Optical-feedback cavity-enhanced absorption spectroscopy for OH radical detection at 2.8 μm using a DFB diode laser

The data in Fig. 2 are obtained by using the formula simulation. They are the changes of the cavity mode signal (2.1) and the coupling frequency (2.2) with the free operating frequency under the optical feedback condition. Fig. 3 shows the light intensity information received by the detector in the case of triangular wave scanning. Fig. 4 is the of-ceas signal of the collected OH radicals, with a time resolution of 2 s, and 4.2 is the corresponding fitting residual. Fig. 5 is a time series diagram of peak point acquisition of a single cavity mode for a long time, and Fig. 5.2 is a corresponding Allan variance analysis diagram with a time resolution of 0.1s. Fig. 6 is a cavity mode obtained by using a 31kHz high frequency modulation laser and a 1F signal corresponding to phase lock demodulation. Fig. 7 is the time series of light intensity obtained for a long time and the corresponding Allan variance analysis chart, with a time resolution of 0.1s.