Volume 5, Issue 3 - Aspheric optics / Guest Editors: Sven Kiontke and Santiago Royo

Beam shaping is a field of research with growing importance. Therefore, a new refractive beam shaping system is presented. The knowledge gained from analyzing patent systems was used to derive our own improved design. It is compared to a patent system, and some selected results are presented in this work. Furthermore, possibilities to scale the entrance and exit beam diameters with the help of SPA™ Beam Expander Kit and SPA™ AspheriColl (both from asphericon GmbH, Jena, Germany) are shown, so that a modular top-hat generation is achievable. Additionally, the large spectral range in which the beam shaping system is applicable is demonstrated, and it is demonstrated how the beam shaping system can be used to improve the performance of other optical elements that require a top-hat beam profile.

Metrology revealing the form deviation of an aspheric surface is a fundamental part of all different production processes of aspheric lenses. Different processing steps have different requirements for the production. A selection of measuring instruments commonly applied in these processes is presented. This contains tactile and optical pointwise measuring instruments and laser interferometer systems. The principle functionality and the properties are presented. An overview of the application of these systems in different production processes is given. In order to show comparability, measuring results of the different types of systems are presented.

Introducing aspheric lenses in optical design broadens the horizons of possibilities and opens up new way to correct aberrations or creating effects that are not possible otherwise. Manufacturing these aspheric surfaces has come a long way during the last 15 years. This article discusses the state of the art concerning optical design, manufacturing, surface form tolerances and roughness to show the possibilities in hand.

Efficient performance assessment is essential during the design of systems involving complex aspheres. We present new classes of pupil sampling schemes that, with a reduced number of rays, yield accurate estimates of the RMS wavefront aberration over a circular pupil. It turns out that the number of samples in the pupil can be reduced by a factor of about 0.7, and these ideas can also be expected to lead to a similar additional reduction factor when averaging over the field and color. Beyond that, analysis of a patented lens system is used to establish the path to further significant reductions.

Injection molded plastic lenses have continuously improved their performance regarding optical quality and nowadays are as usual as glass lenses in image forming devices. However, during the manufacturing process unavoidable fluctuations in material density occur, resulting in local changes in the distribution of refractive index, which degrade the imaging properties of the polymer lens. Such material density fluctuations correlate to phase delays, which opens a path for their mapping. However, it is difficult to transfer the measured variations in refractive index into conventional optical simulation tool. Thus, we propose a method to convert the local variations in refractive index into local changes of one surface of the lens, which can then be described as a free-form surface, easy to introduce in conventional simulation tools. The proposed method was tested on a commercial gradient index (GRIN) lens for a set of six different object positions, using the MTF sagittal and tangential cuts to compare the differences between the real lens and a lens with homogenous refractive index, and the last surface converted into a free-form shape containing the internal refractive index changes. The same procedure was used to reproduce the local refractive index changes of an injected plastic lens with local index changes measured using an in-house built polariscopic arrangement, showing the capability of the method to provide successful results.

In many industrial applications, an inline measurement of a production process poses a difficult challenge for any optical system. Therefore, telecentric optical systems are being used to ensure an independence of the magnification of the object from the working distance. Usually, telecentric optical systems are impractical for inline applications with large objects due to the size of the telecentric optical system, which has to be larger than the object. Therefore, a new approach of telecentric line scanning systems was developed to gain access to this advantage.