Lunar Silicon Cavity

Abstract

The Moon's permanently shadowed regions (PSRs) are among the coldest places in the Solar System and are expected to become key landing sites for upcoming international space agency missions. Their proximity to peaks of perpetual solar power and potential resource richness makes them prime candidates for lunar exploration and future Moon bases. Here we propose to deploy a passive, ultrastable optical resonator in these regions that will enable laser systems with unprecedented phase-coherence. The unique physical environment of lunar PSRs greatly benefits the construction of a cryogenic monolithic silicon cavity that exhibits low $10^{-18}$ thermal noise-limited stability and coherence time exceeding 1 minute, more than a decade better than the current best terrestrial system. Such a stable laser will form a basic quantum technology infrastructure in space to serve many applications, including establishing a lunar time standard, building long-baseline optical interferometry, distribution of stable optical signals across networks of satellites, testing general relativity and gravitational physics, and forming the backbone for space-based quantum networks.

Figures (3)

• Figure 1: Conceptual design of a cryogenic silicon cavity based on radiative cooling. The whole system supported by the thermal insulated posts is constructed on the lunar surface. Two radiators, both facing the deep space, provide cooling for an outer radiation shield and an inner actively controlled thermal shield for a 17 K operating temperature where the silicon thermal expansion coefficient is zero. A continuous-wave laser is sent into the cavity chamber via a fiber-optic feedthrough or free-space motorized mirrors and coupled to the silicon cavity with a collimator.
• Figure 2: Comparison of terrestrial and lunar vibration-induced fractional frequency noise. The blue shaded region denotes lunar seismic vibration noise in the vertical direction) from the Apollo missions, scaled by the measured vertical acceleration sensitivity of the 21 cm cavity ($1.5\times 10^{-11}/g$), and spanning the 10th to 90th percentile range. These data were constructed and analyzed by Nunn2021 from multiple Apollo stations operated in both flat-response and peak-mode seismometer configurations. The orange trace shows an example of typical terrestrial laboratory vibration conditions with considerable vibration control effort. The dashed lines indicate the thermal noise levels for the 21 cm cavity with conventional and crystalline coatings respectively.
• Figure 3: Application of a lunar PSR silicon cavity as the basic infrastructure for lunar time scale, Earth-Moon optical communication, satellite-based space interferometry and imaging, and networking to Earth-bound time scale. Lunar PSR background image produced by NASA's visualization studio NASA_visualization.