MgF2 Retarders: Zero Order

The retarders consist of two single plates which are assembled their optical crystal axes in crossed position. The working principle is identical with that of the zero order retarders made from crystal quartz. The advantages of MgF2 are its broader transmission range of 120 nm – 7µm and the lack of optical activity which can be troublesome in applications which require a high degree of polarization.
The thickness of each plate is about 0.8 mm (total thickness approx. 1.6 mm). The wavefront distortion is λ/10 (at λ = 550 nm) and the wedge error is smaller than 2’’. The accuracy of the path difference is ± 2 nm.
The usable spectral range for a single zero-order plate is much smaller than the transmission range and depends on the required accuracy of the retardation. As for the zero order retarders made of quartz crystal the error of the path differnce is smaller than the production tolerance if the wavelengths deviates by less then 4 nm (λ/2 plates) or ±8 nm (λ/4 plates) from the design wavelength. A deviation considerably larger than the production tolerance is acceptable in many applications resulting in a correspondingly broader usable spectral range.
The deviation ΔR of the path difference from the nominal value R (both in nm) due to a temperature change by ΔT (in K) or due to tilt by Δφ (in degrees) can be estimated as follows:

ΔR≈-(4•10^-5K^-1)•R•ΔT
ΔR≈±(1.5 nm/Grad²)•Δφ²

For λ/2 plate at 633 nm the deviations will be smaller than the production tolerance for a temperature change up to ±160 K order for tilt angles up to ±1.2°.
The plates are delivered without AR coating mounted in a cylindrical holder made of anodized aluminum and engraved with the direction of the fast axis, the path difference and the design wavelength.
Zero order retarders are available either joined by optical contact (cementless) or with air space between the plates (version L). The air spaced version is particularly suited for high power lasers and for applications with strong thermal or mechanical disturbances.

Plates with optical contact

Plates with air space

Important note

Please specify required wavelength when ordering.
The prices apply to standard wavelengths according to the following table:

Available on special order

• non-standard wavelengths have a surcharge:
  clear aperture 9.5 mm and 14.5 mm → RZM 0.1
  clear aperture 19.5 mm and 24.5 mm → RZM 0.2
• Antireflection coating → on request
• other dimensions → on request
• accuracy of retardation ± 1nm → RZM 0.5