Model 66061 Aspherab in 66112 Bench Mount
Negligible spherical aberration and highly efficient light collection are the benefits of our Aspherab Condensers. AspherabsTM are computer designed four-element lens assemblies used for collimation of high intensity, broadband radiation, or for reimaging. The individual lens elements in our Aspherabs are air spaced, so you don't have the power handling and spectral limitations associated with epoxies.
AspherabsTM are comprised of four elements, three positive elements to collimate the collected light, and one negative element to balance the spherical aberration of the positive elements. The elements are housed in a 3/4 inch (86 mm) diameter lens barrel. The clear aperture of most of the assemblies is 2.7 inches (69 mm). The rear plate of the lens holder is made of ceramic. This withstands the high temperatures of arc and quartz tungsten halogen lamps to 1000 W.
For most applications, you don't need an Aspherab; a simple two-element lens system, such as an achromat is often sufficient. Aspheric lenses can almost completely eliminate spherical aberration, however, UV transmissive aspheres are very expensive. We sell Pyrex® aspheric lenses, for such needs.Aspherabs are for demanding applications that require a highly focused spot. Table 1 and Fig.1 illustrate this and compare an Aspherab to other lens systems.
The spherical aberration of a condenser increases as the angle of collection increases. This is a significant problem with the wide F/0.7 collection angle. A condenser with a spherical aberration forms a convergent, rather than a parallel, beam when a point source is positioned at its focus. When you try to refocus this beam, you will get a diffused blur rather than a bright point. In other words, when a condenser with spherical aberration is exposed to an ideally parallel beam it forms a diffuse spot instead of a point image.Spherical aberration is quantified for each zone of a lens by the difference between the focal lengths for the rays passing through the zone and rays passing close to the lens center. For comparative purposes we can define the percentage of spherical aberration by:
Where: Fe = Focal length for rays in a circular zone with radius r = K*R, where R = full radius of the lens. Fc = Focal length for rays at the center of lensFc and Fe are measured with the lens exposed to an ideally parallel beam (i.e. with source at infinity).
We offer four models of Aspherab differing in the material and focal length of the lens elements. We list these in Table 2. If you are using an Aspherab® on an Oriel® Lamp Housing from Newport, you must also consider the bulb diameter and wattage of the lamp.
Due to the surface reflections from each element, overall axial transmittance for Aspherabs is 70 to 75%. On special request, we can coat the elements with an anti-reflection coating on both surfaces, increasing transmittance to ~85%. If you are focusing a small collimated beam (1.3 inches or smaller), we suggest you use our Fiber Bundle Focusing Assemblies for Oriel Light Sources.
The 66112 holds an Aspherab® and mounts to an optical table or baseplate. Slots in the base of the 66112 allow coarse positioning of the focus. To match the optical axis height of our large lamp housings, use spacers or a vertical translator.
We sell Arc and QTH sources with integral Aspherab® Condensers. To retrofit non-Aspherab® sources with an Aspherab Condenser, contact an Applications Engineer for the proper mounting hardware.