Surface form metrology for freeform optical components is a significant challenge that impacts the entire process chain. One of the main aims is that the metrology technique provides sufficiently low measurement uncertainty within a reasonable measurement time. We developed a non-contact, non-part-specific cascade optical coherence tomography (COCT) technique within this metrology context. C-OCT utilizes a primary and a secondary interferometer in a cascade that transforms a difficult-to-measure optical path difference (OPD), which encodes the freeform sag in this case, into a more readily measured OPD in the secondary interferometer. To enable high-speed measurements, we developed the secondary interferometer based on a rotating optical cube. A custom telecentric objective lens and a custom pupil relay enable optical scanning over the sample surface. Experimental results validate the C-OCT technique with consecutive single-point measurements showing precision of ±26 nm (~λ/24 at the He-Ne wavelength) and a preliminary flat surface measurement demonstrating 22 nm RMS (~λ/28) over a central 20 mm diameter region. Developments on the system are underway towards surface measurements on freeform optical components.
The UNESCO International Day of Light, 16 May, serves to highlight the critical and diverse roles that light plays in our daily lives. Light has specific meaning to each local community, and finding that which has the greatest impact can be challenging. In the proper context, local festivals serve as a fertile ground for light appreciation, bringing together diverse local groups. We provide the devices for exploration of colorimetry, imaging, and color matching demonstrations at an otherwise social local festival. Methods of assembly and planning for the multi-day display are outlined.
The recent advances in the optics manufacturing industry to achieve the capability of fabricating rotationally nonsymmetric optical quality surfaces have considerably stimulated the optical designs with freeform components. This opens up new horizons for novel optical systems with larger fields of view and higher performance, or significantly more compact in volume at equal performance compared to conventional systems. A bottleneck to the broad industrial applications of freeform optics remains the lack of a high performance optical metrology tool capable of measuring significant surface departures and slopes of the parts. To address this issue, we have developed a fiber-based swept-source optical coherence tomography (SS-OCT) system for point-cloud freeform metrology, where two-axis galvanometer scanners are leveraged for high-speed lateral scans. We specifically designed a custom all-reflective achromatic pupil relay system to achieve a diffraction-limited scanning configuration. Coupled with a large field-of-view (FOV) telecentric scan lens, the imaging covers 28.9 mm × 28.9 mm FOV with 35 μm lateral resolution and more than 600 μm depth of focus. Freeform metrology is demonstrated for an Alvarez surface of 400 μm surface sag. The high sensitivity of the SS-OCT system allows for capturing the slope variations of the part up to the maximum slope that is 5 degrees in this case. Specific surface reconstruction, rendering and fitting algorithms were developed to evaluate the metrology results and investigate the accuracy and precision of the measurements.
*firstname.lastname@example.org Design study for a 16x zoom lens system for visible surveillance camera Anthony Vella*, Heng Li, Yang Zhao, Isaac Trumper, Gustavo A. Gandara-Montano, Di Xu, Daniel K. Nikolov, Changchen Chen, Nicolas S. Brown, Andres Guevara-Torres, Hae Won Jung, Jacob Reimers, Julie Bentley The Institute of Optics, University of Rochester, Wilmot Building, 275 Hutchison Rd, Rochester, NY, USA 14627-0186 ABSTRACT High zoom ratio zoom lenses have extensive applications in broadcasting, cinema, and surveillance. Here, we present a design study on a 16x zoom lens with 4 groups (including two internal moving groups), designed for, but not limited to, a visible spectrum surveillance camera. Fifteen different solutions were discovered with nearly diffraction limited performance, using PNPX or PNNP design forms with the stop located in either the third or fourth group. Some interesting patterns and trends in the summarized results include the following: (a) in designs with such a large zoom ratio, the potential of locating the aperture stop in the front half of the system is limited, with ray height variations through zoom necessitating a very large lens diameter; (b) in many cases, the lens zoom motion has significant freedom to vary due to near zero total power in the middle two groups; and (c) we discuss the trade-offs between zoom configuration, stop location, packaging factors, and zoom group aberration sensitivity.