Tunable Cr:Nd:GSGG lasers pumped by red diodes

摘要

Summary form only given. Laser operation of Nd<;sup>+3<;/sup>-doped gadolinium scandium gallium garnet (Nd:GSGG) has been first shown by Kaminskii et al. in 1976 [1]. In earlier studies, flaslamp or solar pumping of Nd:GSGG has been explored, and narrow absorption bands of the Nd<;sup>+3<;/sup> ion, that overlaps poorly with these broadband emitters resulted in low laser efficiencies. As a solution, co-doping with chromium ion (Cr:Nd:GSGG) has been applied to generate additional broad absorption bands in the visible to improve the absorption as well as the laser efficiency [2-3]. With the development of semiconductor technology, laser diode pumping has become the dominant excitation scheme for Nd-based laser systems [4-6]. Usually, laser diodes at the sharp absorption peaks of Nd:GSSG around 808 nm or 883 nm have been employed [4-5]. As an alternative, Cr co-doped samples provide broad absorption bands around 645 nm, in a spectral region where low cost laser diodes also exist [6]. While using these broad absorption bands, thermal control of the diode junction temperature, narrowband diode operation, and careful selection of diode central wavelength is not required. However, the quantum defect is higher, lowering the laser efficiencies.In this study, we have investigated continuous-wave (cw) and mode-locked laser performance of a red diode pumped Cr:Nd:GSGG laser in detail. State-of-the-art single-mode and multimode laser diodes around 665 nm were used as pump sources. In cw laser experiments, we have demonstrated lasing thresholds as low as 14 mW, slope efficiencies as high as 23.4%, and output powers up to 738 mW (Fig. 1). The free-running laser wavelength was 1061 nm. Using a birefringent tuning plate, lasing could also be obtained at 1051 nm, 1058 nm, 1065 nm, 1068 nm, 1072 nm, 1103 nm and 1111 nm lines. Moreover, two-color and tree-color cw laser operation has been demonstrated in 11 and 3 different transition combinations. In cw mode-locking experiments, a saturable Bragg reflector was used to initiate and sustain pulsing, where the Cr:Nd:GSGG laser produced 6-ps long pulses around 1061 nm, with an average power of 160 mW. The repetition rate was 142.65 MHz, resulting in pulse energies of 1.1 nJ and peak powers of 175 W. Dual-wavelength simultaneous mode-locked operation was also shown for the 1058 nm & 1061 nm lines at an average power of 45 mW. We acknowledge financial support from The Scientific and Technological Research Council of Turkey (114F191).