According to some scientists, for example Stephen Hawking, it may not be a good idea. But theoretically it could work: with the current technologies we could create infrared radiation powerful enough to be visible from Proxima Centauri.
If somewhere in the Milky Way existed a civilization evolved enough to be able to observe in the direction of the Sun in search of life forms, we could take advantage of the laser technology currently available on Earth to create a sort of interstellar torch, a beacon that signal our presence in space.
According to this study, published in the journal Astrophysical Journal, focusing a 2 megawatt laser power on a 30 to 45 meter diameter telescope pointed towards the sky, we would get a beam of infrared light quite intense to be distinguished from solar radiation, recognizable from those who took the trouble to analyze the light spectrum of our star.
This signal could be captured without too much difficulty by any alien astrophysicists living on nearby planetary systems, for example around Proxima Centauri, the star closest to Earth, or in the star system of TRAPPIST-1, a star about 40 light years, around to which 7 exoplanets orbit, at least 3 of which potentially habitable. If the signal was noticed, the same laser could be used to send short messages in light pulses, in a sort of infrared Morse code. Moreover using a mega telescope to further focus the intensity of the laser, the signal would be at least 10 times more intense than the natural variability of the Sun in infrared emissions.
Proxima centauri b
For example, with a 2 megawatt laser pointing at a 30-meter telescope, we would produce a signal easily distinguishable from Proxima Centauri b, an exoplanet 4 years light away from us. Instead, with a 1 megawatt laser and a 45-meter telescope, we could signal our position to an inhabitant of TRAPPIST-1.
But if someone had sent the same signal in our direction, would we be able to find it with the tools we have?
According to James Clark, researcher at the Department of Aeronautics and Astronautics at MIT and author of the study, a 1 meter telescope would be enough to distinguish such a signal. The problem is that it should be pointed in the exact direction of the laser sent. It is therefore advisable to develop increasingly powerful infrared technologies, not so much to capture alien laser signals, but to analyze the gaseous envelopes around the exoplanets we study, a scientifically more effective method to understand if there are conditions suitable for life.