Laser dye stability

The experimental parameters for solution temperature, solvent purity, and ultraviolet (uv) light removal have been examined as they affect the first-order bleaching constant, lasing slope efficiency, lasing threshold, and laser half-life of three dyes using air as the cover gas. A±10°C change from the ambient temperature was found to reduce the lasing output of solutions of the dyes rhodamine 6G, LD-490, and coumarin 102. Improving the purity of the solvent made no dramatic effects but did tend to yield somewhat lower bleaching rates and longer lasing lifetimes. The first-order bleaching constant for the dye LD-490 in several solvents was found to decrease in the order methanol >95% ethanol>ethanol. Although LD-490 in ethanol had twice the laser lifetime of that in methanol, the use of uv light filtration reversed this order. However, LD-490 still bleached faster in methanol than it did in ethanol. Interestingly using the uv filter, germicil quartz, did not decrease the lasing slope efficiency, but it made a slight increase in both the lasing slope efficiency and the lasing threshold. The use of the more strongly absorbing pyrex filter did, however, decrease the lasing slope efficiency as well as increase the threshold.     

Search for efficient,near UV lasing dyes. III. Monocyclic and miscellaneous dyes

A potential new class of “monocyclic” lasing dyes is discussed and four families out of nine within the class are examined. The 2,6-diaminopyridines in acid are found to lase under flashlamp excitation but show low slope efficiencies and lower stabilities than the “bicyclic” dyes described previously. Other, miscellaneous dyes show oxygen quenching of laser action rather than enhancement and the best of these produces short pulses under long pulse excitation. This study was supported under contract SANL 284 from the Lawrence Livermore Laboratory.     

An algorithm for solving linearly constrained optimization problems

An algorithm for minimization of functions of many variables, subject possibly to linear constraints on the variables, is described. In it a subproblem is solved in which a quadratic approximation is made to the object function and minimized over a region in which the approximation is valid. A strategy for deciding when this region should be expanded or contracted is given. The quadratic approximation involves estimating the hessian of the object function by a matrix which is updated at each iteration by a formula recently reported by Powell [6]. This formula enables convergence of the algorithm from any feasible point to be proved. Use of such an approximation, as against using exact second derivatives, also enables a reduction of about 60% to be made in the number of operations to solve the subproblem. Numerical evidence is reported showing that the algorithm is efficient in the number of function evaluations required to solve well known test problems.This paper was presented at the 7th International Mathematical Programming Symposium 1970, The Hague, The Netherlands.     

Search for efficient,near UV lasing dyes. II. Aza substitution in bicyclic dyes

Two new families of lasing dyes, the 8-azacoumarins and the 8-azaquinolones are described and are found to operate blue-shifted from the coumarins and quinolones. Like the quinolones, they have higher thresholds and lower slope efficiencies than the coumarins. All have yielded long output pulses on long pulse excitation. This study was supported under contract SANL 284 from the Lawrence Livermore Laboratory.     

Measurements of 12C(π+, πN)11C and 19F(π+, πN)18F cross sections near the 32, 32 resonance

Reaction cross sections for ¹²C(π⁺, πN)¹¹C at 134, 161, 177, and 200 MeV and for ¹⁹F(π⁺,πN) at 161, 177, and 200 MeV were measured by activation methods.