Consisted of one quartz and one magnesium fluoride plates
  with the optical axes orthogonally oriented. 
Air-spaced design with high transparency.
Very large wavelength bandwidths 200-1000nm.
Suitable for use with broadband dye or tunable
  femtosecond lasers.
 
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Achromatic Waveplate Specifications

Dimensions Tolerance: +/- 0.1 mm
Wavefront Distortion: < λ/8 @632.8nm
Retardation Tolerance: ±λ/60 - ±λ/100 ( in specified range)
Surface Quality: 20-10 scratch and dig
Coating: AR coating with R < 0.2% at the center wavelength
Holder: Anodized aluminum holder
Clear Aperture: > Diameter - 2.0mm (mounted)

Structure and
the optical axes