Feasibility study of particle manipulation using resonant background gas

If a narrow band laser is tuned in to the Doppler broadened absorption profile of an optical transition in a low pressure gas, velocity selective excitation is achieved. This creates fluxes of the excited molecules parallel or antiparallel to the k-vector. Small objects such as aerosol particles suspended in the gas will now be bombarded by excited molecules, either from the illuminated side or form the 'dark' side, depending on the sign of the laser detuning. If the molecules deexcite on the object's surface while releasing a portion of the excitation energy in the form of the kinetic energy, the resulting superelastic collision will produce a recoil on the object by momentum conservation. Velocity-selective rovibration excitation is brought about by a grating- and piexo-tunable carbon dioxide laser illuminating the 20-μm wire. As the laser is tuned through the Doppler profile of an absorption line, the force on the wire is monitored by a HeNe-laser beam reflected from a mirror attached to the pendulum, using a position-sensing detector.