Single Fresnel Rhomb Quarter Wave Retarder

A single Fresnel rhomb can be manufactured as a quarter wave broad band achromatic retarder by judicious selection of the rhomb angle. Note that the rhomb produces a lateral offset to the input beam. The retardation of a single quarter wave BK7 rhomb (FRQ-BK series) varies smoothly from 91·2° @ 400nm to 89·6° @ 700nm. The retardation of a single quarter wave fused silica rhomb (FRQ-SI series) varies from 93·0° @ 230nm to 86·0° @ 400nm.

Double Fresnel Rhomb Quarter Wave Retarder

Two eighth wave rhombs can form an achromatic quarter wave retarder with no lateral offset to the input beam.

Quarter Wave Fresnel Rhombs Retardation

Four designs are available for quarter wave Fresnel rhombs: single BK7 rhomb (FRQ-BK series) for use from 400nm to 700nm, single fused silica rhomb (FRQ-SI series) from 230nm to 400nm, a double CaF2 rhomb assembly (FRDQ-CA series) for use from 190nm right through to 2mm, and the new double LiF rhomb assembly (FRDQ-LI series) optimised for 120-400nm. This design has the advantage that it does not introduce a lateral beam shift.

Double Fresnel Rhomb Half Wave Retarder

Two quarter wave rhombs bonded together form an achromatic half wave retarder with no lateral offset to the input beam. Both BK7 half wave retardation Fresnel rhomb pairs (FRDH-BK series) and fused silica half wave retardation Fresnel rhomb pairs (FRDH-SI series) are optically contacted for high power handling capacity. The variation of retardance is exactly twice the values quoted above for the single quarter wave rhomb.

BK7 (360-900nm)

BK7 Fresnel rhombs are optically contacted for high power handling, thereby limiting the optical loss to the 2 external glass/air surfaces. The retardation of a double quarter wave BK7 rhomb pair (FRDQ-BK series) varies smoothly from 91·0° @ 360nm to 89·6° @ 900nm.

Silica (220-550nm)

Fused silica Fresnel rhombs are optically contacted for high power handling, thereby limiting the optical loss to the 2 external silica/air surfaces. The retardation of a double quarter wave silica rhomb pair (FRDQ-SI series) varies from 92·0° @ 220nm to 88·3° @ 550nm. Note that the overall length:aperture ratio is approx. 13:1.

Calcium fluoride (190-900nm)

Calcium fluoride Fresnel rhombs are air spaced. The retardation of a double quarter wave calcium fluoride rhomb pair (FRDQ-CA series) varies from 93·6° @ 190nm to 89·0° @ 900nm. Note that the overall length:aperture ratio is approx. 13:1.

Lithium fluoride (120-400nm)

Lithium fluoride Fresnel rhombs are air spaced. The retardation of a double quarter wave lithium fluoride rhomb pair (FRDQ-LI series) varies from 99·3° @ 120nm to 86·8° @ 400nm. Note that the overall length:aperture ratio is approx. 13:1.

Mounts

Fresnel rhombs can be supplied unmounted as free components or mounted as shown. To specify mounted Fresnel rhombs, simply add suffix: