| Cavity ring-down spectroscopy (CRDS) is a laser-based absorption technique of particularly high sensitivity, making it an effective diagnostic tool (of increasing popularity) for sputtering processes. One such process is the parasitic sputtering of boron-nitride that occurs within an ion beam thruster. This erosion is one of the primary limiting factors in the lifetime of the device. Current methods for testing the lifetime of these thrusters involve full-life tests, lasting thousands of hours. CRDS is sensitive enough to measure the amount of boron-nitride being sputtered in real time. | |||
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| Conventional CRDS uses high reflectivity mirrors to enhance the absorption path length of the laser. The sensitivity of this measurement process is strongly dependent upon the mirror quality. However, sufficiently high quality mirrors are not available for UV light that is resonant with the boron-nitride. Our approach will be to use calcium fluoride (CaF2) prisms, based on the principle of total internal reflection, to establish a high quality optical cavity. | |||
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These prisms will provide a higher finesse optical cavity than what is currently available,
thereby increasing the overall sensitivity of boron-nitride detection. Another limitation of typical mirror sets is their small wavelength range over which they are highly reflective. This limits the CRDS method to a single species for a given experimental setup. A prism based optical cavity holds promise for a broadband detection scheme, allowing for detection of multiple species simultaneously. |
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