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Increasing the laser power incident on the recycling mirrors

Doug Cook and Rick SavageLIGO commissioning meeting Dec. 22, 2003

Ref. LIGO-T030288-00-W

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LIGO I design requirementscirca 1995

6 watts of laser power incident on the recycling mirror

8.5 watts of laser power delivered to the IOO subsystem

10 watts of laser power delivered by the 126MOPA laser (Lightwave)» In a circular TEM00 mode

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Present PSL/IOO optical layout

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Example power budget

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

10 Watts 85%

90 %

85 %

92 %

T =

60 %

PSL IOO

RM

8.5 Watts

6.0 Watts

Visibility = 88%

Visibility = 95 %

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Present H1 power budget

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

6.15 Watts

75 %

86 %

64 %

93 %

T =

38 %

PSL IOO

RM

4.61 Watts

2.36 Watts

Modematching = 87.5%

Visibility = 86 %

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Present H2 power budget

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

6.58 watts 85.0 %

75 %

88.5 %

82 %

PSL IOO

RM

5.59 watts

3.04 watts

Visibility = 95 %

Visibility = 97 %

T =

46 %

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Present L1 power budget

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

7.5 watts

73.3 %

83 %

?? %

?? %

PSL IOO

RM

5.5 watts

??? watts

Visibility = 80 % ?

Visibility = ?? %

4.56 watts

T =

?? %

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Options for improvementoutside of the vacuum system

Increase 126MOPA power» Rebuild at Lightwave (LTW) to original specification.

– Doesn’t include NPRO

» Modify upstream PSL layout to facilitate swapping lasers– Mount phase-correcting EOM outside laser head– Add /2 plate and polarizer to set power to FSS and PMC paths– Modematch upstream of FSS/PMC splitter

Mount PMC inside a vacuum chamber» Reduce mirror losses from hundreds to ~ 50 ppm

Implement single EOM modulation scheme» Eliminate two EOMs from beam path

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Proposed upstream PSL layout changes

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PMC transmission vs.mirror losses

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Expected H1 budgetwith only ‘outside’ improvements

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

11 Watts

85 %

90 %

64 %

93 %

T =

46 %

PSL IOO

RM

9.35 Watts

5.01 Watts

Modematching = 87.5%

Visibility = 86 %

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Expected H1 budget ifMC mirrors are also replaced

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

11 Watts

85 %

90 %

90 %

93 %

T =

64%

PSL IOO

RM

9.35 Watts

7.04 Watts

Modematching = 87.5%

Visibility = 95 %

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Expected H2 budgetwith only ‘outside’ improvements

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

11 watts 85.0 %

90 %

88.5 %

82 %

T =

56 %

PSL IOO

RM

9.35 watts

6.11 watts

Visibility = 95 %

Visibility = 97 %

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Expected H2 budget ifFaraday isolator is also replaced

T 126 MOPA

T PMC

T EOMS

T MC

T FARADAY

11 Watts

85 %

90 %

90 %

93 %

T =

64%

PSL IOO

RM

9.35 Watts

7.04 Watts

Modematching = 87.5%

Visibility = 95 %

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Options for increasing the input laser power above the 11 W level

Rebuild the 126MOPA at LTW to 15-20 level» LTW technicians have indicated this is feasible

» May have been demonstrated in another LTW product

Replace the PA pump diodes with higher power units» LTW has identified new vendor and are starting to use them in

another product (Model 6000?). Stability issues?

Add a second amplifier head after the 126MOPA» Stanford has tested this configuration for Adv. LIGO PSL

development work

Accelerate procurement of Adv. LIGO laser from Hannover/LZH.