Direct imaging of the UV absorption or reflection of an object has many applications in medical diagnosis and research. Examples are: identifying abnormal tissue growth, identifying invisible dermal damage, tracking the effectiveness of drug treatments, and others. Many biological molecules absorb UV light, thereby permitting the temporal and spatial monitoring of their concentration. Our innovation provides more information that the typically used UV fluorescence technique. Fluorescent systems require a complex, expensive steep-edge filter to reject the stimulating UV source and permit the fluorescing visible light to be observed, while our approach is simpler and less expensive to implement.
A high degree of Isolation of a band of wavelengths in the UV range at wavelengths shorter than ~400 nm without interference from longer wavelength energy is required because insufficient rejection of long wavelength energy dilutes the desired UV signal. Digital CMOS and CCD array detectors respond to the undesired long wavelength energy with many times higher sensitivity to energy in the UV region below ~400 nm. The traditional long-wavelength rejection solution is to use expensive complicated filters that are generally composed of many individual elements in combination to provide high levels of out-of-band rejection at various parts of the long wavelength spectral range. Additional solutions require special focal plane sensors that have reduced long wave response; such sensors are very expensive. Economics limits available filter sizes to ~50 mm diameter and thereby restricts the use of existing filters to common camera and microscope optics apertures. Our camera system uses common monochrome arrays coupled with our less expensive UV filters that can be economically manufactured to any desired size.
Our solar-blind imager is based on our novel filter designs that provide efficient UV bandpasses while rejecting wavelengths between 400 nm to ~1200 nm to levels varying from 10^5 to 10^8. The integrated system response will depend on the sensor response: some arrays have extended UV sensitivity, resulting in the in-band to out-of-band response level exceeding 10^9. Our process produces solar blind filters that meet the environmentally stability oer MIL and NASA Standards. The fabrication process uses coatings composed of metal oxide layers to produce a transmission band in the UV while reflecting and absorbing non-UV energy. Filters of sizes up to 130 mm diameters can be fabricated in one process run, therefore, the cost of an individual filter is lower than for currently available solar blind filters.
An example of a UV camera system using a our solar blind 365 nm filter employs a normal camera lens with transmission to ~350 nm and a monochrome CCD sensor. Other specific UV bandpasses can be fabricated.