Photothermal characterization and stability analysis of polymeric dye lasers

The millisecond heat dissipation of pump energy in polymeric, solid-state dye lasers has been studied with photothermal deflection spectroscopy (PTDS) to determine the contribution of that process to photodegradation of the active material. The samples were solutions of Rhodamine 6G in 2-hydroxyethyl methacrylate copolymerized with various amounts of methyl methacrylate or ethylene glycol dimethylacrylate to change the microstructure properties of the matrix. Values of the thermal diffusivity measured with PTDS were in the range 0.6-1.1 x 10(-3) cm(2) s(-1) for all the compositions studied here. A comparison of these values with previous optical data on lasing efficiency and photostability for the same samples indicates that the macroscopic rate of thermal diffusion is not the key factor that limits the efficiency and stability of these lasers, at least for low pump repetition rates (<1 Hz).

Self-curing membranes of chitosan/PAA IPNs obtained by radical polymerization: preparation, characterization and interpolymer complexation

Chitosan/polyacrylic acid I PN's were prepared by radical polymerization of acrylic acid, AA, activated at low temperature, in an aqueous/alcoholic chitosan dispersion. AA monomer to polymer conversion and membrane compositions were determined by elemental analysis and FTIR. Evidences of interpolyelectrolite complex formation were found from the FTIR spectra as well. The gravimetric measurements and the elemental analysis after some exhaustive PAA extraction support the existence of some PAA grafting on the reactive amine group of the chitosan. Swelling degree of the membranes is highly dependent on pH and composition, showing a higher swelling in membranes richer in AA and increased pH due to the breaking of interpolyelectrolite salt bonds.

Development of new photopolymerizable dental sealants

This paper describes the results obtained in the optimization of the composition of dental sealants in relation to the nature and proportions of monomer mixtures and photoinitiating system employed. The quantification and variation of certain parameters which determine the quality of a dental sealant (such as viscosity and penetrating power, residual double bonds, solubility and absorption, volume shrinkage and certain specific mechanical properties) have resulted in the development of new formulations. The composition which has achieved the best results of all the above properties was that corresponding to the monomer mixture bis-GMA/tri(ethylene glycol) dimethacrylate (TEGDMA) 40/60 wt%, and the photoinitiating system camphorquinone (CQ) with co-initiators N,N,3,5-tetramethyaniline (TMA) or N,N-dimethyl-p-toluidine (DMPT) in the ratio 1:1. The final properties and characteristics of the obtained formulations are superior to those of commercial dental sealants currently in use.

Long-pulse narrow-linewidth dispersive solid-state dye-laser oscillator

We report on narrow-linewidth long-pulse laser emission from a dispersive solid-state dye-laser oscillator. Output energy was ~0.4 mJ/pulse at laser linewidths of 650 MHz and pulse lengths of 105 ns FWHM. The solid-state gain medium utilized was Rhodamine 6G dye-doped 2-hydroxyethyl methacrylate:methyl methacrylate.

Anticancer drug, ara-C, release from pHEMA hydrogels

This study investigates the controlled release of cytarabine (ara-C), an anticancer drug, from a polymeric matrix of lightly cross-linked poly(2-hydroxyethyl methacrylate) (pHEMA). The swelling of pHEMA discs in water was analysed as a function of temperature and thickness of xerogel discs. The fractional swelling was linear in (time)1/2 for short time periods. Drug release kinetics were examined as a function of temperature, initial drug load and thickness of pHEMA discs. The fraction of available drug release was also linear in (time)1/2 during the initial stages. These studies allow for the determination of diffusion coefficients for both the transport of water into the hydrogel and ara-C release from the polymer.

Proton-transfer lasers from solid polymeric chains with covalently bound 2-(2'-hydroxyphenyl) benzimidazole groups

The lasing properties of a number of newly synthesized 2-(2'-hydroxyphenyl) benzimidazole derivatives copolymerized with methyl methacrylate or dissolved in poly (methyl methacrylate) and pumped with an N(2) laser are reported. The radiation mechanism is based on the intramolecular proton-transfer in the electronic excited state. Both the lasing efficiency and the dye photostability increase significantly when the proton-transfer chromophore is covalently bound to the polymeric chain, and energy-conversion efficiencies comparable to those obtained in liquid solution are demonstrated.

New photopolymer used as a holographic recording material

The composition and the holographic behavior of a new photopolymer with high diffraction efficiencies (30% at 514 and 60% at 633 nm) are described.