Intramolecular TT-energy transfer in bifluorophoric laser dyes

Rates of intramolecular triplet-triplet energy transfer have been measured for three new bifluorophoric laser dyes. Strong dependence of these rates on the length of the link between the two fluorophores was observed.     

Investigation of Spectral-Luminescent and Lasing Properties of Bifluorophoric Molecules. I. Bifluorophores of Linear Structure

Eight bifluorophoric (BF) molecules on the basis of paratherphenyl, stilbene, phenyl, biphenyl (donors) and coumarin 120 and phenylphtalimide (acceptors) connected by the bridging -CH₂- were experimentally studied. It is shown that the absorption spectra of the BF are virtually additive to donor and acceptor fragments. The acceptor band alone is present in the fluorescence spectrum, which points to a complete nonradiative transfer of the electronic excitation energy. The spectra of induced BF emisson under flash-lamp and laser excitations are also examined.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 74–80, February, 2005.     

Dual-band lasing of benzopyran dyes in the red region of the spectrum

We have studied the spectral and energy characteristics of lasing for two benzopyran dyes in a dispersive cavity with a diffraction grating when the dyes are excited at several different wavelengths using an additional flashlamp-pumped dye laser. These dyes have high fluorescence quantum yield and lase efficiently in the red region of the spectrum. The tuning range of their lasing spectrum is greater than 100 nm. We discuss the characteristic features of conversion of the selective excitation energy by these dye molecules. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 401–404, May–June, 2006.     

Luminescent coolants for solid-state lasers

Solutions of 13 fluorescent dyes have been used as energy transfer agents in place of the normal coolant of a Nd-YAG laser. Dye mixtures were used in a few cases where incomplete absorption of flashlamp pump energy was observed. Improvements of over 100% in laser output were observed for some dyes having a long Stokes shift when tested at both a low-input energy and a low-pulse rate. However, the absolute improvement in laser output for these dye solutions was small, and the improvement could be obtained almost as well by merely increasing the pulse rate. Various factors associated with the effectiveness of transfer-dye solutions are discussed.     

Deep levels of iron implanted inn-type silicon

Results of an investigation of 19 organic dyes pumped by a 1.7 MW discharge-pumped XeCl excimer laser are reported. The dye-laser emission covered a wide wavelength range from 340 nm to 710 nm.P-terphenyl shows efficient laser action. The highest energy conversion efficiency exceeds 40% in visible region. In comparison with 250 kW nitrogen laser pumping, higher efficiencies are obtained for most of these dyes in the same dye-laser configuration.     

Laser Performance of Some Oxazole Laser Dyes in Restricted Matrices

This article reports the optical properties such as absorption profile, molar absorptivity, fluorescence profile and photo-physical parameters such as dipole moment, oscillator strength, fluorescence quantum yields, fluorescence lifetimes, laser performance and finally photostability of 2,5-Bis(5-tert-butyl-benzoxazol-2-yl)thiophene (BBOT),1,4-Bis(5-phenyl-2-oxazolyl)benzene (POPOB), 5-diphenyel-oxazole (PPO) laser dyes in different restricted hosts. (BBOT), (POPOB) and (PPO) are embedded in transparent silica-based nanoporous sol-gel glass and copolymer matrix of methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA). The absorption and fluorescence properties of these laser dyes in sol-gel glass matrices are compared with their respective properties in copolymer host. In case of sol-gel matrix, all dyes had higher quantum yields as well as lasing wavelength maxima. The laser performances as well as the photostability of these laser dyes in sol-gel glass displayed senior behavior compared with (MMA/ HEMA) copolymer samples upon using nitrogen laser (337.1 nm) as pumping energy.     

Dye stability under excimer-laser pumping

The stability of polymethine dyes under XeCl laser excitation has been investigated. (For these dyes emitting in the ir the difference between absorbed and emitted photoenergy is 2 eV.) The stability was measured in an amplifier device operating in the saturated regime. While the influence on dye concentration is negligible, the fluence dependence shows the importance of two photon absorptions. A meausure for the stability is the number of photons which can be emitted per dye molecule before the dye solution has degraded to 50% of the initial value. This value is in the range of 150–280. The stability is clearly related to the formation of photoproducts absorbing at the pump and the laser wavelength. A model starting from the change in the dye solution absorption spectra is in very good agreement with the observed energy decays.     

Energy transfer in solid-state dye lasers based on methyl methacrylate co-doped with sulforhodamine B and crystal violet

Laser action in methyl methacrylate(MMA)co-doped with sulforhodamine B and crystal violet dyes was investigated.The dye mixture was incorporated into a solid polymeric matrix and was pumped by a 532-nm Nd:YAG laser.Distributed feedback dye laser(DFDL)action was induced in the dye mixture using a prism arrangement both in the donor and acceptor regions by an energy transfer mechanism.Theoretically,the characteristics of acceptor and donor DFDLs,and the dependence of their pulse widths and output powers on acceptor–donor concentrations and pump power,were studied.Experimentally,the output energy of DFDL was measured at the emission peaks of donor and acceptor dyes for different pump powers and different acceptor–donor concentrations.Tuning of the output wavelength was achieved by varying the period of the gain modulation of the laser medium.The laser wavelength showed continuous tunability from 563 nm to648 nm.     

掺杂红外染料聚叠氮缩水甘油醚工质激光烧蚀推进性能优化探索

选择含能聚合物聚叠氮缩水甘油醚(GAP)作为激光烧蚀微推力器的工质,分析了红外染料掺杂对激光烧蚀GAP工质推进性能的影响.通过对比掺杂红外染料GAP在不同激光功率密度、掺杂浓度、靶材厚度和激光烧蚀模式下的推进性能数据和烧蚀羽流,初步探索了掺杂红外染料GAP工质的推进性能优化方式.实验结果表明:透射式激光烧蚀模式下,激光能量的指数衰减特性和掺杂红外染料GAP的强黏性使得烧蚀羽流中易存在未充分烧蚀的工质; GAP的推进性能受红外染料掺杂浓度和靶材厚度的综合影响,当靶材厚度与激光吸收深度接近时,靶材充分吸收激光能量使中心烧蚀区达到化学能释放的温度阈值,同时沿激光传播方向未充分烧蚀的质量最少,此时推进性能达到最优值.反射式下掺杂红外染料的聚合物的激光烧蚀过程遵循"先吸收激光能量先喷射"的规律,工质分解充分,推进性能优于透射式.     

Study of the energy stability of ultra-short pulses from an yttrium-aluminium garnet laser

The energy stability of ultra-short pulses (USPs) from an yttrium-aluminium garnet laser with passive mode locking (PML) has been investigated. Experimental results of passive mode locking based on solutions of widely used dyes are given for comparison. Using these saturable absorbers we found that the energy distribution of USP did not depend on the laser working frequency nor on the duration of the experiment.     

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     

白色染料激光器

本文报道了利用双激光染料混合体系取得白色激光的实验结果。这种白色激光具有三基色的波长和强度分别可调的特性。文中亦分析了实现多色运转的双激光染料混合体系应满足的条件。 关键词：     

Theoretical analysis of S1-state lifetime measurements of dyes with picosecond laser pulses

Various methods for the determination of the S₁-state lifetime of dye solutions (laser dyes and modelocking dyes) are analysed. A general model of interaction of laser light with dye molecules is presented and reduced to a dye energy level scheme of six levels. Fluorescence emission, light amplification and absorption recovery techniques are investigated theoretically and their limitations revealed. The determination of the S₁-state lifetime of saturable absorbers by single picosecond pulse bleaching experiments is very thoroughly discussed. The influence of various laser and dye parameters on the bleaching experiments are analysed numerically. The results are compared with isotropic steady state two- and three-level dye models.     

High efficiency dye laser with low fluorescence yield pyrromethene dyes: experimental and theoretical studies

A combined experimental and theoretical study of the photo-physical, laser properties and molecular structures of three relatively recent Pyrromethene (PM) class dyes, PM597, PM580 and PM567, have been carried out. Laser characteristics of these three PM dyes were compared with three other widely used Rhodamine (RH) class dyes, RH6G, RHB and KRS, using a narrow-band dye laser setup, transversely pumped by the second harmonic (532 nm) of a Q-switched Nd-YAG laser. In addition to generating comparative data of these dyes for optimal use in dye lasers, we observed that unlike the RH dyes, the PM dyes show high efficiencies and wide tunability, despite the low fluorescence yield and high rate of non-radiative decay. Particularly, PM597 dye, in spite of a very low quantum yield of fluorescence (Φ=0.42), high non-radiative decay rate, and a large distortion from planarity in its excited state, when used in a laser cavity it exhibited similar laser efficiency and a beneficially wider tuning curve in comparison to other two PM dyes. Theoretical studies were carried out applying density functional theory and time-dependent density functional theory (DFT/TDDFT) to obtain new information on ground and the first excited state geometrical parameters of the PM dyes. Good correlation between calculated molecular properties and experimental results was observed for the evolution of the longest wavelength absorption maximum.     

Dopant-enhanced ablation of nitrocellulose by a nitrogen laser

The photoetching behavior of pure nitrocellulose and of nitrocellulose dyed with stilbene-420, coumarin-120 and rhodamine 6G by 337 nm nitrogen laser pulses has been studied. Ablation with a low power nitrogen laser is hereby reported for the first time. A two step photochemical mechanism is proposed to account for the ablation of the pure material. With the addition of dyes strongly absorbing at 337 nm the photoetching rate of nitrocellulose can be increased significantly. This increase is proportional to the molar extinction coefficient of the dye at 337 nm and its concentration in the polymer. The photoetching mechanism and the energy transfer processes from the dye to the polymer are discussed in detail.     

Amplified spontaneous emission from nitrogen laser pumped dye lasers

The nitrogen laser pumped dye laser output has been studied with emphasis on the behaviour of amplified spontaneous emission (ASE) with respect to the tuning wavelength, pump energy, dyes and their concentration and solvents. Spectral spread of ASE is narrower than fluorescence and its maximum is shifted towards the red side. However, lasing occurs beyond the ASE region. ASE is small at high gain wavelength and increases at the edges of the gain curve. Laser energy is highest at the ASE peak with minimum ASE present in the output. ASE is reduced with increased laser energy in the energy transfer dye lasers.     

Enhanced laser performances based on energy transfer in multi-dyes co-doped solid media

Various coumarin dyes are co-doped with perylene red (P-red) and pyrromethene 567 (PM567) into vinyltriethoxysilane-derived solid media, respectively. Energy transfer among laser dyes has been observed, and the effect of coumarin dye concentration on the laser properties has been investigated. With the presence of coumarin dye and pyrromethene 567, enhanced laser performances based on energy transfer of perylene red have been exhibited. The laser efficiency can be improved by two-fold and broad tunable range as wide as 80 nm can be achieved. At the pump intensity of 1.0 J/cm², the laser output of co-doping perylene red decreases less than 30% after 30,000 pulses.     

Laser dye stability. Part 3. Bicyclic dyes in ethanol

A commercial coaxial xenon flashlamp has been used to evaluate the stability of a variety of coumarin and quinolone laser dyes. The lasing characteristics of over 30 dyes have been quantitatively evaluated as a function of the total excitation energy to which recirculating dye solution has been exposed. Degradation constants were determined and an evaluation was made of the effects of functional group variation upon the stability of the dyes. Comparison with the data of other workers revealed that exclusion of excitation energy below 220 nm does not change the stability of 4-methyl coumarins, but can increase the stability of other coumarins as much as 50 fold.     

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).     

Energy transfer in slab dye lasers

A simple model of the energy transfer between a booster dye and the active dye in a flashlamp pumped planar waveguide dye laser is described.Analytical results are compared with experiments for several dyes in the 600–650 nm region.A twofold increase of laser output was found at a wavelength (630 nm) which is of particular interest for several applications.