A head-mounted-display with an optical combiner may introduce significant amount of distortion to the real world scene. The ability to accurately model the effects of both 2-dimensional and 3-dimensional distortion introduced by thick optical elements has many uses in the development of head-mounted display systems and applications. For instance, the computer rendering system must be able to accurately model this distortion and provide accurate compensation in the virtual path in order to provide a seamless overlay between the virtual and real world scenes. In this paper, we present a ray tracing method that determines the ray shifts and deviations introduced by a thick optical element giving us the ability to generate correct computation models for rendering a virtual object in 3D space with the appropriate amount of distortion. We also demonstrate how a Hartmann wavefront sensor approach can be used to evaluate the manufacturing errors in a freeform optical element to better predict wavefront distortion. A classic Hartmann mask is used as an inexpensive and easily manufacturable solution for accurate wavefront measurements. This paper further suggests two techniques; by scanning the Hartmann mask laterally to obtain dense sampling and by increasing the view screen distance to the testing aperture, for improving the slope measurement accuracy and resolution. The paper quantifies the improvements of these techniques on measuring both the high and low sloped wavefronts often seen in freeform optical-see-through head-mounted displays. By comparing the measured wavefront to theoretical wavefronts constructed with ray tracing software, we determine the sources of error within the freeform prism. We also present a testing setup capable of measuring off-axis viewing angles to replicate how the system would perform when worn by its user.

The Hartmann screen test (HST) is a well-known technique that has been used for many years in optical metrology. This thesis describes how the technique has been adapted to create a system for continuous in situ monitoring of the internal stress in thin films during plasma deposition. Stress is almost always present in thin films. Stress can affect the physical properties of film, and also influence phenomena which are important in the technology of thin film manufacture such as adhesion and crystallographic defects. For these reasons, it is very important to control and manage the film stress during manufacture of devices based on thin films. The commonest way to infer stress is to measure the change in substrate curvature that it produces. This is often done by comparison of substrate curvatures before and after deposition with surface profilometry, or interferometry. However, these methods are unsuitable for implementing during film deposition in the vacuum chamber. A novel method for measuring changes in curvature of the thin film substrate in situ has been developed, making use of the HST. An expanded laser beam is passed through a screen containing a number of small apertures, which breaks it up into several rays. After reflecting from the surface of the thin film wafer, the rays are received on an array detector as a spot pattern. Image processing is performed on the recorded spot images to determine the positions of spots accurately. Spot centre positions are recorded at start of deposition as a reference, then their displacement is tracked with time during deposition. The spot deflections are fitted to a theoretical model, in which the change in sample profile is described by a second-order surface. The principal axes of curvature of this surface and their orientation are obtained by a least-squares fitting procedure. From this, the thin film stress can be inferred and monitored in real time. Equipment using this technique has been designed and developed in prototype form for eventual use in the RMIT cathodic arc deposition facility. First experiments with a classic Hartmann screen configuration proved that the technique gave good results, but precision was limited by diffraction and interference effects in the recorded image which made determination of spot centres more difficult. A modified configuration was developed, in which a camera is focused on the Hartmann screen, giving much sharper spot patterns and improved resolution. Tests on the prototype system and comparison with other techniques have shown that it is possible to determine changes in sample curvature with a precision of approximately 0.01 m-1. This corresponds to stress changes of around 0.5 GPa for typical wafer and film thicknesses used in practice. The Hartmann screen test is straightforward to use and to interpret. Image processing and analysis of the recorded spot patterns can be automated and performed continuously in real time during thin film deposition. The system promises to be very useful for monitoring stress and thus controlling the deposition process for improved quality of thin film manufacture.

The testing technique with high dynamic range is required to meet the measurement of refractive wavefront with large distortion from test refractive surface. A general deflectometric method based on reverse Hartmann test is proposed to test refractive surfaces. Ray tracing of the modeled testing system is performed to reconstruct the refractive wavefront from test surface, in which computer-aided optimization of system geometry is performed to calibrate the geometrical error. For the refractive wavefront error with RMS 255 mu m, the testing precision better than 0.5 mu m is achieved.