The authors' experience with the application of the needle optimization technique to the design of optical coating is summarized. A physical interpretation of the technique is provided, and its main features are identified. Guidelines on the application of the needle optimization technique to various types of design problems are given.

Application of the needle optimization technique to the design of optical coatings.

Past research on all-dielectric nonpolarizing beam splitters is reviewed. It is shown that, for a 50-nm spectral region, it is possible to design and manufacture a two-material nonpolarizing plate beam splitter for use at an angle of 45° (with a measured rms reflectance of 0.50 ± 0.01 for both s- and p-polarized incident light).

Design and manufacture of all-dielectric nonpolarizing beam splitters

The reflectance and transmittance of dielectric thin films at oblique angles of incidence have strong polarization effects. For some applications these effects are undesirable. A nonpolarizing beam splitter design concept is shown, which is based on the fact that in a quarter-wave stack at λ0 two effective indices that obey the Brewster condition affect only the spectral performance of the s state at λ0. This property is used as a design tool. The concept can be applied to a wide range of angles and transmittance values, with the use of effective quarter-wave layers of at least three different materials. A few examples are elaborated where these values are designed and optimized to give either Tp = Ts or Tp + Ts = constant, in the vicinity of λ0.

Design of a nonpolarizing beam splitter inside a glass cube.

Truly polarization-independent beam splitters for 0.6328- and 10.6-microm (He-Ne and CO(2)) laser radiation are designed using single-layer-coated (Cleartran) ZnS and Ge prisms. These devices are found to be reasonably achromatic, their reflectance (beam-splitting ratio) can be varied over a wide range with little accompanying polarization error, and they are tolerent to small film-thickness and film refractive-index errors.

Variable-reflectance thin-film polarization-independent beam splitters for 0.6328- and 10.6-microm laser light.

The design and construction of a hexagonal interferometer beam splitting prism is described in which the light falls onto the all-dielectric partially reflecting coating at an angle of 30° with respect to the normal. For a beam that undergoes one transmission and one reflection by the device, the average effective transmittance ½(T‖R‖ +T⊥R⊥) in the 0.55–0.75-μm spectral region is ∼0.23. This quantity is not strongly dependent on the plane of polarization of the incident light, nor on small changes of the angle of incidence from the design angle of 30°. Ways to improve further the performance of the beam splitter are indicated. Coating designs for other angles of incidence are also given.

Beam splitter for a wide-angle Michelson Doppler imaging interferometer.

A three-step design procedure is developed for dielectric stacks which are required to be nonpolarizing for a given wavelength λr and angle of incidence θ0,r, at which the reflectance Rr is prescribed. The method leads to solutions in which only three layer materials occur and can be applied for a wide range of values of θ0,r and Rr. The media can be chosen from the available coating materials. Furthermore, the procedure offers the possibility of optimizing with respect to the behavior of the reflectance in the neighborhood of λr and θ0,r. An example is elaborated, and its results are compared with an actually produced coating.

C. M. de Sterke

Papers

Nonpolarizing beam splitter design