Laser communication with Proxima and Alpha Centauri using the solar gravitational lens

A search was conducted for laser signals, both sub-second pulses and continuous emission, from the regions of the sky opposite Proxima and Alpha Centauri. These regions are located at the foci of the gravitational lensing caused by the Sun, ideal for amplifying transmissions between our Solar system and those two nearest stellar neighbours. The search was conducted using two objective prism telescopes operating with exposure times of 0.25 s, enabling detection of sub-second laser pulses coming from the solar gravitational foci. During 6 months in 2020 and 2021, 88 000 exposures for Proxima Cen and 47 000 exposures for Alpha Cen were obtained. No evidence was detected of light pulses or continuous laser emission in the wavelength range of 380-950 nm. We would have detected a laser having a power of just 100 W, for a benchmark 1-m laser launcher that was diffraction-limited and located at the Sun's gravitational focus 550 au away. To be detected, that beam must intercept Earth either by intention or, by accident, or if intended for a probe near Earth that is communicating with another one at the solar gravitational lens. These non-detections augment a previous non-detection of laser light coming directly from Proxima Centauri conducted with the HARPS spectrometer on the ESO 3.6-m telescope.