50 W Laser Concepts for Initial LIGO

Lutz Winkelmann, Maik Frede, Ralf Wilhelm, Dietmar Kracht

Laser Zentrum Hannover

LSC March 05Livingston

G050161-00-Z

Overview:

• Two concepts for a 50W laser for initial LIGO

– Conceptional design

– Experimental Setup

– Presentation of computational and measured data

• Comparison of both concepts

• Summary

High-Power Nd:YAG Multi-Pass Amplifier

First Concept

High-Power Nd:YAG Multi-Pass Amplifier

First Concept

- water-cooled rod mount

- 40 mm Nd:YAG 0.1at.% doped crystal with 7 mm undoped end caps on both sides

laser-head with:

- 10x400 µm fibers each 30 W

- pump light homogenizer

- pump light optics

Single-Pass Output PowerCalculated Data

0 50 100 150 200 250 300 3500

5

10

15

20

25

30

outp

ut p

ower

(W

)

pump power (W)

Pcal @ 1W Input Pcal @ 6.3W Input Pcal @ 9W Input

max. estimated output power 26.5W

Single-Pass Output PowerExperimental Data

max. measured output power 26.1W

0 50 100 150 200 250 300 3500

5

10

15

20

25

30

outp

ut p

ower

(W

)

pump power (W)

Pcal

@ 1W Input

Pcal

@ 6.3W Input

Pcal

@ 9W Input

Pout

@ 1W Input

Pout

@ 6.3W Input

Pout

@ 9W Input

Single-Pass GainCalculated Data

0 2 4 6 8 100

1

2

3

4

5

sing

le-p

ass

gain

seed power (W)

Pcal

@ 300W pump power

Pcal

@ 163W pump power

max. estimated small signal gain of 4.3

@ 300W pump power

Experimental Data

Single-Pass Gain

0 2 4 6 8 100

1

2

3

4

5

sing

le-p

ass

gain

seed power (W)

Pcal

@ 300W pump power

Pcal

@ 163W pump power

Pout

@ 300W pump power

Pout

@ 163W pump power

max. measured small signal gain of 4.4

@ 300W pump power

Double-Pass Output PowerCalculated Data

0 50 100 150 200 250 300 3500

5

10

15

20

25

30

35

outp

ut p

ower

(W

)

pump power (W)

Pcal

@ 1W Input

Pcal

@ 6.3W Input

Pcal

@ 8.2W Input

max. estimated output power 31W

@ 300W pump power

Experimental Data

Double-Pass Output Power

0 50 100 150 200 250 300 3500

5

10

15

20

25

30

35

outp

ut p

ower

(W

)

pump power (W)

Pcal

@ 1W Input

Pcal

@ 6.3W Input

Pcal

@ 8.2W Input

Pout

@ 1W Input

Pout

@ 6.3W Input

Pout

@ 8.2W Input

max. measured output power 31.2W

@ 315W pump power

Double-Pass GainCalculated Data

0 2 4 6 8 100

2

4

6

8

10

12

14 Pcal

@ 300W pump power

Pcal

@ 163W pump power

doub

le-p

ass

gain

seed power (W)

max. estimated small signal gain of 15

@ 300W pump power

Double-Pass GainExperimental Data

0 2 4 6 8 100

2

4

6

8

10

12

14 Pcal

@ 300W pump power

Pcal

@ 163W pump power

Pout

@ 300W pump power

Pout

@ 163W pump power

doub

le-p

ass

gain

seed power (W)

max. measured small signal gain of 11

@ 300W pump power

Second ConceptNd:YVO4 4 Rod Amplifier

Experimental SetupNd:YVO4 Laser Amplifier

Nd:YVO4 Laser Amplifier

Experimental Setup

- passively cooled crystal mount

- 8 mm Nd:YVO4 rod with 2 mm undoped end cap

- first experimental setup for single-pass measurements

Single-Pass Output Power

Calculated Data

0 5 10 15 20 25 30 350

5

10

15

20

25

30

outp

ut p

ower

(W

)

pump power (W)

Pcal

@ 14W seed power

Pcal

@ 10W seed power

max. estimated output power 18.2W

@ 10W seed power

Single-Pass Output Power

Experimental Data

0 5 10 15 20 25 30 350

5

10

15

20

25

30

outp

ut p

ower

(W

)

pump power (W)

Pcal

@ 14.5W seed power

Pcal

@ 10W seed power

Pout

@ 14.5W seed power

Pout

@ 10W seed power

max. measured output power 17.9W

@ 10W seed power

Single-Pass GainCalculated Data

0 2 4 6 8 10 12 14 160,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

sing

le-p

ass

gain

seed power (W)

Pcal

@ 30.5W pump power

max. estimated small signal gain of 3.6

@ 30.5W pump power

Single-Pass Gain Experimental Data

0 2 4 6 8 10 12 14 160,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

4,0

4,5

5,0

5,5

sing

le-p

ass

gain

seed power (W)

Pcal

@ 30.5W pump power

Pout

@ 30.5W pump power

max. measured small signal gain of 5

@ 30.5W pump power

Simulation of a 4 Rod Amplifier

Amplifier with multiple single-pass rod cascade Pin = 10W

estimated output power 50W @ 125W pump power

0 5 10 15 20 25 30 350

10

20

30

40

50

60ou

tput

pow

er (

W)

pump power per crystal (W)

single rod amplifier double rod amplifier triple rod amplifier quadruple rod amplifier

Comparison of Both Concepts

Single-pass output power at 10W seed power:

26.1W 17.9W

Single-pass opt.-opt. efficiency:

8.3% in single-pass operation

at 315W pump power

26% in single-pass operation at 30.5W pump power

Estimated efficiency of 40% for 4 rod cascade

Depolarization compensation:

thermal birefringence

=> compensation required

natural birefringence

=> no compensation necessary

Mechanical design: water-cooled rod mount passively cooled rod mount

Nd:YAG Amplifier

Nd:YVO4 Amplifier

Summary

• Both concepts seems to be suitable for the 50W initial LIGO laser

• More experimental measurements and simulations have to be performed to make a final decision

Beam Profile Measurements

Seed source Full pumped amplifier