EFFECT OF INTENSE UV FLASHES FROM LASER DISCHARGES IN GASES - OBSERVATION OF A FAST-RISING PHOTODISSOCIATION HALO LEADING A SHOCK-WAVE

The photodissociation of gases near intense laser sparks have been stu died experimentally. The power and flux density of UV light have been estimated. It is shown on the basis of the results that the ''kern'' o f the breakdown is an intense source of UV light, in fact, a source wi th a record-high flux density. It is also shown that over a short time , on the order of the length of the laser pulse, a new physical effect is observed: a fast-rising halo of intense photoionization of the gas . This halo leads the shock wave and generates its own shock wave. It is shown that there is a bleaching of the media for UV light because o f intense photodissociation and photoionization. Chlorofluorocarbons a re used as examples to demonstrate the fate of polyatomic impurities i n a background gas subjected to UV light. Some new possibilities for r emoving harmful pollutants from the atmosphere by means of new sources of UV light (excimer lamps and the radiation from lasers, laser spark s, and laser plumes) are discussed. An analogy is drawn between the ef fect of the ''kerns'' of laser sparks and that of the streamers of mic rowave discharges.