Frequency Modulation Spectroscopy (FMS) Technology

Frequency modulation spectroscopy (FMS) is a special wavelength modulated optical heterodyne absorption spectrum. Its modulation mode is current modulation or electro-optic modulation. Current modulation is the high-frequency modulation of the input current of the semiconductor laser, and electro-optical modulation is the modulation of the optical path using an electro-optical phase modulator (EOM). FMS is different from DAS and WMS in that the variation term of transmitted light intensity is linearly proportional to the absorbed light information, rather than exponentially, which facilitates more accurate absorbance. In addition, because FMS can obtain phase information, it is also used to study the difference of particle number between two energy levels, and obtain the relevant information of particle transition from high energy level to low energy level, which provides help for the detection of amplified emission spectrum.