Nano structured optics for gw detectors
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Max-Planck-Institut Für Gravitationsphysik (Albert-Einstein-Institut). Universität Hannover. Nano-structured Optics for GW Detectors. Bunkowski, O. Burmeister, D. Friedrich, K. Danzmann, and R. Schnabel in collaboration with T. Clausnitzer, S. Fahr, E.-B. Kley, and A. Tünnermann

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Nano-structured Optics for GW Detectors

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Max-Planck-Institut

Für Gravitationsphysik

(Albert-Einstein-Institut)

Universität

Hannover

Nano-structured Optics for GW Detectors

Bunkowski, O. Burmeister, D. Friedrich,

K. Danzmann, and R. Schnabel

in collaboration with

T. Clausnitzer, S. Fahr, E.-B. Kley,

and A. Tünnermann

Institute of Applied Physics, Jena


Outline

Summary of:

All-reflective

Interferomtry

(with multilayer coatings)

Outlook to:

High reflective

diffractive structures

(without multilayer coatings)


Motivation #1

Interferometers beyond LIGOII

(MW of power)

Transmission  Absorption

 Thermal problems

All-reflective interferometers:

  • Allow opaque test mass

  • materials

  • New interferometer

  • topologies


MI with all-reflective beamsplitter


Grating equation:

What kind of gratings?

d>>l: scalar approach

d~l: rigorous theories

(RCWA, Modal method)

d<<l: effective medium

theories (ETM)

Period defines # of

orders & direction

Coating on top

Coating below


Appl. Opt. (in press)

99.62% achieved

(Finesse of 1580)

A. Bunkowski et al, Applied Optics (in press) http://ao.osa.org/upcoming_pdf.cfm?id=66481

Cavity couplers

1st order Littrow

2nd order Littrow

Input

Input

Input

Input

1R

1R

0R

2R

0R

Need high efficiency

(which is hard

to achieve)

Only low efficiency

(3 ports are more

Complicated)


99.62% achieved

(Finesse of 1580)

A. Bunkowski et al, Applied Optics (in press) http://ao.osa.org/upcoming_pdf.cfm?id=66481

Cavity couplers

1st order Littrow

2nd order Littrow

Input

Input

Input

Input

1R

1R

0R

2R

0R

Need high efficiency

(which is hard

to achieve)

Only low efficiency

(3 ports are more

Complicated)

A. Bunkowski et al, Applied Optics (in press) http://ao.osa.org/upcoming_pdf.cfm?id=66481


f [°]

f [°]

3-port couplers

A. Bunkowski et al, Opt. Lett. 30, 1183 (2005)

R. Schnabel et al, Opt. Lett. 31 658 (2006)

A. Bunkowski et al, Opt. Lett.

29, 2342 (2004)

A. Bunkowski et al, Opt. Lett. (in press)

http://ol.osa.org/upcoming_pdf.cfm?id=69970


Angle resolved scattering

-1st

+1st

E-beam exposure

„Variable shaped beam“

diffraction orders

due to e-beam

writing errors

electron

beam

work field stitching

apertures

shaped

beam

background

due to statistical roughness


Grating beneath coating

same diffraction efficiency

systematical errors

reduced

statistical background

reduced

Small fill factor

groove depth 40nm

fill factor 50%

T. Clausnitzer et. al., Optics Express, 13, 4370 (2005)


diffraction efficiency

1.5%  0.03%

systematical errors

statistical background

Grating beneath coating II

Large fill factor

groove depth 40nm

fill factor 82%

T. Clausnitzer et al, Optics Express, 13, 4370 (2005)


Conclusion #1

Summary:

  • High quality all-reflective components

  • Demonstration of new cavity coupling concept

  • Reduction of scattering loss

    Outlook:

  • Further reduction of loss

  • Scale to large test mass

  • Suspended 10 m all-reflected cavity to be

    built in Glasgow later this year


Motivation #2

Several fundamental noise sources as currently estimated for advanced LIGO:

S. Penn et.al, LIGO-P050049-00-R (2005)


Coating stack

Substrate

Beating Coating Noise

  • The high refractive material tantala

  • (Ta2O5) has been identified to be the

  • main source of coating thermal noise.

  • Some ideas so far:

  • Less tantala in stack

  • Innocenzo Pinto’s talk

  • Doping of tantala with TiO2

  • Harry et al, Appl. Opt. 45, 1569 (2006)

  • Total internal reflection

  •  Adalberto Giazotto’s talk

  •  V. Braginsky and S. Vyatchanin,

  • Phys. Lett. A 324, 345 (2004)

  • Double mirrors:

  •  F. Ya. Khalili, Phys. Lett. A 334, 67 (2005)

AR-Coating stack


Coating stack

Substrate

Substrate

Coating Thermal Noise

Another approach:

AR-Coating stack

Grating waveguide reflector


waveguide

nHigh

nLow

(substrate)

Total internal

reflection

Grating waveguide Structures

0R

100%

reflection

(Simplified ray picture)

see for example: Sharon et al, J. Opt. Soc. Am. A, 14 (1997)

1T

Interfere

destructively

0T


Narrow reflection peak

Liu et al,Opt. Lett. 23, 1556 (1998)


d

r

g

s

n=2.04

n=1.45

(substrate)

Fill factor

Design width of reflection peak

[%]

g [µm]

d: period

g: groove depth

r: ridge width

s: film thickness

r/d: fill factor


1-R

g [µm]

Fill factor

Design width of reflection peak

[%]

X


Broadband mirror for 1550nm

Poly-Si

SiO2

Si

0dB  reference mirror with R=98.5%

Mateus et al,

IEEE PHOTONICS TECHNOLOGY LETTERS,

VOL. 16, NO. 7, JULY 2004


Conclusion #2

Summary:

  • High reflectivity is possible with single layer

    Outlook:

  • Check fabrication tolerances, finite size effects…

  • Design, build and test gratings

  • Think of better suited wave guide structures


great, greater, grating


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