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Sensors 2018, 18(12), 4255;

Dual Path Lock-In System for Elimination of Residual Amplitude Modulation and SNR Enhancement in Photoacoustic Spectroscopy

School of Information Science and Engineering and Shandong Provincial Key Laboratory of Laser Technology and Application, Shandong University, Jinan 250100, China
School of Physics Science and Information Technology and Shandong Key Laboratory of Optical Communication Science and Technology, Liaocheng University, Liaocheng 252059, China
Author to whom correspondence should be addressed.
Received: 22 October 2018 / Revised: 21 November 2018 / Accepted: 30 November 2018 / Published: 4 December 2018
(This article belongs to the Section Physical Sensors)
Full-Text   |   PDF [1750 KB, uploaded 4 December 2018]   |  


A technique for elimination of residual amplitude modulation (ERAM) in photoacoustic spectroscopy based on dual path lock-in was proposed and experimentally demonstrated. There are two lock-in amplifiers, one is for gas concentration demodulation and another for residual amplitude modulation (RAM) measurement by tuning the reference signal in different phases, and then a dual path lock-in technique based on subtraction is applied to RAM removal, improving the second harmonic profile significantly. In this system, the signal to noise ratio (SNR) increases about two times based on our dual path lock-in technique compared to one distributed feedback laser diode (DFB-LD). The system achieved a good linear response (R-square = 0.99887) in a concentration range from 100 ppmv to 2400 ppmv and a minimum detection limit (MDL) of 1.47 ppmv. View Full-Text
Keywords: dual path lock-in; RAM; photoacoustic spectroscopy dual path lock-in; RAM; photoacoustic spectroscopy

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Zhang, Q.; Chang, J.; Cong, Z.; Wang, Z.; Wang, F. Dual Path Lock-In System for Elimination of Residual Amplitude Modulation and SNR Enhancement in Photoacoustic Spectroscopy. Sensors 2018, 18, 4255.

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