Kramers–Kronig relation in a Doppler-broadened Λ-type three-level system*
Wang Menga),b), Lu Xiao-Ganga), Bai Jin-Haia), Pei Li-Yac), Miao Xing-Xua), Gao Yan-Leia),b), Wu Ling-Ana), Fu Pan-Minga), Yang Shi-Pingb), Pang Zhao-Guangb), Wang Ru-Quana), Zuo Zhan-Chuna)
       
(a) Energy level diagram. (b) Experimental setup (DL1 and DL2: diode lasers; AOM: acousto-optic modulator; λ /2: half-wave plate; PZT: mirror mounted on a piezoceramic transducer; BS: 50/50 beam splitter; PBS: polarizing beam splitter; D1, D2, and D3: photo detectors; SG: signal generator; LIA: lock-in amplifier).