Laser beam clean-up using mutually pumped phase conjugation

Abstract

A mutually pumped phase conjugator (MPPC) is used to remove spatial distortions from a high power laser beam. The high power beam with its 'dirty' spatial profile is directed into one side of the MPPC. A spatially clean beam at the same nominal frequency as the high power beam is output from a continuous wave (CW) laser and directed into the opposite side of the MPPC. As a result of mutually pumped phase conjugation, the MPPC returns a phase conjugate beam that retains the clean spatial profile of the CW beam but acquires the temporal characteristics of the high power beam. A Faraday isolation system may be used to separate the phase conjugate beam from the incident CW beam to provide an output beam having a clean spatial profile. If desired, the high power beam can be transformed into an image bearing output beam simply by modifying the incident CW beam with a transparency or spatial light modulator. If the average intensity of the dirty beam is much higher than that of the CW beam, only a small fraction of the dirty beam needs to be directed into the MPPC for beam clean-up. The larger fraction of the dirty beam can be directed into a photorefractive crystal for two-beam coupling with the clean beam output by the MPPC. By means of photorefractive two-beam coupling, energy from the dirty high power beam serves to amplify the clean beam, thereby improving the overall energy efficiency of the laser beam clean-up system.