Er,Yb:GdAl 3 (BO 3 ) 4 Laser Passively Q-switched by MBE-grown Cr:ZnS Thin Films K.N. Gorbachenya 1 , V.E. Kisel 1 , A.S. Yasukevich 1 , N. Tolstik 2 , E. Karhu 2 , V. Furtula 2 , E. Sorokin 3 , V.V. Maltsev 4 , N.I. Leonyuk 4 , A. Galinis 5 , T. Lipinskas 5 , U. Gibson 2 , I.T. Sorokina 2 , and N.V. Kuleshov 1 1. Center for Optical Materials and Technologies, Belarusian National Technical University, 65/17Nezavisimosti Ave., Minsk, Belarus 2. Department of Physics, Norwegian University of Science and Technology, Høgskoleringen 5, N-7491 Trondheim, Norway 3. Photonics Institute, Vienna University of Technology, Gusshausstrasse 27/387, A-1040 Vienna, Austria 4. Department of Crystallography and Crystal Chemistry, Moscow State University, 119992 GSP-2 Moscow 5. UAB «Optogama», Mokslininku str. 2A, 08412, Vilnius, Lithuania Q-switched erbium lasers emitting in the 1.5-1.6 ȝm spectral region are widely used in laser rangefinders and LIBS systems.These applications require compact and low-cost sources of laser pulses with high average output power. Passive Q-switching is one of the most simple and reliable method to achieve the abovementioned requirements. Er,Yb:GdAl 3 (BO 3 ) 4 (Er,Yb:GdAB) crystal was shown to be an efficient laser material for the 1.5-1.6 μm spectral range [1]. Recently a passively Q-switched Er,Yb:GdAB laser was demonstrated with Co 2+ :MgAl 2 O 4 , graphene and SWCNT saturable absorbers [2-4]. Here we report Er,Yb:GdAB laser passively Q-switched by using of MBE-grown Cr:ZnS thin films. Thin films of Cr-doped ZnS were deposited using the high purity materials (99.999% purity) in the UHV MBE deposition system at base pressure of ~4x10 -9 Torr and thermal evaporation. As a result high-quality polycrystalline films transparent through the visible and infrared regions were obtained. Film thickness was kept in the range of 2 to 10 μm with Cr content varied from 0.01 to 3 at.%.The Er(1 at.%),Yb(11 at.%):GdAB crystal was obtained by dipping seeded high-temperature solution growth. The laser cavity consisted of pump mirror (PM) (R>99.5% at 1522 nm and T>95% at 976 nm) deposited onto external side of the 1.0-mm-thick active element (AE) and a flat output coupler (OC) with transmission of 9% at 1522 nm. As a saturable absorber (SA) – 8.8-μm-thick Cr(0.11 at.%):ZnS film with initial transmission of 98.4% at 1522 nm deposited on a 1-mm-thick sapphire substrate was used. The minimal geometrical cavity length was 4 mm, that was limited by the design of the active element cooling system. The setup for laser experiments is schematically shown in Fig. 1. Stable passively Q-switched mode of laser operation was obtained with maximum average output power of 0.39 W at 1522 nm and TEM 00 mode (M 2 <1.5) spatial profile of the output beam. Laser pulses with energy of 9.2 μJ and duration of 8 ns were obtained at a repetition rate of 42 kHz when the incident pump power was 5 W. The oscilloscope traces of single Q-switched pulse and corresponding pulse train are shown in Fig. 2. Fig. 1 Setup for laser experiments Fig. 2 Output pulses of the Er,Yb:GdAB passively Q-switched laser. (a) Single pulse with width of 8 ns; (b) pulse train with repetition rate of 42 kHz In conclusion, passively Q-switched Er,Yb:GdAB laser with MBE-grown Cr:ZnS thin film saturable absorber was demonstrated for the first time to our knowledge. Optimization of the Cr 2+ concentration and film thickness will result in better laser performance. Moreover, important technological aspect is that MBE growth technique allows deposition of the Cr:ZnS saturable absorber film directly onto the active crystal, thus demonstrating approach to fully integrated microchip laser emitting in the 1.5-1.6 ȝm spectral region. References [1] K. N. Gorbachenya, V. E. Kisel, A. S. Yasukevich, V. V. Maltsev, N. I.Leonyuk, and N. V. Kuleshov, “Highly efficient continuous-wave diode- pumped Er,Yb:GdAl3(BO3)4 laser,” Opt. Lett. 38, 2446–2448 (2013). [2] K. N. Gorbachenya, V. E. Kisel, A. S. Yasukevich, V. V. Maltsev, N. I.Leonyuk, and N. V. Kuleshov, “Eye-safe 1.55 ȝm passively Q-switched Er,Yb:GdAl3(BO3)4 diode-pumped laser,” Opt. Lett. 41, 918–921 (2016). >3@ K. Gorbachenya, V. Kisel, A. Yasukevich, S. Kurilchik, V. Maltsev,N.Leonyuk, S. Choi, F. Rotermund, and N.Kuleshov,“Diode-pumped Er,Yb:GdAl3(BO3)4 laser passively Q-switched with a SWCNT saturable absorber”in 7 th EPS-QEOD Europhoton Conference, EPS Technical digest (2016), paper PO-1.4. [4] K. Gorbachenya,V. Kisel, A. Yasukevich, P. Loiko, X. Mateos, V. Maltsev, N. Leonyuk, N. Kuleshov, M. Aguiló, F. Díaz, U. Griebner, and V. Petrov,“Graphene Q-Switched Er,Yb:GdAl3(BO3)4 Laser at 1550 nm” in Advanced Solid-State Lasers Conference,OSA Technical Digest (2016), paper AM5A.22.