Sinusoidal Amplitude Modulation and Coherent Demodulation Technique for Chlorophyll Fluorescence Measurement

As a quick and non-intrusive probe of photosynthesis, the chlorophyll fluorescence has been widely studied. Extracting the weak fluorescence signal from the strong noise is necessary to the chlorophyll fluorescence measurement and analysis. In this paper, the time-domain and frequency-domain characteristics of the chlorophyll fluorescence signal and noise caused by the actinic light and the saturation pulse light were analyzed, and a new fluorescence measurement technique, sinusoidal amplitude modulating and coherent demodulating the fluorescence signal, was presented. Using the new technique, the measurement light was modulated by a 1KHz sinusoid, the modulated noisy fluorescence was demodulated using the coherent method with several different cut off frequencies, and signal to noise ratios and measurement errors were calculated and analyzed. The results indicated that the new measurement technique can be employed to measure accurately and efficiently the chlorophyll fluorescence in situ.