Patent ID: 7259914

Claim:
An apparatus for attenuating the power of a laser beam from an initial level to a lower target level, comprising: first and second polarizing beamsplitters and at least one reflector, each of said polarizing-beamsplitters arranged to transmit radiation plane-polarized in a first orientation and reflect radiation plane-polarized in a second orientation; said first and second polarizing beamsplitters and said at least one reflector being arranged such that said first polarizing beamsplitter receives the beam to be attenuated and divides the beam into a first component transmitted along a first path to said second beamsplitter and a second component reflected along a second path, including said reflector, to said second beamsplitter; said first and second beamsplitters and said at least one reflector being further arranged such that any portion of said first beam-component transmitted by said second polarizing beamsplitter propagates along a common path with any portion of said second beam-component reflected by said second polarizing beamsplitter; first and second polarization rotators located in respectively said first and second beam paths wherein said first polarization rotator is rotatable about an axis aligned with said first beam path and said second polarization rotator is rotatable about an axis aligned with said second beam path in a manner to selectively vary the polarization orientation of said first and second beam components; and means for synchronously controlling the orientation of the polarization rotators so that the sum of the power of said portion of the first beam-component transmitted by said second polarizing beamsplitter and said portion of said second beam-component reflected by said second polarizing beamsplitter corresponds to said target level and will remain substantially at that target level even if an initial polarization state of the laser beam varies.