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CW Oscillation of End-Pumped Rectangular Thin-Rod Yb 3 þ : Y 3 Al 5 O 12 Laser
| Content Provider | Semantic Scholar |
|---|---|
| Author | Sakae Shin’ichi Matsubara Yasushi Sugiura Shingo Takasaki Masa-Aki Fukuda Kazuhiro Hata Takao Kobayashi |
| Copyright Year | 2007 |
| Abstract | Efficient nanosecond and sub-picosecond pulse lasers with high average power are needed for various applications such as micromachining, laser processing, and remote sensing. In comparison with the conventional neodymium-doped yttrium aluminum garnet (Nd:YAG) laser, the diode-pumped ytterbium-doped yttrium aluminum garnet (Yb:YAG) laser is particularly useful for high-power and ultrashort-pulse oscillation and amplification because of low heat generation with a quantum defect of 9% and a wide gain spectrum of 9.5 nm full width at half maximum (FWHM) with a long fluorescence lifetime of 0.95ms. It also exhibits a simple two-level electronic structure without undesired loss processes such as excited-state absorption and concentration quenching. The broad absorption spectrum of 18 nm is useful for efficient and temperature stable pumping using high-power InGaAs laser diodes. However, a high pumping intensity of more than 10 kW/ cm is required to reduce the reabsorption loss originating from the lower level population of the quasi-four-level system. An efficient cooling mechanism is required to prevent temperature increase in the laser crystal by high intensity pumping. Several types of Yb pumping architectures have been developed for high-power and efficient oscillation, including end-pumped thin disk, edge-pumped microchip or thin disk, end-pumped zigzag slab, edge-pumped zigzag slab, end-pumped circular rod, side-pumped circular rod, and fiber structures. Recently, a diode end-pumped thin-rod Yb:YAG scheme was proposed and analyzed in detail for high-average-power laser oscillation and amplification. In this paper, CW oscillation characteristics of an endpumped rectangular thin-rod Yb:YAG laser are presented. A schematic of the thin-rod Yb:YAG laser gain module is shown in Fig. 1. Two fiber-coupled laser diodes (JOLD100-CAXF-15A, JENOPTIK, Laserdiode GmbH, Germany) were used for pumping. The laser diodes deliver CW 100W output power through a fiber with a 0.6mm core diameter with a numerical aperture of NA 1⁄4 0:22. The center wavelengths at maximum output power of the two laser diodes are 935 and 939 nm. The pump beam of the laser diodes is focused on the end surface of the rod by 1 : 1 imaging optics using two planoconvex lenses with a focal length of 50mm. The focus diameter of the beams is 0.85mm. A low ytterbium concentration of 0.5 at.% is selected to reduce the temperature increase in the rod. The cross section of the rectangular rod is 1 1mm. The pump beam axis is tilted by p 30 from the laser beam axis to separate the pump beam and the laser beam and to obtain a high pump absorption efficiency and a high pump intensity uniformity by multiple reflection along the rod axis. The optical transfer efficiency of the pump system was measured to be higher than 95%. The fluorescence distribution at the rod end is measured and is shown in Fig. 2. A uniform intensity distribution was observed. It is shown in ref. 10 that the optical-to-optical conversion efficiency of the quasi-four-level systems is decreased when the total number of the ytterbium ions in the rod Nt is extremely large, thus, optimization of the pump absorption efficiency is required. When the spatial distribution of the fractional population is assumed to be uniform in the rod, the optimum pump absorption efficiency for maximum opticalto-optical conversion efficiency is obtained from |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | https://core.ac.uk/download/pdf/61358716.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
