Mr. Timothy N. Miller Profile

Timothy N. Miller

Optical Engineer

SPIE Involvement:

Author

Publications (20)

Proceedings Article | 10 July 2018 Presentation + Paper

Fabrication of the DESI corrector lenses

Timothy Miller, Robert Besuner, Michael Levi, Michael Lampton, Patrick Jelinsky, Henry Heetderks, David Schlegel, Jerry Edelstein, Peter Doel, David Brooks, Stephen Kent, Gary Poczulp, Michael Sholl

Proc. SPIE. 10706, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III

KEYWORDS: Telescopes, Optical design, Astronomy, Polishing, Data modeling, Silica, Lenses, Glasses, Tolerancing, Surface finishing

Read Abstract +

Proceedings Article | 10 July 2018 Presentation + Paper

Broadband anti-reflection coating for the meter class Dark Energy Spectroscopic Instrument lenses

Charles Kennemore, Debi Archer, Russ Barbaria, Joe Bertolina, Rick Dix, Katy Dodson, Sharon Doi-Okray, Aaron Gallon, Bill Sweet, Timothy Miller, Robert Besuner, Michael Levi, Michael Lampton, Pat Jelinsky, Jerry Edelstein, David Schlegel, Jeremy McCauley, Henry Heetderks, Michael Sholl, Peter Doel, David Brooks, Stephen Kent

Proc. SPIE. 10706, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III

KEYWORDS: Antireflective coatings, Astronomy, Lenses, Coating, Computer aided design, Spectroscopes

Read Abstract +

The Dark Energy Spectroscopic Instrument (DESI), currently under construction, will be used to measure the expansion history of the Universe using the Baryon Acoustic Oscillation technique. The spectra of 35 million galaxies and quasars over 14000 sq deg will be measured during the life of the experiment. A new prime focus corrector for the KPNO Mayall telescope will deliver light to 5000 fiber optic positioners. The fibers, in turn, feed ten broad-band spectrographs. We will describe the broadband AR coating (360 nm to 980nm) that was applied to the lenses of the camera system for DESI using ion assisted deposition techniques in a 3 m coating chamber. The camera has 6 lenses ranging in diameter from 0.8 m to 1.14 m, weighing from 84 kg to 237 kg and made from fused silica or BK7. The size and shape of the surfaces provided challenges in design, uniformity control, handling, tooling and process control. Single surface average transmission and minimum transmission met requirements. The varied optical surfaces and angle of incidence considerations meant the uniformity of the coating was of prime concern. The surface radius of curvature (ROC) for the 12 surfaces ranged from nearly flat to a ROC of 611 mm and a sag of 140 mm. One lens surface has an angle of incidence variation from normal incidence to 40°. Creating a design with a larger than required bandwidth to compensate for the non-uniformity and angle variation created the ability to reduce the required coating uniformity across the lens and a single design to be used for all common substrate surfaces. While a perfectly uniform coating is often the goal it is usually not practicable or cost effective for highly curved surfaces. The coating chamber geometry allowed multiple radial positions of the deposition sources as well as substrate height variability. Using these two variables we were able to avoid using any masking to achieve the uniformity required to meet radial and angle performance goals. Very broadband AR coatings usually have several very thin and optically important layers. The DESI coating design has layers approaching 3 nm in thickness. Having sensitive thin layers in the design meant controlling layer thickness and azimuthal variation were critical to manufacturing repeatability. Through use of strategically placed quartz crystal monitors combined with stable deposition plumes, the manufacturing variability was reduced to acceptable levels. Low deposition rates and higher rotation rates also provided some stability to azimuthal variation.

Proceedings Article | 6 July 2018 Paper

Keck Planet Finder: preliminary design

Steven Gibson, Andrew Howard, Arpita Roy, Christopher Smith, Sam Halverson, Jerry Edelstein, Marc Kassis, Edward Wishnow, Michael Raffanti, Steve Allen, Jason Chin, David Coutts, David Cowley, Jim Curtis, William Deich, Tobias Feger, Daniel Finstad, Yulia Gurevich, Yuzo Ishikawa, Ean James, Elisha Jhoti, Kyle Lanclos, Scott Lilley, Tim Miller, Steve Milner, Tom Payne, Kodi Rider, Constance Rockosi, Dale Sandford, Christian Schwab, Andreas Seifahrt, Martin Sirk, Roger Smith, Julian Stuermer, Marie Weisfeiler, Mavourneen Wilcox, Adam Vandenberg, Peter Wizinowich

Proc. SPIE. 10702, Ground-based and Airborne Instrumentation for Astronomy VII

KEYWORDS: Doppler effect, Calibration, Spectroscopy, Planets, Zerodur

Read Abstract +

Proceedings Article | 9 August 2016 Paper

Stray light assessment and mitigation for the DESI front-end optical system

Timothy Miller, Michael Lampton, Robert Besuner, Michael Sholl, Ming Liang, Scott Ellis