Lasers, PTFE compounds, and diffractive optics
A novel laser beam shaping system was designed to demonstrate the potential of using high power UV laser sources for large-scale disinfection of liquids used in the production of food products, such as juices, beer, milk and other beverage types. It is also possible to consider such a device for gang disinfection of aluminum cans, other beverage containers and preparing medical packaging. The design incorporates a patent pending assembly of optical components including a diffractive beam splitting/shaping element and a faceted pyramidal or conically shaped Lambertian diffuser made from a compression molded PTFE compounds, such as Spectralon® a product manufactured by Labsphere.
When properly sintered to an appropriate density, as an example between 1.10 and 1.40 grams per cubic centimeter, the compressed PTFE compounds shows a ~99% reflectance at wavelengths ranging from 300 nm to 1500 nm, and a ~98.5% refection of wavelengths from 250 nm to 2000 nm. The unique diffuser configuration also benefits from the fact that the PTFE compounds do not degrade when exposed to ultraviolet radiation in comparison to barium sulfate materials and silver or aluminized mirror coatings. These components contained within a hermetically sealed quartz tube form a closed system. Once assembled a laser beam is directed through at one end of the tube.
This window takes the form of a computer-generated diffractive splitter or diffractive shaper element to split the laser beam into a series of spot beamlets, circular rings or other geometric shapes. As each of the split beamlets or rings cascade downward, they illuminate various points along the tapered PTFE cone or faceted pyramidal form. As they strike the surface they each diffuse in a Lambertian reflectance pattern creating a pseudo-uniform circumferential illuminator along the length of the quartz tube enclosing the assembly. The compact tubular structure provides a unique UV disinfection source within a centrifugal reactor, a pipe based reactor chamber or inserted into a package for disinfection.