Using high power lasers to improve material properties is one of the most important industrial applications of lasers.  Lasers can transmit controllable beams of high energy radiation for metalworking.  Primarily, the laser can generate a high power density that is localized and controllable over a small area.  This allows for cost effective and efficient energy utilization, minimizes distortions in surrounding areas, and simplifies material handling.  Since the laser pulse involves the application of high power in short time intervals, the process is adaptable to high speed manufacturing.  The fact that the beam can be controlled and focused, allows parts having complex shapes to be processed.  Also accuracy, consistency, and repeatability are inherent to the system. 
Improving the strength of metals by cold working undoubtedly was discovered early in civilization, as ancient man hammered out his weapons and tools.  Shot peening has been used as a means to improve the fatigue properties of metals.  Another method of shock processing involves the use of high explosive materials in contact with the metal surface. 
Copending patent application Ser.  No.  334,612 discloses the use of a split beam to simultaneously laser shock the opposing two sides of the target material.  However, the split beam method has several inherent disadvantages.  1.  To shock process two sides simultaneously requires that the laser generate twice the power as for only doing one side.  High powered lasers are extremely expensive and such cost may be prohibitive.  2.  The split beam method requires the use of precisely calibrated and positioned lenses and mirrors.  This precision may be difficult to achieve in a high production manufacturing environment.  3.  In many applications only one side of the metal substrate is subject to fatigue, so there is no need to use the split beam method.  In other applications, it is not possible to have line of sight access to both sides of the fatigue critical region for split beam processing. 
The object of this invention is to provide an effective method of shock processing metal substrates from one side only with high pressure laser pulses of short duration.