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Using a quite uniformly side-around arranged compact pumping system, a high power Nd:YAG ceramic quasi-CW laser has been demonstrated with high optical-to-optical conversion efficiency over 50% for the first time. With 450 W quasi-CW stacked laser diode bars pumping at 808 nm, 236 W output at 1064 nm was obtained and no saturation phenomena were observed.
Introduction: There are three main kinds of solid laser hosts: single crystal, glass and ceramic. The first two have been rapidly developed and widely used in various application fields while the third one has been ignored since its scattering losses were too high to gain laser output effectively. However, ceramic began to attract much attention as a promising active media for highly efficient and high power all-solid-state lasers emitting in the 1 mm region with the breakthrough of high optical quality Nd:YAG ceramic developed in 1999 [1, 2]. Compared to Nd:YAG crystal grown by the conventional Czochralski method [3], transparent Nd:YAG ceramic made by the novel NTVS method (nano-crystalline technology and the vacuum sintering method) has several remarkable advantages: (i) easily fabricated; (ii) less expensive; (iii) large size and high concentration; (iv) multilayer and multifunctional materials structure; (v) mass production is possible, etc. These advantages may give greater flexibility in high efficiency, high power laser design and introduce greater innovation for today's marketplace for solid-state lasers. Using these Nd:YAG ceramic samples, high slope efficiency of 60.9% was achieved under an end-pumping disk laser [4] and high power laser output from 31 W to 1.46 kW and their corresponding optical-to-optical efficiencies from 12.5 to 41.7% were reported one by one [5-8]. In this Letter, using a quite uniformly side-around arranged compact pumping system, we demonstrate a high efficiency quasi-CW high power laser with an Nd:YAG ceramic rod. With 450 W quasi-CW stacked laser diode bars pumping at 808 nm, a 236 W quasi-CW output laser at 1064 nm was obtained. The optical-to-optical conversion efficiency was 52.5%, which is comparable to the best performance of Nd:YAG single...