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High Power Laser System for Advanced Virgo

C.N.Man

• Design goals• Present technology• Other activities in the world• Virgo+ and Laser System - possible planning

• Advanced Virgo HP laser• HP related photonics (fibers as MC, modulators,…)

• All-fibered laser system• Conclusion

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• Laser power: 200W • Wavelength : 1 m to 1.6 m, linked to

SiO2 or Si, laser material, optical technology,…

• Input Beam propagation: free space, fibre ?• Beam cleaning: resonant MC or fibre MC?• Modulation:

– Bulk, or fibre components ? Which frequency(ies) ?

Design goals

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Present technology : laser designs

High power cooling problem (birefringence induced by thermal loading, …) large surface/volume ratio and material conductivity high efficiency

Solutions : new crystals, or ceramics disk amplifiers or fibres

Today, kW single mode lasers are available with both disks and fibre

amplifiers

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Other activites in the world

- Laser systems (< kW)- GW groups activities: mainly Germany and Australia

-Scientific and telecom lasers (> 100 W)-Disks and fibre lasers, many European small companies

Yb and Er doped Fiber lasers: 1,06 and 1,3 m

-Nb: telecom lasers MTBF > 100 000 h Fibre integrated isolators, modulators, etc

1.3- 1.5 m wavelength

-Very high power lasers ( up to MW CW)-Disk lasers for military and industry : Boeing, …-Fibre lasers for welding, cutting (kW`s)

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Virgo + : First Step in the Studies

Virgo+: as master laser, Fiber laser or SSL HP Solid State laser/amplifier (LZH)

To start :1 - investigations on the FL as a

potential new Master laser2 - development of a 50 W

laser/amplifier in SS technologyDeliverables in 07-08:A Single-Frequency Fiber laser of 2W A laser amplifier to scale up the 20W to 50W

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Laser System for Virgo +

injection locking

20W laser

Master Laser

50W Amplifier PMC

Fiber laser

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Fiber Master Laser for Virgo +

100 mW Oscillator amplified to 2 W at 1.06 m

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Virgo + : Nd:YVO4 50WAmplifier (LZH)

Four-stage end-pumped Nd:YVO4

Each stage pumped by 45 W laser diode

Each diode indiv temp controlled

Each 2diodes connected in series to 1 current driver

Diodes current controlled

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Possible Planning for Virgo + Laser System

Task # 1 Master fiber laser

#1.1 Purchase a commercial fiber laser (Nice)

#1.2 Test of the free-running fiber laser (Nice)

#1.3 Design and realization of servo-loops (Nice)

#1.4 Charact. of the frequency stability (Nice)

#1.5 Injection locking o f the slave laser (Nice)

Tasks #2 50W laser amplifier

#2.1 Definition of specifications (Nice)

#2.2 Realization of laser amplifier (LZH)

#2.3 Test and characterization of amplifier (EGO & Nice)

#2.4 Design for slave–amplifier integration (EGO)

#2.5 Integration slave –amplifier (EGO & Nice)

#2.6 Virgo+ laser characterization (Nice & EGO)

2005 2006 2007 2008

Tasks and Deliverables Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3

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Adv. Virgo: HP single-mode fiber lasers

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HP related photonics

Modulation: Bulk, or fibre modulators ? (Which frequency(ies) ?)

Beam propagation: free space or through fibre ?

Fiber laser : no MC needed

SSL: resonant cavity MC or fibre MC?

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Requirements for mode cleaning

• Spatial filtering of modes

• Resonant mode close to a gaussian beam

• Output beam independent of input beam or ouput phase

noise independent of input beam jitter

• No addition of any extra noise

• Power standing required

Why using a fiber: simplicity of the system, its control and its maintenance

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PCF as Input Mode Cleaner

Photonic Crystal Fiber offers this possibility of power handling

Use of monomode fibers not realistic up to now, due to power handling capabilities

What is a PCF ?

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High Index Guiding Fiber

Light is guided in the core by total internal reflection: the airholes in the cladding make its effective index lower than

that of the core

NA = 0.8

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Low Index Guiding Fiber: Photonic bandgap fiber

Light is guided in the core by Bragg reflection caused by the spatial periodicity

of the holes in the cladding

B

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Fabrication of PCF

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PCF R&D financed by EGO

Started in 11/04 - Goals: test of a commercial PCF hollow-core fiber in terms of :

** Handling, Coupling efficiency, loss measurements

* Output Beam analysis, comparison with numerical modeling

(coll with IRCOM-Limoges, Blaze Photonics)

** Measurement of phase noise introduced by the fiber in a

normal environment

*** Power standing of 20W, Induced amplitude noise, Polarisation

noise (this fiber is not polar.maintaining fiber now),

dependency of input/output noise

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Results on hollow-core HC-1060-02

HC-1060-02 Blaze Photonics

Core 10 m, pitch 2.75 m, holey region diam 50 m

Attenuation < 0.1 dB/mMode field diameter 6.5 mFresnel reflection at end faces <10-4

No bend loss at 3 mm radius

Quasi-gaussian monomode >90%

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Experimental results (2005)

Coupling and handling like standard fibers; Attenuation loss measured 0.05 dB/m

coupling of 90% obtained: further improvements with a phase plate or an adaptive mirror

Transmission : output/input of 45% loss of 4.5% with a bending of 0.8 cm

Residual coupling between core and cladding modes due to imperfections

Measured near-field intensityInput face of the PCF

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Extra Noise measurement

The ouput of the PCF is

sent into a high finesse

Fabry-Perot as discriminant

=> no evidence of extra

frequency noise

No fast polarization &

amplitude noises

Power handling of 20W

To be done: Choice between hollow core PCF and large silica core PCF (30

µm)

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Available fiber components (for power <1W)

Faraday isolators (> 55 dB isolation)

Polarization controllers (20 kHz bandwidth)

Phase and amplitude modulators (GHz bandwidth, low voltage drive)

55 mm35 mm

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All-fibered Laser System

Amplifier

Beam monitoring

Oscillator(Nd-YAG or fibre

Frequency control

Amplitude control

Polarization control

Vacuum

Vacuum (optional)

Faradayisolator

100Wto interferometer

100 mW

Monomode fibre (PM?)

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Conclusion: Proposed main steps

- 2006 Acquisition and test 1-2 W fibre laser (Yb @ 1064 nm)

- Evaluation and control in Nice

- 2007 Test as a master laser in Cascina

Acquisition of a high power Yb-doped fiber amplifier

- 2009 ? Test of a HP Yb-doped fiber amplifier

- 2006-2008 Development and tests of a fibre mode-cleaner

- After the choice of advanced mirrors material:

- Definition and acquisition of the advanced laser system prototype

( 3 years ahead of installation)