Crystalline Waveplates
For applications that require higher power/energy handling capabilities and superior UV and IR performance crystalline waveplates consisting of one or more plane-parallel plates of birefringent material is recommended. Waveplates can be constructed in many different ways, commonly achromatic and compound zero-order waveplates can be optically contacted (using Van der Waals forces), cemented or air spaced.
Typically, Mica is used for true zero-order (WPM) waveplates and quartz for compound zero-order. Improved performance is achieved by combining two spaced multiple-order quartz waveplates with the desired retardance difference. The fast axis of one plate is aligned with the slow axis of the other, cancelling the large retardance values and leaving only the desired fractional retardance difference (typically quarter- or half-wave). Thermal stability of compound zero-order quartz retarders is improved as temperature effects of the two retarders cancel.
For lower power/energy requirements we recommend our lower cost cemented compound zero-order waveplates (WPQ) or for higher powers our air gaped compound zero-order waveplate (WPQG).
Broadband Waveplates
For broadband performance Bi-Crystalline waveplates or Fresenel Rhomb prisms can be used. These achromatic retarders can span the UV, Visible, NIR and IR portions of the spectrum. Bi-Crystalline Achromats (CH/CQ & WPQW) are similar in achromatic performance to polymer achromats in the visible, but they excel in the IR. They have higher power handling capability than polymer achromats and can withstand higher storage temperatures. Their field of view is narrow compared to polymer achromats. Typically, they cannot be expected to meet their retardance accuracy for rays whose incidence angles exceed 1.5°
Two multi-order crystalline retarders, one made of crystalline quartz and the other magnesium fluoride, are combined in a subtractive mode to give an effective zero-order waveplate. By a careful choice of waveplate thicknesses, retardance dispersion is balanced to give a nearly constant retardance (in waves) over a broad range of wavelengths. The useable wavelength range is defined to give a retardance value within λ/100 of the nominal value. Custom designs with larger achromatic ranges or deeper UV wavelengths are available on request
Fresnel Rhomb Waveplates (FRB) can be used when working with broadband, multi-line or tunable laser sources. The process of internal reflection introduces a relative phase change between the two orthogonal field components. In glass a phase shift of 45° occurs at the particular angle of 54.6° and the Fresnel rhomb utilises this effect by causing the beam to be internally reflected twice, implementing a 90° (λ/4) phase change. By combining two rhombs end to end we can produce a λ/2 retardation. As the phase shift is a function of the slowly varying rhomb dispersion, the retardance change with wavelength is much lower than other types of retarder and hence can operate over a broad wavelength range. We offer holder specifically designed for mounting our fresnel rhomb waveplates. For a λ/2 plate (FRH-**2), the optical axis of the waveplate and rotation axis of the holder are aligned.
Quartz Depolarisers
(DEQ) convert linearly polarised input beams into unpolarised beams.
DEQ-1N type is made of single optical quartz plate. It has a wider transmission range, but has a larger beam deviation due to the 2 degree wedge shape.
DEQ-2S type consists of cemented plates of optical quartz and synthetic fused silica. It does not have beam deviation, but the transmission range is not as wide as the single type.
DEQ-2OP type consists of optical contact. It has a wider transmission range without beam deviation.
It is similar to waveplate and mounted in a frame of ø30mm diameter.
