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

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.