Thin Diamond Radiator Fabrication for the GlueX Experiment

Brendan Prattwith

Fridah MokayaRichard Jones

University of Connecticut

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Outline

Overview of GlueX

UConn Laser Ablation Setup

Analysis of Radiator Samples

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The GlueX Experiment

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Thin and Flat Diamonds

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Radiators restricted to 20μm thickness due to multiple scattering

Must also have well defined crystal structure with whole crystal rocking curves less than 35μr

Techniques for thinning diamond exist, but they leave samples stressed and “potato chipped”

Laser ablation as a viable method for machining while keeping internal crystal structure unchanged

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UConn Laser Ablation Facility

LASER

L1L2

L3

DiamondAblation Chamber

X-Y Translation

Stage

LabView

• CNC style XY translation and laser pulsing via LabView• Ablation Chamber optimized to reduce amorphous carbon deposition on windows• Enhanced optics to reduce spherical aberrations (sub micron beam spot)

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X-ray assessment: S150surface of S150 was polished with RCMP process

limited bylimited byinstrumentalinstrumentalresolution !resolution !

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X-ray assessment: S90surface of S90 was not treated after VPIE process

not as flat not as flat as S150, butas S150, butstill in spec.still in spec.

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X-ray assessment: S30 – the real targetsurface of S30 was not treated after VPIE process

challengechallengelies here!lies here!

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new idea tested in 2012: add add a framea framediamonds appear to warp

severely when thinned to20 microns

try to stiffen the diamond byleaving a thick outer frame

around the 20 micron region

frame around 20 micron is still part ofthe single crystal, maintains planarity

warping is from combination ofmounting and internal stresses

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First “picture frame” sample: U40

3 mm

315 micronframe aroundoutside edge

thinned innerrectangularwindow

residual rasterpattern is froma coarse laserstep size

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3D Zygo Images of U40

-300

-250

-200

-150

-100

-50

0

50

100

150

0 0.5 1 1.5 2 2.5 3

x (mm)z

(μm

)

approximate bottom surface depth,Zygo measurement on next slide

White-light interferometer gives surface and thickness profiles with sub-micron prec.

top surface measurements with Zygo

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3D Zygo Images of U40White-light interferometer gives surface and thickness profiles with sub-micron prec.

average thickness

40μm

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X-ray rocking curve for U40

excellent excellent result for result for thinned thinned diamond!diamond!

surface of U40 was not treated after ablation

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Observations on ablated sample Central region looks good Sharpness of the walls does not degrade with depth Pileup of amorphous carbon is not catastrophic So far no clouding of the ablation chamber window from

residue

Excellent flatness of the central regionExcellent flatness of the central region So far no need for active correction to cutting rate, So far no need for active correction to cutting rate,

but pulse-by-pulse recording of laser power is being collected, can be used to keep the milling rate even more uniform

Exploring annealing techniquesExploring annealing techniques

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Questions?

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Extra Slides

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New vs. Old Spot Profile

Approx. 0.3mm

Appr

ox. 0

.2m

m

Approx. 0.60mm

Approx. 0.15mm

Wider spot size in y allows for larger step sizes and faster rasterizing.

Aspect Ratio 1.5

Aspect Ratio 4before

after

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