5 W ultra-low-noise 2 µm single-frequency fiber laser for next-generation gravitational wave detectors
Qian Zhang, Yubin Hou, Xi Wang, Weihua Song, Chen Xu, Bin Wu, L. Ju, C. Zhao, Pu Wang
Abstract
We demonstrated an ultra-low-noise polarization-maintaining (PM) single-frequency fiber laser at 2 µm. Both relative intensity noise (RIN) and frequency noise were improved by suppressing the pump source RIN using feedback control. After a two-stage <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msup> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">T</mml:mi> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mn>3</mml:mn> <mml:mo>+</mml:mo> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> -doped PM fiber amplifier, the output power reached about 5 W, and the amplifier did not introduce any observable extra frequency noise. The frequency noise was less than <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mn>100</mml:mn> <mml:mspace width="thickmathspace"/> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">z</mml:mi> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mo>/</mml:mo> </mml:mrow> </mml:mrow> <mml:msqrt> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:mi mathvariant="normal">H</mml:mi> <mml:mi mathvariant="normal">z</mml:mi> </mml:mrow> </mml:msqrt> </mml:math> above 13 Hz, which is comparable to the frequency noise of a typical seed laser of the Advanced LIGO high-power laser. The central wavelength was measured to be 1990.25 nm, with a polarization extinction ratio above 24 dB.