Aspherical lenses

Even if the first attempts at making aspherical lenses had been successful, chromatism (Fig. 6, which was not properly understood, would have prevented such lenses to deliver acceptable images anyway. Solutions to the problem of chromatic aberrations had been delayed by Newton himself, who incorrectly... 

Photopolymerization and photocrosslinking processes have been in use for many years in the electronics industry, for example in the making of printed circuit boards and in the fixation of color dots in TV tubes. More recent applications of light-induced chain crosslinking polymerization processes are the replication of optical discs (1,2) of aspherical lenses (3,4) and the in-line coating of optical fibers (5,6). 

Lens. A transparent object with two refracting surfaces. Usually the surfaces are flat or spherical (spherical lenses). Sometimes, to improve image quality. Lenses are deliberately made with surfaces which depart slightly from spherical (aspheric lenses). 

Simple systems such as that shown in Fig. 5.11 yield an excellent optical efficiency, and are almost free of pulse dispersion and wavelength-dependent pulse shift. Another benefit is that the detection path is almost free of polarisation effects compared to monochromator-based systems. The high numerical aperture of the light eollection system further reduces the influence of the rotational relaxation see Fig. 5.9. With aspheric lenses an NA of around 1 can be achieved, and at an NA this high the polariser in the detection path can often be omitted. In the setup in the left graphic of Fig. 5.11, residual depolarisation effects can be removed by slightly tilting the polarisation direetion of the laser. 

Since polymers can be easily molded into aspheric lenses with high productivity and low cost, they have been applied positively. In order to diminish shift of focal distance... 

Magnetorheological finishing of aspheric lenses with interferometric measiffements integrated in the process (Kunzmann et al. 2005)... 

ELID grinding was employed to process several t5q3es of materials like ceramics, hard steels, ceramic glass, ceramic coatings, and so forth, with various shapes (plane, cylindrical external and internal, spherical and aspherical lenses, etc.) and dimensions. Various ELID applications and their reference literature are listed here ... 

The replication of aspherical lenses, used for laser read-out of these discs. 

Fi. a and b. Schematic drawing of Compact Disc light pens with conventional optics (a) and with aspherical lenses (b). The laser beam passes through a beam-splitting prism, is focused on the disc and the reflected beam is directed towards a set of 4 photodiodes. (From Ref. with permission)... 

The replication process for aspherical lenses for CD players is shown schematically in Fig. 9 A small quantity of hquid coating is applied to the surface of a spherical glass substrate. This in turn is pressed into a quartz glass mold with the desired aspherical profile. The quality of the mold is decisive for the performance... 

Most geometric aberrations can be eliminated by a single lens, if its surface is not spherically shaped, but is an asymmetric rotation surface. However, preparation of such surfaces is a rather complicated technical problem that makes difficulties for wide diameter aspherical lenses. 

Fig. 8 Experimental result of linear shrinkage (a) Sample plate at 125n for 12 hrs (b) aspheric lenses at 153 C for 1 hr (c) same as (b) but for 4 hrs.

Another relevant extension of the pinhole SANS technique is the focusing of a small source aperture by refractive lenses in front of the sample onto high-resolution deteaor. Aspherical lenses of Mgp2 are the latest development permitting... 

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