Zoom Objective Research Articles

基于变形镜的三反射离轴变焦物镜设计

基于变形镜的三反射离轴变焦物镜设计

Distortion correction of all-reflective unobscured optical-power zoom objective

We present the correction of distortion for a novel type of an all-reflective zoom objective. The all-reflective unobscured optical-power zoom (OPZ) objective with four mirrors has been previously designed and presented. The magnification of the OPZ can be varied by changing the curvatures of the first and the last mirror, which results in a zoom factor of 3. However, the objective exhibits significant distortion. For the unobscured design principle, we present the basic distortion model with its different types of distortion. Based on simulation data of the objective design, we optimized the parameters of the model and verified that model by applying it to images taken with the objective.

Design of an all-reflective unobscured optical-power zoom objective

A novel design for an all-reflective unobscured optical-power zoom (OPZ) objective with a zoom factor of 3 is presented. In contrast to OPZ objectives based on liquid lenses, all-reflective objectives use only reflective elements and are therefore free of chromatic aberrations. Thus, they can be used for a wide spectral range or in combination with image sensors that differ in their spectral characteristics. To avoid a decrease in image contrast encountered in on-axis designs with central obscuration, an unobscured off-axis or "Schiefspiegler" approach is adopted. The effective focal length of the objective is changed by two deformable mirrors, each with one actuator only. The simulated final design shows adequate image quality over the whole zooming range. Before starting the complex and cost-intensive development of deformable mirrors with the size, curvature, and dynamic range needed, the optical design should be evaluated first with respect to the practical achievable optical performance. Therefore, optomechanical setups with ultraprecision-manufactured solid mirrors were realized for three different focal lengths.

Optical characterization of thin films non‐uniform in thickness by a multiple‐wavelength reflectance method

AbstractAn original method enabling us to characterize the non‐uniformity of thin‐film thickness is described. This method employs the interpretation of data obtained by multiple‐wavelength reflectometry (MWR). Within this MWR method the values of the reflectance are measured for several wavelengths in many points lying along the area of the film. The spectral dependence of the refractive index of the material forming the film is determined using variable‐angle spectroscopic ellipsometry (VASE). The MWR method is then used to evaluate the values of the thickness along the area of the non‐uniform film under investigation. Within the experimental set‐up employed for applying the MWR method, a multi‐wavelength laser is used as a light source. A CCD camera equipped with a zoom objective is utilized as a detector. A suitable beamsplitter allows to measure the values of the relative reflectance of the film against a reference sample with known reflectance. By using the set‐up employed it is possible to characterize the thin‐film spreading over large areas of substrates. Copyright © 2002 John Wiley & Sons, Ltd.