Background Fluorescence in an Aerosol Biodetector Based on 266-nm Excitation
Abstract
Background fluorescence in an aerosol biodetector based on 266-nm excitation has been investigated, using a gas cell which could be evacuated and then filled with a gas (of interest) at a known pressure. A frequency-quadrupled, Q-switched Nd:YAG microchip laser with a pulse width of less than I ns and a pulse repetition rate of ^10(4) pps was used to measure both fluorescence and Rayleigh scattering in a direction at 900 to the 266-nm excitation beam, as a function of the gas pressure for nitrogen, oxygen, and room air. Rayleigh scattering was also measured for helium and xenon gases. The relative Rayleigh scattering cross sections measured in this work are consistent with their previously reported values, ensuring that the observed fluorescence was originating from a region of the gas in the direct path of the 266-nm excitation beam. Fluorescence signal observed in the spectral range of interest 300-650 nm under nominal vacuum conditions (^1 x 10(-5) torr) exhibited strong quenching upon filling the gas cell with oxygen, but not with nitrogen. Strong oxygen-induced quenching leads us to believe that the background fluorescence is due, at least in part, to the presence of residual hydrocarbons in the atmospheric air.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 17, 1999
- Accession Number
- ADA363355
Entities
People
- Roshan L. Aggarwal
Organizations
- Massachusetts Institute of Technology