Athermalizing Refractive Optics with Fluid Lenses

Fabricant, Daniel G.

doi:10.1086/343218

Cited by 6 publications

(5 citation statements)

References 16 publications

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“…The detailed camera model shows that this axial gradient peaks at 0.14ЊC. Epps & Fabricant (2002) have shown that 0.2ЊC gradients negligibly affect image quality and image scale.…”

Section: Temperatures and Temperature Gradientsmentioning

confidence: 90%

“…Under extreme conditions at the MMT, we find that these gradients and offsets double. Epps & Fabricant (2002) have shown that these temperature gradients and temperature offsets in the optics have a negligible effect on image quality and image scale, even under extreme conditions.…”

Section: Discussionmentioning

confidence: 99%

“…The optics are athermalized using a new technique described in Epps & Fabricant (2002). Briefly, the weak lenses formed in the fluid used to couple the multiplets exploit the thermally sensitive refractive index of the coupling fluid to compensate for thermally dependent lens properties: refractive indices, spacings, and dimensions.…”

Section: Introductionmentioning

confidence: 99%

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A Detailed Thermal Analysis of the Binospec Spectrograph

Brown

Fabricant

Boyd

2002

PUBL ASTRON SOC PAC

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Refractive optics in astronomical instruments are potentially sensitive to temperature gradients and temperature transients. This sensitivity arises from thermally dependent refractive indices, lens spacings, and lens dimensions. We have therefore undertaken a detailed thermal analysis of Binospec, a wide-field optical spectrograph under development for the converted MMT. Our goals are to predict the temperature gradients that will be present in the Binospec optics and structure under realistic operating conditions and to determine how design choices affect these gradients. We begin our analysis by deriving thermal time constants for instrument subassemblies. We then generate a low-resolution finite difference model of the entire instrument and high-resolution models of sensitive subassemblies. This approach to thermal analysis is applicable to a variety of other instruments. We use measurements of the ambient temperature in the converted MMT's dome to model Binospec's thermal environment. During moderate conditions we find that the Binospec lens groups develop 0.14 C axial and radial temperature gradients and that lens groups of different mass develop 0.5 C temperature differences; these numbers are doubled for the extreme conditions. Internal heat sources do not significantly affect these results; heat flow from the environment dominates. The instrument must be periodically opened to insert new aperture masks, but we find that the resulting temperature gradients and thermal stresses in the optics are small. Image shifts at the detector caused by thermal deflections of the Binospec optical bench structure are approx 0.1 pixel/hr. We conclude that the proposed Binospec design has acceptable thermal properties, and briefly discuss design changes to further reduce temperature gradients.Comment: 11 pages, to appear in PASP v114 Dec 200

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“…The detailed camera model shows that this axial gradient peaks at 0.14ЊC. Epps & Fabricant (2002) have shown that 0.2ЊC gradients negligibly affect image quality and image scale.…”

Section: Temperatures and Temperature Gradientsmentioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

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A Detailed Thermal Analysis of the Binospec Spectrograph

Brown

Fabricant

Boyd

2002

PUBL ASTRON SOC PAC

Self Cite

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“…There have been some efforts to use the oil couplant as part of an athermalizing strategy, 51 although there may be easier ways to accomplish the same goal. The strong dn/dT effect that Epps and Fabricant mention could be something to check in other oil-coupled applications.…”

Section: Special Cases: Doublets With a Problematic Glassmentioning

confidence: 99%

Guidelines for predicting stress in cemented doublets undergoing temperature change: theory, practice, and data

Kaufman,

Frayer,

Malone

et al. 2024

Opt. Eng.

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This work explores quick predictive methods for calculating potentially risky stresses and deflections in cemented doublets experiencing temperature change that agree well with finite element analysis. There are three failure modes of interest: cohesive failure of the adhesive, delamination (surface bond failure or debonding), and glass fracture. Adhesive theory, confirmed by finite element analysis, predicts stress singularities that complicate interpretation of the stress calculations. The presence of a stress singularity indicates the breakdown of linear elastic assumptions, but damage initiation and stress singularities are related. The authors find that geometry details near a bond edge can exacerbate or minimize damage initiation and stress concentrations. Because the interpretation of the stress results is complicated, the authors investigated predicted stresses in doublets that have been successfully tested between −40°C and 85°C. This study found that the thermal strain ðΔT • ΔαÞ should be less than 189 ppm, where ΔT is the temperature excursion and Δα is the difference in the two glass coefficients of thermal expansion. If the thermal strain is equal to or greater than 189 ppm, further analysis and testing is warranted. But the authors also show that the fabrication process can significantly influence stress failure, particularly with large diameter doublets.

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“…Harland Epps suggested that we allow the coupling fluid interfaces to have a small amount of power. Because the LL5610 has a large negative dn/dT, these weak fluid lenses can be used to athermalize the optics (Epps & Fabricant 2002). Making this athermalization work in practice requires careful analysis and a detailed knowledge of the thermal properties of all the optical materials and the optics mounts.…”

Section: Optics Athermalizationmentioning

confidence: 99%

Binospec: A Wide-field Imaging Spectrograph for the MMT

Fabricant

Fata

Epps

et al. 2019

PASP

111

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Binospec is a high throughput, 370 to 1000 nm, imaging spectrograph that addresses two adjacent 8ʹ by 15ʹ fields of view. Binospec was commissioned in late 2017 at the f/5 focus of the 6.5m MMT and is now available to all MMT observers. Aperture masks cut from stainless steel with a laser cutter are used to define the entrance apertures that range from 15ʹ long slits to hundreds of 2ʺ slitlets. System throughputs, including the MMT's mirrors and the f/5 wide-field corrector peak at ~30%. Three reflection gratings, duplicated for the two beams, provide resolutions (λ/Δλ) between 1300 and >5000 with a 1ʺ wide slit. Two through-the-mask guiders are used for target acquisition, mask alignment, guiding, and precision offsets. A full-time Shack-Hartmann wave front sensor allows continuous adjustment of primary mirror support forces, telescope collimation and focus. Active flexure control maintains spectrograph alignment and focus under varying gravity and thermal conditions.

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Athermalizing Refractive Optics with Fluid Lenses

Cited by 6 publications

References 16 publications

A Detailed Thermal Analysis of the Binospec Spectrograph

A Detailed Thermal Analysis of the Binospec Spectrograph

Guidelines for predicting stress in cemented doublets undergoing temperature change: theory, practice, and data

Binospec: A Wide-field Imaging Spectrograph for the MMT

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