Abstract
The authors delivered 20 MW laser pulses through an optical fiber with a core diameter of 1.5 mm and a lengthof 5 m, using a beam homogenizer which divided laser beam into 7×7 squares and folded it up into a singlesquare of 0.81×0.81 mm at the front entrance of the fiber. The laser pulses, which were emitted from afrequency-doubled Nd: YAG laser with an energy of 138 mJ and a pulse duration of 5 ns, were irradiated to theall silica step index multi-mode fiber via the homogenizer. The peak intensity of laser pulses reached 42 TW/m2 (4.2 GW/cm2) at the fiber entrance. As an example of practical applications, we demonstrated the feasibilityof fiber-delivered laser peening through experiments in which the residual stress of an SUS304 test samplewas improved from tensile to compressive.
