Non-linear laser dazzling an off-band filtered mid-infrared imager

Infrared (IR) imaging is crucial for military surveillance, targeting, and detection systems. In common with all electro-optical imaging devices, they are vulnerable to in-band laser strikes, causing pixel saturation, image dazzling and potential array damage. An obvious safeguard is inserting a filter that blocks the expected laser wavelengths without significantly reducing the imager’s performance. The perfect countermeasure! However, our results indicate a side effect: a high power-density laser that permits dazzling even in the transmission band of the filter. A continuous-wave Quantum Cascade Laser (QCL) with a peak wavelength of 4.57 microns and output power of approximately 300 mW irradiates the thermal infrared imager sensing in the Mid-Wave Infrared (MWIR). The IR imager has a filter wheel with two dielectric-stacked infrared bandpass filters outside the laser’s wavelength, positioned internally between the detector dewar and telescope. The images were radiometrically calibrated over four integration times under conditions with and without each filter. In summary, our observations indicate a counterintuitive result. There are dazzling effects observed through filters out of band with the laser, with the most significant being for the bandpass filter closest to that of the laser wavelength.