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Achromatic Prism-Pair Beam Expander

IP.com Disclosure Number: IPCOM000116337D
Original Publication Date: 1995-Aug-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 3 page(s) / 75K

Publishing Venue

IBM

Related People

Dewey, AG: AUTHOR

Abstract

Commercially available prism pairs are designed with identical prisms oriented so that the output beam is parallel to the input, as shown in the Figure.

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Achromatic Prism-Pair Beam Expander

      Commercially available prism pairs are designed with identical
prisms oriented so that the output beam is parallel to the input, as
shown in the Figure.

      The prism pair is not achromatic, and when used with diode
lasers - their main application - there are potential problems
because the laser is not a stable, single-frequency device.
Multimode laser operation causes chromatic aberration, and mode
hopping causes a shift in the output beam.  The obvious way to make
the circularizer achromatic is to make each prism an achromatic
bonded pair of prisms.  However, this reduces the power of each
prism, thus requiring higher incidence angles for the same
magnification.

      By making the two prisms from different materials whose indexes
and dispersions satisfy a simple formula, the pair may be made
approximately achromatic.  Using lens design software, it would be
possible to refine the initial design to make the pair achromatic at
the desired laser wavelength.  The following variables are defined:
  &beta.&sub1., &beta.&sub2., &theta.&sub1.  and &theta.&sub2.
  are the angles shown in the Figure
  &Delta.&sub1. = clockwise deviation produced by first prism
  &Delta.&sub2. = counter-clockwise deviation produced by second
prism
  n&sub1. = index of first prism
  n&sub2. = index of second prism

At the design wavelength with n&sub1. = n&sub2. = n, it follows
that &theta.&sub1. = &beta.&sub1. and &Delta.&sub2. = &D...