Measurement of the laser beam profile

at PSL to Mode Cleaner interfacefor the 40 Meter Prototype

Interferometer

A table of contents 1. Introduction 1.1 LIGO Caltech 40 meter prototype 1.2 Mode Cleaner

2.Measurement of the laser beam profile

at PSL to Mode Cleaner interface 2.1 Objective 2.2 Method 2.3 Result

3.Conclusion

1.1 LIGO Caltech 40 meter

Output Mode Cleaner

⇒ Now we try to lock the mode cleaner !

⇒RSE for advanced LIGO

PSLTable

Mode Cleaner

Photo detector

What is general objective of 40m?

What is present status of 40m?⇒ PSL table

CompletedIoo

1.2 Mode　Cleaner

Why is Mode Cleaner needed?

Mode Cleaner delivers good quality beam

Low higher order mode Low frequency and amplitude

noise Low beam position and pointing

jitter Providing error signal to PSL to

stabilize frequency fluctuation

13m

MC2

MC1

MC3

TEM00

Laguerre-gaussian mode

Complete characterization of input optics and beam:

At “hand-off” for PSL to Mode Cleaner, andat periscope lens we have “IOO diagnostics” Beam transverse profile correctly mode-matched Beam position and angle are stable Beam intensity is stable (ISS, installed soon) Beam frequency fluctuations are stable (FSS)

2.1 objective

Lenses at correct position for maximum power transmission through EOM, Mode Cleaner

We call this Mode Matching

What is objective of my experiment?

Why do we need Mode Matching?Mode Matching transmits Maximum power of

beam from PMC cavity to MC cavity

Mode Cleaner (MC)

PSL Table Interferometer

Mode Matching lenses

Pre Mode Cleaner

2.2 MethodMeasurement of the laser beam profile

Step1Step1Measurement of the beam Profile after lens

Step2Step2Estimation of the error of

the lens position

Step3Step3Adjusting the lens

position. Repeat step1- 3 for 4

lenses

StepStep11

StepStep22

StepStep33

2.2 MethodPosition of profiling

laserpremode cleaner

EOM

Camera of BeamScan

①②③

④

⑤

PSL Table Vacuum Chamber

-W W

1/e2

2.2 Method

Inte

nsit

y BeamScan

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

0

0.5

1

1.5

2

2.5

3

3.5

distance from laser (mm)

beam

wid

th (

mm

) Gaussian Beam (TEM00) Propagation in PMC

positions of lensespositions of PMC/EOMxcoords of beamycoords of beam

2.3 Step1Step1Data of profilingBefore adjusting lenses

Reflected light 40%Transmitted light 60%

2.3 Step2Step2 Estimation of the error of the lens position

Error of the lens position

Error of the beam profile

adjusting the lenses2.3 Step2Step2

9mm 18mm

① ② ③ ④

8mm 0.2mm

Data of profilingAfter adjusting lenses

① ②③ ④ ⑤

2.3 Step3Step3Reflected light 13 ％Transmitted light 87 ％

Miss mode matching ratio(MM) 2%

ZdesignZdesignZmeasure

WdesignWdesignWmeasure

MM

22

2.3 Resultof improving mode matching

3. Conclusion

Before the experiments a lot of ring mode Profiling and Adjusting the lenses

Reflected light 40% ⇒ 13％ Transmitted light 60% ⇒ 87％

After the experiments TEM00 mode

Acknowledgment

Mentor : Dr. Alan Weinstein Osamu MiyakawaSurf Students : Ilya Berdnikov, Surjeet Rajendran, David Bonfield, Marcus Benna