LSC meeting, LLO, March, 18, 2004 LIGO-G040071-00-Z

Modeling of remote in situ monitoring of  weak distortions in ETM 

Ilya Kozhevatov, Efim Khazanov, Anatoly Malshakov, Oleg Palashov,

Anatoly Poteomkin, Alexander Sergeev, Andrey Shaykin, Victor Zelenogorsky

Optics group

Modeling of remote in situ monitoring of  weak distortions in ETM 

Ilya Kozhevatov, Efim Khazanov, Anatoly Malshakov, Oleg Palashov,

Anatoly Poteomkin, Alexander Sergeev, Andrey Shaykin, Victor Zelenogorsky

Optics group

Institute of Applied Physics of the Russian Academy of Sciences,603950, Nizhny Novgorod, Russia

White Light In Situ Measurement Interferometer

(WLISMI)

White Light In Situ Measurement Interferometer

(WLISMI)

Standard interferometers Proposed interferometers

Measurement of optical length of air spacing between two surfaces. In profilometers one of them is a sample surface, and the other is a reference surface. The problem of precise measurement of phase in the interferogram is solved by phase modulation according to a known time law.

The proposed method relies on measurements of the phase of interferogram of radiation reflected from two surfaces of one sample under study. The precise phase measurements are ensured by the modulation of the probing radiation spectrum. The method provides a two-dimensional pattern of a sample's optical thickness distribution simultaneously over the whole aperture. The method is applicable to remote testing of optical elements with flat, spherical and cylindrical surfaces, and also with a wedge between them.

White Light In Situ Measurement Interferometer. Experimental setup

White Light In Situ Measurement Interferometer. Experimental setup

1 - light source;

2 - objective;

3 - sample;

4 - ocular;

5 - measurement interferometer;

6 - unit for synchroni- zation and control;

7 - CCD camera;

8 - PC computer;

9 - modulating mirror;

10 - adjusting mirror;

11, 13 - motors;

12 - wave front shaper

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Setup.

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Setup.

Optical sample bulk heating by the fundamental or second harmonic of Nd:YAG laser at a power of 10-20 W

Surface heating with the use of a CO2 laser at power of several Watts

Inducing contamination of a small region (characteristic size of 20-100 micron) on the optical element's surface and focusing of low-power laser radiation (<100 mW) on it

2

Vacuum chamber

1

1

2 2

Heating CO2 laser

Sample

Heating Nd laser

1 - WLPMI 2 - NHS and PIT

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Simulation.

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Simulation.

RR

ZZ

TT

l

zzkliikl dzUnn

TnL

003

0

30 1

2

2

dL/dT effectdL/dT effect

dn/dT effectdn/dT effect

photoelastic effectphotoelastic effect

Z

R Rz

laser

sample

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Results.

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Results.

-0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04-0.5

0

0.5

1

1.5

2

2.5x 10

-7

R, mR, m

• BK7 glass• cylinder length 2 cm• cylinder radius 3.2 cm• CO2 laser power 0.1 W

experiment

theory

ddL,10L,10-7-7mm

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Results (2).

Remote in situ monitoring of weak distortions emerging under auxiliary laser heating. Results (2).

Heated by CO2 laser.No heating

rms=0.32nm (/2000)

How to install WLISMI in LIGO-I interferometer?Important points.

How to install WLISMI in LIGO-I interferometer?Important points.

1.     Interfering beam propagate mostly on the same path. The paths are different in the vacuum chamber.

2.     Interference pattern appears only if three following item coincide

         optical paths;

         angles of beams wave front;

         planes where image of the source is related

This tripled coincidence neglects influence of Fresnel reflections on the interference.

How to install WLISMI in LIGO-I interferometer?ETM, ETM telescope and vacuum window.

How to install WLISMI in LIGO-I interferometer?ETM, ETM telescope and vacuum window.

How to install WLISMI in LIGO-I interferometer?Idea.

How to install WLISMI in LIGO-I interferometer?Idea.

How to install WLISMI in LIGO-I interferometer?Experimental modeling of ETM in situ monitoring.

How to install WLISMI in LIGO-I interferometer?Experimental modeling of ETM in situ monitoring.

Glass type Radius of curvature, mm

Distance form vacuum window, mm

Lens LIGO IAP setup LIGO IAP setup LIGO IAP setup

L1 BK7 K8 368,3

4494.2

369.8

4529.0

2958.74 2974.75

L2 BK7 K8 78.88

-165.33

79.8

-165.96

2572.92 2537.45

L3 SF6 K8 - 64.39

- 70.49

- 63.68

- 70.05

2481.40 2481.40

How to install WLISMI in LIGO-I interferometer?Improvement of interferometer pattern.

How to install WLISMI in LIGO-I interferometer?Improvement of interferometer pattern.

How to install WLISMI in LIGO-I interferometer?Final design.

How to install WLISMI in LIGO-I interferometer?Final design.

How to install WLISMI in LIGO-I interferometer?Phase distortion dynamics movie.

How to install WLISMI in LIGO-I interferometer?Phase distortion dynamics movie.

CO2 laser power=1mW

CO2 laser beam diameter =1mm

Heating duration = 4min

Total movie duration= 12min

Sample aperture = 35mm

ConclusionConclusion

LIGO-IAP Lab has been equipped with several instruments developed at IAP for High-Precision Characterization of LIGO Optical Components

White Light In Situ Measurement Interferometer (WLISMI) for control of LIGO Core Optics has been implemented

Version of WLISMI for installation on the end station is modeled experimentally and ready to be installed.