The system is a solution to saturated absorption spectra detecting, based on external cavity diode laser SAS100. It consists of four main parts: external cavity diode laser SAS100, optical isolator, light path for saturated absorption spectra and low noise photo detector. The system works as the following: The probing light and the re-pumping beam counter-propagate into the sampling cell, and overlap in space. While the frequency of diode laser is scanned to resonant on the transition frequency of the sampling material, the pumping light will pump the sampling material to the excited states and the probing light will pass the excited material with less absorption, which is detected by the photo detector showing transmission peaks on the Doppler absorption background. Generally, the spectra from alkali metals shows six transmission peaks, three of which are resonant lines and others are crossover lines. According to the demands of customers, spectra with or without Doppler background can be both obtained. The system can be utilized in such diverse applications as cold atom physics[1], laser spectroscopy[2], laser frequency stabilization[3], quantum information, metrology, environmental monitor and industrial measurement etc.

[1] Lin Xia, Xu Xu, Rui Guo, Fan Yang, Wei Xiong, Juntao Li, Qianli Ma, Xiaoji Zhou, Hong Guo, and Xuzong Chen,  Phys. Rev. A 77, 043622 (2008)

[2] Yimin Li, Xuzong Chen, Jianhua Gan, Wangxi Ji, Jingshan Hua, Donghai Yang, Yiqiu Wang，Chin.Phys.Lett., Vol.13,No.6,424(1996)

[3] X.Z. Chen, K. Zhang, J. Zang, Y. Akimoto, T. Kasahara, K. Sakamoto, H. Inaba, Proceedings of SPIE, Vol 3547, 194-202 (1998)