title: High-sensitive measurement of water vapor: shot-noise level performance via a noise canceller.
abstract: Taking advantages of distributed feedback laser diode a technique is described to achieve high-sensitive measurement for water vapor concentration. This technique, with a modified balanced ratio metric detection system, has improved the accuracy of measured absorption spectrum by two main aspects. Improvement by matching equivalent conductivity of signal or reference photo detector (PD) is presented, and with the additional matched resistance suppression for the power variation in the signal-beam has been improved from 53 to 88 dB. The importance of integrating amplifier bandwidth design from the circuit to the measured absorption spectrum has been demonstrated in our experiment. For a scan rate of 32 Hz with an optimal corresponding bandwidth of 15.9 kHz, the absorption spectrum is well described by Voigt profile, with a difference of 1% at an atmosphere pressure of 1 atm and a room temperature of 296 K. With the application of averaging and filtering, absorption sensitivity of 1.093×10(-6) for water vapor at 1368.597 nm has been demonstrated, and the corresponding concentration is 71.8 ppb in just a 10 cm path length.
authors: School of Information Science and Engineering and Shandong Provincial Key Laboratory of Laser Technology and Application, Shandong University, Jinan 250100, China.
authors: Qiang
authors: Q
authors: Wang
authors: Jun
authors: J
authors: Chang
authors: Cunguang
authors: C
authors: Zhu
authors: Yongning
authors: Y
authors: Liu
authors: Guangping
authors: G
authors: Lv
authors: Fupeng
authors: F
authors: Wang
authors: Xiangzhi
authors: X
authors: Liu
authors: Zongliang
authors: Z
authors: Wang