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A cw laser using a 2.5×10−4 M solution of rhodamine 6G in water containing a deaggregating agent (1.5% Triton-X100) is described. The laser consists of a 4.5-mm transverse-flow hemispherical cavity excited longitudinally by the 5145-Å output of a 1-W argon ion laser. With mirror reflectances of 97.5% and 99.5%, a 200-mW threshold excitation was measured. Power output was approximately 30 mW at 597 nm with 960 mW excitation power.

This paper describes the results of an investigation of the interrelated physical parameters that determine laser threshold for three organic dyes: rhodamine B, rhodamine 6G, and fluorescein. Not only are these dyes (rhodamine 6G in particular) among the most widely used and important laser dyes, but insights into the threshold condition derived from our studies of these particular dyes should be generally applicable to future dye laser research. Our detailed characterization of threshold for these dyes and our novel insights result from the use of triplet state spectral data in a thorough and quantitative way for the first time, coupled with the physically realistic approximation that the triplet population is proportional to the singlet excited state population. For the case of self-tuning of the laser emission wavelength, solutions to the threshold equations are presented that establish relations between all the parameters affecting lasing: critical inversion, emission wavelength, extrinsic losses, dye concentration, length of active medium, and triplet to excited singlet population ratio. For reasonably high extrinsic cavity losses, the critical inversion is a simple power law function of extrinsic loss, and the emission wavelength is self-tuned in such a manner that the ratio of extrinsic losses to intrinsic singlet absorption losses is substantially constant. There exists a region of low, but still physically realizable, cavity losses, where laser action is determined exclusively by intrinsic characteristics of the dyes (triplet absorption, singlet emission, and absorption). Asymptotic limits on the maximum wavelength of emission and on the minimum critical inversion appear in this region, beyond which there is no point in reducing extrinsic cavity losses. The fraction of triplet state molecules also determines long wavelength cutoffs for an externally tuned laser. Methods are outlined for measuring the ratio of triplet state to excited singlet state populations for dyes with known triplet absorption spectra and for determining semiquantitatively the triplet effects in dyes where this information is not known. A final interesting conclusion is that molecular modifications of rhodamine 6G cannot be expected to improve its threshold characteristics as a laser dye by much more than a factor of 4.

Laser emission is reported from flashlamp-excited polymethyl methacrylate rods containing rhodamine dyes. Quenching of stimulated emission by the molecular triplet state is apparently reduced in the solid with respect to that observed for the same dyes in liquid solution.

Broadly tunable laser operation has been obtained at room temperature from the vibronic bands of single-crystal BeAl(2)O(4):Cr(3+) under Xe-flashlamp excitation. Continuous tuning is obtained from 701 to 794 nm, with maximum power at 750 nm. Long-pulse operation employing 6.3-mm x 76-mm rods easily provides 500 mJ in 200-microsec bursts, whereas 70-mJ, 120-nsec pulses are obtained under Q-switch operation.

Articles you may be interested inExcited state lifetime and intersystem crossing rate of asymmetric pentaazadentate porphyrin-like metal complexes Appl. Phys. Lett. 84, 5174 (2004); 10.1063/1.1763983 Internal heavy atom effect on the triplet spin sublevels of the lowest triplet state of naphthalene. II. Intersystem crossing processes from the singlet excited state to the individual spin sublevels of the lowest triplet state J. Chem. Phys. 72, 1713 (1980); 10.1063/1.439282Intersystem crossing rates and saturation parameters in the triplet state for rhodamine, fluorescein, and acridine dyes Triplet state kinetics for rhodamine 6G in alcohol have been studied. The singlet-to-triplet intersystem crossing rate kST and triplet lifetime TT have been determined in air-saturated alcohol, where the spinforbidden decay from the triplet manifold into the singlet ground state is enhanced by collision with oxygen molecules dissolved in the solution. Values of the kinetic parameters for air-saturated ethanol solutions at room temperature were determined to be TT=250±40 nsec and kST= (3.4±1.3) X1()6 sec-l.

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