Increasing the energy efficiency of dye lasers with highly monochromatic radiation

Abstract

The tunable laser oscillator was built in the traditional manner with transverse pumping [4]. The pump radiation (10% of the total excimer laser power) was focused by a cylindrical lens onto a flow-through 20 mm long cuvette containing the dye solution. A dispersing resonator included a 600 gr/mma diffraction grating, a prism beam-splitter, and a quartz output mirror with Fresnel reflector. Continuous wavelength tuning was achieved by rotating the diffraction grating using a high precision sinusoidal mechanism provided with indicator. The oscillator construction resulted in a line width of approximately 0.01 run and continuous wavelength tuning with the same precision. First, changes in the spectral and energy characteristics were studied for previous studies, as well as for a host of new dyes from terphenyl, oxazole, pyrazolynyl, and coumarin classes. The laser power was recorded with a IMO-2N meter, and the wavelength with a KSVU-23 spectrum analyzer. All the characteristics were taken under identical conditions. Ethyl alcohol was used as a solvent. In order to achieve the maximum efficiency of pump radiation conversion, the dependence of laser power on dye concentration at a wavelength near the center of the lasing region was determined. Then, using the determined optimum concentration, the dependence of radiation power as a function of wavelength was measured. The basic results of the measurements are presented in Table i. As can be seen from the data presented, the collection of organic dyes used permitted tunable lasing to be achieved over the 332-515 nm spectral range with the excimer laser pump radiation. The value of the conversion efficiency ~o for the maximum oscillator power at the wavelength Xma x ranged from 1.7-10.8%, depending onthe type of dye. The relatively low value of the conversion efficiency for laser radiation in the oscillator is associated with the large losses necessary when using a highly selective laser resonator. A high conversion efficiency for pump radiation is observed with coumarin dyes, which is associated with a higher quantum yield for fluorescence in these compounds and with a high absorption value at the pump wavelength (308 nm). The second part of the study investigated the feasibility of increasing the pump radiation conversion efficiency achieved in the oscillator. Under the given conditions of radiation monochromaticity, traditional method for solving this problem is to use an amplifier. To this end, an amplifier stage was included in the laser design, consisting of a 40 mm long flow-through cuvette and a pump path with 3 nsec optical delay line. The cuvette