A SCALAR IRRADIANCE FIBEROPTIC MICROPROBE FOR THE MEASUREMENT OF ULTRAVIOLET-RADIATION AT HIGH-SPATIAL-RESOLUTION

The construction of a new type of microprobe for the measurement of scalar irradiance (integral dose rate) in the UV down to wavelengths of 250 nm is described. The microprobes were made from tapered standard optical fibers and a tip-diffuser of magnesia/silica vitroceramic. The sensing tips were ca 100 mu m in diameter and had maximal deviations in the angular response of +/- 15%. I present measurements of scalar irradiance at high spatial resolution within dry beach sand and suspensions of microorganisms. These two media are environments in which microorganisms are exposed to UV, either under natural (sand) or laboratory conditions (suspensions). In both cases, the space distribution of UV scalar irradiance, and thus the distribution of integral dose rates, departed significantly from that predicted by absorptive effects alone. The results underscore the importance of small-scale, in situ measurements of scalar irradiance for UV dosimetry in such scattering media.