[1] Capital Normal Univ, Dept Phys, Beijing 100048, Peoples R China
[2] Minist Educ, Key Lab Terahertz Optoelect, Beijing 100048, Peoples R China
[3] Beijing Key Lab Terahertz Spect & Imaging, Beijing 100048, Peoples R China
[4] Beijing Adv Innovat Ctr Imaging Theory & Technol, Beijing 100048, Peoples R China