Krieger waves were a potential energy source developed by Dr. Nel Apgar in the 2360s. The waves were created by converting a series of energy pulses from a lambda field generator on the surface of Tanuga IV into a form of radiation by a Krieger wave converter. Krieger waves are capable of melting through duranium and could be harnessed to produce a similar energy signature to that of a hand phaser. Starfleet had much interest in acquiring this technology, but Dr. Apgar denied having developed Krieger waves since he had become motivated by profit, and was developing the technology to be used as a weapon. Apgar's research on Krieger waves ended in 2366 when he was killed in an explosion that destroyed the space station on which he was conducting his research.
Commander Will Riker and Lieutenant Commander Geordi La Forge were sent to Apgar's research station to determine whether or not Starfleet should grant Dr. Apgar's request for extra dicosilium in his research.
The explosion which destroyed the station was the result of an energy pulse which Dr. Apgar used in an attempt to kill Commander Riker, who believed that Riker knew of his intentions to turn the Krieger wave converter into a weapon. The pulse ricocheted off of a transporter beam from the USS Enterprise-D and into the Krieger wave converter, destroying it and the station. (TNG: "A Matter of Perspective")