LISA symp 19-24 July 02, PSU 1 Technologies for the Future of interferometric detectors C. Nary MAN...

LISA symp 19-24 July 02, PSU 1

Technologies for the Future of interferometric detectors

C. Nary MAN UMR 6162, Observatoire Cote d’Azur, BP 4229, 06304 Nice Cedex 4, France

•Introduction : fundamental limits of ground-based detectors•Possible solutions in the MF range:

High power lasers new materials for opticscontrols of optics behaviour

•A lot of ideas to extract better signals with sophisticated configurations of signal recycling….•Other optical configurations ……


Sensitivity curve and fundamental limitations

Pendulum thermal noise Mirror thermal noise Shot noise 20W

Gravity gradients

Quantum limit

Seismic wall


Issues in MF range

QM

Tkh B

th .∝

Mirror thermal noise limit : - Q of test-mass (substrate, coatings)- T of test-mass, M of test-mass

Shot noise limit :- directly by laser power - indirectly by optical imperfections

˜ h shot( f ) = 1.08 x 10−24.fpole. 1+f

fpole

⎛

⎝ ⎜

⎞

⎠ ⎟

2

.1

η.Srec.PBS

Increase laser power but increase also thermal effects

(radiation pressure problem : larger masses )

New materials for mirrors, high Q even at low T, large size, optical quality

Coatings of high Q ?

˜ h rad.press=1

M.Larm.f2

h .P2π3cλ


High power single-frequency laser

Front End Power stages50 W > 500 W ?

Low power master

1-3 W Medium power slave

50 W

•Rod systems (LZH)•Stable-unstable slab oscillator

(Adelaide)•MOPA type (Stanford)•Ceramic laser •Fiber laser

Stringent demands on frequency stability 10-6 Hz/√Hz (of ground-based detectors):


Rod Laser systems

LZH: Laser medium is rod, end-pumped by fibre-coupled diode lasers, good wall-plug efficiency, delivers @ 20W


Realized (02):•4 diode boxes have been set up (1200 W of pump power)•temperature stabilization•pump light homogenization has been demonstrated•45 W single mode and 75 W multi mode laser has been demonstrated (single rod, no compensation)

LZH: Power scaling of End Pumped rod to 100W

Modeling :• 100 W of output power will be achieveable•aberrations , to be compensated for•aberrations comparable in end pumped and transversally pumped rod

Mitsubishi: > 200 W achieved in TEM00 output with transverse diode-pumped rod laser


Adelaide 100 W slab laser configuration

Nd:YAG slab pumped by 520 W fibre-coupled diode lasersResonator stable in the zig-zag H direction, unstable in V direction


Stanford MOPA design

amplification goal > 100W with 2 zig-zag slab amplifiers and 20W master oscillator

27 W stable operation achieved at 1st stage


High power lasers: ceramic lasers

Ceramic laser : any size (23 cm long max for YAG xtals, twice this length for ceramic), any shape, high Nd doping, mass production…

first Nd:YAG ceramic laser gives 300 mW output (Ikesue et al. in 1995)

1.46 kW obtained in multimode operation with YAG ceramic

98 in Japan, development of highly transparent Nd:YAG ceramic: efficiency comparable to single xtal lasers , 1.5 kW cw output ( Ueda et al,2001)

Quality of the beam has to be worked out

Wavefront quality, distributions of Nd ions to be compared vs xtals…

Possibility of having Nd:Y2O3 ceramic where thermal conductivity twice of YAG with similar thermal expansion coef.


High power lasers: Fiber lasers

Erbium doped SilicaYtterbium doped all glass (eff > 80%)Ytterbium doped Silica (eff 85%)

Used as power amplifier with NPRO, emits 20 W on single-frequency output (Jena, 2001)Possibility of scaling up to 100 W with 9m fiber.

Fiber lasers based on rare-earth doped silica: very high output powers up to 2 kW cw operation in June 02 (IPG Photonics).


Substrate for future mirrors

low absorption material with good conductivity, high Q, good optical quality ….

Fused Silica (today substrate): • Absorption: best quality has 0.7 ppm/cm• Numata et al (Amaldi 01): measured Q of 13 kinds of FS, Q = 7.105 to 4.107 : no simple

correlation with known specs, seems to increase with annealing process… • Homogeneity and roughness of polishing: meet specs

Sapphire: • Absorption : around 20 ppm/cm, vary following samples• Q = 6.5x 107 at room temperature and low temperatures behavior studied extensively, • but direct measurement of thermal noise necessary• Homogeneity: need to be improved by factor 5 to 10 (Caltech, CSIRO)

Silicon: • Used in reflection only (suitable for all-reflective interferometers)• Q around 2x108 confirmed for a variety of samples, thermal noise improves at low T


New Candidate Materials for mirrors: CaF2

(VIRGO, Elba 2002 )

Low absorption, high resistance to thermal & mech shocks, high Q, good candidate for cryogenic solution

(Silicate bonding not working )


Coatings: optical performances (1)

Optical performances achieved today in Virgo-SMA:

1992 1994 2000 to Virgo

Absorption at 633 nm20

ppm10 ppm

< 5 ppm

4 ppm

Absorption at 1064 nm - 2 - 3 ppm

0,5 ppm

0.6 ppm

Scattering at 633 nm50

ppm5 ppm

1,2 ppm

Scattering at 1064 nm - 2 ppm

0,6 ppm

4 ppm over

150 mm

Wavefront - - - 3.8 nm

rms over m

m

Components diameter

25 mm

50 mm 25 mm 350 mm

4 ppm


Coatings : optical performances (2)

Mask

X

YRobot

Sputtered Atoms

SiO2 target

Ion Source

MirrorInterferometer

Wavefront control

80 mm high reflectivity mirror wavefront before

and after corrective coating


Coatings : mechanical loss

•Levin (98) showed coatings could be a limiting source of loss•Preliminary measurements at Glasgow, Stanford & Syracuse: fcoating = 2.5 x10-4

•To be used in avanced/future detectors, loss factor < 10 –5

•Coating program initiated to measure thin and thick substrates with different number of coating layers , ….•Loss factor at low T (Yamamoto, Elba 02): fcoating < 10- 4 without change of reflectivity

First conclusions:•First interface between layers is not dominant source of loss•Interfaces between multi-layer are not dominant source of loss•Interface substrate-coating is not a signicant source of loss•Ta2O5 layer has higher loss than SiO2

•What is the way forward? Other high index materials than Ta2O5?

•Will it be a trade-off between absorption and mechanical loss ?


Thermal effects

Thermal lensing of test-mass:•large efforts to reduce thermal lensing by reducing absorption in sapphire, but not very reliable ? (Fejer 2001 LSC, Blair 97, Benabid 00)•Tomaru et al (Amaldi 01) reported efficient reduction of thermal lensing in the cryogenic sapphire mirrors

Wavefront distorsion of optical components:•Active wavefront corrections via direct thermal actuation are being developed at MIT•R&D to measure aberrations (Shack-Hartmann type sensors, and correct with deformable mirrors (Stanford) the wavefront distorsion of high power lasers.•Reshaping of laser beams with intracavity deformable mirrors•Reshaping of laser wavefronts with deformable mirrors outside the lasers


Compensation of wavefront deformations

Mirror heating with outer ring and scanned beam heating (MIT)

M.Zucker LSC meeting 02

Ottaway PAC 12


Laser cooling of solids

Cooling a 3-level atom

E2

E1

E3

Radiative transitionsLaser pumping

Phonon absorption

Three-level atom example:•Laser pumps atom from E2 to E3•Radiative deexcitation from E3 to E2•Fluorescence from E3 to E1 => absorption of a phonon E2-E1 => decreasing the thermal energy

1929: anti-Stokes fluorescence is basis of optical refrigeration cycle.

60 ’s: GaAs, Nd:YAG,…90 ’s; Yb doped ZBLAN: up to 48°C (Los Alamos)

Applications to GW detectors:•Identify materials also with high Q, high homegeneity •Recycle the anti-Stokes fluorescence to remove its th.effects out of the solid


All-reflective interferometers

Advantages: •Higher light power because no bulk absorption•Use of test mass materials giving lower thermal noise such as xtal silicon

Drawbacks come from use of gratings:•Conversion of laser frequency noise to pointing noise: retroreflecting compensator•Laser center frequency drift < max deviation •Distort spatial profile of diffracted beam•Scattered light

Improvement needed

Experimental demonstration in 98 by Sun & Byer in a Sagnac configuration


+ signal recycling configurations

Future detector: with thermal correction/compensation

Single -frequency front end

High Power stages (with deformable

mirror)

Wavefront sensor

Pre-mode-cleaner

Faraday isolatorsPhase modulators

50W 500W

Long Input mode cleaner

Correction by Deformable mirrors

Wavefront correction

Power stabilisation


Future detector: all-reflective Sagnac

Single -frequency front end

High Power stages (with deformable

mirror)

Wavefront sensor

Pre-mode-cleaner

Faraday isolatorsPhase modulators

50W 500W

Long Input mode cleaner

Correction by Deformable mirrors

Wavefront correction

Power stabilisation

Transmission port

M1

M2

M3

grating

SR

+ thermal compensation

of mirrors


Intelligent digital controls

•Digital electronics to monitor and control the complex seismic isolation (gain and phase re-adjusted automatically with the drift /ageing of mechanics due to environment…..)Low noise digital electronics for all position controls (test-mass, laser beam, beam shape, beam pointing, etc…)

•Fast digital electronics to lock the laser parameters (frequency, amplitude)

•Neural networks to manage all the controls , from the locks sequence, the automatic relocks of each servo, the electronic gain/phase adjustments due to the ageing of mechanical actuators, etc….., also the kind of signal extraction ?

LISA symp 19-24 July 02, PSU 1 Technologies for the Future of interferometric detectors C. Nary MAN...

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Transcript of LISA symp 19-24 July 02, PSU 1 Technologies for the Future of interferometric detectors C. Nary MAN...