A system method for depositing a sample of a threat agent is deposited onto a substrate. The threat agent is illuminated via an illumination source along an optical path with a plurality of photons to thereby produce photons transmitted, reflected, emitted or Raman scattered by the threat agent. An optical system collects elastic scatter photons produced by the threat agent and at least one of photons transmitted, reflected, emitted or Raman scattered by the threat agent, wherein said illumination source is located along an optical path, and said substrate is located along a plane wherein the optical path is at an angle other than 90.degree. with respect to the substrate plane. The depth of field of the optical system is extended by passing at least one of the following through a phase mask: elastic scattered photons, and photons transmitted, reflected, emitted or Raman scattered by the threat agent.