254nm Bandpass Filter

Context: A forensic imaging system designed to detect latent fingerprints on smooth, non-porous surfaces (like glass or plastic) without using powders or chemicals.

Usage of Filter: The filter is positioned in the optical path between the objective lens and the digital image sensor (CCD/CMOS).

Function: It serves as a "solar blind" blocking mechanism. It blocks all visible light and infrared light, passing only the narrow 254nm UV band emitted by the scene illumination.

Result: The camera captures a high-contrast image where fingerprints (which scatter 254nm light) appear bright against a dark background, even in a lit room, allowing investigators to see prints invisible to the naked eye.

Context: An environmental sensor system used to monitor ozone O3 concentration in air or industrial processes.

Usage of Filter: The filter is integrated directly onto the window of the semiconductor photodiode detector located at the end of the gas sampling chamber.

Function: It isolates the 254nm spectral line from the UV source (typically a mercury lamp). Ozone has a maximum absorption cross-section specifically at 254nm. The filter prevents interference from other gases or stray light wavelengths.

Result: The system achieves precise, quantifiable readings of ozone concentration (down to parts per billion) by measuring exactly how much the 254nm light intensity drops as it passes through the gas sample.

Context: A quality control system using Optically Stimulated Electron Emission (OSEE) to check metal surfaces for cleanliness (e.g., grease or oxidation) before bonding or painting.

Usage of Filter: The filter is used in the illumination assembly to condition the light output from a mercury discharge lamp.

Function: It purifies the light source by passing only the high-energy 254nm photons (4.9 eV). This specific energy level is required to eject electrons from the metal surface via the photoelectric effect, while avoiding heating the sample or causing unwanted photochemical reactions from other wavelengths.

Result: The system provides a consistent and accurate "cleanliness score" by measuring the current of emitted electrons. If the surface is dirty, the contaminants absorb the 254nm photons and the electron current drops, alerting the operator to a defect.