| 摘要 |
A method and apparatus for matching the transmission characteristics of two beam modulators (4,4') comprises radiation generating means (30); and the first and second beam modulators (4,4'), the radiation generating means causing beams of radiation (16,16') to impinge on each modulator. Control means (20) generates first and second control functions for application to the first and second modulators (4,4') respectively, the first control function cyclically varying between first upper and lower values (V1,V2) and the second control function cyclically varying between second upper and lower values (V3,V4) at the same rate and at the same time as the first control function, the range of the first and second control functions being such that the transmission characteristics of the first and second beam modulators overlap. Detecting means (18,19) detects the phase relationship between the radiation transmitted by the first and second beam modulators and having the higher or lower intensity and the first or second control function; and storage means (32) stores the second upper value (V3) when the detecting means determines a change in the phase relationship.
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