Thermal bleaching of organic laser dyes

Thermal bleaching of organic laser dyes in the temperature range from +20°C to +220°C is investigated.     

Time resolved spectroscopy in laser grade organic dyes

Time resolved spectroscopy is discussed along with the theoretical and experimental methods used to measure the fluorescence lifetimes in various laser grade organic dyes. The role of solvents and their viscosities in the fluorescence life time is also discussed. Different photophysical parameters have been obtained in rigid and non-rigid dye molecules.     

New laser dyes

A list of 73 new laser dyes is given. These dyes were found in screening fluorescent dyes from a dye collection using a powerful nitrogen laser of 1 MW peak power and 2.5 nsec pulse width.     

Influence of various coumarin dyes on the laser performance of laser dyes co-doped into ORMOSILs

Several kinds of coumarin dyes (C440, C460, C500, C503 and C540A) were co-doped with perylene red (p-red) or pyrromethene 567 (p567) into VTES- and MTES-derived organically modified silicates (ORMOSILs) respectively, by the sol-gel process. The effects of coumarin dyes and their concentration on the laser properties and photostabilities of p-redand p567 were studied and the mechanisms involved were discussed. At optimized coumarin dye concentration, the slope efficiency of co-doped p-redincreased by a factor of 2 while only minor increases in the laser efficiency of p567 were observed. A broader tunable range with increased conversion efficiency and at least a 3-fold improvement in the photostabilities of p-redand p567 in the presence of coumarin family dyes have also been achieved. The mechanism responsible for the improvement in the laser performances and photostabilities of p-redand p567 resulted from the energy transfer between p-red/567 and coumarin dyes. PACS PACS 42.55.Mv; 42.55.Rz; 42.70.Hj     

Ion-photon emission of metal-containing organic dyes

The main parameters of ion-photon emission are investigated under ionic bombardment of metal-containing organic dyes and their mixtures with cholesterol. The spectral composition, quantum yield, and spatial distribution of emission from knocked-out excited particles have been determined. Several assumptions about the processes inherent to organic compounds under consideration have been made on the basis of the received data.     

Anomalous fluorescence behaviour of organic dyes

Subject to certain excitation conditions, organic-dye molecules in solution can fluoresce at higher energies than those of the S₁ → S₀ transition. This paper investigates the anomalous fluorescence behaviour of differently substituted polymethine dyes when excited by ruby-laser radiation and the ruby harmonic respectively. All dyes, including those which are not aromatically substituted, show a short-wave fluorescence. The results of investigation suggest that in the excited state the conjugation over the total molecule is lost and that the anomalous fluorescence reflects the transition between two levels of this de-coupled system.     

Photoacoustic spectra of some laser dyes

Photoacoustic spectra of rhodamine 110, rhodamine 6 G, rhodamine B, rhodamine 101 and coumarin 102 laser dyes have been recorded at room temperature of 25°C in the spectral range of 350–750 nm. These samples were taken in powder as well as in solution forms. For this purpose the closed and the open photoacoustic cells have been used. It is hoped the present study would be useful for characterization of these dyes.     

Emission of organic dyes in the case of nonlinear absorption upon excitation by the XeCl* laser

Spectral luminescent properties of eight organic dyes are studied upon excitation by focused radiation from the XeCl* laser at the pump power up to 200 MW/cm². The transmission of pump radiation by dyes is investigated as a function of the pump power. It is shown that variations in the energy, spectral, and temporal parameters of radiation of organic dyes upon high-power excitation are explained by the development of superluminescence (amplified spontaneous emission).     

Photophysical properties and laser performance of photostable UV laser dyes

The photophysical properties such as singlet absorption and fluorescence spectra, the fluorescence quantum yield and fluorescence decay time as well as the laser performance data such as the tuning range, the conversion efficiency, and the photochemical stability of 12 sterically hinderedp-quaterphenyls have been measured in ethanol and/or dioxane at room temperature. The sterically hinderedp-quaterphenyls exhibit shorter laser dye emissions in the 330–380 nm range than the parent compoundp-quaterphenyl. The conversion efficiencies of the sterically hinderedp-quaterphenyls range between 1 and 21%. The photochemical stability of the sterically hinderedp-quaterphenyls is by a factor of 10 to 20 better in dioxane than in ethanol. 2-Methyl-5-tert. butyl-p-quaterphenyl and 2,5,2,5-tetramethyl-p-quaterphenyl are among the most stable UV laser dyes known today.     

Optical phase conjugation in laser dyes

The nonlinear optical response of four laser-active dyes (Pyridine 1, DCM, Pyridine 2 and Styryl 9) is reported at a wavelength of 532 nm. The dyes show phase conjugate reflectivities in the 5 to 85% range. Polarization discrimination experiments and comparison with the Caro-Gower model suggests thermal origin of the nonlinearity.     

Violet-to-red photoluminescence of spiro-TAD organic films doped with different organic dyes

Photoluminescence (PL) and photoluminescence excitation (PLE) spectra of undoped spiro-TAD films and spiro-TAD films doped either by the organic dyes coumarin 7 or DCM as well as by both of these dyes simultaneously were investigated at different dye concentrations. A widened PL spectrum caused by doping was encountered and violet-to-red emission was obtained. It was established that excitation of the dyes is realized most efficiently through spiro-TAD. The overall integral PL intensity of the coumarin 7 doped films increased with dye concentration due to the suppression of nonradiative recombination in the film caused by a transfer of spiro-TAD excitation energy to the dye molecules. Mainly radiative energy transfer from semiconductor to dye molecules occurs in the case of DCM doping. No mutual influence on the luminescence of both dyes in the spiro-TAD film was observed and as a consequence, the PL band intensity of each dye can be adjusted separately.     

New laser dyes with blue-green emission

Several new derivatives of 7-amino coumarin and 7-amino-(2)-quinolone were synthesized and tested for lasing performance. Relative output, stability and lasing wavelength for these dyes are reported.     

Laser dyes III: Concepts to increase the photostability of laser dyes

Two approaches of increasing the photostability of the laser dye POPOP are reported. Desensibilisation against singlet oxygen was accomplished either by substitution with electron acceptor groups or by linking the dye molecule with a suitable quencher unit, e.g. tertiary amines. To test the efficiency of the modifications of the dye molecules the rate of their continuous UV-bleaching (λ = 366 nm) was investigated.     

Products of photodegradation for coumarin laser dyes

The products of conventional photolysis of the coumarin laser dyes, C1, C35, C153, and C152 have been investigated. The previously reported dealkylation of C1 is documented for the fluorinated dyes, C35, and C152 in deaerated solvents. In addition, a reduction product is identified for C1, consistent with a radical mechanism for decomposition. Evidence is provided that the concentration quenching (self quenching) of singlet dye is important to the degradation mechanism. For the rigid dye, C153, a photooxidation product involving the amine functionality results from decomposition in aerated media. For several dyes, very low triplet yields have been measured.     

Continuously tunable external-cavity diode laser with a double-grating arrangement

A new external-cavity diode laser system based on an extended version of the Littman configuration is investigated. In our laser system the tuning mirror is replaced with a second grating mounted at the Littrow angle. This double-grating design provides a smaller passive bandwidth than the grating-mirror configuration, which is used to compensate for the large angle-of-incidence-dependent losses of the grazing-incidence grating. This results in a broader continuous tuning range with an improved mode stability. Because two laser diodes, emitting at 820 and 775 nm, respectively, are used, the external-cavity laser is continuously tunable without mode hops across 35 nm at 820 nm and 27 nm at 775 nm. Such a laser was used to measure the absorption lines of the oxygen A band around 762 nm. The complete R - and P -rotational branches of the b summation operator(g)(1) (+)(nu(??)=0)?X (3) summation operator(g)(-)(nu (?)=0) transition were recorded in a single-wavelength scan.