Optical Elements

Abstract

Great variety of optical elements for visible domain available on the market is summarized in seven structural sections: mirrors, simple lenses, plates and prisms, retroreflectors, beamsplitters, imaging lenses, and microscope objectives. The first section presents mirrors: types of reflecting surfaces, broadband and narrowband coatings, mounting options, typical mounting mistakes. Polarization rotation after several reflections may be unexpected. Basic functionality of simple lenses is described, beginning from the lens maker equation for the thick lens. Its derivation, however, is postponed until the Chap. 12 where it is obtained from the matrix formalism (ABCD law). Spherical aberration for basic single lens geometries is presented graphically and its minimum for the plano-convex configuration is explained. Best practical lens mountings are summarized and consequences of birefringence are emphasized in context with magneto-optics (Chap. 8). Spectral transparency of various optical materials should be considered as the first priority for the ultra-violet domain. High power applications require some simple but important know-how in order to avoid breakdowns. In aspheric lenses, spherical aberration may be almost completely removed by optimizing conic coefficients. Ray tracing is presented in the form of a picture, while detailed mathematics and computer codes are left to Chap. 12. Achromatic doublets is the better choice for wide spectrum, and the front surface must be chosen wisely to obtain the design performance. Steinheil and Hastings triplets are considered as the most popular choice for relay optics. Optical flat plates and prisms are discussed starting from the defocusing they produce, being installed in the focused rays. Simple practical formulas are given for estimating deviation of rays, passing through tilted flats. Along with an ordinary dispersive prism that is both chromatic and deflecting, some special types of combined prisms may be helpful to reduce either chromaticity or deflection. Functionality of reflecting prisms like penta, Amici, Porro, Dove, and Littrow is explained. The concept of the corner cube reflector can be easily understood geometrically, using three-dimensional vector presentation. Its imaging and polarizing peculiarities are also explained in context with interferometers (Chap. 6). The section devoted to beamsplitters summarizes performance of the basic types: plates and cubes, including rather rare type—the energy separator. Among the imaging lenses, the C-mount TV lens is most frequently used. Design, formats, and recommended mounting techniques are carefully explained. Physical idea of the telecentric lens—a very popular element in machine vision—is presented in succinct form with minimum mathematics, and the design of multi-element commercial products is demystified. The last section provides practically indispensable but not widely published specifications for microscope objectives, like mounting thread diameters, tube lens focal distances, marking legend, etc. Finally, the so-called inspection objective is introduced—a handy tool to quickly assemble an electronic imaging system.

Optical manufacturers offer a wide variety of optical elements, covering almost all possible laboratory applications. The problem is not how to design what you want but how to choose what you need.