We report on experimental preparation of the second-harmonic-wave laser and the single-mode squeezed vacuum state of 795 nm (rubidium atom D1 line) with periodically-poled KTiOPO4 (PPKTP) bulk crystals. By using a four-mirror bow-tie type ring doubling cavity we achieved ~111 mW of continuous-wave single-frequency ultra-violet (UV) laser radiation at 397.5 nm with ~191 mW of 795 nm fundamental-wave laser input. The corresponding doubling efficiency is 58.1%. To our knowledge, this is the highest doubling efficiency at 795 nm so far. Employing the 397.5 nm UV laser as a pump source of an optical parametric oscillator (OPO) with a PPKTP crystal, we achieved 5.6 dB of 795 nm single-mode squeezed vacuum output at analyzing frequency of 2 MHz. To our knowledge, this is the highest squeezing level of 795 nm single-mode squeezed vacuum so far. We analyzed the pump power dependence of the squeezing level, and concluded that UV laser induced losses of PPKTP crystal are main limiting factors for further improving the squeezing level. The generated 795 nm vacuum squeezing has huge potential applications in quantum memory and ultra-precision measurement with rubidium atoms.
Junmin Wang, Yashuai Han, Xin Wen, Baodong Yang, Yanhua Wang, and Jun He, "Preparation of 5.6dB vacuum squeezing on 795nm rubidium D1 line via an OPO
(Conference Presentation)," Proc. SPIE 9900, Quantum Optics, 990016 (Presented at SPIE Photonics Europe: April 08, 2016; Published: 3 August 2016); https://doi.org/10.1117/12.2227484.5042345229001.
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