1. Fiber lasers for GW detectors
Alain Brillet
ARTEMIS
Observatoire de la Côte d’Azur
21/10/2011
ASPERA meeting

2. Main requirements CW, single frequency, single mode
High power: 10W (1990)  200W (2015)
Low noise : frequency: linewidth in µHz range
power: RIN in -180 dB range
geometry: Gaussian coupling > 90%
Lifetime, MTBF : >> hours
Low scatter ( IR)
Stability, No maintenance: 24h/day operation
Good efficiency: thermal management
21/10/2011
ASPERA meeting

3. First laser generations
Before 1985 : few possibilities  Argon lasers (515 nm)
satisfy points 1 and 2, can be stabilized, but ineficient and irreliable
1985 Diode pumping introduces stable Nd-YAG’s (low power)
1986 Stanford promises 100 W green Nd-YAG (532 nm) to LIGO…
1989 Virgo chooses 1064 nm and develops 1st 18W injection-locked Nd-YAG amplifier
1993 (?) GEO and TAMA (Japan) choose 1064 nm
1996 LIGO moves from Argon to Nd-YAG
1998 (?) LZH produces 20 W Nd-YVO4 amplifier for Virgo
2008 (?) LZH produces 200W amp. For LIGO
2009 Virgo tests 100W fiber amplifier from NUFERN (USA)
2010 Virgo chooses fiber technology
2011 Virgo tests 100W rod-fiber amp. from EOLITE (F)
21/10/2011
ASPERA meeting

4. Present laser design EOM 0.5-1 W Nd:YAG
Fibre coupled 1W Nd:YAG oscillator
(Innolight)
Frequency control via PZT and EOM
(as for Virgo)
EOLITE 2 stage rod amplifier
300 mW 12W by 80 cm rod
(50W pump diode)
12W  100W by 110 cm rod
( 200W pump diode)
Power control via pump current
(as for Virgo)
Fiber links  stable alignment
Rod design : air clad all silica: no polymers  robust
976 nm pump diodes : h MTBF
21/10/2011
ASPERA meeting

5. 2nd amplifier stage : recent results
21/10/2011
ASPERA meeting

6. What next ? Higher power: 3 possibilities
Higher pump power (400W pump already available)
3 rd stage : 100W  200W
Shorter wavelength
Efficiency is higher at 1030 nm:
220W pump  150W output instead of 100W for 220W at 1064nm
Fiber delivery and mode cleaning
Requires PM-LMA fiber with acoustic antiguiding
21/10/2011
ASPERA meeting

7. Limitations SBS (Stimulated Brillouin Scattering) PD (PhotoDarkening)
Brillouin scattering generates a contrapropagative signal (and phonons)
Power threshold is proportional to core area, and to inverse fiber length, typically Pth = 1014 m-1 (i.e. 100W  S=100µm2, L=1m)
Solutions : phonon anti-guiding  Pth = 1015, 500µm2  50 kW.m
PD (PhotoDarkening)
A high concentration of Yb doping ions generates sites for absorbing color centers  fiber absorption increases, (efficiency drops), then saturates.
(no obvious PD problem up to now in 300W EOLITE lasers)
Solution, if needed : fiber co-doping with Cerium (Ce) or Phosphorous (P) ions
21/10/2011
ASPERA meeting

8. 21/10/2011
ASPERA meeting