Performance improvement on fiber-based CW modulation laser absorption spectrometer system for CO2 sensing

For the application to the global CO
2
sensing, DIfferential Absorption Lidar or Laser Absorption Spectrometer (LAS) systems using the conventional coherent and incoherent methods have been studied
^1–4
. But the conclusion about the best system configuration has not been determined yet, because of the severe requirements for the satellite-borne sensor in addition to the precise measurements in real-time. As the results of our consideration to overcome this issue, we invented the compact fiber-based Continuous Wave (CW) modulation LAS system, which enables simultaneous transmission of two (ON and OFF) wavelength and discrimination of wavelengths in the electrical signal domain. And we have developed the ground-based model and demonstrated high precision measurement corresponding to 4 ppm with short time interval of 32 s
⁵
. This high precision measurement was not easy to achieve and we have found out some important points to improve the performance and added some functions, which have not been shown in our previous literature. In this paper, we show the functions to realize this high precision measurement.