Cavity-Enhanced Sum Frequency Generation for 2 um Interferometer Readout

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Abstract:: Next-generation gravitational-wave detectors are exploring interferometry at 2 um laser wavelength to reduce thermal noise sources and improve detector performance. Efficient photodetection at these wavelengths remains a challenge due to the lack of high-quantum-efficiency detectors. Sum-frequency generation (SFG) offers an alternative way by upconverting 2 um light to visible wavelengths, where high-QE detectors are readily available. In the proposed experiment, a strong 1064 nm pump beam is resonantly enhanced in a bow-tie cavity and combined with a weak 2 um signal beam inside a PPLN crystal to produce 700 nm light. This project works toward a proof-of-principle demonstration of this scheme, beginning with locking and characterizing the 1064 nm cavity before introducing the crystal and signal beam. The developments in this work bring the cavity meaningfully closer to a stable lock laying the groundwork for crystal integration and SFG measurement planned in subsequent stages of the project.

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LIGO Document T2600275-v2