Abstract: A method and apparatus for perforating a well casing and surrounding formation are disclosed. The perforating apparatus includes a laser source for projecting a high intensity laser beam transversely through the well bore and surrounding formation and a nozzle assembly for injecting exothermically reactive gas along the path of the laser beam. The gas stream shields the output lens of the laser while accelerating the rate of laser beam penetration. The laser beam is actuated as the exothermic gas is discharged through the nozzle during a penetrating cycle, and the laser beam is interrupted while the exothermic gas is discharged during a melt ejection cycle following the penetrating cycle. When the laser tool is used for perforating materials such as concrete, stone and sand which do not react exothermically with the gas, a fluxing agent is discharged into the flow path of the nozzle and is entrained by the exothermically reactive gas during the penetrating cycle.