these data show that resonance is dominant rather than the collisional transfer process.     

Polymethine dye lasers

The polymethine dyes are important materials for dye lasers in the longer wavelength range. It is a remarkable feature of these dyes that there are many whose chemical structures differ little from each other. Using these dyes, intense coherent light at any wavelength from 710 to 1100 nm can be obtained by ruby laser pumping. We report the spectroscopic properties of polymethine dyes and give some discussion about the influence of chemical structure. Several correlations, found between chemical structure and spectroscopic properties, are useful for the estimation of the properties of unknown polymethine dyes. Two experiments on chemical discoloration of polymethine dyes are also reported.     

Analytical Methods for the Characterization of Organic Dyes in Artworks and in Historical Textiles

Abstract

Dyes are among the most significant components in works of art and archaeological findings. In the scientific examination of historical artefacts, the identification of natural dyestuffs is a challenging task, due to the complexity of their chemical composition and the possible presence of mixtures of chromophores and degradation products. For this reason, in the last few decades, new analytical procedures and techniques have been developed and improved for the characterization of organic dyes and their identification in microsamples. This review looks at the chemical composition of natural organic dyeing materials used in the field of the cultural heritage and focuses on several analytical methods based on spectrometric and chromatographic techniques that have contributed to the study of organic dyes in works of art and archaeological findings.     

Thermal rotations and relaxation of vibrational energy of excited dye molecules in solution

Measurements of polarization and decay time of fluorescence of dyes in solution as a function of excitation wavelength were performed. The rate of thermal rotational depolarization was found to be independent of vibrational energy excess. To explain the observed influence of excitation wavelength on the emission anisotropy, a change in the magnitude of torsional vibrations, in addition to possible mixing of states, is proposed.     

Biscoumarins - New Laser Dyes in Coumarin Series

With a view to extend the tunability range using new derivatives in the coumarin series of dyes, a novel series have been synthesized, viz. the biscoumarins where two coumarin nuclei are coupled. These are studied for their lasing characteristics, optical spectra and quantum efficiencies. Laser spectra of these dyes in various solvents are also studied. Tunability range of these dyes have been found to cover blue green region of the spectrum and though there is shift to longer wavelength as compared to monocoumarins, extending the tunability range, it is not as much as would be normally expected with extended conjugation involving two coumarin nucled.     

Polarization of radiation of distributed-feedback dye lasers with one- and two-component gain media

Polarization of the radiation generated by a distributed-feedback laser on one-component solutions and binary mixtures of coumarin dyes is investigated. It is established that, with a marked excess of the generation threshold, the degree of polarization P of the radiation generated by one-component solutions is practically independent of the wavelength. For binary mixtures, the spectral behavior of P depends on the donorlacceptor concentration ratio. Here, with the anisotropy of the distribution of excited molecules being partially disrupted in the process of energy transfer (from the donor to the acceptor), the degree of polarization decreases appreciably when radiation frequency is tuned from the short-wavelength region to the long-wavelength one. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 3, pp. 340–343, May–June, 2000.     

Kinetics of the Weigert effect in azo dyes embedded in polymeric matrices with different activities

Experimental data for the photoanisotropy kinetics in azo dyes embedded in various polymer matrices are reported. The Weigert effect in these dyes is shown to depend on the polarized actinic radiation wavelength and matrix constitution. The effect of dark relaxation in the dyes is found.     

Factors affecting the low-dose gamma irradiation of hydrocarbons

The effect of differing conditions on the extent and nature of the damage produced in organic substances by γ-irradiation at low dose rates has been examined by a new chromatographic method which makes detection possible in a region where all other standard techniques fail. Use is made of the fact that certain surface active dyes profoundly affect the shape of a chromatographic band in a manner related to the composition of the material undergoing chromatography.

Taking length of outline per unit area as a measure of the shape of the band on paper impregnated with such dyes, a method of chromatography has been evolved, having a completely standardized development technique for all mixtures which does not require the separation of the components of the mixture.

This outline/area index varies with the temperature according to the nature of the polar groups of the compounds present in the mixture under investigation and with the concentration of the individual components.

It is thus possible to construct a three dimensional diagram having as axes, temperature, concentration and index. The diagram obtained is absolutely characteristic of the composition of a given mixture.     

Novel benzanthrone aminoderivatives for membrane studies

The potential of novel benzanthrone aminoderivatives to trace the changes in physicochemical properties of lipid bilayer has been evaluated. Binding of the dyes to the lipid bilayers composed of zwitterionic phospholipid phosphatidylcholine (PC) and its mixtures with anionic phospholipid cardiolipin (CL) and cholesterol (Chol) was followed by significant quantum yield increase with small blue shift of emission maximum. Analysis of partition coefficients of the dyes under study showed that all aminobenzanthrones possess high lipid-associating ability. The dyes A8 and AM2 proved to be sensitive to the variations in membrane chemical composition responding to the changes in bilayer hydration induced by CL and Chol.     

Electrically induced storage effects in smectic A phase of dyed low molar mass siloxane liquid crystals

A newly synthesized low molar mass liquid crystal having a flexible mesogenic group attached to methylene siloxane exhibiting smectic A phase has been used as a host for 2% (wt./wt.) dichroic dyes. The electro-optic properties of these guest–host mixtures have been studied as a function of temperature, frequency and the applied voltage. At low frequency (≲1 Hz), turbulent scattering texture was induced influenced by conduction mechanism. This texture was transformed to a clear homeotropic state due to dielectric reorientation of the smectic molecules at high frequency (>2 kHz). These materials have shown storage effects similar to monomeric and polymer smectogens. The effects of dichroic dyes on the electro-optic performances have been discussed. These systems are expected to prove functional materials for electronic displays.     

Spray diagnostics using an all-solid-state Nd:YAlO<Subscript>3</Subscript> laser and fluorescence tracers in commercial gasoline and diesel fuels

A new diode-pumped Nd:YAlO₃ laser system emitting pulse bursts at 671 nm has made it possible to apply tracer-laser-induced-fluorescence (LIF) techniques for spray diagnostics not only by using model fuels but in real diesel or gasoline fuel sprays. In this work we characterize possible candidates for LIF tracers that can be excited in the wavelength region of 650–680 nm where commercial diesel fuel is transparent. Two fluorescent dyes, Rhodamine 800 and Atto 680, were identified as possible tracers and tested for their relative fluorescence quantum yield and absorption cross section in a diesel fuel environment as well as their behavior at different temperatures. First results of laser-dropsizing experiments with Rhodamine 800 as a fluorescence tracer are presented. PACS 42.62.Fi; 32.50.+d; 42.62.Cf     

Effect of Matrix Treatment on Spectroscopic Properties of HCl Catalysed Sol-Gel Glasses Containing Coumarin Laser Dyes

Coumarin 1, Coumarin 2 and Coumarin 120 are embedded in transparent sol-gel glass samples prepared by sol-gel process using dip method. The sol-gel matrix is given dip treatment with Methanol /Distilled Water (50/50vol) for 1 to 16h before dipping into dye solution. The effect of dipping time of matrix in Methanol/ Distilled Water on spectroscopic properties of coumarin dye doped glass samples has been studied. The Optical Density (OD) at absorption maximum wavelength and Fluorescence Intensity (FI) at fluorescence maximum wavelength of all coumarin dyes increase with the time of dipping of the sol-gel sample. These absorption/fluorescence properties of coumarin dyes in sol-gel glass matrices are compared with its respective properties in methanolic solution in acidic environment. The cause of these changes in OD/FI with dipping time is discussed by taking into account the absorption / fluorescence of dye in acidified methanol.     

AIE Based Coumarin Chromophore - Evaluation and Correlation Between Solvatochromism and Solvent Polarity Parameters

A new class of red emitting extensively conjugated donor-π-acceptor type dyes bearing coumarin units have been synthesized by condensation of 7-(diethylamino)-2-oxo-2 H-chromene-3-carbaldehyde with different active methylenes. All the dyes are characterized by ¹H NMR, ¹³C NMR and HRMS spectroscopy. The photophysical behaviour and the relation between structure and properties of the coumarin “push–pull” derivatives were investigated experimentally. The dyes exhibited positive solvatochromism and solvatofluorism in solution of varying polarity. These coumarin dyes show aggregation induced emission properties with red emitting fluorescence. They show absorption in the range of 501–528 and emission in the range of 547–630 nm. We evaluated photophysical properties of coumarin dyes using solvotochromism and solvent dependent shift in the emission wavelength. All the synthesized coumarin dyes COS1-COS4 are showing very good solvatochromic properties.     

Tunable,narrow bandwidth, 2 MW dye laser pumped by a KrF1 discharge laser

Characteristics of p-terphenyl and PBD, the most efficient uv dyes, have been investigated under high intensity pumping by a multi-atmosphere KrF¹ discharge laser at 248 nm wavelength. Energy conversion efficiencies, spectral features and temporal behaviour of the dyes were studied parametrically. A maximum powerof 2 MW uv emission with a bandwidth of ～2×10^-2 nm was obtained for PBD. It was found that a mixture of both dyes provided higher (by a factor of 1.3) output in the range 348–366 nm than either of the dyes alone. Significant pump intensity dependent conversion efficiency and pulse shape variations were observed for the most efficient uv dye, p-terphenyl and were related to triplet-triplet adsorption processes in the dye.     

Protein adsorption drastically reduces surface‐enhanced Raman signal of dye molecules

There is an increasing interest in developing surface enhancement Raman spectroscopy methods for intracellular biomolecule and for in vitro protein detection that involve dye or protein–dye conjugates. In this work, we have demonstrated that protein adsorption on silver nanoparticle (AgNP) can significantly attenuate the surface‐enhanced Raman spectroscopy (SERS) signal of dye molecules in both protein/dye mixtures and protein/dye conjugates. SERS spectra of 12 protein/dye mixtures were acquired using 4 proteins [bovine serum albumin (BSA), lysozyme, trypsin, and concanavalin A] and three dyes [Rhodamine 6G, adenine, and fluorescein isothiocyanate (FITC)]. Besides the protein/dye mixtures, spectra were also obtained for the free dyes and four FITC‐conjugated proteins. While no SERS signal was observed in protein/FITC mixtures or conjugates, a significantly reduced SERS intensity (up to 3 orders of magnitude) was observed for both R6G and adenine in their respective protein mixtures. Quantitative estimation of the number of dye molecules absorbed onto AgNP implied that the degree of R6G SERS signal reduction in the R6G/BSA sample is 2 to 3 orders of magnitude higher than what could be accounted for by the difference in the amount of the absorbed dyes. This finding has significant implications for both intracellular SERS analyses and in vitro protein detection using SERS tagging strategies that rely on Raman dyes as reporter molecules. Copyright © 2009 John Wiley & Sons, Ltd.     

Polarization and pitch dependence of cholesteric blue-phase structures

For cholesteric mixtures of two biphenyl liquid crystals, we show: (1) The BPI-BPII wavelength gap vanishes discontinously with pitch, thereby suggesting two possible BPII structures. (2) The Bragg reflections are all circularly polarized, contrary to existing theories. The temperature dependence of the BPI-BPIIA wavelength is well described by Alexander's theory.