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We describe the optimum telescope focal ratio for a two-element, three-surface, telecentric image-transfer microlens-to-fiber coupled integral field unit within the constraints imposed by microoptics fabrication and optical aberrations. We create a generalized analytical description of the microoptics optical parameters from first principles. We find that the optical performance, including all aberrations, of a design constrained by an analytic model considering only spherical aberration and diffraction matches within ± 4 % of a design optimized by ray-tracing software such as Zemax. The analytical model does not require any compromise on the available clear aperture; about 90% mechanical aperture of hexagonal microlens is available for light collection. The optimum telescope f-ratio for a 200-μm core fiber-fed at f / 3.5 is between f / 7 and f / 12. We find the optimum telescope focal ratio changes as a function of fiber core diameter and fiber input beam speed. A telescope focal ratio of f / 8 would support the largest range of fiber diameters (100 to 500 μm) and fiber injection speeds (between f / 3 and f / 5). The optimization of the telescope and lenslet-coupled fibers is relevant for the design of high-efficiency dedicated survey telescopes, and for retrofitting existing facilities via introducing focal macro-optics to match the instrument input requirements.
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The optical design for Cryoscope: a wide-field NIR telescope with low thermal emission
We present the optical design for Cryoscope, a 0.26 m aperture telescope that is a f/2 objective operating over the photometric K band (1.99 to 2.55 μm) with diffraction limited imaging. It has a 16 deg2 FoV with a 7.1′′/pix plate scale on a 2048×2048 18 μm/pixel Teledyne H2RG detector array. The objective is a catadioptric design incorporating two thin fused silica meniscus lenses near the entrance aperture, a spherical primary mirror, and a doublet immediately in front of the detector to flatten the image surface. The design solution is capable of delivering diffraction limited images over a 10° field diameter at f/1.25 in the NIR. The use of fused silica for the first two lens elements allows the design to be used for a broad range of applications from the vacuum ultraviolet to thermal IR with only re-optimization of the field flattening doublet. In the VUV (185 to 300 nm) the design is no longer diffraction limited, but can still be made to be pixel limited with detector arrays having pixels as small as 10 μm. The design provides a compact, wide field, and fast objective that can scale to a 1 m-class telescope and offers several benefits over a classical Schmidt telescope. The convex fused silica meniscus lens is strong enough to serve as a vacuum window allowing the entire optical path to be cryogenically cooled to maintain low thermal emission while delivering two orders of magnitude larger field of view than previous ground-based designs for the thermal infrared.
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- Award ID(s):
- 2010041
- PAR ID:
- 10628230
- Editor(s):
- Marshall, Heather K; Spyromilio, Jason; Usuda, Tomonori
- Publisher / Repository:
- SPIE
- Date Published:
- ISBN:
- 9781510653450
- Page Range / eLocation ID:
- 169
- Subject(s) / Keyword(s):
- Infrared telescope widefield cryogenic optics
- Format(s):
- Medium: X
- Location:
- Montréal, Canada
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1117/12.2630557
