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Monochromator
Improvements and FocusingElke Jackson
Research performed by Elke Jackson, Shannon Lunt, and Yenny Martinez
With the support of Drs. Steven Turley and David Allred
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Monochromator OverviewMonochromator Overview
vacuum
vacuum
Octagonal Chamber
XUV Source
Monochromator Chamber
XUV SourceXUV Source Hydrogen gasHydrogen gas High voltageHigh voltage PlasmaPlasma XUV lightXUV light SlitsSlits VacuumVacuum
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Octagonal ChamberOctagonal Chamber
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Octagonal ChamberOctagonal Chamber
Pinhole
Channeltron Photon
Detector
Stage
θ
2θ
• Pinhole selects beam
• Stage/Detector: θ/2θ
• Channeltron:
Multiplier Tube
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ChamberChamber
Entrance Beam
Exit Beam
First Order Diffractions
To XUV Source
To Octagonal Chamber
Entrance Slits Exit Slits
Specular Reflection
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Reflective Diffraction Grating
Grating Equation:
mλ = d (sin α + sin β)
Gmλ = (sin α + sin β)
mλ = d cos K sin φ
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Reflective Diffraction Grating
Grating Alignment• Mount new grating• Outside alignment
with laser• Inside alignment with
laser– Aligning the laser– Adjusting the grating
• Alignment with source
New grating:• 1200 lines per mm,
twice that of the old grating
• Half the width of the old grating
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Reflective Diffraction GratingAdjustments
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FocusingFocusing
Detector placementDetector placement Reduce slit width, keeping counts upReduce slit width, keeping counts up 10 micron goal10 micron goal Centered beamCentered beam
Small entrance beam focuses Small entrance beam focuses to small exit beamto small exit beam
Adjust monochromator settings Adjust monochromator settings to find beam through small slitsto find beam through small slits
Slit, adjustable width
Centering beam
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Detector Scans at Given Slit Widths
0
100
200
300
400
500
600
700
4
4.2
5
4.5
4.6
4.7
4.8
4.9 5
5.1
5.2
5.3
5.5
5.7
5
angle
co
un
ts/h
alf
se
c
20 um
10 um
30 um
40 um
Focusing:Focusing:Detector scans at given slit Detector scans at given slit widthswidths
• Curve shape does not change with slit size
• Beam centered in slits
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Focusing:Focusing:Wavelength scans at given Wavelength scans at given lever arm micrometer settingslever arm micrometer settings
Lever Arm
Lever Arm Adjustment Micrometer
• Adjusting the lever arm micrometer moves the grating
• Maximize counts to the detector around wavelengths of greatest intensity by comparing wavelength scans at various micrometer settings
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Focusing:Focusing:Wavelength scans at given Wavelength scans at given lever arm micrometer settingslever arm micrometer settings
Norm alized Averaged Wavelength Scans
00.10.20.30.40.50.60.70.80.9
1
2430.4 2430.8 2431.2 2431.6 2432 2432.4
monochromator wavelength reading
2.52.752.252.42.62.55
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Focusing:Focusing:Wavelength scans at given Wavelength scans at given lever arm micrometer settingslever arm micrometer settings
Full Widths at 2/3 Max
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2.2 2.3 2.4 2.5 2.6 2.7 2.8
m icrom eter setting
mo
no
ch
rom
ato
r w
av
ele
ng
th d
iffe
ren
ce
(.5
An
gs
tom
s)
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Focusing:Focusing:Wavelength scans at given Wavelength scans at given lever arm micrometer settingslever arm micrometer settings
Peaks of 16,000 counts (2 second intervals)Peaks of 16,000 counts (2 second intervals) Average standard deviation of 112 countsAverage standard deviation of 112 counts
Now:Now: Wavelength scans, lever arm at < 2.25Wavelength scans, lever arm at < 2.25 Similar optimization with cam micrometerSimilar optimization with cam micrometer Place pinhole and locate beamPlace pinhole and locate beam Bug fixes in computer programBug fixes in computer program Stabilize source or determine its riseStabilize source or determine its rise Write new standards of procedure to reflect Write new standards of procedure to reflect
changeschanges
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