aLIGO test masses, revisited

Scattering and loss by test mass
 Discrepancy between the measured arm loss, 50ppm/mirror, and the loss
based on optics data, 25ppm/mirror
 Understand about the defects in coating
 Integrating sphere measurement with extension (Liyuan Zhang)
 Preliminary and proof of concept, but very interesting
 Small angle (θ≤1°) and large angle (θ≥1°) scattering
 Missing energy in the small angle scattering
 Defect size/distribution information

Excess PSD at λspatial < 3mm (system meeting)
 PSD of the coated mirror using the latest coating setup is larger than PSD
using the original mask by more than 10 at λs=3mm~1/3mm
 Effect on the aLIGO performance when ETM is replaced
 Increase of arm loss and scattered light which hits beam tube baffles
 PRG and scattering noise
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
1
Reflection and propagation of field
Spherical wave
from source point
far field
near field
* total power of far field =
total power of near field
* power distribution of far field =
interference of near fields
from various source points
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
2
Far field and mirror ASD
wide smooth surface characterized by ASD
ASD:
λS→θfar field:
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
3
Uncoated surface PSD
not simple, pretty complex
7.6e 2 nm
3e 2 nm
2
3e nm
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
4
Far field and small size defects
small defects cannot be characterized by PSD
reflected power = power density at defect ∙ defect size ∙ |A|2
circle with radius a
small
rectangle size of du x dv
log( power ) axis : k a θ = 0.1 a(μm) θ(degree)
k a θ =1 when
a = 1μm, θ=10°
or
a=10μm, θ=1°
Defect size
looks different
seen at different
angle
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
5
interference and angle dependence
of far field
Small defect
LIGO-G1501419
Hiro Yamamoto
Periodic defect
LIGO seminar on Dec. 1st, 2015
6
Power distribution depends on the
defect size
Fractional power out of an angle : simple vs Mie
100
10-1
Power fraction
10-2
θ
10-3
10-4
Mie 1 um
Mie 10 um
Mie 100 um
Geometry 1 um
Geometry 10 um
Geometry 100 um
10-5
10-6
0
2
4
6
8
10
12
14
16
18
20
opening angle (degree)
1.0
Power fraction out
of an angle
0.8
Mie
0.6
Circle
0.4
Square
0.2
Geometry
LIGO-G1501419
0.0
Hiro Yamamoto
0
1
2
LIGO seminar on Dec. 1st, 2015
3
4
axis : k a θ = 0.1 a(μm) θ(degree)
5
7
Comparison of 1° vs 5° dead region
Comparison of 1° and 5° coverage
1
0.9
power fraction covered by detector
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
2
4
6
8
10
12
14
16
18
20
defect size (um)
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
8
Clustered defects behave like a
single defect
Power distribution
generated by small
defects in a square
Same distribution
generated by
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
9
TIS measurement in small angle
using integrating sphere
by Liyuan Zhang
l
Scattering loss of mirrors
» Total loss in the arm cavity vs mirror data
» Understanding the defects in the coating
l
Integrating sphere covering θ≥1° predicts scattering loss /
mirror ~ 10ppm
» Solid angle of the hole in θ≤1° is (π/180)2=3 x 10-4, so correction should be
negligible.
l
l
If there are defects with size > 1μ, this may cause something
unexpected
Integrating sphere + pickoff to measure TIS in the small
angle region θ ≤ 1° in addition to large angle θ ≥ 1°
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
10
Setup for measuring
TIS(θ≤1°) and TIS(θ≥1°)
Laser
Integrating
sphere
Opening
angle = 1°
PD1
PD2
Mirror
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
11
Very preliminary results
mirror : initial LIGO ETM04
TIS (θ≥1°)
TIS (0.7°≤ θ≤1°)
scratch
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
12
TIS(θ≤1°) vs TIS(θ≥1°)
very preliminary
Quadrants no scratch
105
Quadrant with scratch
LIGO1-ETM04 HR TIS : good quadrant
LIGO1-ETM04 HR TIS : scratch
105
brighter
104
104
(3) Large defect
103
103
102
102
101
101
100
100
101
LIGO-G1501419
102
103
(4) Clustered
small defects
Large
TIS(θ≥1°),
10
10
small TIS(θ≤1°)
4
Hiro Yamamoto
5
100
100
(2) Scratch
Large defect
on surface
(1) Isolated small
defect or micro
roughness
101
102
LIGO seminar on Dec. 1st, 2015
103
104
105
13
Defect size and total loss
assuming defect shape is circle
2
16
1.9
14
1.8
12
Defect size (um)
1.7
10
1.6
1.5
8
1.4
6
1.3
4
1.2
2
0
101
1.1
102
103
104
Defect size vs TIS(θ≥1°)
LIGO-G1501419
Hiro Yamamoto
105
1
101
102
103
104
105
Total / TIS(θ≥1°) vs TIS(θ≥1°)
LIGO seminar on Dec. 1st, 2015
14
aLIGO ETM TIS(θ≥1°)
low end of TIS(θ≥1°) by continuous roughness
ETM16 case
peak of count / loss by RMS of uncoated surface
7
6
5
Zygo 50x PMM
rms → loss
4
3
2
1
0
7
8
9
10
11
12
13
14
15
16
ETM ID
Ratio of teak of measured TIS and
loss using uncoated surface RMS
of 10 aLIGO ETMs
Majority of the scattered data
are by continuous roughness
LIGO-G1501419
Hiro Yamamoto
Integrating sphere counts
peak
LIGO seminar on Dec. 1st, 2015
15
ETM PSDs with different coating
Does it cause any problems?
ETM coated PSD : coating by time
102
Reduction of spiral height
101
100
PSD (nm2 mm)
10-1
10-2
Same color,
same mask
10-3
ETM07-LX
ETM09-LY
ETM08-HX
ETM12-HY
ETM11
ETM14
ETM10
ETM15
ETM13
ETM16
10-4
10-5
10-6
10-7
10-2
LIGO-G1501419
Hiro Yamamoto
Original mask
New mask
Increase of short
wavelegth noise
Coating with jiggling
10-1
100
LIGO
seminar
on(1/mm)
Dec. 1st, 2015
spatial
frequency
16
PSDs with and without coating
102
ETM PSD : coated vs polished
ETM07 coated
ETM07 polished
ETM11 coated
ETM11 polished
ETM16 coated
ETM16 polished
101
100
Original mask
New mask
Coating with jiggling
PSD (nm2 mm)
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-2
All uncoated surfaces
have similar PSD
10-1
100
spatial frequency (1/mm)
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
17
Same high PSD
in the central region as well
102
PSDs in different apertures
ETM10 ? 8cm
ETM10 ? 16cm
ETM15 ? 8cm
ETM15 ? 16cm
ETM13 ? 8cm
ETM13 ? 16cm
ETM16 ? 8cm
ETM16 ? 16cm
ETM16 uncoated ? 8cm
ETM16 uncoated ? 16cm
101
100
PSD (nm2 mm)
10-1
10-2
10-3
10-4
10-5
10-6
10-7
10-2
10-1
100
spatial frequency (1/mm)
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
18
PSD(coated)/PSD(uncoated) > 10:
Is this increase real?

Three independent
measurements of
phasemaps of the coated
ETM16 are consistent
ETM16 PSDs
 (1) Measured by LIGO Fizeau IFO
without magnification
 (2) Measured by LIGO Fizeau IFO
with x10 magnification
 (3) Measured by LMA Fizeau IFO
without magnification
(1) LIGO x1
(3) LMA
(2) LIGO x10
Uncoated surface
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
19
One complication we don’t/can’t
handle/understand properly
Zygo PSDs by different devices
LIGO Fizeou IFO
Instrument transfer function
1
Low statistics
0.9
0.8
0.7
Poor efficiency
ITF
0.6
BEX 1x
0.5
BEX 2x
Bre 1x
0.4
Bre 2x
0.3
0.2
0.1
0
0.1
1
10
Cycles/mm
x1
@1mm 0.2
LIGO-G1501419
Hiro Yamamoto
x10
@0.1mm 0.1
LIGO seminar on Dec. 1st, 2015
20
Change of rms and loss
loss=1.3~2ppm @ λs =3~1/3mm
Uncoated
rms / loss
Coated ETM16 PSD by LIGO
coated ETM16 PSD : effect of ITF
Coated x1
10
0
(1)
x1 without ITF
x1 with IFT
x10 without ITF
x10 with ITF
ETM16 polished
(2)
PSD (nm2 mm)
10-1
(3)
10-2
Uncertainty due to
Interferometer
transfer function
10-3
10-4
10-5
10-6
10-2
Uncoated
(measured by Zygo)
10-1
Coated x10
100
101
spatial frequency (1/mm)
Uncoated ETM16 by Zygo
(4)
LIGO-G1501419
Hiro Yamamoto
Total loss (4)0.1m (3)0.3mm (2)1mm (1) 3mm
λs < 3mm m~ 1μm ~ 0.1mm ~0.3mm ~1mm
101
Coated
rms / loss
0.03nm
0.1ppm
0.08nm ~ 0.1nm
1.0ppm ~ 1.5ppm
0.02nm
0.06ppm
0.06nm ~ 0.07nm
0.50ppm ~ 0.75ppm
0.02nm
0.08ppm
same as uncoated
-assumed
0.076nm
0.83ppm
same as uncoated
-assumed
1.1ppm
2.4ppm ~ 3.2ppm
LIGO seminar on Dec. 1st, 2015
21
Scattering by periodic aberration
vs point defects
 Periodic aberration reflects to a
fixed direction
 point defects reflects uniformly
⇒ θ2 ~ O(10-4)
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
22
Noise by sparial on ETM07
vs periodical aberration ~1mm on ETM16
Lb
(
dP 2
)
dW ms
dP
dW bs
rbaff
Scattering = 4.5ppm by spiral in a narrow region
by mirror = 1.5ppm by λs ~ 3~1/3mm in wide spread
Scattering
by baffle
dP = 0.02 for forward (spiral)
dW bs = 0.005 for backward (λ < 4mm)
s
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
23
Summary
l
Extended Integrating Sphere measurement
» Preliminary result – proof of concept
» Comparison of large angle TIS (θ≥1°) and small angle TIS(θ≦1°)
provides information about the defect size and uncovered scattering
» Measurement of aLIGO test masses coated by LMA using better
setup and detector.
l
Large PSD at short wavelength region
» Looks real, cause unknown
» PRG loss and back scattered noise by beam tube baffle, OK
» Any other issue by higher roughness in the short wavelength region
which tends to scatter light to wider angle?
LIGO-G1501419
Hiro Yamamoto
LIGO seminar on Dec. 1st, 2015
24