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Title
Sine Condition Test Plus: Development of a novel alignment method using deflectometry and the sine condition test
Abstract
An appropriate alignment plan for building an optical system is crucial to obtaining good image quality. Even the simplest form of telescope requires an alignment process for properly positioning its optical elements to avoid aberrations. It is necessary to aim for accurate measurements of the misalignment aberrations to achieve an accurate alignment. This dissertation introduces the Sine Condition Test Plus (SCT+), a novel alignment method that combines deflectometry and the sine condition to create a highly advantageous alignment approach. The SCT+ is based on relative measurements with an on-axis test setup composed of a pixelated camera and a monitor. One major advantage of this new method is that, unlike other conventional methods, it eliminates the necessity of moving a test instrument to multiple field points. It can measure the state of alignment for both off- and on-axis performances with a simple on-axis setup. Also, it can be a cost-effective option for certain projects as a monitor and a camera may be substituted for the return optic and the interferometer required in a conventional interferometric method.
Firstly, the concept of the SCT+ is explained using a meter-class Ritchey-Chrétien telescope as an example. Then, the concept's validity is presented by presenting telescope alignment simulations, including potential errors in real systems, such as uncertainties in the monitor, camera distortion correction, and fabrication errors in optics. The simulation results show that this method has a larger dynamic range than the interferometric method. Even considering realistic levels of noise, the SCT+ works successfully, as there are two orders of magnitude improvements in the state of alignment after three iterations of alignment.
In addition, this dissertation presents experimental results of the SCT+ applied to an air-space doublet system. The experimental demonstration fulfills two major goals: to check the validity of SCT+ with the interferometric method and to show that we can predict the alignment of the perturbed system with the SCT+. The misalignment aberrations measured with the SCT+ matched the interferometer measurements within the calculated uncertainty level. Then, the alignment state of the air-spaced doublet system converged after a few iterations. These results strongly support the idea that the SCT+ possesses the potential to offer convenience and effectiveness in optical alignment. The new method does not require multiple field point movements, provides a large dynamic range, only requires a pixelated camera and monitor, and eliminates the need for accurate positional adjustments of the testing equipment.