apparatus in accordance with the present invention is desirably employed as an oscillator in a laser equipment layout of an oscillator amplifier type for substantially increasing the energy of the emitted radiation in such an arrangement illustrated in fig7 amplifier 19 is provided by a further nd yag module of a standard type while the reference number 15 indicates the apparatus according to the invention which serves as the oscillator blocks 15 and 19 are coupled in a conventional manner using optical system consisting of two facing total reflection mirrors 16 arranged at about 45 u00b0 relative to the optical axes of the blocks and a pinhole 17 on the optical path between the two mirrors for blocking undesired components of the laser beam as well as a lens 18 downstream of the mirrors for concentrating the beam onto amplifier 19 a further lens 20 is provided downstream of x amplifier coupling the beam into the optical fiber using an optical fiber connector 21 the time patterns of some pulses obtainable by and apparatus in accordance with the present invention are included herein by way of example in this connection fig4 5 and 6 show laser pulses having durations of 500 1000 and 1800 nanoseconds at half height corresponding to a cavity length modified through the successive insertion of optical fibers having lengths of about 13 about 30 and about 35 meters respectively and a core diameter between about 300 and about 400 microns the energies of these pulses are greater than a u201d 100 mj and are already suitable for many material cleansing applications if necessary the emission can be further increased up to about one joule per pulse and even greater by including an additional laser.