Recycling cavity ghost beams and HAM3 scatter
Considerations for H1 vent May 2025
MC3 to MC2
PRM to MC2
It that the part of the wall that had the bellow?
PR3 to ITMx
This is incorrect, it’s from BSC
?
What direction the stray beam is coming from?
-03 and 04 available at the sites
-05 QTY 4 potentially available at CIT, need to verify
0.0974028251722393
0.0315126787321951 deg
CPy aligned
CPy exaggerated misalignment
Arm
BS
CPy side view to show direction of misalignment
CPy
CPy
CPy
ITMy only
HR
AR
HR->AR->HR
1
2
3
1
2
3
1
2
3
ITMy AR ghost
ITMy HR ghost
ITM HR ghost reflecting of ITMy AR and then HR again. This beam only involves one AR face reflection therefore is same order of power as a direct AR reflection
CPy+ITMy
ITMy AR off
These ghosts only involve one AR bounce therefore are similar power as direct AR reflection
ITMy HR->
CPy ->
ITMy HR
ITMy HR->
CPy ->
ITMy HR
CPy+ITMy
ITMy AR on
8 total hits
ITMy AR,
CPy
CPy
ITMy HR
1. ITMy: HR->AR->HR,
2. ITMy HR->CPy ->ITMy HR
2. ITMy HR->CPy ->ITMy HR
CPx
CPx
CPx only
HR
AR
HR->AR->HR
ITMx only
CPx off
CPy+ITMy
ITMy AR on
8 total hits
ITMy AR,
CPy
CPy
ITMy HR
1. ITMy: HR->AR->HR,
2. ITMy HR->CPy ->ITMy HR
2. ITMy HR->CPy ->ITMy HR
ITMx AR,
CPx
CPx
ITMx HR
1. ITMx: HR->AR->HR,
2. ITMx HR->CPx ->ITMx HR
2. ITMx HR->CPx ->ITMx HR
BS AR
CPx+ITMx
ITMx AR on + BS
9 total hits
ITMx AR,
ITMy AR,
CPx
CPy
CPx
CPy
ITMx HR
ITMy HR
ITMx: HR->AR->HR,
ITMx HR->CPx ->ITMx HR
ITMy: HR->AR->HR,
ITMy HR->CPy ->ITMy HR
ITMx HR->CPx ->ITMx HR
ITMy HR->CPy ->ITMy HR
ITMx HR -> BS HR->BS AR
ITMy HR -> BS HR->BS AR
Main beam
17 hits total
ITMx AR,
ITMy AR,
CPx
CPy
CPx
CPy
ITMx HR
ITMy HR
ITMx: HR->AR->HR,
ITMx HR->CPx ->ITMx HR
ITMy: HR->AR->HR,
ITMy HR->CPy ->ITMy HR
ITMx HR->CPx ->ITMx HR
ITMy HR->CPy ->ITMy HR
ITMx HR -> BS HR->BS AR
ITMy HR -> BS HR->BS AR
Main beam
17 hits total
???
ITMx HR
BS AR
Only BS and ITM HR are on
ITM HR -> BS HRt
ITM HR -> BS HRr ->BS ARr -> BS HRt
Beam from the X arm
Beam from the Y arm
ITMx + CPx
Increased wedge on ITM to show the overlap
CPs alignment
aligned
CPy misaligned
Both CPs misaligned
CPx misaligned
See eDrawing: https://dcc.ligo.org/LIGO-D0900365
All coatings on
CPs aligned
CPy pitch = 0.0315126787321951
CPy pitch = 0.0315126787321951
CPx pitch =-1.744030002E-01
Sweeping CPy
Sweeping CPy
+300 urad
Sweeping CPy
+200 urad
Sweeping CPy
+100 urad
Sweeping CPy
0 urad
Sweeping CPy
-100 urad
Sweeping CPy
-200 urad
Sweeping CPy
-300 urad
New style scraper baffles?
CPy pitch 0.0315 deg
CPy pitch 0 deg
CPy ghosts
CP y pitch =-0.0315126
CPy p = -0.0315126
CPx p = -0.077
CPy ghosts
CP y pitch =0
CPy ghosts
when beam on PR2 is shifted by 15 mm to +Y
CPy +Y side AR ghost
CPy -Y side AR ghost
miss
X align
Both aligh
Ignore curve, both align
CPy p = 0
CPx p = -0.077
CPy p = -0.01
CPx p = -0.077
CPy p = -0.02
CPx p = -0.077
CPy p = -0.03
CPx p = -0.077
CPy p = -0.031513
CPx p = -0.0974
CPy p = -0.031513
CPx p = -0.087
CPy p = -0.031513
CPx p = -0.097
CPy p = -0.031513
CPx p = -0.0974
Sweeping CPy +/- 300 urad
CPy p = -0.01432426615
CPx p = -0.0974
CPy +300 urad
CPy p = -0.0200538441
CPx p = -0.0974
CPy +200 urad
CPy p = -0.02578342205
CPx p = -0.0974
CPy +100 urad
+0
CPy p = -0.031513
CPx p = -0.0974
CPy p = -0.03724257795
CPx p = -0.0974
CPy -100 urad
CPy p = -0.0429721559
CPx p = -0.0974
CPy -200 urad
CPy p = -0.04870173385
CPx p = -0.0974
CPy -300 urad
CPy only
missaligned
22
CP y ghosts are moving up to 48 if ignore the curvature on pr3
44
CPy+ITM y
+BS
CPx ghosts shoot about PR3
ITMx ghosts shoot under PR3
CPs aligned
CPs misaligned
CPy misaligned only
CPx misaligned
pitch CPx by 0.001 deg (17.45 microrad) is equivalent to 1 pixel shift of the ghosts. 1 pixel is about 4 mm on this detector
CPy only
CPx Yaw +0.001 deg
CPx Yaw +0.002 deg
CPx Yaw +0.003 deg
CPx Yaw +0.004 deg
CPx Yaw +0.000 deg
CPx Yaw +0.001 deg
CPx Yaw +0.002 deg
CPx Yaw +0.003 deg
CPx Yaw +0.004 deg
CPx Pitch +0.000 deg
CPx Yaw +0.000 deg
CPx Pitch +0.001 deg
CPx Yaw +0.000 deg
CPx Pitch +0.002 deg
CPx Yaw +0.000 deg
CPx Pitch +0.003 deg
CPx Yaw +0.000 deg
CPy yaw
0
CPy Pitch +0.000 deg
CPy Yaw +0.000 deg
CPy Pitch +0.001 deg
CPy Yaw +0.000 deg
CPy Pitch +0.003 deg
CPy Yaw +0.000 deg
CPy Pitch +0.004 deg
CPy Yaw +0.000 deg
CPy Pitch +0.010 deg
CPy Yaw +0.000 deg
All coating on
CPx made ideal
CPy made ideal
BS AR made ideal
Eddie camera view from VP9 (MC2 cam)
~20 mm
~125 mm
~50 mm
~55 mm
PR2 scraper
Beam to pr2
Beam from pr2
+Y
+X
28 mm
70 mm
30 mm
25 mm
15 mm
33 mm
12 mm
25 mm
70 mm
Roberts slides, move as desired
Lessons learned
Suspended baffles, ACB, cryo, have been problematic, partly because of high-Q suspensions.
Watch for noise from elliptical baffles
High-Q baffles amplify motion, contaminating DARM with higher harmonics
Damp or further damp all suspended baffles and other undamped baffles - all resonances should have Qs of 10 or below.
Stray beams are often required to reach enough recombined power to show in DARM
Map and control all stray beams
Regions where actuation produces micron-scale relative motion are particularly sensitive
Focus baffling on these regions, reduce relative motion
Specular reflections from baffles
Make sure baffles can not retro-reflect light from beamspots or specularly reflect light to another optic
Corner reflections in baffles
Make sure corners do not retro-reflect light
Nearby non-specular reflectors are more likely to be problematic
Priorities based on lessons learned
Further damping and likely redesign of cryopump-manifold baffles. We only reduced motion, not light, determine if they are likely to again be problematic as low-frequency sensitivity increases
Redesign ACBs
Baffling on TM suspension cages
Redesign or damp elliptical baffles
Map stray beams, measure CP angles for this
Improve materials for baffles
Redesign of HAM3 scraper baffle
MC tube baffles, input and output arms, should be tilted to at least 10 degrees (check this for output arm), further damped
Damping of other important baffles like scraper baffles. All panels should be damped
Nozzle baffles over all blank-off flanges in sensitive areas
CPs aligned - ghosts still clip the mass baffle/the mass
CPs aligned
CPs misaligned
CPs aligned
CPs misaligned
CPs aligned
CPs misaligned
CPy&
ITMy HR
CPy
CPy aligned
CPx off
Misalign R nom R sweep
CPy misaligned per the aLog
CPx off
Misalign R nom R sweep
CPy at the sweeping start position from https://www.youtube.com/watch?v=0f0F7cWqpwQ&ab_channel=RobertSchofieldLIGO
CPx off
Misalign R nom R sweep
CPy at the sweeping end position from https://www.youtube.com/watch?v=0f0F7cWqpwQ&ab_channel=RobertSchofieldLIGO
CPx off
Misalign R nom R sweep
CPy reflection when misaligned goes higher
CPy- ITM HR reflection when misaligned goes lower
Photo of H1 ballast mass baffle as installed
ITMy HR-AR ghost does position is independent from CPy orientation
CPy aligned
PR3
HAM3
HAM2
550 urad CPy misalignment (pitching more down toward the arm)
PR3
HAM3
HAM2
707 urad CPy misalignment (pitching more down toward the arm)
PR3
HAM3
HAM2
The ballast mass baffle is pitched up by 10 deg. It send the reflection up to the MC baffle. So replacing it with a baffle angled down prob not going to make it better
CPy aligned
SR2
HAM5
HAM4
SR3
550 urad CPy misalignment (pitching more down toward the arm)
SR2
HAM5
HAM4
SR3
707 urad CPy misalignment (pitching more down toward the arm)
SR2
HAM5
HAM4
SR3
HAM2