The present invention generally relates to the field of soil penetration probes, and more particularly, to a translation mechanism for directing an optical signal emitted by an optical system mounted in a soil penetration probe through predetermined coordinates of a window fitted in the wall of the probe.
Increasing concern with soil and groundwater contamination and governmentally mandated requirements to clean up hazardous waste sites have created a need for cost effective systems and methods for determining the characterization of a subsurface environments. In response to such needs, soil-penetrating probes have been developed generally comprising a tube with a tapered tip, which is forced into the ground. Instrumentation inside the tube detects various properties of the surrounding geological environment.
Laser induced Breakdown Spectroscopy (LIBS) is a method for detecting the presence of various elements in a sample by directing a high power emission from a laser onto the sample to form a plasma. The plasma then is analyzed spectroscopically to determine the composition of the sample. The LIBS technique offers promise as a method suitable for use with a soil-penetrating probe to detect heavy metal contamination in soil, because it is highly sensitive and requires no sample preparation. Usually the LIBS technique involves delivery of the laser energy to the sample through air due to the high power densities required to ionize the sample. Recently, fiber optic cable has been used successfully in LIBS measurements, allowing measurement of samples that are located at a considerable distance away from the excitation laser and analyzing equipment.
In a typical LIBS probe, laser light emitted from an optical fiber is collimated and then directed through a focusing lens and into the surrounding soil through a window mounted in the wall of the probe. However, the laser energy density required to stimulate the soil to generate atomic emissions tends to damage the sapphire window generally used in such probes. After several bursts of laser energy, the windows are damaged to the extent that the capability of the LIBS probe to detect atomic emissions from the soil is greatly impaired. Continued use of the probe requires that it be withdrawn from the soil so that the window may be replaced. Such repair is time consuming and hence, costly. Therefore, a need exists for a way to extend the life of the window to reduce the frequency of replacement.
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