Size measurement of nano-particles with a self-mixing laser

摘要

We demonstrate and analyze a novel self-mixing laser particle sizing instrument using a He-Ne laser centered at around 632.8 nm and output power is 35 mW. A single mode fiber is used to deliver the incident light to the sample cell and the fiber probe is worked as an optode. The scattered light is collected by the same fiber and re-injected into the laser. Experimental investigations are presented for particle sizing using polystyrene particles in water from 100 to 400 nm in diameter. Diameter of the scattering particle can be obtained by analyzing the optical power spectrum which is related to the autocorrelation of the measured scattering intensity. The result has a good agreement with theory. As a significant improvement, we gather the back-scattering light using a fiber optic probe accomplishes a task that is almost impossible using conventional optics because the multiple scattering in a concentrated opaque suspension. Fiber optics also has the advantages of being less prone to damage, less expensive and allowing for remote access in transmitting and collecting light.