Passively Q-switched Nd:Sc0.2Y0.8SiO5 dual-wavelength laser with the orthogonally polarized output S.D. Liu,1 L.H. Zheng,2 J.L. He,1* J. Xu,2 X.D. Xu,2 L.B. Su,2 K.J. Yang,1B.T. Zhang,1 R.H. Wang,1 and X.M. Liu1 1 2
State Key Laboratory of Crystal Materials, Shandong University, Ji’nan 250100, China Shanghai Institute of Ceramics, Chinese Academy of Science, Shanghai 200050, China *
[email protected]
Abstract: We have demonstrated a laser-diode pumped continuous-wave (CW) and passively Q-switched laser with a Nd:Sc0.2Y0.8SiO5 (Nd:SYSO) crystal for the first time. In the CW operation, the laser was found to oscillate in tri-wavelength regime at 1074.8 nm, 1076.6 nm and 1078.2 nm, respectively. The maximum CW output power of 1.96 W was obtained, giving an optical-to-optical conversion efficiency of 35% and a slope efficiency of 39%. Using either Cr4+:YAG or V3+:YAG crystal as saturable absorber, stable passively Q-switched laser was obtained at dual-wavelength of 1074.8 nm and 1078.2 nm with orthogonal-polarization. The maximum average output power, pulse repetition rate, and shortest pulse width were 1.03 W, 50 kHz, and 24 ns, respectively. The passively Q-switched dual-wavelength laser could be potentially used as a source for generation of terahertz radiation. ©2012 Optical Society of America OCIS codes: (140.3380) Laser materials; (140.3540) Lasers, Q-switched.
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1. Introduction With the development of high-energy physics and medical imaging, the need for the scintillating crystal has lately become pressing [1]. Binary and ternary inorganic silicate crystal #171941 - $15.00 USD (C) 2012 OSA
Received 4 Jul 2012; revised 29 Jul 2012; accepted 29 Jul 2012; published 17 Sep 2012 24 September 2012 / Vol. 20, No. 20 / OPTICS EXPRESS 22448
doped with rare-earth Cerium (Ce) can be used as scintillating crystal and have attracted much attention, due to the good properties of high density, high output and short decay time. In this regime, Ce-doped Lu2SiO5 (LSO), Y2SiO5 (YSO) and LuYSiO5 (LYSO) are the representative crystals [2,3]. As the multifunctional crystal, the silicate crystals have been used as not only the scintillating crystal but also laser gain medium doped with different rare ions including Nd3+, Yb3+, Tm3+ and Ho3+ etc [4–8]. Zhuang et al have experimentally demonstrated continuous-wave and actively Q-switched Nd:LSO crystal, with the dual-wavelength output power of 1 W [4]. Comaskey et al have realized 1.8 J signal pulse energy output at 1.074 nm with Nd:YSO crystal [9]. By substituting part of yttrium ions with scandium ions, a novel laser crystal Nd:Sc0.2Y0.8SiO5 (Nd:SYSO) was grown with Czochralski method along the crystallographic b axis by Shanghai Institute of Ceramics. The mixed Nd:SYSO crystal has the same structure as Nd:YSO, which is a monoclinical biaxial positive crystal (class 2/m, space group C2/c). As a consequence, the Nd:SYSO crystal is birefringent. The strong natural birefringence of monoclinical biaxial crystal overwhelms the thermally induced stress birefringence, which can induce the thermal depolarization observed in isotropic media such as YAG [9]. Multiple types of the substitutional sites in this crystal provide a strong inhomogeneous lattice field for rare earth dopants, which results in large ground-state splitting and broad emission spectra. Therefore, it is possible to realize the multi-wavelength and ultra-fast laser operation. In this paper, we have demonstrated a novel continuous-wave (CW) and passively Q-switched laser with a Nd:SYSO crystal. The CW laser was operating in tri-wavelength regime at 1074.8 nm, 1076.6 nm and 1078.2 nm, respectively. Under an absorbed pump power of 5.6 W, a maximum CW output power of 1.96 W was obtained, corresponding to an optical-to-optical conversion efficiency of 35% and a slope efficiency of 39%. In the passive Q-switching regime, the laser was stably operating at dual-wavelength of 1074.8 nm and 1078.2 nm. The maximum average output power, pulse repetition rate, and shortest pulse width were 1.03 W, 50 kHz, and 24 ns, respectively. 2. Experimental setup A compact concave-plano cavity was employed, as shown in Fig. 1. The pump source was a fiber-coupled laser diode emitting at 811 nm with a radius of 200 µm and a numerical aperture (N.A.) of 0.22. The pump beam was coupled into the laser crystal with a coupling system and the waist radius was about 200 µm. The laser cavity consists an input mirror M1, a Nd:SYSO crystal, a saturable absorber and an end mirror M2. M1 was a plano-concave mirror with a curvature radius of 500 mm. The plane face was anti-reflection at 811 nm (R
