In the modern economy, reliable identification of products has been accorded increasing importance not only for improved logistics, but also for preventing product piracy. Recently, “luminescent nano-pigments” (LNPs) have been utilized to provide products with a permanent, distinguishable, spectral fingerprint that is visible only upon appropriate optical stimulation. Such LNPs can be provided as non-toxic, bio-compatible, stable and very long-lasting inorganic materials that are introduced into the product surfaces and are not modifiable therein. The LNPs are stable at high and low temperatures, are insensitive to solar radiation and are available in particle sizes of, e.g., 0.3 μm to 60 μm. When irradiated, e.g., with laser radiation, they can be excited to luminesce. The delay or lag of the luminescent radiation relative to the excitation irradiation can be practically zero (fluorescence) or can have predetermined values that are characteristic for the respective LNPs.
An apparatus for detecting laser-stimulated luminescent radiation is known from European Patent Application No. 0 802 499 A2. This apparatus has an opening designed for the emission of excitation irradiation, generally in the UV-range, generated by a semiconductor diode housed in the housing of the apparatus and for the admission of luminescent radiation, generally in the visible range, that emanates from a surface of an object as a result the excitation radiation applied thereto. However, this apparatus lacks a safety mechanism for preventing, e.g., the user's eyes from being accidentally exposed to harmful excitation irradiation.
An apparatus for examining objects such as currency, paintings, stamps, etc. using UV-light is known from German patent publication no. 1 673 140. This apparatus has a downward-opening housing for irradiating the object and for monitoring the luminescence emanating therefrom. During the inspection process, the UV-lamp and the object are disposed in the apparatus housing so that the UV-light is confined therein. Consequently, the design of this apparatus does not lend itself to convenient, e.g., portable, inspection of a wide-variety of product sizes.