Raman spectroscopy has been studied and used as a laboratory tool in chemistry for many years. It is now reaching a level of maturity that is transitioning from the laboratory to a variety of field applications. The Raman effect occurs when a photon encounters a molecule, during which time there is a chance that the energy from the scattered photon will be exchanged with vibrational bond energy of the molecule. This energy exchange manifests itself as a shift in frequency (or wavelength) in a small amount of the scattered light. Because each different chemical bond in a material causes a different frequency shift, the pattern of these shifts, known as the Raman spectrum, is unique to that material.
The Raman spectrum reveals the molecular composition of materials, including the specific functional groups present in organic and inorganic molecules. The Raman spectrum is a characteristic property of a material, just like its color or melting point, and can be used to determine the presence or absence of the material.
The detector will always be measuring an agent spectrum in the presence of the spectrum from the background or from any other material that may be present. Fortunately, in most real-world situations, the ratio of the amount of agent to the background and any other materials has significant spatial variation. This variation in composition leads to slightly different Raman spectra from different areas on the sample surface. These differences in spectra provide enough information for chemometric processing of the data, allowing identification of the agent and the background materials. The Raman Bio Identification (RBI) system computer receives a command initiated by the operator to acquire and analyze a sample from the UGV central processing unit (CPU). Using software previously developed by the ChemImage Corporation of Pittsburgh, Pennsylvania, up to 19 spectra are acquired from the sample. The laser power is typically 12 milliwatts, resulting in a laser power density of 86 watts per square centimeter. The exposure time used to acquire the spectra in testing was 10 seconds, and each measurement is the product of 10 averages (see Figures 20-1 and 20-2).
The overall concept of the RBI robot demonstration system (Wolverine) was to integrate an RBI point sensor (the RBI head) onto a UGV manipulator arm, and then couple it to an instrument package mounted on the main chassis of the UGV. The coupling of the point sensor is accomplished through both electrical and fiber optic cables running along the manipulator structure.
The RBI detector is a Raman point sensor or a Raman proximity detector. To operate, it needs to be close but not necessarily touching the surface to be measured. The RBI detector contains subsystems to allow targeting of the head (video camera and fine-positioning system), laser illumination of the sample to induce