Local control sensors for iKAGRA payloads and perspective (Optical lever) Kazuhiro Agatsuma 2013/Dec./5 ELiTES meeting at Tokyo1

Contents Optical lever (OpLev) development for KAGRA Selection of components Performance test Layout Toward bKAGRA (cryo-condition) 2013/Dec./5ELiTES meeting at Tokyo2

OpLev is used for Local angular control for each mirror Alignment control to lead to lock the interferometer Monitoring drift motion Objectives To decide detail design of OpLev Engineering test (prototype test) 2013/Dec./5ELiTES meeting at Tokyo3 mirror Position sensor Light source

Requirement (spectrum) ( ※ ) In this calculation, following parameters are assumed Intensity noise of light source: RIN ~ 1e-7 /rtHz Shot noise or dark noise ： ~1e-11 m/rtHz (as the spot fluctuation) 2013/Dec./5ELiTES meeting at Tokyo4 by Michimura and Sekiguchi, JGW document (2012/4/27) To lock IFO RMS: 0.1 urad (for cavity) RMS: 1 urad (for BS mirror) Intensity noise, shot noise Requirement

Requirement (drift) 2013/Dec./5ELiTES meeting at Tokyo5 To hold fringe for a day Drift: 10 urad/day 3 km 3 cm / 3km = 10 urad 10 urad/week? 10 urad/day? 10 urad/h? => 3 cm To be locked by referring to optical lever remaining fringe If commissioning phase is assumed

Selection of components Light source –SLD (Super Luminescent Diode) –Wave length: nm –Thermal control –Power: mW Collimator lens –Beam-spot size ： it affects the linear range and sensitivity ⇒ mm for PSD (c.f. 2mm in case of aLIGO) Photo receiver (Rec.) –PSD –Φ: 9 mm x 9 mm 2013/Dec./5ELiTES meeting at Tokyo6

Light source Selected parameters –Fiber coupled SLD ： to avoid interference with a reflection from cladding –Center of wave length: nm Visible is useful at the installation and commissioning phase Tradeoff with lifetime (switchable to IR SLD, which has longer lifetime) –Power: 1~2 mW –Thermal control (to avoid the mode hop) –PM fiber (to keep polarization because of high incident angle) –FC/APC (to avoid reflected light) 2013/Dec./5ELiTES meeting at Tokyo7

Measured RIN and lifetime 2013/Dec./5ELiTES meeting at Tokyo8 This is much lower than the requirement from LIGO document

Position sensors PSD (Position Sensitive Detector) Large linear dynamic range Low speed response Spot-size-independent sensitivity QPD (Quadrant Photo Detector) Small linear dynamic range High speed response Spot-size-dependent sensitivity 2013/Dec./5ELiTES meeting at Tokyo9 Performance has been checked for below candidates ( ※ Spot size affects the linear dynamic range)

Calibration factors 2013/Dec./5ELiTES meeting at Tokyo10 Φ 2mm: linear range: 7mm Φ 0.5mm: linear range: 8mm Sensitivity is independent on the spot size => easy adjustment Linear range of PSD (7mm) is much larger than that of QPD (0.5mm) PSD: 7 mm (Φ 2 mm) QPD: mm (Φ 2-6 mm) X-Y stage

Collimator lens and launcher Selected lenses Spot size is 1-2 mm with the working distance of 4m Adjustable-focus lens for PSD 2013/Dec./5ELiTES meeting at Tokyo11

Layout design 2013/Dec./5ELiTES meeting at Tokyo12 mirror Position sensor Light source mirror Turning mirror Length coupling θ Large θ causes length coupling

Comprehensive drift 2013/Dec./5ELiTES meeting at Tokyo13 ~1m PSD Thermometer Paper box was used as windshield

Comprehensive drift 2013/Dec./5ELiTES meeting at Tokyo14 Fitting: Y = α + β*T + γ*(x – t) T: temperature,β: temperature response x: time,γ: constant drift t: time delay X direction: β = 8 um/ ℃, γ = 14 um/day => 2 urad/day Y direction: β = 50 um/ ℃, γ = 170 um/day => 30 urad/day (3m OpLev length) To hold fringe for a day Drift: 10 urad/day Origin of this drift is in investigation

Layout design 2013/Dec./5ELiTES meeting at Tokyo15 BS Option 1 (Mixed signal) Option 2 (Broad range & length) BS Default Input port Turning port Range: 8mm/(2*3m) = 1.3 mrad lens Range: 8mm/(2*1m) = 4 mrad PSD Chamber for Type-B SAS

Turning port 2013/Dec./5ELiTES meeting at Tokyo16 BS Option 1 (Mixed signal or Length information) Option 2 (Broad range & Length) BS lens PSD PSDs have to be placed on the focal plane and image plane using sliders with about 10-um accuracy Merit: Clear separation between longitudinal and angular motion Demerit: Extra optics (PSD, lens and their sliders) increase total cost. Subtraction of angular signal (input port) from the mixed PSD output produces the longitudinal signal Merit: Cheap and simple Demerit: Direct coupling between longitudinal and angular motion Option 1.5 lens (Broad range or Length information) To adjust the focal or image plane by adding a lens Option 1Option 1.5Option 2 CostLowMiddleHigh InformationMix or LengthBroad or LengthBroad and Length

Layout design for Type B (preliminary) 2013/Dec./5ELiTES meeting at Tokyo17 Drown by Gianni Gennaro Breadboard

Toward bKAGRA (perspective for cryogenic system) 2013/Dec./5ELiTES meeting at Tokyo18

Layout 2013/Dec./5ELiTES meeting at Tokyo19 test mass chamber for iKAGRA test mass chamber for bKAGRA ~15 m

Layout for iKAGRA 2013/Dec./5ELiTES meeting at Tokyo20 ~ 1 m OpLev length: 3m Optical path length: 4m Pylon Range: 8mm/(2*3m) = 1.3 mrad Input port Turning port

Layout for bKAGRA 2013/Dec./5ELiTES meeting at Tokyo21 ~ 15 m OpLev length: 15 m Optical path length: 30 m aLIGO Pylon Range: 8mm/(2*15m) ~ 0.3 mrad ! Detection port Design of collimator lens is needed Observable range becomes small (1.3 mrad => 0.3 mrad)

Additional OpLev 2013/Dec./5ELiTES meeting at Tokyo22 Merit inside cryostat  Observing Intermediate mass  Short length OpLev (broad range) Technical misc. ・ No optical window ・ Fiber coupled SLD is useful ・ Cryo-compatible PD What should be the reference? - Cryostat => deformation by changing temperature - Making special pylon (super invar?) => difficult…

Summary Selection and prototype test for the OpLev of iKAGRA Laser source: Superlum SLD (670 nm) with PM fiber, Position sensor: PSD (9mm x 9mm), Collimator lens: Adjustable-focus lens is selected for PSD (Φ2 mm at 2-m WD, Φ1 mm at 4-m WD) Comprehensive drift Three times worse (30 μrad/day) than the requirement (10 μrad/day) =>Now in investigation Layout Current range (PSD, 8mm range, and input port) is 1.3 mrad for the angular motion of mirrors. It is useful to detect the signal at not only input port but also the turning port. (It is said that 10 mrad range is sufficient for SA in VIRGO) Perspectives Long-length OpLev have a high sensitivity but small range Additional OpLev inside cryostat has some merits (broad range and seeing intermediate mass) 2013/Dec./5ELiTES meeting at Tokyo23

Acknowledgements Riccardo DeSalvo Ettore Majorana Ryutaro Takahashi Takanori Sekiguchi all member of VIS, AOS, and QND group. 2013/Dec./5ELiTES meeting at Tokyo24