Magnetooptical spectrometer based on photoelastic modulator with optical feedback and its application in study of f-electron materials Vasiliy O. Pelenovich a , Uygun V. Valiev b , Lin Zhou c , Igor’ A. Ivanov d , Oleg V. Pelenovich b , Umid R. Rustamov b , Dejun Fu a,⇑ a Key Laboratory of Artificial Micro- and Nano-Materials of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China b Faculty of Physics, National University of Uzbekistan, Vuzgorodok, 100174 Tashkent, Uzbekistan c Center of Information & Optomechatronics, Research Institute of Tsinghua University at Shenzhen, Shenzhen 518057, China d Technodesing Consulting Ltd., 521-44, Zelenograd, Moscow 124536, Russia article info Article history: Received 30 January 2016 Received in revised form 24 February 2016 Accepted 7 March 2016 Keywords: Photoelastic modulation Magnetic circular polarized luminescence Faraday rotation Rare-earth garnets abstract A spectroscopic apparatus for measurement of magnetooptical and optical properties of f-electron mate- rials has been designed and established using a polarization modulation technique based on photoelastic modulator with optical feedback. The magnetooptical system is able to provide a sensitivity of 0.004 arc- deg at the wavelength of 380 nm. The versatile applications of the spectrometer have been verified by the measurements of the magnetic circular polarized luminescence and Faraday rotation angle in holmium- and terbium-containing garnet crystals. Ó 2016 Elsevier B.V. All rights reserved. 1. Introduction Magnetooptical spectroscopy is an advanced and important technique in characterization of solid state materials. Magnetoop- tics gives not only information on influence of magnetic field on energy levels of a quantum system (Zeeman polarization spec- troscopy), but also information on energy structure of both 3d transition-metal ions and 4f rare-earth ions in compound crystals. It may also give physical insights into interband and intraband opti- cal transitions in semiconductors and metals, revealing symmetry of paramagnetic centers and displaying magnetic domain patterns. At present time to obtain specific information on excited states of 3d- and 4f-ions, magnetic circular polarized luminescence (MCPL) technique is frequently utilized. The ‘‘absorbing” analog of MCPL is the widely used method of magnetic circular dichroism (MCD). Both techniques allow measuring of important physical parameters such as Zeeman splitting, g-factors, ratio between velocities of the radiative and spin-lattice relaxations in the excited state, and degree of thermalization of the excited states. For realization of the dedicated magnetooptical measurement, it is necessary to use polarization modulation techniques, among them the method of elliptical polarization modulation is com- monly applied [1,2]. This technique operates on the basis of differ- ent polarization modulators, such as Faraday rotators, Pockels cells, and photoelastic modulators [3,4]. In practice photoelastic modu- lation has shown special advantages and is frequently utilized. The principles of polarization modulation using photoelastic mod- ulators have been given in Refs. [5,6]. Modulation of the light ellip- ticity caused by oscillation in the bar of an isotropic material is employed in the optical spectroscopy and ellipsometry [5,6]. The main advantage is its capability to measure signals with 100% depth of modulation, which is very important in the case of strong absorption and weak reflection or emission. In addition, for such kinds of modulators broad-aperture beams can be used [5]. In the present study we have designed and established a magne- tooptical spectrometer based on the light modulation created by the photoelastic modulator of an original design [8]. The system has been tested by measurements of the MCPL degree and Faraday rota- tion (FR) angle in the holmium- and terbium-containing garnet crys- tals, carried out in strong magnetic field using different light sources. 2. Basic principles of measurement of the linear magnetooptical effects It is well-known that the mechanical longitudinal oscillations in the quartz bar lead to the periodical modulation of its index of refraction along the largest dimension due to the photoelastic http://dx.doi.org/10.1016/j.optmat.2016.03.011 0925-3467/Ó 2016 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: 592563827@qq.com (D. Fu). Optical Materials 55 (2016) 115–120 Contents lists available at ScienceDirect Optical Materials journal homepage: www.elsevier.com/locate/optmat