Infrared OD 4 bandpass filters that provide the high transmission and deep rejection necessary to isolate narrow spectral regions have been unveiled by Edmund Optics. They are durable, and their single-substrate dielectric construction ensures easy maintenance. The bandpass interference filters have a diameter of 25 mm and provide center wavelengths of 2.7 to 5.3 μm. They selectively transmit a narrow range of wavelengths while blocking out all others. The filters feature >OD 4 blocking with center wavelengths optimized for analyzing water vapor, ethanol, formaldehyde, CO2, CO and NO. They are suitable for use in environmental monitoring, gas analysis, biotech, biomedical, quantitative chemical and forward-looking infrared applications. Interference filters can be used in instrumentation and for clinical chemistry, elemental and laser line separation, fluorescence and immunoassays.