[1] Univ Rochester, Inst Opt, Rochester, NY 14627 USA
[2] Tianjin Univ, Ctr Terahertz Waves, Tianjin 300072, Peoples R China
[3] Tianjin Univ, Sch Precis Instruments & Optoelect Engn, Tianjin 300072, Peoples R China
[4] Univ Ottawa, Dept Phys, Ottawa, ON K1N 6N5, Canada