A novel Vision ray metrology technique is reported that estimates the geometric wavefront of a measurement sample using the sample-induced deflection in the vision rays. Vision ray techniques are known in the vision community to provide image formation models even when conventional camera calibration techniques fail. This work extends the use of vision rays to the area of optical metrology. In contrast to phase measuring deflectometry, this work relies on differential measurements, and hence, the absolute position and orientation between target and camera do not need to be known. This optical configuration significantly reduces the complexity of the reconstruction algorithms. The proposed vision ray metrology system does not require mathematical optimization algorithms for calibration and reconstruction – the vision rays are obtained using a simple 3D fitting of a line.
Precision glass molding is a viable process for the cost-effective volume production of freeform optics. Process development is complex, requiring iterative trials of mold manufacture and metrology, molding prototyping, optic metrology, and functional testing. This paper describes usage of chalcogenide glass molding as a lower cost, faster turnaround mold prototyping process for an Alvarez lens intended for use in visible light. The target optic has a clear aperture of 42 mm, aspect ratio of 16:1, error specifications of 20 nm – 25 nm RMS across a spatial wavelength band from 1 mm to the clear aperture (e.g. form and mid-spatial frequencies) and microroughness of 2 nm Sq. The evaluation process uses diamond turning of trial molds in metal, molding of chalcogenide glass prototypes, and comparative metrology of molds and optics to close the manufacturing and metrology loops and more rapidly converge on a viable process starting point for visible glass.
Precision glass molding is a viable process for the cost-effective volume production of freeform optics. Process development is complex, requiring iterative trials of mold manufacture and metrology, glass mold prototyping, metrology and functional testing. This paper describes the first iteration in the development of a process for an Alvarez lens for visible light. The challenges of this optic are extremely tight band-RMS tolerances on a freeform shape over a maximum clear aperture of 45 mm, a 16:1 aspect ratio and a freeform departure of 329 micrometers. A freeform glass mold for an Alvarez lens was manufactured by coordinated-axis diamond turning in a mold substrate using a custom tool error correction method. The results of prototype precision glass molding are also reported. Mold surfaces and molded optical surfaces are analyzed with scanning white light interferometry. A surface roughness of approximately 3 nm RMS is obtained for both the mold substrate and the glass optic with high-fidelity reproduction of micro-surface structure in the glass. These measurements also identify challenging areas, particularly the presence of mid-spatial frequency errors on the optic originating from the machine thermal control system. The form of the molds was also measured with a profilometer; however, the mold surface does not agree with the expected prescription with an overall deviation in form of approximately 10 μm. The machining process is expected to have sub-micrometer error and the sources of this discrepancy are still being determined. Metrology of the glass optics is currently in progress.
The design proposed in this abstract, for a monocular see through smart glass, i.e. Design Challenge #1, leverages a varifocal lens to accommodate human eyes with different focusing abilities. The eyepiece is made of three separate segments. The varying focus of the system is achieved by using two freeform Alvarez surfaces. The Alvarez lens proposed here has the advantage of achieving different focal lengths by laterally shearing the optics with respect to each other. As a proof of concept, it is shown that the Alvarez lenses provide the ability of a constant performance for different eye conditions.
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