All gravitational-wave observatories (GWOs) have been using the laser wavelength of 1064 nm. Ultra-stable laser devices are at the sites of GEO 600, Kagra, LIGO, and Virgo. Since 2019, not only GEO 600, but also LIGO and Virgo have been using separate devices for squeezing the uncertainty of the light, so-called squeeze lasers. The sensitivities of future GWOs will strongly gain from reducing the thermal noise of the suspended mirrors, which involves shifting the wavelength into the 2 µm region. This Letter aims to reuse the existing high-performance lasers at 1064 nm. Here we report the realization of a squeeze laser at 2128 nm that uses pump light at 1064 nm. We achieve the direct observation of 7.2 dB of squeezing as the first step at megahertz sideband frequencies. The squeeze factor achieved is mainly limited by the photodiode’s quantum efficiency, which we estimated to $({92}\;{\pm}\;{3})\%$. Reaching larger squeeze factors seems feasible also in the required audio and sub-audio sideband, provided photo diodes with sufficiently low dark noise will be available. Our result promotes 2128 nm as the new, to the best of our knowledge, cost-efficient wavelength of GWOs.

中文翻译：

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用于未来引力波天文台的 2128 nm 压缩光

所有引力波天文台 (GWO) 一直在使用 1064 nm 的激光波长。超稳定激光设备位于 GEO 600、Kagra、LIGO 和 Virgo 的站点。自 2019 年以来，不仅 GEO 600，LIGO 和 Virgo 都在使用单独的设备来压缩光的不确定性，即所谓的挤压激光器。未来 GWO 的灵敏度将从降低悬浮反射镜的热噪声中大大提高，这涉及将波长转移到 2 µm 区域。这封信旨在重复使用现有的 1064 nm 高性能激光器。在这里，我们报告了使用 1064 nm 泵浦光的 2128 nm 挤压激光器的实现。作为在兆赫边带频率的第一步，我们实现了对 7.2 dB 压缩的直接观察。$({92}\;{\pm}\;{3})\%$。如果提供具有足够低暗噪声的光电二极管，在所需的音频和亚音频边带中达到更大的压缩因子似乎也是可行的。据我们所知，我们的结果将 2128 nm 推广为新的、具有成本效益的 GWO 波长。