STABLE VACUUM ULTRAVIOLET IRRADIANCE METER DEVELOPED BY NIST.

NIST scientists have constructed and characterized a probe that is suitable for making accurate measurements of irradiance in the vacuum ultraviolet spectral region. Many industrial applications such as semiconductor chip fabrication, photo-lithography, and UV curing, require accurate measurement of the irradiance and will benefit from having a stable, accurate UV probe. In the past, the ability to measure irradiance accurately has been limited by the stabil-ity of detectors at short wavelengths.

The probe consists of a PtSi detector behind a precision 5 mm aperture, and was characterized at various wavelengths ranging from 157 nm to 325 nm using synchrotron radiation from SURF III. This range encompasses many of the important wavelengths for industrial applications. The principle of measurement is based on scanning the probe through a UV light field and measuring the spectral responsivity at regular intervals. Measurement of the spectral responsivity in the center along with the integrated total responsivity yields the spectral irradiance. Alternatively, this method can be used to calculate aperture areas by measuring the ratio of the total responsivity and the responsivity at the aperture center.