CC BY
12LS-I-13
Direct generation of vortex beam from a Er:Y2O3 ceramic laser at 2.7 ^m
Y. Zhao1, M. Ding2, Y. Chen2, D. Shen2
1Shandong University, State Key Laboratory of Crystal Materials and Institute of Crystal Materials, Jinan, China
2Jiangsu Normal University, Jiangsu Key Laboratory of Advanced Laser Materials and Devices, XuZhou, China
Optical vortices characterized by doughnut-shaped intensity profile and helical phase front, carry orbital angular momentum (OAM) of lh per photon, where l is topological charge [1]. Generation of vortex beams in the mid-infrared spectral range is now mainly focused on nonlinear frequency conversion technique [2], which suffers from low conversion efficiency and complex setups. In comparison, "direct generation" technique [3] using a robust laser cavity features with high beam quality, power scaling capability and low cost.
Here we demonstrate, to the best of our knowledge, the first vortex beam in the 3-micron spectral region from an Er:Y2O3 ceramic laser pumped by a ring-shaped beam. The 7 at.% Er:Y2O3 ceramic has a dimension of 3*4*14.5 mm3. A Brewster plate was inserted in the cavity to obtain linear polarized laser. Handedness of the scalar vortex lasers was controllable by introducing asymmetric cavity loss. To further improve the purity of generated vortex beam, an etalon was inserted in the cavity to reduce longitudinal modes. The topological charge (l) was detected using a mid-infrared CCD camera and a home-made Mach-Zehnder interferometer, and was quantitatively analyzed by using a cylindrical lens. The l of LG0-1 was calculated to be -0.9878, and 0.9884 in the case of the LG0+1 mode, indicating a high purity of the generated vortex beams. The optical spectra were recorded by high resolution optical spectrum analyzer (OSA, AQ6376, YOKOGAWA). The central wavelength of LG0+1 mode was 2710.8 nm and 2710.5 nm for the LG0-1 laser mode.
References
[1] L. Allen, M. W. Beijersbergen, R. J. C. Spreeuw, and J. P. Woerdman, "Orbital angular momentum of light and the transformation of Laguerre-Gaussian laser modes," Phys. Rev. A 45, 8185-8189 (1992).
[2] T. Yusufu, Y. Tokizane, M. Yamada, K. Miyamoto, and T. Omatsu, "Tunable 2-^m optical vortex parametric oscillator," Opt. Express 20, 23666-23675 (2012).
[3] Y. G. Zhao, Q. Y. Liu, W. Zhou, and D. Y. Shen, "~1 mJ pulsed vortex laser at 1645 nm with well-defined helicity," Opt. Express 24, 15596-15602 (2016).
