Analogues of the dipyrromethene-BF2 dye PM567 modified at the 8-position by methacryloyloxymethyl (P1MA), smethacryloyloxypentyl
(P5MA), and p-methacryloyloxymethylphenyl (PAr1MA) groups have been copolymerized with methyl methacrylate (MMA), and these solid samples were studied by absorption, fluorescence, and photo-degradation
spectroscopy. The absorption cross-section and stimulated emission cross-section spectra are determined. The fluorescence quantum distributions and fluorescence lifetimes are measured. High fluorescence quantum yields, ΦF ≈ 0.9, have been obtained. The photo-degradation of the dyes is studied under cw laser excitation conditions. A high photo-stability was observed.
New hybrid matrices based on silica aerogels obtained under supercritical conditions, a highly porous material with porosityt up to 90%, have been synthesized. The open porous network of the aerogel was saturated with pyrromethene dyes solved in organic mooners, and polymerization took place inside of the silica structure. The resulting polymer filled nanoporous aerogels, cast in the form of cylindrical monoliths, were used as gain media in solid-state dye lasers. Under the demanding conditions of tightly focused transversal pumping with 532 nm, 5 mJ pulses at 10 Hz repetition rate, highly photostable laser emission was obtained.
New analogs of the commercial dye Pyrromethene 567 (PM567), where the chromophore core is maintained but different substituents are introduced in position 8, have been synthesized, and their lasing properties when incorporated (dissolved or copolymerized) in polymeric matrices, using both linear and crosslinked polymers with different degrees of functionalization, have been studied. In general, the new materials exhibited laser emission with efficiencies and photostabilities much higher than those of the commercial dye PM567, demonstrating that by incorporating adequate chemical modifications in teh dipyrromethene.BF2 complexes, and selecting the appropriate polymeric formulations, efficient and photostable solid-state dye lasers competitive with their liquid counterparts can be developed.
The caloric energy accumulated during the laser excitation process of dye doped polymeric materials as a function of the laser pump rate (f) was analyzed by using Photothermal Deflection Spectroscopy (PTDS). Results show that the thermal effects should be very important for pump rates larger than 1 Hz and that the possibility of chemical degradation of the laser material increase with the enlargement of the sample temperature under the pump process. Experimental results have been theoretically simulated by using an optical dense material model of PTDS.
The main shortcoming of the use of synthetic polymers as host in the development of dye laser materials is their low laser-damage threshold and the photodegradation of the dye. The more important process that limit the lifetime of the material should be a photochemical mechanism although photothermal processes produce some contributions. In this work, we have investigated the thermal response of the material when different quantities of energy are loaded during the pump process. Photothermal deflection spectroscopy was used in the investigation. The characteristics of the photothermal signal were analyzed as a function of the laser repetition rate. This study is related wit the decay of the laser output energy with the pump rate due to photodegradation observed previously in similar samples. Results show that the photothermal signal follows a linear dependence with the pump rate. The thermal effects increase strongly when the pump rate is larger than 1 Hz. This fact affects the mobility of the dye molecules and reactive species in the matrix, increasing the possibility of chemical degradation. Results of a theoretical simulation of the deflection signal using an optical dense materials model is included.
In this communication we present the experimental results obtained when diffraction gratings are stored using pulsed exposure in polyvinyl alcohol/acrylamide photopolymer deposited in a dry film. The influence of the energy of the irradiation pulse was studied and the number of pulses needed to reach maximum diffraction efficiency was obtained. The recording was performed using a n holographic copying process. The original patten employed was a gratin of 1000 lines/mm processed according to sliver halide sensitized gelatin, with a beam ratio of 1:2 and transmittance of 75 percent. We exposed the samples by recording holograms with as collimated beam from a frequency-doubled Nd:YAG Q- switched laser. The pulse duration was approximately 8 ns and the frequency of repetition varied between 2 and 10 Hz. The pulse fluence was increased from 0.07 mJ/cm2 to 6.7 mJ/cm2. Our initial results show that it is possible to obtain diffraction gratings with a diffraction efficiency of 60 percent. The energetic sensitivities achieved are close to those obtained when working with the same material and continuous irradiation, without processing of the gratings.
Two different monomers containing in the same molecule the Rhodamine 6G chromophore and an allyl or a methacrylic group were synthesized. These new monomers were copolymerized with mixtures of 2-hydroxyethyl methacrylate and methyl methacrylate. The resulting solid laser samples were transversely pumped by 337-nm pulses from a N2 laser, and their lasing properties were compared with those of the corresponding model dyes dissolved in the same methacrylic copolymers. Lasing efficiencies similar to those found for Rhodamine 6G in ethanol solution under the same experimental conditions have been achieved with some of the compounds. In addition, important increases in photostability have been obtained in some of the new terpolymers: lifetimes (number of pulses that produce an 80% drop in the laser output) in excess of 20,000 shots at 2 Hz and in excess of 9,000 shots at 15 Hz have been demonstrated in static samples. By using a rotating mechanism to move the laser rod in a continuous way the laser output remains stable with no sign of degradation after 500,000 shots at 2 Hz repetition rate.
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