The possibility of constructing a Fourier transform spectrometer by uniform motion of a permanent magnet cylinder falling in an upright conductive tube was researched. Two identical permanent magnet cylinders were reversely connected to two ends of a non-magnetic rod, making a compound permanent magnet cylinder, to reduce the lateral swing of a single permanent magnet cylinder as it falls. Falling velocity fluctuation of the compound permanent magnet cylinder was measured by laser diode self-mixing interferometry. Spectral lines with a frequency interval of about 9 GHz could be clearly distinguished on a cosine transform spectrum of the self-mixing interference signal under a weak feedback situation. (C) 2018 Optical Society of America
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