Single particle caloric absorption spectrometer

Abstract

A single particle caloric absorption spectrometer for directly measuring the absorption spectra in situ of individual aerosol type particles comprises a differential arrangement of two identical electrodynamic traps (separated by a series of pneumatic valves) capable of suspending a charged particle in free-space in a non-intrusive manner in one of the traps; a source of monochromatic radiation, e.g., a laser, which is split and directed equally through transmission windows into the traps; and, a high precision capacitance manometer capable of detecting the pressure differential between the traps. After a particle has been trapped in one of the traps and the traps have been sealed from the atmosphere and from each other by the pneumatic vales, the radiation source is turned on and is evenly split/directed into both trap volumes via an appropriate beam splitter and transmission windows. This results in identical illumination of both the target and reference trap regions. A certain fraction of energy will be absorbed by the particle resulting in its heating. The heat generated within the particle is rapidly transferred to the surrounding air resulting in a net change in pressure between the target and reference traps. This change in pressure is recorded by the capacitance manometer and is shown to be proportional to the actual absorption cross section of the particle. The wavelength of the laser is then shifted slightly and the measurement is repeated until the desired spectra are completely recorded.