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Published April 1987 | Published
Journal Article Open

Fourier transform infrared spectrometer for a single aerosol particle


A spectrometer is reported here for obtaining the infrared spectrum of a single aqueous aerosol particle by a Fourier transform technique. The particle is held in an electrodynamic balance and irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The size of the particle is modulated by chopping the IR beam, and the resulting visible scattered light fluctuation is detected at 90° with a photomultiplier tube. The amplitude of the scattered light fluctuation is measured with a lock-in amplifier at each interferometer mirror position. The electronic circuitry for stepping the interferometer mirror is presented and discussed. Inverting the lock-in signal by a discrete fast Fourier transform routine (FFT) yields the particle absorption spectrum. The resulting spectrum for an (NH4)2SO4 droplet is presented.

Additional Information

© 1987 American Institute of Physics. Received 2 December 1986; accepted 18 December 1986. This research was supported by U.S. Environmental Protection Agency Grant R-810857 and by gifts from General Motors Corporation and Mobil Oil Corporation. S. Arnold was supported by a Chevron Visiting Professorship at the California Institute of Technology and by National Science Foundation Grant ATM-8413574. The authors thank Anthony B. Pluchino of the Aerospace Corporation and Ralph Waniak of Advanced Kinetics for helpful advice during this work.

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