Active infrared illumination in fog for driver assistance

We report preliminary results on the use of a far infrared emitting quantum cascade laser for active illumination in foggy conditions. The applications would be e.g. in cooperative driving and improvement of visibility for car drivers in adverse road weather conditions. It has long been known that the infrared wavelengths in the thermal band of 9 - 13μm allow better visibility in foggy conditions, compared to near infrared or visible bands. Therefore already thermal cameras have been installed in cars, with dashboard displays, in order to improve safe driving. However, these units are only utilising the emittance of the targets themselves, without the possibility of active illumination. This is because until recent years, no practical solid state laser illuminators have been available for the purpose. Recent increase of availability and powers of quantum cascade or distributed feedback lasers has changed the situation. We show some preliminary results on the use of a high peak power, pulsed quantum cascade diode laser in an experimental fog chamber for active illumination, viewed with a compound semiconductor, direct bandgap infrared camera.