Juan M. Figuera

Pulsed liquid lasers from proton transfer in the excited state

Abstract The application of photoinduced intramolecular proton transfer to generate stimulated radiation is reported. Tunable laser pulses are produced with a 10% efficiency using sodium salicylate or 2-( o -hydroxyphenyl)benzimidazole as the active medium. In both compounds a large population inversion results from the proton transfer taking place in the electronically excited state.

Solid-state dye lasers based on copolymers of 2-hydroxyethyl methacrylate and methyl methacrylate doped with rhodamine 6G

Rhodamine 6G has been dissolved in copolymers of 2-HydroxyEthyl MethAcrylate (HEMA) and Methyl MethAcrylate (MMA) and the resulting solid-state solutions have been pumped at 337 nm and 532 nm. Lasing efficiencies similar to those found in ethanol solution have been obtained with a 1:1 vol/vol HEMA: MMA copolymer matrix, and lifetimes of ca. 10 000 (337 nm pumping) and ca. 75 000 (532 nm pumping) pulses at repetition rates up to 15 Hz and 10 Hz, respectively, have been demonstrated.

Solid-state dye laser based on Coumarin 540A-doped polymeric matrices

Abstract Coumarin 540-A has been dissolved in a copolymer of 2-hydroxyethyl methacrylate (HEMA) and methyl methacrylate (MMA) 1:1 v/v and in a pure poly(methyl methacrylate) homopolymer (PMMA). Laser action has been induced in the resulting solid-state solutions pumped with 1.2 mJ pulses at 337 nm from a nitrogen laser. The effects on the laser performance of different polymerization methods, dye concentration and polymeric matrix composition have been evaluated. Energy conversion efficiencies of 11% and lifetimes of about 2000 pulses at 2 Hz repetition rate have been demonstrated.

Proton-transfer lasing from solid organic matrices

Abstract Solid-state laser oscillation has been induced in 2-(2′-hydroxy-5′-fluorophenyl)benzimidazole dissolved in poly(methyl methacrylate), based on a four-level excited-state proton-transfer mechanism. The energy conversion efficiency at 493 nm was ≈ 1% for N2 laser pumping with pulses of 2 mJ at 337 nm.

Laser action from rhodamine 6G-doped poly (2-hydroxyethyl methacrylate) matrices with different crosslinking degrees

Abstract The lasing properties of rhodamine 6G dissolved in poly (2-hydroxyethyl methacrylate) matrices with different amounts of ethylene glycol dimethacrylate as crosslinking monomer are investigated. Increasing the rigidity of the matrix by decreasing the polymer free volume results in significant increases of both lasing efficiency and photostability. There exists an optimum degree of crosslinking for which efficiency and photostability reach the highest values.

Solid‐state dye lasers based on modified rhodamine 6G dyes copolymerized with methacrylic monomers

Modified rhodamine 6G molecules with polymerizable double bonds have been copolymerized with methacrylic monomers and the resulting polymers have been pumped at 337 nm with a N2 laser in a transversal configuration. The preparation of these new materials is described in detail and their lasing properties are evaluated. Important increases in photostability, with lasing efficiencies similar to those found for the parent dye rhodamine 6G in ethanol solution, have been obtained for some of these materials. Lifetimes (measured as an 80% efficiency drop) in excess of 20 000 shots at repetition rates of 2 Hz have been demonstrated. Strong dependence on pump repetition rate was observed. Possible mechanisms and processes responsible for the behavior of these materials are discussed. By using a rotating system where the sample is scanned in a continuous way, the laser output remained stable, with no sign of degradation, after 500 000 shots.

Phenylbenzimidazole proton-transfer laser dyes: spectral and operational properties

Abstract The efficient emission of tunable stimulated light in the 420–550 nm range from solutions of a number of derivatives of 2-(2 hydroxyphenyl) benzimidazole is reported. The lasing mechanism is based on an intramolecular proton-transfer reaction taking place in the initially populated excited state. These dyes, when pumped with a XeCl or N 2 lasers, produce tunable radiation covering a range of more than 100 nm with efficiencies up to 15.5%.

SOLID-STATE DYE LASERS BASED ON POLYMERS INCORPORATING COVALENTLY BONDED MODIFIED RHODAMINE 6G

We report on the lasing action of modified rhodamine 6G dyes copolymerized with methacrylic monomers. The laser samples were transversely pumped with a N2 laser at 337 nm. Lasing efficiencies similar to those found for rhodamine 6G in ethanol solution have been achieved. Important increases in photostability, with lifetimes in excess of 20 000 shots at 2 Hz, have been obtained. By using a rotating mechanism, a stable output with no sign of degradation after half a million shots has been demonstrated.

LASER ABLATION OF POLYMERIC MATERIALS AT 157 NM

Results are presented on the ablation by 157 nm laser radiation of polytetrafluoroethylene (PTFE), polyimide, polyhydroxybutyrate (PHB), poly(methyl methacrylate) (PMMA), and poly(2‐hydroxyethyl methacrylate) with 1% of ethylene glycol dimethacrylate as a crosslinking monomer. Direct photoetching of PHB and undoped PTFE is demonstrated for laser fluences ranging from 0.05 to 0.8 J/cm2. The dependence of the ablation process on the polymer structure is analyzed, and insight into the ablation mechanism is gained from an analysis of the data using Beer–Lambert’s law and the kinetic model of the moving interface. Consideration of the absorbed energy density required to initiate significant ablation suggests that the photoetching mechanism is similar for all the polymers studied.

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.