A novel method and apparatus is presented wherein an output of infra-red solid state laser or multiple of such lasers is quadrupled in frequency to obtain a laser output that emits energy in ultra violet C spectrum, and wherein this energy is then provided within an air duct as is normal in HVAC systems so as it kill pathogens that are airborne and being carried through the conduit. Further such a method reduces production of ozone, detrimental to human health and produced in other means of generating UVC and provides ease of control of such energy so as to maintain the required energy at a steady level for prolonged period of time.
