Abstract: An airborne particle-measuring device quantifies and qualifies contaminants of an air environment in clean-rooms, open spaces, and enclosed spaces such as homes, offices, industrial environments, airplanes in flight, cars and others. The device may include a sensor system, an electronics system, communications and information storage. The sensor system may include a high-power low-wavelength single-frequency continuous laser, an open-cavity high-efficiency mirror having an optical surface tuned to the laser frequency and a flow system that includes a vacuum pump to sample the air. The electronics system may be mounted on a single multilayer PC board with a microprocessor, firmware, electronics and a touch-screen LCD display. Innovations in light source, flow control, analog and digital signal processing, components integration and software allow provision of equipment in a wide range of high-complexity settings that require precise particle measurements.