互变异构激光染料奇通红发光特性研究

本文报道应用微微秒脉冲技术测量奇通红染料荧光寿命,发现该体系荧光衰减呈现双指数衰减形式,证实了奇通红染料分子的互变异构特性.     

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.     

Refractive indices and thermo-optical properties of dye laser solvents

By measuring the wavelength tuning of a distributed feedback dye laser, solvent refractive-index changes as small as 0.0002 may be determined. This technique hence allows precise measurement of refractive-index dependence on temperature (dn/dT) and therefore enables the thermo-optical properties of solvents used in dye lasers to be assessed. In addition to single component solvents, the thermo-optical properties of solvent mixtures and additives are reported here. The refractive-index change with temperature (dn/dT) is related to solvent density change with temperature (dq/dT) through molecular polarizability.     

Photophysical parameters and fluorescence quenching of 7-diethylaminocoumarin (DEAC) laser dye

The optical properties including electronic absorption spectrum, emission spectrum, fluorescence quantum yield, and dipole moment of electronic transition of 7-diethylaminocoumarin (DEAC) laser dye have been measured in different solvents. Both electronic absorption and fluorescence spectra are red shifted as the polarity of the medium increases, indicating that the dipole moment of molecule increases on excitation. The fluorescence quantum yield of DEAC decreases as the polarity of solvent increases, a result of the role of solvent polarity in stabilization of the twisting of the intramolecular charge transfer (TICT) in excited state, which is a non-emissive state, as well as hydrogen bonding with the hetero-atom of dye. The emission spectrum of DEAC has also been measured in cationic (CTAC) and anionic (SDS) micelles, the intensity increases as the concentration of surfactant increases, and an abrupt change in emission intensity is observed at critical micelle concentration (CMC) of surfactant. 2×10⁻³ mol dm⁻³ of DEAC gives laser emission in the blue region on pumping with nitrogen laser (λ_ex=337.1 nm). The laser parameters such as tuning range, gain coefficient (α), emission cross section (σ_e), and half-life energy have been calculated in different solvents, namely acetone, dioxane , ethanol, and dimethyforamide (DMF). The photoreactivity of DEAC has been studied in CCl₄ at a wavelength of 366 nm. The values of photochemical yield (?_c) and rate constant (k) are determined. The interaction of organic acceptors such as picric acid (PA), tetracyanoethylene (TCNE), and 7,7,8,8-tetracynoquinonedimethane (TCNQ) with DEAC is also studied using fluorescence measurements in acetonitrile (CH₃CN); from fluorescence quenching study we assume the possible electron transfer from excited donor DEAC to organic acceptor forming non-emissive exciplex.     

Macroscopic and microscopic parameters of laser dye solvents: m-xylene and dioxane

For the laser designer and other users the optical, electrical and refractive parameters have been obtained for pure nonpolar laser dye solvents m-xylene and dioxane. The refractive index (n) and its thermo-optic constant (dn/dT) at argon laser wavelength 514.5 nm and He–Ne laser wavelength 632.8 nm, are measured. The values of n and dn/dT are used to calculate the optical permittivity ε=n² and its variation with temperature dε/dT. Applying Cauchy's equation the optical and dielectric dispersion (dn/dλ and dε/dλ) are determined. The variation of −dn/dT, −dε/dT, molar refractivity and thermal volume expansion coefficient as a function of wavelength are calculated and represented. Furthermore Cauchy's constants A and B as a function of temperature are plotted. The specific and molar refractivities, specific and molar dispersivity total polarizability, distortion polarizability, ratio of atomic to electronic polarizability, molecular radius, relaxation time, electric susceptibility characteristic impedance, and other physical parameters were calculated. Additionally, density, thermal linear expansion coefficient and molar polarization as a function of temperature were calculated at the laser wavelengths 514.5 nm.     

Spectral narrowing of a flashlamp-pumped,waveguide dye laser by amplification of tunable narrow-band cw radiation

Spectral narrowing of the broad-band emission from a flashlamp-pumped dye laser, which consisted of a slab waveguide high-gain amplifier in conjunction with a high-loss resonator, is reported.The pulsed laser oscillator was driven by a cw dye laser oscillating in several longitudinal modes. An energy output up to 10 mJ per pulse has been obtained with a driving power of 10 mW, showing the possibility of substantial power amplification of the narrow-band emission from a cw dye laser.     

A tunable,frequency-doubled,continuous-wave dye laser using ADA

A tunable, continuous-wave, frequency-doubled, rhodamine 6G dye laser has been developed using an ADA crystal placed in an astigmatic and coma compensated cavity. Generated UV powers of the order of 30mW cw in a single direction in gaussian form over the range 292–302 nm have been obtained by temperature phase matching, and with a 4.5 W pump. Power output is affected by thermal phase mismatching, and is ultimately limited by thermal lensing. Two scanning systems have been developed; a broadband arrangement of linewidth 0.02 nm continuously tunable over a range of 2 nm, and a narrowband system of linewidth 0.002 nm continuously tunable over a range of 1 nm. The laser has been used to detect the Rydberg states of Rb up to a principal quantum of n = 74.     

Parametric generation of shortened,narrow-band picosecond pulses using a Yag-pump laser

Using a single path parametric system pumped by a YAG laser, shortened pulses are produced at various frequencies. Starting with a duration of the pump pulse of 21 ps at 9400 cm^?1 we achieve a duration of 4 ps between 2700 cm^?1 and 6700 cm^?1, of 8 ps between 13 500 cm^?1 and 16 100 cm^?1, and of 8 ps between 27 000 cm^?1 and 32 000 cm^?1. Typical bandwidths are 10 cm^?1 in the infrared, 4 cm^?1 in the visible, and 5 cm^?1 in the ultraviolet.     

The study of green laser performances by using composite crystals of different initial transmissions

This paper reported a passively Q-switched green laser of LD pumped linear cavity structure by using Nd:YAG/Cr⁴⁺:YAG composite crystal and the type II phase matching KTP crystal. The dependence of average output power, pulse width and pulse repetition rate on pump power at different initial transmissions of Cr⁴⁺:YAG were measured and analyzed. With Cr⁴⁺:YAG of 80% initial transmission, under pump power of 13.97 W, the output average power is up to 681 mW, with pulse width of 200 ns and pulse repetition rate of 9.1 kHz. The laser operates in a fundamental mode.     

Photophysical properties and laser characteristics of a new rigid aminocoumarin dye lasing in the blue-green region

The photophysical properties of a new dye, 7-Diethyl AminoCoumarin with a Rigid substitution in the 3-position (referred to as DARC) have been studied in three solvents: dioxane, DMF and DMSO. The dye has been found to have a fluorescence quantum efficiency (_fl) between 0.40 and 0.80 in these solvents. The dye-laser performance of this dye has also been investigated in dioxane, DMF and DMSO, under nitrogen-laser pumping and compared with that of the commercially available standard laser dye, Coumarin 515 (C-515). A tuning range of nearly 70 nm was obtained in the blue-green region with an efficiency up to 80% of that of the standard dye. The observed characteristics of the dye are explained in terms of the sructural rigidization of the dye in the 3-position which inhibits the formation of the Twisted Intramolecular Charge Transfer (TICT) conformation in the excited state leading to an enhancement of the _fl and a considerable improvement in the laser performance.Research carried out at U.D.C.T., Bombay, India     

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     

A tunable,frequency-doubled cw dye laser using an RDP crystal

We report a c.w. intracavity, frequency doubled, rhodamine B dye laser using an RDP crystal 5 cm long. Generated uv powers up to 15 mW are obtained in a single direction with a linewidth of 2 GHz over the range 314–318 nm. A conversion efficiency of about 1.25 × 10^-3 W^-1 is measured.     

Off-axis continuous-wave cavity-enhanced absorption spectroscopy of narrow-band and broadband absorbers using red diode lasers

We present an application of continuous-wave (cw) cavity-enhanced absorption spectroscopy (CEAS) with off-axis alignment geometry of the cavity and with time integration of the cavity output intensity for detection of narrow-band and broadband absorbers using single-mode red diode lasers at λ=687.1 nm and λ=662 nm, respectively. Off-axis cw CEAS was applied to kinetic studies of the nitrate radical using a broadband absorption line at λ=662 nm. A rate constant for the reaction between the nitrate radical and E-but-2-eneof (3.78±0.17)×10^-13 cm³ molecule^-1 s^-1 was measured using a discharge-flow system. A nitrate-radical noise-equivalent (1σ≡ root-mean-square variation of the signal) detection sensitivity of 5.5×10⁹ molecule cm^-3 was achieved in a flow tube with a diameter of 4 cm and for a mirror reflectivity of ∼99.9% and a lock-in amplifier time constant of 3 s. In this case, a noise-equivalent fractional absorption per one optical pass of 1.6×10^-6 was demonstrated at a detection bandwidth of 1 Hz. A wavelength-modulation technique (modulation frequency of 10 kHz) in conjunction with off-axis cw CEAS has also been used for recording 1f- and 2f-harmonic spectra of the ^RR(15) absorption of the b¹Σ_g ⁺-X³Σ_g ^- (1,0) band of molecular oxygen at =14553.947 cm^-1. Noise-equivalent fractional absorptions per one optical pass of 1.35×10^-5, 6.9×10^-7 and 1.9×10^-6 were obtained for direct detection of the time-integrated cavity output intensity, 1f- and 2f-harmonic detection, respectively, with a mirror reflectivity of ∼99.8%, a cavity length of 0.22 m and a detection bandwidth of 1 Hz. Received: 24 June 2002 / Revised version: 12 August 2002 / Published online: 15 November 2002 RID="*" ID="*"Corresponding author. Fax: +44-1865/275410, E-mail: vlk@physchem.ox.ac.uk     

Photoluminescence and photostability investigations of biocompatible semiconductor nanocrystals coated with glutathione using low laser power

Polybutylcyanoacrylate nanoparticles (PBCA NPs) are candidates for a drug delivery system, which can cross the blood–brain barrier (BBB). Because little is known about their toxicity, we exposed cells to PBCA NPs in vitro and in vivo and monitored their life and death assays. PBCA NPs were fabricated with different surfactants according to the mini-emulsion technique. Viabilities of HeLa and HEK293 cells after NP incubation were quantified by analysing cellular metabolic activity (MTT-test). We then repetitively injected i.v. rhodamine-labelled PBCA NP variations into rats and monitored the survival and morphology of retrogradely labelled neurons by in vivo confocal neuroimaging (ICON) for five weeks. To test for carrier-efficacy and safety, PBCA NPs loaded with Kyotorphin were injected in rats, and a hot plate test was used to quantify analgesic effects. In vitro, we found dose-dependent cell death which was, however, only detectable at very high doses and mainly seen in the cultures incubated with NPs fabricated with the tensids SDS and Tween. However, the in vivo experiments did not show any NP-induced neuronal death, even with particles which were toxic at high dose in vitro, i.e. NPs with Tween and SDS. The increased pain threshold at the hot plate test demonstrated that PBCA NPs are able to cross the BBB and thus comprise a useful tool for drug delivery into the central nervous system (CNS). Our findings showing that different nanoparticle formulations are non-toxic have important implications for the value of NP engineering approaches in medicine.     

Tunable energy transfer distributed feedback dye laser using pyronin B and crystal violet dye mixture

Using pyronin B and crystal violet dye mixture, the characteristics of energy transfer distributed feedback dye laser (ETDFDL) pumped by 532 nm Nd:YAG laser were investigated. The characteristics of donor DFDL and acceptor DFDL as well as the dependence of their pulse widths and output powers on pump power and acceptor concentrations were studied. The output energy of DFDL was measured at the emission peaks of donor and acceptor dyes for different pump powers and acceptor concentrations, and tunability was observed from 570 to 645 nm using prism dye cell arrangement.     

Catalyst efficiency, photostability and reusability study of ZnO nanoparticles in visible light for dye degradation

Polydispersed ZnO nanoparticles (ZnO1000 and ZnO600) with two different windows of particle size distributions (∼120 and 30 nm) were synthesized using citrate gel route and different annealing treatments (1000 and 600 °C, respectively). Photocatalytic efficiency of these samples was compared with TiO₂ in its commercial form-P25, on two dyes, Methylene blue (MB) and Methyl orange (MO). The X-ray diffraction data showed wrutzite ZnO and anatase and rutile phases of P25. UV-visible absorbance spectra of ZnO1000 showed broad absorption range from UV-to-visible (from 382 to 700 nm), as against sharp absorption peaks in UV range for both ZnO600 and P25. The microstructural morphology as seen through scanning electron micrographs showed ZnO1000 with tetrapod-like structures while the ZnO600 showed almost spherical morphologies. Upon subjecting these catalysts to dye solutions in sunlight it was found that both the dyes were completely decolorised within 20 min by ZnO1000, as against partial decolorisation by ZnO600 and P25 ( 53% and 78% for MO and 77% and 88% for MB samples). The effect of catalyst loading (from 125 mg to 1 g) on decolorisation showed that ZnO1000 had good efficiency for all concentrations which was followed by P25 and then by ZnO600. Small perturbations are attributed to the competition between sunlight scattering-induced, reduced irradiation field and the exposed surface area offered by catalyst, which work as active sites for decolorisation. The reusability of the catalysts when studied on fresh dye samples (4 trials), the decolorisation efficiency decreased merely from 99.2% to 99.12% for ZnO1000 as compared to ZnO600 (53.3% to 19.94%) and P25 (78.3% to 31.42%), indicating the efficient reusability of ZnO1000. The effective half life of the catalysts, in terms of number of reuses, were calculated and found to be ∼3 for both ZnO600 and P25 and was >3000 for ZnO1000, which justifies its extremely high reuse. The byproduct analysis (compared with standards prescribed by World Health Organisation (WHO) and Central Pollution Control Board of India (CPCB)) showed cleavage of the chromophore and of other bonds with opening of benzene rings, indicating degradation of the dyes in concurrence with decolorisation, in the stipulated time. Further, cytotoxicity studies performed on SiHa cell lines showed non-toxicity of the byproducts with ZnO1000 as compared to ZnO600 and P25.     

Determination of natural radiative lifetimes for S and D states in rubidium and cesium using a pulsed dye laser

Using delayed-coincidence techniques we have measured the natural radiative lifetimes of several S and D states in Rb and Cs. The states were excited by a pulsed dye laser from the first P state, populated using an rf discharge lamp.     

Stilbazolium merocyanine dye determination in different solutions,concentrations and colloids using SERS

Surface‐enhanced Raman scattering (SERS) measurements were carried out on stilbazolium merocyanine dye in methanol and pyridine solvents. Both solutions were measured in a series of concentrations covering a range of 5 × 10⁻⁵ M to 5 × 10⁻⁸ M . In these measurements, Ag and Au colloids were used, and the results have shown that Ag colloids yield better enhancement in the Raman spectra of this dye. Moreover, the effect of adding NaCl solution to the SERS samples was also studied. All measurements were carried out using the state‐of‐the‐art ChiralRaman instrument, which utilizes a 532 nm laser source. We report here on the success of using SERS to obtain Raman spectra of merocyanine dye at very low concentrations in an attempt to find a new approach that can be used for further investigations of the dye. The SERS spectra are reported here, and the results from different solutions, colloids, concentrations and pH values are compared. Copyright © 2006 John Wiley & Sons, Ltd.     

Tunable picosecond energy transfer distributed feedback dye laser using Rhodamine 6G and Thionine dye mixture

The characteristics of Nd:YAG laser pumped energy transfer distributed feedback dye laser (ETDFDL) is studied both theoretically and experimentally. Using theoretical model proposed the behaviour of ETDFDL for dye mixture Rhodamine 6G and Thionine is studied in detail. The characteristics of donor DFDL, the acceptor DFDL, the dependence of their pulse widths and output powers on donor–acceptor concentration and pump power are studied. The output energy of DFDL is measured experimentally at the emission peaks of donor and acceptor dyes for different pump powers and donor–acceptor concentrations. In addition, the tunability of DFDL emission is measured both in donor and acceptor emission ranges.     

Z-scan studies and optical limiting of nanosecond laser pulses in neutral red dye

The nonlinear optical absorption, refraction and optical limiting behaviour of an organic dye, neutral red, were investigated under excitation with nanosecond laser pulses at 532 nm. The nonlinear optical responses of the material were studied both in solution and solid film, made in methanol and polyvinyl alcohol, respectively, using single-beam Z-scan technique. The open aperture Z-scans of the solution samples displayed a switch over from saturable absorption to enhanced absorption with increase in input intensity. Theoretical fit to the experimental data indicated that the dominant mechanism of nonlinear absorption is two-photon absorption. The closed aperture Z-scans of both the samples denoted positive nonlinearity, which was three orders larger in magnitude in solid film, compared with that in solution. The results of optical limiting experiments revealed that neutral red exhibited strong optical limiting of nanosecond laser pulses with a threshold lower than that of C₆₀ in toluene.