©Lin Yangchen


The UV excitation source (hidden behind filter) is an array of indium gallium nitride light-emitting diodes with peak excitation wavelength 365 nm. A Nikon PN-11 extension tube serves as an improvised lamp holder with a tripod mount. A Baader U2 Venus narrow-bandpass (320—380 nm) interference filter is mounted on the front using a Nikon BR2A lens reversing ring and a 48–52 mm step-up ring. The filter has a dielectric multi-coating on optically polished Schott borosilicate glass, which eliminates contamination by visible wavelengths. It is usually employed in astronomical observations of the atmosphere of Venus, where unknown UV-absorbing agents produce heterogeneous cloud structures.

In laser-induced ultraviolet fluorescence spectroscopy, stamps were epi-illuminated with a 325 nm helium-cadmium ultraviolet laser (Kimmon IK Series) through a Thorlabs UV (325–500 nm) achromatic 40× microscope objective with fused silica and calcium fluoride lens elements. The resultant laser power was 5.16 μW. See Judge (2020) for more philatelic applications.

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