Fluorescence of a Liquid Drop with a Dye Excited by Femtosecond Laser Pulses

Results of investigations into the spectral and power characteristics of two-photon fluorescence of a liquid drop with the Rhodamine 6G dye irradiated by femtosecond laser pulses are presented. It is demonstrated that stimulated emission of two types is realized in drops with the concentrated dye solution, namely, superfluorescence within the drop volume and lasing on whispering gallery modes.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 15–19, April, 2005.     

A simple,efficient plastic dye laser

A simple efficient plastic dye laser is described. A conversion efficiency of 47% was obtained from Rhodamine 6G doped PMMA, when pumped by the second harmonic of a Q-switched Nd: YAG laser in a near longitudinal pumping configuration. Lifetime tests performed on 0.3 cm² surface area of plastic, indicates a drop in efficiency from an initial 47% to 25% after 3.2 × 10⁴ shots. By defocusing the pump beam and doubling the sample thickness, the lifetime increases to 1 million shots before the dye laser efficiency drops from an initial 35% to 25%, for a scanned area of 2 cm², similar results have been obtained with rhodamine B.     

A new laser dye with potential for high stability and a broad band of lasing action: Perylene-3,4,9,10-tetracarboxylic acid-bis-N,N′(2′,6′ xylidyl)diimide

We have obtained high gain lasing action from a dye in the calss of perylene-tetracarboxylic acid diimides. These dyes have been used in the past as microcrystalline pigments and more recently as molecularly dissolved fluors having both an orange absorption color and orange fluorescence. In dimethylformamide this dye absorbs with a main maximum at 527 nm, well coupled to the exciting radiation from a frequency-doubled YAG exciting laser. The dye lases primarily in the 0′→ 1″ satellite of the fluorescence band from 566–585 nm, with intermittent output pulses to 605 nm. While this dye overlaps the lasing bands of the rhodamine dyes, we believe that it may be considerably more stable than even Rhodamine 6G, the most stable of that class.     

Heavy-water-based solutions of rhodamine dyes: photophysical properties and laser operation

Photophysical properties of heavy-water-based rhodamine dye solutions have been investigated, with a view to assess the suitability of heavy water as a solvent for high-power, high-repetition-rate dye lasers and amplifiers. We have measured the quantum yield of fluorescence of the commonly used dyes rhodamine-6G, rhodamine-B and kiton-red, dissolved in heavy water, ethanol and normal water. The performance of a heavy-water-based pulsed rhodamine-6G dye laser has been investigated in broadband, as well as in narrowband wavelength-tunable resonator configurations, yielding laser efficiencies comparable to those achieved with ethanolic solutions of the same dye. We have also studied the thermo-optic properties of normal and heavy water, using the Z-scan technique. Finally, photodegradation rates for laser dyes have been compared in heavy water, normal water and ethanol. Our results establish heavy water as a solvent superior to both ethanol and normal water, on account of the lower thermo-optic effects and the higher photostability of rhodamine dyes when dissolved in heavy water. Received: 8 February 2002 / Published online: 8 August 2002     

The influence of silver nanoparticles on the stimulated luminescence of rhodamine 6G solutions

The influence of silver nanoparticles on the spontaneous and stimulated luminescence of rhodamine 6G molecules in aqueous solutions is studied. It is found that the laser photoexcitation of the dye solution gives rise to spontaneous fluorescence, which, with increasing pump power, transforms into stimulated laser radiation and superluminescence. Addition of silver nanoparticles to rhodamine 6G solutions enhances all types of luminescence and lowers the generation threshold for both types of the stimulated emission. The dependences of the laser radiation and superluminescence intensities on the concentration of silver nanoparticles correlate with the data on the spontaneous fluorescence.     

Fluctuations in synchronously mode-locked dye lasers

We present detailed experimental data on random fluctuations of the pulse properties of a cw rhodamine 6G dye laser synchronously pumped by an acousto-optically mode-locked argon ion laser. It is shown that quantitative information about the fluctuations of the energy, the pulse repetition time and the duration of the pulses can be obtained from the power spectrum of the laser intensity which is measured with the use of an electronic spectrum analyser. This method is capable of revealing small, subpicosecond temporal pulse jitter. We show that the dye laser pulses exhibit an absolute r.m.s. jitter of 20 ps which is induced by the pump laser. The relative jitter in a dual system can be less than 1 ps because well defined correlations of the output fluctuations exist when two lasers are pumped by a common source.     

On the mechanism of rhodamine 6G fluorescence quenching

The fluorescence of the widely used TPF dye rhodamine 6G is quenched by photons of the ruby as well as the Nd-glass laser. Taking into consideration the polarisation of the ground- and excited-state absorptions of rhodamine 6G a simple model of quenching results. The main process is an S₁ absorption with subsequent leave of the ordinary rhodamine 6G singlet system. For Nd-laser photons the cross section of the concerned transition following from our quenching experiments is σS₁→S₂ = 1.2×10^-16 cm².     

Spectroscopic and lasing characteristics of 1,3,5,7-tetramethyl-8-ethyl-pyrromethene-BF2 complex

The basic optical properties of the newly synthesized pyrromethene-BF2 derivative (Compound 1) were investigated systematically by its ultraviolet to visible (UV-visible) absorption, fluorescence and triplettriplet absorption. Its lasing characteristics were measured on a dye laser system pumped by a continuous wave Ar ion laser. The results suggest that, compared with the typical pyrromethene-BF2 dye such as P546, Compound 1 possesses stronger fluorescence and lower triplet-triplet absorption over its fluorescence spectral region. Excellent laser properties were also observed for Compound 1. It outperforms the commercially available benchmark laser dye rhodamine 6G in laser wavelength tuning range, which proves that Compound 1 is probably a potential candidate to be developed as the all-solid-state laser material.     

Energy Parameters and Spectral Characteristics of Lasing of a Liquid Dye Drop Incorporating Nanoparticles

The spectral characteristics and the energy parameters of the fluorescence of a liquid rhodamine-6G dye drop incorporating suspended TiO₂ nanoparticles are presented. It is demonstrated that the lasing threshold for modes of the whispering gallery of liquid dye drops is halved in the presence of nanoparticles.     

A grating tuned cw dye laser

We report on the operation of a rhodamine 6G cw dye laser involving a simple tuning mechanism capable of achieving high output powers (～500 mW) and resolving power (0.004 nm) close to the Doppler limit for a range of light gases. The system employs a 600 line/mm diffraction grating external to, but coupled with a high Q laser cavity; continuous tuning over 50 nm of the fluorescence spectrum of the dye was obtained.     

Laser-induced synthesis of metal–carbon materials for implementing surface-enhanced Raman scattering

Metal–carbon materials exhibiting surface-enhanced Raman scattering have been synthesized by laser irradiation of colloidal systems consisting of carbon and noble metal nanoparticles. The dependence of the Raman scattering intensity on the material composition and laser irradiation conditions has been investigated. The possibility of recording the Raman spectrum of organic dye rhodamine 6G, deposited in amount of 10^–6 M on the substrate obtained from a colloidal solution is demonstrated.     

High average power from a long pulse dye laser

A reliable rhodamine 6G dye laser with a 60μs pulse duration, a repetition rate up to 100 Hz and an average power of 4W is described.     

Comparative laser performances of pyrromethene 567 and rhodamine 6G dyes in copper vapour laser pumped dye lasers

Narrowband laser performances and photochemical stability of alcoholic solutions of pyrromethene 567 and rhodamine 6G dyes, under high-repetition rate copper vapour laser (at 510 nm), as well as, high-peak intensity Nd:YAG laser (at 532 nm) excitation have been investigated. We have observed that pyrromethene 567 dye solutions offer higher efficiency, wider tuning range, but lower photochemical stability and higher lasing threshold than that of rhodamine 6G dye solutions. An addition of about 100 mM DABCO, as a singlet oxygen quencher, in pyrromethene 567 dye solutions improved its photochemical stability close to that of rhodamine 6G. The observation of higher slope efficiency, in spite of higher threshold pump energy for pyrromethene 567 dye than that of rhodamine 6G dye solutions, was explained by a predictive model on gain characteristics of both dye solutions as a function of pump energy. PACS 42.55.Mv; 42.55.Rz; 42.70.Hj; 42.70.Jk     

Efficient amplification of sub-picosecond pulses of a non-CW dye laser

Efficient amplification in a dye laser amplifier is investigated theoretically and experimentally. A five-level rate equation approach is considered including rotational relaxation of the dye molecules. The effects of the pump pulse duration and of the parameters of the input pulse are discussed. The results are compared with experimental data for 0.5 ps pulses of a pulsed dye laser. Conversion efficiencies >10% are achieved for a single pass amplifier using Nd:YAG pump pulses of 2 ns while an effective fluorescence lifetime of 1.7±0.2 ns is determined for the gain medium rhodamine 6G. The triple pass amplifier stage of the laser system achieves an energy conversion of 4% with 40 J output pulses.     

Ultrafast nonlinear optical properties of dye-doped PMMA discs irradiated by 40 fs laser pulses

The two-photon absorption (TPA) characteristics of PMMA discs doped with three different dyes were studied using an fs-pulsed Ti-Sapphire laser as the pump source, and employing the open-aperture Z-scan technique. TPA cross-sections obtained for PMMA doped with the dyes PM597, DCM and rhodamine 6G–rhodamine B (co-doped) were found to be equal to 24.7, 33.3 and 32.3 GM, respectively (1 GM=10^?50 cm⁴ s phot^?1 mol^?1). Furthermore, two-photon fluorescence was measured for the samples containing DCM and rhodamine 6G–rhodamine B (co-doped). Compared to the one-photon fluorescence spectrum, the peaks in the two-photon fluorescence spectrum were red shifted and the extent of red shift increased with increasing doping concentration. We have also observed that the red shift in the two-photon fluorescence peak of the samples in the solid form is much larger than that in the solution state. This phenomenon could be explained by a twisted intra-molecular charge transfer model.     

Dye-Laser Fluorescence of 4-Methylumbelliferone and Related Coumarins

During tha eight years since phthalocyanine solution was used by Sorokin and Lankard in the original dye laser¹ and DTTC bromide and iodide were used in the work of Schafer, Schmidt and Volze², laser emission has been reported³ from close on 400 combinations of laser dye and solvents covering a wavelength range extending from 340 to 1175 nm. Many hundreds or even thousands of attempts to induce laser action in a vast number of available chemicals have proved unsuccessful, either by pulsed or continuous laser pumping, or by flashlamp techniques. In fact, relatively few combinations have established themselves as highly efficient, reliable and entirely satisfactory dye laser media. The compound rhodamine 6G is probably the most widely used in the range 540–640 nm. However, some ten different solvents and a variety of excitation techniques have been necessary to maintain maximum fluorescence intensity over this range. A t shorter wavelengths an acidic solution of 4,6- dimethyl-7-methylamino-coumarin in ethanol was observed to lase⁴ over the range 430–530 nm and a particular solution of 4-methylumbelliferone to lase from 391 to 567 nm⁵. This offered the possibility of achieving narrow linewidth tunability using dye lasers based on single solutions. It represented a significant advance on the first experiments² in which it was possible by changing the solvent, varying the solute concentration or changing the reflectivity of the resonator mirror, to Shift the wavelengths by up to 60 nmm in the infra-red region.     

Photophysical and laser characteristics of pyrromethene 567 dye: Experimental and theoretical studies

Narrow-band laser performance of alcohol solutions of pyrromethene 567 (PM567) and rhodamine 6G (RH6G) dye was investigated using a home-made GIG-configured dye laser, excited by the second-harmonic radiation (at 532 nm) of a pulsed Nd:YAG laser. Higher laser efficiency was observed with PM567 dye (∼23% peak) in comparison to the commonly used RH6G dye (16.5%), in spite of much lower fluorescence quantum efficiency of the PM567 (0.83) vis-à-vis RH6G (0.98) dye solutions in ethanol. First principle-based electronic structure calculations were performed on PM567 dye in the ground (S ₀) and excited states (S ₁) using density functional theory to elucidate the structure and photophysical properties of the dye.     

Femtosecond pulse duration measurement by two-photon fluorescence detection

The two-photon absorption induced fluorescence in a methanolic rhodamine 6G solution is used to measure the pulse duration of a cw femtosecond Kerr–lens mode-locked Ti:sapphire laser by a Michelson-interferometer-type autocorrelator arrangement. Interference-free autocorrelation traces are obtained by correlating perpendicular polarized pulses. The two-photon polarization parameter of rhodamine 6G is determined by contrast ratio measurement. The time resolution limits are discussed.     

等色染料离子对浮选光度法研究-四溴荧光素*罗丹明6G体系

本文研究了四溴荧光素（ＴＢＦ）、罗丹明６Ｇ（Ｒ６Ｇ）等色染料离子对浮选光度法测定锗、铂和铁的方法。首先将被测金属离子形成的［ＭｅＬｎ（Ｒ６Ｇ）ｍ］（Ｌ：配位体,ｍ、ｎ为整数）有机溶剂浮选物,用碱解析并反萃于水相。而后加入与罗丹明６Ｇ等色的四溴荧光素溶液继续浮选,将形成的等色染料离子对Ｒ６ＧＴＢＦ浮选物溶解于丙酮。于５３０ｎｍ处测定吸光度值。由于２ｍ个染料同时吸收同一波长的光,而提高了方法灵敏度。测定Ｇｅ、Ｐｔ和Ｆｅ的摩尔吸光系数均在１０５Ｌｍｏｌ－１ｃｍ－１以上