Terence A. King

Performance and photostability of xanthene and pyrromethene laser dyes in sol-gel phases

The photostability of rhodamine 6G, rhodamine 610 and pyrromethene 567 in solutions, wet-gel and dried sol-gel host media has been determined. A method for the synthesis of xerogel monoliths has been modified to reduce the preparation time for the doped sol-gel samples, and high optical quality sol-gel samples doped with laser dyes have been prepared. A high efficiency and photostability is observed for xanthene laser dyes in wet and dried sol-gel phases but not for a pyrromethene laser dye.

Theoretical modeling of Tm-doped silica fiber lasers

The theoretically determined slope efficiency and threshold pump power for continuous wave (CW) operation of a Tm-doped silica fiber laser are presented. The associated rate equations are solved using standard techniques and, in conjunction with the published and our measured spectroscopic parameters as input, the model was used to examine the fiber laser output for a variety of fiber and pump configurations. After good agreement was achieved between the model calculations and the published experimental measurements, the model was used to examine the relative performance of the fiber laser when the pump wavelength was varied over the /sup 3/F/sub 4/, /sup 3/H/sub 5/, and /sup 3/H/sub 4/ absorption bands of Tm/sup 3+/. The calculated maximum slope efficiencies were determined to be /spl sim/40, /spl sim/57, and /spl sim/84%, respectively, for each of the /sup 3/F/sub 4/, /sup 3/H/sub 5/, and /sup 3/H/sub 4/ absorption band pump schemes and the threshold pump power over the range of pump schemes was determined to vary by only 28%. The model was further used to analyze the fiber laser output when the fiber length, Tm/sup 3+/ concentration and /sup 3/H/sub 4/ energy level lifetime were varied and the consequences on the operation of the fiber laser with these variations are discussed.

COMPARISON OF LASER PERFORMANCE OF DYE MOLECULES IN SOL-GEL, POLYCOM, ORMOSIL, AND POLY(METHYL METHACRYLATE) HOST MEDIA

Laser performance is described for Rhodamine 590, Pyrromethene 567, Perylene red, and Perylene orange in inorganic porous sol-gel glass, poly(methyl methacrylate)(PMMA), a composite of porous sol-gel glass with PMMA and organically modified silicate ormosil glass. Lasers were excited with a flash-lamp-pumped dye laser in the long-pulse-length regime (3 µs, 506 nm, 300 mJ) and a second-harmonic Nd:YAG laser in the short-pulse-length regime (6 or 15 ns, 532 nm, 60 mJ). The feasibility of long-pulse-length operation is demonstrated, detailed characteristics of short-pulse operation are described, and laser damage measurements are given. The nonpolar perylene dyes had better performance in partially organic hosts, and the ionic rhodamine and pyrromethene dyes performed best in the inorganic sol-gel glass host.

Photostability enhancement of Pyrromethene 567 and Perylene Orange in oxygen-free liquid and solid dye lasers

We investigated the effect of oxygen on the photostability of the laser dyes Pyrromethene 567, Perylene Orange, and Rhodamine 590 by determining their longevity of laser operation when pumped by the second harmonic of aQ -switched Nd:YAG laser. In solution, dissolved oxygen accelerated the photodegradation of Pyrromethene 567 and Perylene Orange but not Rhodamine 590. The photostability of Pyrromethene 567 was also found to be dependent on the solvent and on the lifetime of singlet oxygen. Deoxygenated Pyrromethene 567 doped polycom glass and modified poly(methyl methacrylate) (MPMMA) samples were tested for longevity of laser operation. A factor of 6 improvement in photostability was found for Pyrromethene 567 in MPMMA upon deoxygenation, and the total absorbed energy per mole of dye molecules to one-half output pulse energy was 36 GJ mol-1 .

Diode-pumped 17-W erbium 3-µm fiber laser

We follow a theoretical proposal to scale the output power of the erbium 3-/spl mu/m fiber laser to the 1-W region. Ground-state bleaching and consequent ESA losses are avoided by the combination of 1) a highly erbium-doped fiber and the relatively low pump intensity present in a cladding pumped fiber with 2) an active reduction of the excitation density by energy transfer to a Pr/sup 3+/ codopant. Recently, the first investigation of the validity of this approach has led to 660 mW of output power at 2.7 /spl mu/m under diode pumping.

Thermal effects of the Er:YAG laser on a simulated dental pulp: a quantitative evaluation of the effects of a water spray

OBJECTIVESnTo quantify the temperature increments in a simulated dental pulp following irradiation with an Er:YAG laser, and to compare those increments when the laser is applied with and without water spray.nnnMETHODSnTwo cavities were prepared on either the buccal or lingual aspect of sound extracted teeth using the laser. One cavity was prepared with water spray, the other without and the order of preparation randomised. Identical preparation parameters were used for both cavities. Temperature increments were measured in the pulp chamber using a calibrated thermocouple and a novel pulp simulant.nnnRESULTSnMaximum increments were 4.0 degrees C (water) and 24.7 degrees C (no water). Water was shown to be highly significant in reducing the overall temperature increments in all cases (p<0.001; paired t-test). None of the samples prepared up to a maximum of 135 J cumulative energy prepared with water spray exceeded that threshold at which pulpal damage can be considered to occur. Only 25% of those prepared without water spray remained below this threshold.nnnDISCUSSIONnExtrapolation of the figures suggests probably tolerable limits of continuous laser irradiation with water in excess to 160 J. With the incorporation of small breaks in the continuity of laser irradiation that occur in the in vivo situation, the cumulative energy dose tolerated by the pulp should far exceed these figures.nnnCONCLUSIONSnThe Er:YAG laser must be used in conjunction with water during cavity preparation. As such it should be considered as an effective tool for clinical use based on predicted pulpal responses to thermal stimuli.

High-peak-power operation of a Q-switched Tm 3+ -doped silica fiber laser operating near 2 µm

A peak output power of greater than 4.1 kW and a pulse duration at FWHM of 150 ns have been obtained in a Q-switched Tm3+-doped silica fiber laser in the wavelength region near 2 microm when the laser was pumped with a Nd:YAG laser operating at 1.319 microm. An acousto-optic modulator was used as a Q-switching element and operated at repetition rates of as much as 30 kHz. A core diameter of 17 microm was used to increase the laser gain volume, permitting high-pump-power absorption and an output of high pulse energy and peak power. Stimulated Brillouin scattering was directly observed in the output pulse, and as much as 10 orders of stimulated Brillouin scattering was recorded. This is the first report to the authors knowledge of high-peak-power operation of a Tm3+-fiber laser.

High-energy, high-brightness Q-switched Tm3+-doped fiber laser using an electro-optic modulator

Abstract Q-switched operation of a 2 μm Tm3+-doped silica fiber laser using an electro-optic modulation (EOM) is described for the first time. A larger multimode core of 17 μm diameter is used to increase the laser gain volume and achieve higher pulse energy. Experimentally this laser produced pulses with a peak power of ∼3.3 kW at a low repetition rate of 70 Hz and a pulse energy up to 2.3 mJ, limited by excited state absorption with only slightly compromized spatial-mode quality (M2∼1.5). This approach using an EOM offers significant scope for extending the range of single-mode output powers and energies that are achievable from fiber lasers and amplifier systems.

Singlet oxygen and dye-triplet-state quenching in solid-state dye lasers consisting of pyrromethene 567-doped poly(methyl methacrylate).

Solid-state dye lasers based on poly(methyl methacrylate) (PMMA) doped with Pyrromethene 567 dye (P567) have been investigated. The preparation techniques employed provided high photostability and laser damage threshold for P567 in pure PMMA with 270,000 pulses emitted before the conversion efficiency fell to half its initial value for a pump fluence of 0.16 J cm(-2). When PMMA was modified with 1, 4-diazobicyclo [2, 2, 2] octane singlet oxygen quencher, the longevity increased to 550,000 pulses, corresponding to a normalized photostability of 270 GJ mol(-1). Modification of PMMA with a triplet quencher (perylene) yielded no improvement, but in ethanol solutions both additives enhanced photostability. It is possible that in PMMA, stabilization by means of triplet quenching that depends on dye diffusion is prevented but that stabilization by means of singlet oxygen quenching that depends on the faster oxygen diffusion rate will succeed.

Photostability of lasers based on pyrromethene 567 in liquid and solid-state host media

Abstract The photostability of the laser dye pyrromethene P567 in various liquid and solid samples has been measured by determining the longevity of laser operation when pumped by the second harmonic of a Q-switched Nd:YAG laser. A large improvement in photostability for pyrromethene was found in deoxygenated non-polar solvents, with a normalised photostability value of 1000 GJ/mol compared to deoxygenated polar solvents (100 GJ/mol). A high photostability has been observed in a heptane–1,4-dioxane azeotrope mixture and improvements observed in systems incorporating triplet quenching agents. Doped solid polymer samples showed an increased photostability up to 200 GJ/mol for the pyrromethene laser dye when samples were modified with triplet quenchers.