Abstract
Highly efficient, laser-diode pumped Yb:YAG/Cr,Yb:YAG self-Q-switched microchip lasers by bonding Yb:YAG crystal have been demonstrated for the first time to our best knowledge. The effect of transmission of output coupler (T(oc)) on the enhanced performance of Yb:YAG/Cr,Yb:YAG microchip lasers has been investigated and found that the best laser performance was achieved with T(oc) = 50%. Slope efficiency of over 38% was achieved. Average output power of 0.8 W was obtained at absorbed pump power of 2.5 W; corresponding optical-to-optical efficiency of 32% was obtained. Laser pulses with pulse width of 1.68 ns, pulse energy of 12.4 μJ, and peak power of 7.4 kW were obtained. The lasers oscillated in multi-longitudinal modes. The wide separation of longitudinal modes was attributed to the mode selection by combined etalon effect of Cr,Yb:YAG, Yb:YAG thin plates and output coupler. Stable periodical pulse trains at different pump power levels have been observed owing to the longitudinal modes coupling and competition.
Highlights
Laser-diode pumped passively Q-switched solid-state lasers with Cr4+:YAG as saturable absorber are compact and robust lasers with high pulse energies and peak powers in a diffraction-limited output beam, and have many applications such as remote sensing, range finders, pollution detection, lidar, material processing, medical systems, laser ignition, and so on [1,2,3]
Coating damage on the output coupler was occurred when the transmission of output coupler, Toc, was equal to or less than 20% at high pump power levels owing to the high intracavity intensity with low transmissions of output coupler
There is an optimum transmission of output coupler, Toc = 50%, for best laser performance obtained in laser-diode pumped Yb:YAG/Cr,Yb:YAG microchip lasers
Summary
Laser-diode pumped passively Q-switched solid-state lasers with Cr4+:YAG as saturable absorber are compact and robust lasers with high pulse energies and peak powers in a diffraction-limited output beam, and have many applications such as remote sensing, range finders, pollution detection, lidar, material processing, medical systems, laser ignition, and so on [1,2,3]. Cr4+:YAG crystal with high damage threshold, low cost, and simplicity is widely used in passively Q-switched lasers. Another advantage of Cr4+:YAG crystal is that self-Qswitched laser materials can be fabricated by co-doping Cr4+ ions and lasants in YAG host crystal. Compared with Nd:YAG laser material, Yb:YAG crystal has several advantages such as a long storage lifetime (951 μs) [7], a very low quantum defect (8.6% with pump wavelength of 941 nm and laser wavelength of 1030 nm), resulting in three times less heat generation during lasing than comparable Nd-based laser systems [8], broad absorption bandwidth and less sensitive to laser-diode wavelength specifications [9], a relatively large emission cross section [10] suitable for Q-switching operation, and easy growth of high quality and moderate doping concentration crystals without concentration quenching [11]. Chromium and ytterbium co-doped YAG (Cr,Yb:YAG) crystals have been grown successfully and optical properties of these self-Q-switched laser materials have been
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