Arrangement for shaping a laser beam and for reducing the coherence thereof

Claim 1

An arrangement for shaping a laser beam having a predetermined coherence length and for reducing the coherence thereof, the laser beam having a first cross section and the arrangement comprising: a transparent carrier block having two mutually opposite planar surfaces approximately parallel to each other and at an angle to the laser beam and said planar surfaces being disposed at a distance from each other which is greater than half of said coherence length; first and second mirrors being applied to corresponding ones of said planar surfaces to reflect said laser beam therebetween; said first mirror being fully reflective and said second mirror being partially reflective and partially transmissive so as to multiply reflect said laser beam between said first and second mirrors and to transmit a component beam through said second mirror with each reflection with no gap between mutually adjacent component beams transmitted through said second mirror and which are reflected a different number of times in said arrangement accompanied by a corresponding intensity change for each reflection; said component beams conjointly defining a composite beam of reduced coherence exiting from said second mirror and having a second cross section greater than said first cross section; and, said second mirror being reflectively coated in varying amounts over the width thereof to compensate for said intensity change with each reflection thereby making said composite beam more homogeneous across said second cross section.