Nonlinear optical characteristics and lasing ability of merocyanine dyes having different solvatochromic behaviour

Lasing characteristics and two-photon absorption (TPA) of merocyanine dyes with solvatochromism of different types are first investigated. Efficient lasing is excited in solutions pumped by radiation of the 2nd harmonic of a Nd-YAG laser (532 nm) with the lasing efficiency exceeding 40% and by XeCl laser radiation (308 nm) with the lasing efficiency up to 19%. The TPA cross-section at a wavelength of 1064 nm is determined. It is established that for merocyanines possessing the highest positive and negative values of solvatochromism, the TPA cross-section reaches maximum values of 115 and 125 GM, respectively. Influence of the special features of the electronic structure, spectral and luminescent properties, solvatochromic behavior, and nature of the medium on the lasing characteristics and nonlinear absorption of merocyanine dyes is investigated. Prospects for merocyanine application in modern optical technologies are demonstrated.     

Laser dye stability

The experimental parameters for solution temperature, solvent purity, and ultraviolet (uv) light removal have been examined as they affect the first-order bleaching constant, lasing slope efficiency, lasing threshold, and laser half-life of three dyes using air as the cover gas. A±10°C change from the ambient temperature was found to reduce the lasing output of solutions of the dyes rhodamine 6G, LD-490, and coumarin 102. Improving the purity of the solvent made no dramatic effects but did tend to yield somewhat lower bleaching rates and longer lasing lifetimes. The first-order bleaching constant for the dye LD-490 in several solvents was found to decrease in the order methanol >95% ethanol>ethanol. Although LD-490 in ethanol had twice the laser lifetime of that in methanol, the use of uv light filtration reversed this order. However, LD-490 still bleached faster in methanol than it did in ethanol. Interestingly using the uv filter, germicil quartz, did not decrease the lasing slope efficiency, but it made a slight increase in both the lasing slope efficiency and the lasing threshold. The use of the more strongly absorbing pyrex filter did, however, decrease the lasing slope efficiency as well as increase the threshold.     

Laser dye DCM: CW,synchronously pumped,cavity pumped and single-frequency performance

Laser dye DCM exhibits a tuning range of 605 to 725 nm with a lasing efficiency as high as 34% when pumped by the 488 nm line of the argon ion laser, placing it among the most efficient and broadly tunable dyes known. Performance of the dye is characterized for four laser systems: 1) continuous wave, 2) synchronously pumped (SP), 3) cavity dumped synchrompously pumped (SPCD) and 4) single-frequency ring dye laser. Pulse peak powers were as high as 520 W and 2.8 kW for SP and SPCD systems respectively.     

Solid‐State Active Elements Based on Dyes and Prepared by a Sol‐Gel Method

A new method is suggested for producing the solgel matrices with the molecules of laser dyes introduced into them. The curves of tuning lasing in Rhodamine 6G, Rhodamine 4S, Rhodamine 101, and phenylamine 430 in these matrices are obtained. The total range of tuning is 550–650 nm at a pumping energy of 4 mJ. The halfwidth of the generation spectrum is independent of the pumping energy to 4 mJ and comprises 0.3 ± 0.1 nm. The main factors forming the generation spectrum are noted.     

CW operation of laser dyes styryl-9 and styryl-11

Laser dyes Styryl-9 and Styryl-11 exhibit large tuning ranges of 780 to 900 nm respectively 770 to 850 nm with a lasing efficiency as high as 14% respectively 8% when pumped by all lines of the argon-ion laser, placing them among the most efficient and broadly tunable dyes known in the near-infrared wavelengths. Performance of these dyes is investigated for both cw standing wave and cw single-frequency travelling wave laser operation.     

Lasing efficiency of dyes incorporated into a nanoporous glass-polymer composite

We have used microsecond coherent pumping to study the lasing efficiency of active elements based on a nanoporous glass-polymer composite activated by organic dyes, as a function of the spectral composition of the pump within the main absorption band of the dye. We have shown that under the indicated excitation conditions, the lasing efficiency can exceed 40% and can be comparable with the lasing of liquid elements. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 5, pp. 708–716, September–October, 2008.     

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.     

A new family of lasing dyes from an old family of fluors

We report the development of a new series of laser dyes and describe the performance of these materials. This work was spurred by the realization that few laser dyes have an optimally shaped fluorescence emission for lasing action. Most of the dipole strength of the transition is concentrated in the 0.0 band, where lasing cannot occur, and very little is concentrated in the vibrational satellites 0–1 and 0–2 where lasing is possible. The new dyes are unsymmetrical materials which may be considered as a hybrid of a rhodamine molecule and a fluorescein molecule (fig. 1), and we consider them to be cyclized merocyanines. One dye in particular, 6-dimethylamino-9-o-carboxyphenylxanthen-3H-one (labelled SNH-8), has given power output and time stability better than the preferred lasing dye Rhodamine 6G. The effects of dye structure and of acid-base transitions on lasing activity will be discussed briefly. The theory of band-shaping and the detailed optical parameters of the new dyes will be presented separately.     

Energy transfer in flashlamp pumped organic dye lasers

The pumping characteristics of dye lasers using multiple dyes are discussed. It turns out that varying the dye concentration may change considerably the portion of the pump light spectrum which is effective in creating population inversion. Thus the effect of an energy transfer dye depends strongly on the concentration of the lasing dye. Multiple dye systems are shown to have larger tuning ranges than single dye systems, and should exhibit improved tuned linewidth as well as better dye stability. Experimental results are presented for a common dye combination (Rhodamine 6G and Coumarin 6). Measurements were made both by directly mixing the auxiliary dye with the lasing dye, and also by using the auxiliary dye as a fluorescent spectral filter placed between the pump light source and the laser cell; the results are compared.     

3-(2-Benzimidazolyl)coumarin derivatives —highly effective laser media

New laser dyes based on derivatives of 3-(2-benzimidazolyl)coumarin are proposed that lase under lamp and coherent (nanosecond and microsecond) pumping in the spectral range 420–700 nm and feature a high generation efficiency reaching 40% under coherent pumping (1% when lamp-pumped) and an increased operational life that surpasses that for most popular laser dyes. The nature of the substituents in the 6- and 7-positions of the coumarin ring and the ionic structure of the dyes are found to influence their spectral and lasing characteristics.     

Photophysical properties and laser performance of rubrene

The potential of rubrene as a laser dye was investigated in deaerated solutions with a XeCl excimer laser as pump source. Laser tuning range, quantum efficiency and photostability as well as excited singlet state absorption (ESA) spectra were measured. The (S₁-S₂) absorption band strongly overlaps with the fluorescence spectrum and thus ESA constitutes an important loss factor in the lasing process while triplet absorption can be neglected in the wavelength region of interest. Laser performance of rubrene is superior compared to other polycyclic aromatic hydrocarbons which can be considered as model compounds of the lasing process in organic dyes.     

Efficient and highly photostable solid-state dye lasers based on modified dipyrromethene.BF2 complexes incorporated into solid matrices of poly(methyl methacrylate)

We report on the laser action of modified dipyrromethene.BF₂ complexes both dissolved in poly(methyl methacrylate) and copolymerized with methyl methacrylate. All recently synthesized dyes have the chromophore core of laser dye pyrromethene 567, differing in the substituent in position 8. The new dyes showed important and most significant increases in both lasing efficiency and photostability. When the laser samples were pumped transversely at 534 nm, laser emission was obtained with efficiencies of over 30% in most cases, to be compared with a lasing efficiency of 12% exhibited by reference dye pyrromethene 567 under the same experimental conditions. Some of the materials exhibited highly photostable laser action, with no sign of degradation in the laser output after 60000 pump pulses at the same position of the sample at a repetition rate of 10 Hz, whereas the laser emission of reference dye pyrromethene 567 dropped to zero after less than 40000 pump pulses. Received: 19 November 2002 / Revised version: 20 February 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +34-91/564-2431, E-mail: acostela@iqfr.csic.es     

Experimental test of a four-level kinetic model for excited-state intramolecular proton transfer dye lasers

The nanosecond pulses of a dye laser oscillator based on the excited-state intramolecular proton-transfer reaction (IPT) of salicylamide and 2-hydroxylphenyl benzimidazole dyes have been studied as a function of several experimental parameters. To explain the operation of this laser a numerical four-level kinetic model was developed until the lasing properties of these dyes, in the presence of a variable oxygen concentration and pumped with a double pulse technique, could be reproduced. This was possible only by assuming that the efficiency of the laser is controlled by the absorption cross-section of a transient state with a lifetime in the nanosecond-picosecond range, which was tentatively identified as a ground state tautomeric species.     

Solid Dye Lasers Based on 2-Hydroxypropyl Methacrylate and Methyl Methacrylate Copolymers

Polymers are a kind of attractive hosts for laser dyes because of their superior optical homogeneity, and high transparency in pumping and lasing range. Copolymers usually have higher damage threshold and better photostability than mono-polymers. Solid dye samples based on copolymer of methyl methacrylate （MMA） with 2-hydroxypropyl methacrylate （HPMA） doped with 1-, 3-, 5-, 7-, 8-pentamethyl-2, 6-diethylpyrromethene-BF2 （PM567） are prepared. Spectra and lasing properties of the samples are studied. Compared to the samples based on monopolymer polymethyl methacrylate （PMMA）, enhanced slope efficiency and photostability are obtained in the copolymers. The highest slope efficiency is 45.1%, and nearly one-fold increase of photostability is obtained. The longest useful lifetime of 4390 pumping pulses is presented with the pump energy as high as 183 mJ per pulse at repetition rate of 10 Hz. The results indicate that the laser performances of solid dye mediums can be greatly increased using copolymer of MMA with HPMA as host.     

Advanced multichannel laser systems with phase conjugation and interchannel phase locking by laser-gain-hologram long- and short-range coupling

Compact schemes of the phase-locked multichannel Nd:YAG laser system with the long- and shortrange coupling via the holographic gain gratings in the active elements are developed. The phase locking of various loop Nd:YAG lasers with an interference contrast of the laser channels of 0.50–0.87 and a single-mode lasing efficiency of up to 0.64% is experimentally demonstrated. The experimental results for the two- and three-channel laser systems are generalized on multichannel laser systems using the numerical simulation. It is demonstrated that the maximum number of the short-range-coupled laser channels can be increased owing to the leveling of the parameters of laser channels to a value that is greater than that the maximum number of the channels in the presence of the long-range coupling, which is limited by the damage threshold of the active element of the interchannel coupling.     

Nitrogen laser excitation of polymethine dyes for emission wavelengths up to 9500 Å

We have pumped polymethine dyes with a nitrogen laser and achieved tunable infrared stimulated emission up to a wavelength of 9500 Å. The dye laser output decreases during operation due to destruction of lasing molecules; this is measured as a function of the number of exciting laser pulses.     

PM567-Doped solid dye lasers based on PMMA

Polymers are a kind of attractive hosts for laser dyes due to their high transparency in both pumping and lasing ranges and superior optical homogeneity. In this paper solid dye samples based on polymethyl methacrylate (PMMA) doped with different concentrations of 1, 3, 5, 7, 8 -pentamethyl-2, 6-diethylpyrromethene-BF$_{2 }$ (PM567) are prepared. The absorption, fluorescence and lasing spectra of the samples are obtained. Wide absorption and fluorescence bands are obtained and a red shift of the maxima of the lasing emission spectra is observed. With the second-harmonic generation of Q-switched Nd:YAG laser (532\,nm, $\sim $20\,ns) pumping the samples longitudinally, the slope efficiencies of the samples are obtained. There is an optimal dye concentration for the highest slope efficiency when the pumping energy is lower than some typical value ($\sim $250\,mJ), and the highest slope efficiency 35.6{\%} is obtained in the sample with a dye concentration of $2\times10^{ - 4}$\,mol/L. Pumping the samples at a rate of 10Hz with a pulse energy as high as 200\,mJ (the fluence is 0.2\,J/cm$^{2})$, the output energy drops to one-half of its initial value after approximate 15500 pulses and the normalized photostability is 5.17\,GJ/mol. A kind of solid dye laser which could have some applications is built.     

Investigation of a copper-vapor laser pumped by trains of damped sine pulses

A copper-vapor laser the lasing medium of which is pumped by damped sine voltage pulses is studied experimentally. It is shown that this laser can operate at megahertz lasing pulse repetition rates. Each current pulse in a train of damped sine excitation pulses generates a lasing pulse. The time between lasing pulses is no more than 224 ns, which corresponds to a lasing pulse repetition rate of more than 4.5 MHz. According to estimates, the use of the megahertz sine voltage to excite the copper-vapor laser may raise the specific power of laser radiation by at least an order of magnitude at an efficiency of ≈15%.     

Linear and cross-linked polymeric solid-state dye lasers based on 8-substituted alkyl analogues of pyrromethene 567

The lasing properties of analogues of the commercial laser dye pyrromethene 567 (PM567) incorporated (dissolved or copolymerized) into polymeric matrices have been studied using both linear and cross-linked methyl methacrylate-based copolymers with different degrees of functionalization. All synthesized dyes have the chromophore core of PM567 but with an ω-acyloxypolymethylene chain at position 8. In general, the new materials exhibited laser emission with higher efficiencies and much higher photostabilities than those containing the commercial dye PM567 under the same experimental conditions. Lasing efficiencies of up to 40% were obtained under transversal pumping at 534 nm. The highest photostabilities, with the laser output remaining stable or dropping by less than 15% after 100 000 pump pulses at the same position of the sample, were reached in cross-linked materials with dyes covalently linked to the polymeric chains. When the polymeric samples were incorporated into a grazing-incidence grating oscillator, narrow-line-width operation with tuning ranges of up to 40 nm was obtained. These results show that efficient and photostable solid-state dye lasers competitive with their liquid counterparts can be developed by adequate chemical modifications in the dye molecules, as well as by the selection of appropriate polymeric formulations.     

Laser dye stability

Lasing characteristics and bleaching of four Eastman Kodak ir dyes have been examined in dimethyl sulfoxide. These ir dyes are shown to improve in performance in the absence of oxygen. Their photochemical stability was found to be comparable to the quinolone laser dyes when exposed to flashlamp excitation. Photodecomposition of the ir dyes under lasing conditions was found to vary between 1.6 and 6×10⁻¹⁰ moles of dye for each joule (electrical) of input energy; in comparison, the photodecomposition values for the better coumarin dyes was 0.2 to 1.0×10⁻¹⁰ moles/J at a concentration of 1.0×10⁻⁴ M in ethanol. It was also found that increasing the concentration of these tricarbocyanine dyes gives a marked improvement in the useful lifetime of these solutions as lasing media in the absence of oxygen.