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We propose and test an exchange gas technique for improving the cooldown times of cryocooled gravitational-wave interferometers. The technique works by utilizing low-pressure dry nitrogen gas to create a path for heat conduction to test masses while protecting the rest of the in-vacuum equipment from unwanted heat leakage. We show that the technique is capable of shortening the total wait time to reach the operating temperature by a factor of 3.5. Additionally, our tests show that the improvement in the heat transfer rate can be predicted to be within 10% error by using the Sherman-Lees interpolation equation. The technique is compatible with vibration isolation requirements of the cryogenic shielding of 124 K silicon interferometers and has the potential to improve the iteration time for research and development. The scalability of the prototype, the ability to predict the heat conduction, and the simplicity of the engineering make the strategy a good candidate to be included in the cryogenic design of future cryocooled gravitational-wave interferometers. The findings mark a first step in the investigation for a strategy to mitigate ice formation on the interferometer optics during initial cooldown. 

Small, highly absorbing points are randomly present on the surfaces of the main interferometer optics in Advanced LIGO. The resulting nanometer scale thermo-elastic deformations and substrate lenses from these micron-scale absorbers significantly reduce the sensitivity of the interferometer directly though a reduction in the power-recycling gain and indirect interactions with the feedback control system. We review the expected surface deformation from point absorbers and provide a pedagogical description of the impact on power buildup in second generation gravitational wave detectors (dual-recycled Fabry–Perot Michelson interferometers). This analysis predicts that the power-dependent reduction in interferometer performance will significantly degrade maximum stored power by up to 50% and, hence, limit GW sensitivity, but it suggests system wide corrections that can be implemented in current and future GW detectors. This is particularly pressing given that future GW detectors call for an order of magnitude more stored power than currently used in Advanced LIGO in Observing Run 3. We briefly review strategies to mitigate the effects of point absorbers in current and future GW wave detectors to maximize the success of these enterprises.