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

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 : >> 10 000 hours Low scatter ( IR) Stability, No maintenance: 24h/day operation Good efficiency: thermal management 21/10/2011 ASPERA meeting

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

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 : 100 000 h MTBF 21/10/2011 ASPERA meeting

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

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

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

21/10/2011 ASPERA meeting