[1] San Francisco State Univ, Dept Phys & Astron, San Francisco, CA 94132 USA
[2] Univ Cent Florida, CREOL, Coll Opt, Orlando, FL 32816 USA
[3] Harbin Inst Technol, Natl Key Lab Tunable Laser Technol, Harbin 150080, Peoples R China
[4] Nankai Univ, TEDA Appl Phys Sch, Tianjin 300457, Peoples R China