Patent ID: 6795177
Filing Date: 2004-09-21
Classification: G01J,G01N

Abstract:
A multi-pass Raman sampling system that illuminates a sample with laser excitation radiation to produce Raman shifted radiation, the system comprising:an injection element located in an optical path, the injection element obscuring only a portion of the optical path while injecting a substantially collimated beam of laser excitation radiation toward the sample in a first direction; an objective lens positioned in the optical path and defining an optical axis and a focal point, the objective lens focusing the collimated beam of laser excitation radiation traveling in the first direction into the sample to produce Raman shifted radiation, the objective lens collecting radiation that is emanating from at or near the focal point and then transmitting the radiation into the optical path in a second direction that is substantially opposite to the first direction; a mirror located within or behind the sample at or near the focal point, the mirror reflecting both laser excitation radiation and Raman shifted radiation back through the sample toward the objective lens and the injection element in the second opposite direction; a blocking filter located optically beyond the injection element such that the injection element is in the optical path between the objective lens and the blocking filter, the blocking filter being substantially reflective to the laser excitation radiation and substantially transparent to the Raman shifted radiation, the blocking filter passing the Raman shifted radiation out of the system for analysis and reflecting the laser excitation radiation back in the first direction toward the objective lens, the sample, and the mirror; and signal enhancement means for causing at least a portion of the laser excitation radiation that is reflected by the mirror to miss the injection element and strike the blocking filter where it is reflected back to the sample through the objective lens to produce further Raman shifted radiation.