Problem
The application of optical coherence tomography for the metrology of freeform optical components requires objective lens systems that are highly telecentric and broadband achromatic.
Solution
To meet these requirements, two new objective lens designs are invented: a large field-of-view objective, and a large numerical aperture objective. Specifications and performance of the new objective lenses are provided below. We have also developed a novel pseudo-bistatic scanning configuration to enable the integration of both lens systems within one instrument for extended measurement dynamic range in terms of sample slope and rugosity. Both objective designs as well as the new scanning configuration are essential for the next-generation of OCT systems for metrology of freeform optical components.
https://patents.google.com/patent/US20200011651A1/en
Additional information can be found in the following publications:
Di Xu, Romita Chaudhuri, and Jannick P. Rolland, "Telecentric broadband objective lenses for optical coherence tomography (OCT) in the context of low uncertainty metrology of freeform optical components: from design to testing for wavefront and telecentricity," Opt. Express 27, 6184-6200 (2019). https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-5-6184.
Di Xu, Andres Garcia Coleto, Benjamin Moon, Jonathan C. Papa, Michael Pomerantz, and Jannick P. Rolland, "Cascade optical coherence tomography (C-OCT)," Opt. Express 28, 19937-19953 (2020). https://www.osapublishing.org/oe/abstract.cfm?uri=oe-28-14-19937.
Di Xu, Andres Garcia Coleto, Zhenkun Wen, Benjamin Moon, Jonathan C. Papa, Michael Pomerantz, John C. Lambropoulos, Jannick P. Rolland, "Cascade optical coherence tomography (C-OCT) towards freeform metrology," Proc. SPIE 11490, Interferometry XX, 114900K (21 August 2020). https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11490/114900K/Cascade-optical-coherence-tomography-C-OCT-towards-freeform-metrology/10.1117/12.2567080.short?SSO=1.
Large FOV Objective
1. Spectral range: 720 – 1080 nm
a. Design wavelength: 720, 900, 1080 nm
b. Reference wavelength λ: 900 nm
c. Weighting: 1:1:1
2. Entrance pupil diameter: 10 mm
3. Effective focal length: 154 mm
4. Image space NA: 0.0324
5. Full scanning FOV, diameter: 40 mm
6. Full optical scan angle: ±7.4°
7. RMSWE, nominal maximum: 0.05 λ
8. Telecentricity, nominal maximum: 0.00036°
9. Vignetting: 0 %
10. F-θ distortion, nominal maximum: 33.13 μm
11. F-θ distortion, nominal maximum: 0.16 %
12. Overall length, vertex to vertex: 160 mm
13. Working distance: 100 mm
Large NA Objective
1. Spectral range: 720 – 1080 nm
a. Design wavelength: 720, 900, 1080 nm
b. Reference wavelength λ: 900 nm
c. Weighting: 1:1:1
2. Entrance pupil diameter: 5.5 mm
3. Effective focal length: 5 mm
4. Image space NA: 0.55
5. Full scanning FOV, diameter: 0.088 mm
6. Full optical scan angle: ±0.5°
7. RMSWE, nominal maximum: 0.041 λ
8. Telecentricity, nominal maximum: 0.067°
9. Vignetting: 0 %
10. F-θ distortion, nominal maximum: 0.037 μm
11. F-θ distortion, nominal maximum: 0.15 %
12. Overall length, vertex to vertex: 12 mm
13. Working distance: 2.5 mm