High power, single-frequency, monolithic fiber amplifier for the next generation of gravitational wave detectors

Abstract

Low noise, high power single-frequency lasers and amplifiers are key components of interferometric gravitational wave detectors. One way to increase the detector sensitivity is to increase the power injected into the interferometers. We developed a fiber amplifier engineering prototype with a pump power limited output power of 200 W at 1064 nm. No signs of stimulated Brillouin scattering are observed at 200 W. At the maximum output power the polarization extinction ratio is above 19 dB and the fractional power in the fundamental transverse mode (TEM 00) was measured to be 94.8 %. In addition, measurements of the frequency noise, relative power noise, and relative pointing noise were performed and demonstrate excellent low noise properties over the entire output power slope. In the context of single-frequency fiber amplifiers, the measured relative pointing noise below 100 Hz and the higher order mode content is, to the best of our knowledge, at 200 W the lowest ever measured. A long-term test of more than 695 h demonstrated stable operation without beam quality degradation. It is also the longest single-frequency fiber amplifier operation at 200 W ever reported.

Ultra-low intensity noise, all fiber 365 W linearly polarized single frequency laser at 1064 nm

“…For an undoped fiber with the same geometry we would expect to observe the onset of Brillouin scattering below 200 W. We think that the strong thermal gradient in the short length of doped fiber acts to broaden the Brillouin gain profile to push the SBS limit to higher powers. The fundamental question of frequency noise in fiber amplifiers has been investigated many time [19,20,23,24]. Apart from low frequency noise added from thermal and mechanical fluctuations, degradation of frequency noise in the amplification process is not expected but was not tested.…”

“…This large wideband control is a key factor for atomic physics [30]. The fundamental question of frequency noise in fiber amplifiers has been investigated many time [19,20,23,24]. Apart from low frequency noise added from thermal and mechanical fluctuations, degradation of frequency noise in the amplification process is not expected but was not tested.…”

“…Beam quality is an important parameter in high power lasers. Such LMA fibers are known to have a good modal content, where the TEM00 mode contains more than 95% of the power [19,20,29]. The M² measurement plotted on Fig 6. is below 1.1 on both optical axes.…”

“…More recently, Buikema et al [19] and Wellmann et al [20] proposed SF amplifiers using commercial fibers delivering respectively 178 W and 200 W of low noise optical power, suitable for next generation of GWD. In-depth investigations on the modal content or beam jitter shown that LMA fibers can guide highly stable beams with 95% of the power contained in the fundamental TEM00 mode.…”

“…In-depth investigations on the modal content or beam jitter shown that LMA fibers can guide highly stable beams with 95% of the power contained in the fundamental TEM00 mode. It is noticeable that in [20], the fiber is coiled in two parts to create a thermal gradient aiming to increase the SBS threshold. In addition, it is in a counter-propagative configuration with a free space injection of the signal in the final amplifier, adding complexity in the system.…”