a LIGO test masses revisited Scattering and loss

a. LIGO test masses, revisited Ø Scattering and loss by test mass Ø Discrepancy between the measured arm loss, 50 ppm/mirror, and the loss based on optics data, 25 ppm/mirror Ø Understand about the defects in coating Ø Integrating sphere measurement with extension (Liyuan Zhang) Ø Preliminary and proof of concept, but very interesting Ø Small angle (θ≤ 1°) and large angle (θ≥ 1°) scattering Ø Missing energy in the small angle scattering Ø Defect size/distribution information Ø Excess PSD at λspatial < 3 mm (system meeting) Ø PSD of the coated mirror using the latest coating setup is larger than PSD using the original mask by more than 10 at λs=3 mm~1/3 mm Ø Effect on the a. LIGO performance when ETM is replaced Ø Increase of arm loss and scattered light which hits beam tube baffles Ø PRG and scattering noise LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 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-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 2

Far field and mirror ASD wide smooth surface characterized by ASD: λS→θfar field: LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 3

Uncoated surface PSD not simple, pretty complex LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 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-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 5

interference and angle dependence of far field Small defect LIGO-G 1501419 Hiro Yamamoto Periodic defect LIGO seminar on Dec. 1 st, 2015 6

Power distribution depends on the defect size θ Mie Geometry LIGO-G 1501419 Hiro Yamamoto Power fraction out of an angle LIGO seminar on Dec. 1 st, 2015 axis : k a θ = 0. 1 a(μm) θ(degree) 7

Comparison of 1° vs 5° dead region LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 8

Clustered defects behave like a single defect Power distribution generated by small defects in a square Same distribution generated by LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 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 ~ 10 ppm » 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-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 10

Setup for measuring TIS(θ≤ 1°) and TIS(θ≥ 1°) LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 11

Very preliminary results mirror : initial LIGO ETM 04 TIS (θ≥ 1°) TIS (0. 7°≤ θ≤ 1°) scratch LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 12

TIS(θ≤ 1°) vs TIS(θ≥ 1°) very preliminary Quadrants no scratch Quadrant with scratch brighter (2) Scratch Large defect on surface (3) Large defect (4) Clustered small defects Large TIS(θ≥ 1°), small TIS(θ≤ 1°) LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 (1) Isolated small defect or micro roughness 13

Defect size and total loss assuming defect shape is circle Defect size vs TIS(θ≥ 1°) LIGO-G 1501419 Hiro Yamamoto Total / TIS(θ≥ 1°) vs TIS(θ≥ 1°) LIGO seminar on Dec. 1 st, 2015 14

a. LIGO ETM TIS(θ≥ 1°) low end of TIS(θ≥ 1°) by continuous roughness ETM 16 case Zygo 50 x PMM rms → loss Ratio of teak of measured TIS and loss using uncoated surface RMS of 10 a. LIGO ETMs Majority of the scattered data are by continuous roughness LIGO-G 1501419 Hiro Yamamoto Integrating sphere counts peak LIGO seminar on Dec. 1 st, 2015 15

ETM PSDs with different coating Does it cause any problems? Reduction of spiral height Same color, same mask Original mask New mask Increase of short wavelegth noise Coating with jiggling LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 16

PSDs with and without coating Original mask New mask Coating with jiggling All uncoated surfaces have similar PSD LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 17

Same high PSD in the central region as well LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 18

PSD(coated)/PSD(uncoated) > 10: Is this increase real? Ø Three independent measurements of phasemaps of the coated ETM 16 are consistent ETM 16 PSDs Ø (1) Measured by LIGO Fizeau IFO without magnification Ø (2) Measured by LIGO Fizeau IFO with x 10 magnification Ø (3) Measured by LMA Fizeau IFO without magnification (1) LIGO x 1 (3) LMA (2) LIGO x 10 Uncoated surface LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 19

One complication we don’t/can’t handle/understand properly Zygo PSDs by different devices LIGO Fizeou IFO Instrument transfer function Low statistics Poor efficiency x 1 @1 mm 0. 2 LIGO-G 1501419 Hiro Yamamoto x 10 @0. 1 mm 0. 1 LIGO seminar on Dec. 1 st, 2015 20

Change of rms and loss=1. 3~2 ppm @ λs =3~1/3 mm Uncoated rms / loss Coated x 1 (1) Uncoated (measured by Zygo) (2) (3) Uncertainty due to Interferometer transfer function Coated x 10 Uncoated ETM 16 by Zygo (4) LIGO-G 1501419 Hiro Yamamoto Total loss (4)0. 1 m (3)0. 3 mm (2)1 mm (1) 3 mm λs < 3 mm m~ 1μm ~ 0. 1 mm ~0. 3 mm ~1 mm Coated ETM 16 PSD by LIGO Coated rms / loss 0. 03 nm 0. 1 ppm 0. 08 nm ~ 0. 1 nm 1. 0 ppm ~ 1. 5 ppm 0. 02 nm 0. 06 ppm 0. 06 nm ~ 0. 07 nm 0. 50 ppm ~ 0. 75 ppm 0. 02 nm 0. 08 ppm same as uncoated -assumed 0. 076 nm 0. 83 ppm same as uncoated -assumed 1. 1 ppm 2. 4 ppm ~ 3. 2 ppm LIGO seminar on Dec. 1 st, 2015 21

Scattering by periodic aberration vs point defects Ø Periodic aberration reflects to a fixed direction Ø point defects reflects uniformly ⇒ θ 2 ~ O(10 -4) LIGO-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 22

Noise by sparial on ETM 07 vs periodical aberration ~1 mm on ETM 16 Lb rbaff Scattering by mirror = 4. 5 ppm by spiral in a narrow region = 1. 5 ppm by λs ~ 3~1/3 mm in wide spread Scattering by baffle LIGO-G 1501419 = 0. 02 forward (spiral) = 0. 005 for backward (λs < 4 mm) Hiro Yamamoto LIGO seminar on Dec. 1 st, 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 a. LIGO 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-G 1501419 Hiro Yamamoto LIGO seminar on Dec. 1 st, 2015 24