DYE LASER AMPLIFIER SYSTEM PUMPED BY COPPER VAPOR LASER USING FIBER OPTIC BEAM DELIVERY FOR BOTH PUMPING AND INJECTION José W. Neri, Marcelo G. Destro, Nicolau A. S. Rodrigues,,Rudimar Riva, Carlos Schwab Instituto de Estudos Avançados - São José dos Campos, SP, Brazil jwneri@ieav.cta.br Abstract We present a dye laser amplifier system pumped by copper vapor laser that uses fiber optic beam delivery device for pumping and injecting the power to be amplified. In high-gain devices, particularly under strong pumping conditions, considerations about amplified spontaneous emission are of fundamental importance to optimize the operation characteristics. Furthermore, the amplified spontaneous emission can spoil the spectral width of the dye laser system lowering the selectivity in the uranium atomic vapor laser isotope separation process. Hence, these beam delivery devices can improve the stability and flexibility of the alignment as well as eliminate the amplified spontaneous emission. An appropriate fiber length avoids the coupling of the amplified spontaneous emission into the dye oscillator. Besides that, due to its small diameter, the fiber also works as a spatial filter and helps to reduce the amplified spontaneous emission. Introduction Fiber-optic beam delivery systems are replacing conventional mirror systems because of their flexibility, stability and easy alignment. Commercial products are available that use fiber optic delivery for laser surgery [1] and materials processing [2-4]. Many laser wavelengths have been transported through optical fiber and high power delivery has been reported for argon, Nd:YAG, and excimer lasers [5]. However, few papers have been published about fiber optical beam delivery systems in a visible range, in special for dye laser amplifiers pumped by copper vapor lasers [6,7]. We present a dye laser amplifiers system pumped by copper vapor lasers that uses fiber optic beam delivery as system to pump and inject the power to be amplified. In high-gain devices, particularly under strong pumping conditions, considerations about amplified spontaneous emission (ASE) are of fundamental importance to optimize the characteristics of operation of the dye oscillator-amplifier system [8]. Furthermore, the ASE may increase the spectral width of the dye laser system lowering the selectivity of the AVLIS process[7]. Hence, these beam delivery devices can improve the stability and flexibility of the alignment as well as eliminate the ASE. An appropriate fiber length avoids the preamplifier ASE of being coupled into the dye oscillator. Besides that, due its small diameter, the fiber also works as a spatial filter and helps to reduce the ASE. Results and Discussions The experimental setup is shown in Figure 1. The dye laser (DL) is tunable around 5900 Å and has 15 mW average output power with a pulse repetition rate of 5 kHz, pulse duration of 25 ns, and linewidth of 1 GHz. The DL and the preamplifier (PA) and amplifier (A) are pumped by 20 W total average power CVLs with a pulse duration of 40 ns. Filters (F) were used to split the CVL yellow and green wavelengths (l y and l g ). Effective green CVL pumping power used was ~10 W from each CVL. The used power values were: 5 W to pump the DL, 3.0 W to pump the PA and the other 2 W were lost on the optical system. To pump the amplifier we used only 4.5 W to avoid the ASE. A mixture of Rhodamine 590Cl (Rh590Cl) and Kiton Red 620 (KR620) in ethanol solvent was used. The fiber-optic (FO) used is a commercial 3M, model FG-400-UAT, 0.16 numerical aperture, with large-core of 400 mm, silica/silica, multimode fiber. Using this apparatus we obtained an input of 12 mW just behind the preamplifier telescope T1 and thus a preamplifier output of 190 mW, and therefore a power extraction efficiency of 5.9 %. Besides that, the ASE power measured was bellow 5 mW, in spite of the preamplifier being located very near the oscillator. Behind the amplifier telescope T3 we have ~ 120 mW to be launched into the amplifier and we obtained an amplifier output of ~ 1,3 W with approximately 1.5 GHz linewidth, which is adequate for the AVLIS process, with an efficiency of ~25%, and the measured ASE power was bellow 100 mW. Figure 2 shows the theoretical results of preamplifier output and efficiency in function of green CVL pump power.