Performance study of a high-power single-frequency fiber amplifier architecture for gravitational wave detectors

Widely-tunable single-frequency diamond Raman laser

We report a diamond Raman laser that is continuously-tunable across the range from 590 nm to 625 nm producing continuous wave output with up to 8 W. The system is based on an all-fiber and tunable (1020-1072 nm) Yb-doped pump laser with a spectral linewidth of 25 GHz that is Raman-shifted and frequency doubled in a cavity containing diamond and a lithium triborate second harmonic crystal. Despite the broad pump spectrum, single frequency output is obtained across the tuning range 590-615 nm. The results reveal a practical approach to obtain tunable high-power single-frequency laser in a wavelength region not well served by other laser technologies.

Low noise 400 W coherently combined single frequency laser beam for next generation gravitational wave detectors

Design studies for the next generation of interferometric gravitational wave detectors propose the use of low-noise single-frequency high power laser sources at 1064 nm. Fiber amplifiers are a promising design option because of their high output power and excellent optical beam properties. We performed filled-aperture coherent beam combining with independently amplified beams from two low-noise high-power single-frequency fiber amplifiers to further scale the available optical power. An optical power of approximately 400 W with a combining efficiency of more than 93% was achieved. The combined beam contained 370 W of linearly polarized TEM₀₀-mode and was characterized with respect to the application requirements of low relative power noise, relative beam pointing noise, and frequency noise. The noise performance of the combined beam is comparable to the single amplifier noise. This represents, to our knowledge, the highest measured power in the TEM₀₀-mode of single frequency signals that fulfills the low noise requirements of gravitational wave detectors.

Advanced LIGO Laser Systems for O3 and Future Observation Runs

The advanced LIGO gravitational wave detectors need high power laser sources with excellent beam quality and low-noise behavior. We present a pre-stabilized laser system with 70 W of output power that was used in the third observing run of the advanced LIGO detectors. Furthermore, the prototype of a 140 W pre-stabilized laser system for future use in the LIGO observatories is described and characterized.