**4. Conclusions**

In this paper, a laser gas analyzer based on a second derivative laser absorption spectroscopy method has been developed to achieve a 100 Hz fast data rate, which is faster than that of a well-established 20 Hz commercial instrument. In combination with an ultrasonic anemometer, we applied the new laser gas analyzer for measurements of gas fluxes by using the eddy covariance method. Two DFB lasers operating at ~2.004 μm for CO2 and ~1.392 μm for H2O were used as optical sources. We built a multi-pass absorption cell of 20 m optical path length for CO2 measurements, and a single-pass absorption cell of 15 cm optical path length for H2O detection. A miniaturized TDLAS electronics system was designed for the operation and analysis of the gas concentration measurements. The gas analyzer achieves a detection limit of 8.17 ppmv for H2O and 0.40 ppmv for CO2 at 0.01 s integration time. Meanwhile, we made field measurements by installing the integrated instruments in two different environments to verify the influence of different wind speeds on flux measurements against a commercial instrument LI-7500. In general, the 100-Hz gas analyzer we developed has a wide prospect for flux measurement applications, especially when rapid turbulence is involved.

**Author Contributions:** Conceptualization, M.L. and B.C.; Methodology, M.L., L.Y. and R.K.; Project management, J.L.; Software, M.L., H.X. and H.D.; Validation, Z.X. and R.K.; Formal Analysis, J.R. and X.F.; Investigation, B.T. and X.C.; Resources, J.L., B.T. and X.C.; Writing-Initial Draft Preparation, M.L.; Writing-Revising, Y.H. and M.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by the National Program on Key Research and Development Project of China under Grant 2018YFC0213103, the National Natural Science Foundation of China under Grant 41901081.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** All data will be made available on request to the correspondent author's email with appropriate justification.

**Conflicts of Interest:** The authors declare no conflict of interest.
