Meaning
Imaging techniques that utilize ultraviolet light to excite certain substances cause them to emit visible light of a different color. In document forensics, ultraviolet fluorescence microscopy allows examiners to see differences in inks and fibers that are invisible under normal lighting. This method is used to detect erasures and alterations on a single page.
It provides a non invasive way to inspect the physical integrity of a legal document.
Optical Mechanism
The equipment consists of a microscope equipped with an ultraviolet light source and specific filters that block the excitation light while allowing the fluorescence to pass through. When a sample is viewed through the ultraviolet fluorescence microscopy system, specific chemical compounds glow brightly against a dark background. Different manufacturers use different fluorescent additives in their ink and paper coatings.
These differences become apparent when the document is subjected to specific wavelengths of light. This allows examiners to map the distribution of specific materials across a surface without needing to take physical samples.
Forensic Application
The tool is effective for identifying the presence of chemical erasers that have been used to remove original text. Under ultraviolet fluorescence microscopy, the area where the chemical was applied often shows a distinct stain or a change in the background glow of the paper. Examiners can also identify security features in banknotes or official certificates that are designed to fluoresce.
This helps in the quick detection of counterfeit documents during a supply chain audit.
Practical Constraint
Analytical results are qualitative and often provide a preliminary step before more detailed chemical analysis is performed. Some materials may lose their fluorescent properties over time due to environmental degradation, which can complicate the interpretation of older documents. Ultraviolet fluorescence microscopy does not identify the specific chemical formula of a substance but rather its optical behavior.
