Modifying coherent radiation

摘要

A method and apparatus for modifying the phase characteristics of a coherent beam of radiation (7) are described. The apparatus comprises a laser (6) for generating a coherent beam of optical radiation (7). A support (1) for a record medium (1') sensitive to the radiation is provided, the beam of radiation (7) and the record medium (1') being relatively movable whereby the beam of radiation scans the record medium. First modulation means including an E/O modulator (8) and beam computer (9) is provided for modulating the beam (7) in accordance with image information. Second modulation means including an A/O modulator (10) or phase diffraction grating is responsive to a control function generated by a control function generator (11). The control function has a frequency which is repeatedly swept through a range of frequencies at a relatively fast rate to control the transmission characteristics of the grating. A substantially spatially incoherent beam of radiation is transmitted from the phase diffraction grating.