Optical submicron aerosol particle detector

A particle detector for detecting particles within an enclosed volume, said detector comprising:

• laser means for producing an optical beam and directing it along a path;
• beam splitting means in said path for dividing said optical beam into first and second beams;
• means for directing said first beam into said volume to interact with a particle and acquiring resultant back scattered optical energy from said first beam interacting with said particle, and directing said back scattered optical energy to said beam splitting means for being combined with said second beam such that said back scattered optical energy and said second beam overlap in a region and in the overlap region said back scattered optical energy and said second beam are in substantially the same state of focus, of substantially the same polarization and are substantially parallel;
• and
• optical detection means disposed at said overlap region for detecting the presence of a particle in said enclosed volume from said combined back scattered optical energy and said second signal.