Lasers- how are they use in communication... can a laser beam reach other planets with existing tech?

thats a negative

As far as I know, the farthest laser beam reflections we've detected are reflections from retro-reflectors placed on the Moon by the Apollo astronauts back 40 years ago.

Radar reflections have been detected from Venus, Mars, the Moon.

It is quite likely that a sensitive laser detector on Mars or Jupiter could detect a powerful laser beam from Earth.

The main scientific data derived from the laser experiments with the lunar retro-reflectors is precise measurement of lunar distance and the rate at which the Moon's orbit is growing larger with time. The radar experiments with Venus measured its distance, and gave us the first measurements of its rotational speed. Some terrain features (large mountains) were identified as well, but orbiting spacecraft radars and landers have given us good maps of the Venusian surface that confirmed the radar data.

Laser and radar remote sensing from Earth has the problem that signal levels of reflected energy fall off at a rate proportional to the fourth power of range. (Inverse square both ways!) Laser receivers are not as sensitive as the microwave receivers used in the planetary radar work. (The Venus radar work was done from Arecibo's huge radio telescope in Puerto Rico, back in the 1960s.)

It's easier just to send a probe there, and have the probe use radar on the planet, rather than trying to use it all the way from here. This has already been done a number of times, and has told us a lot about the surface features of Venus and Titan, and subsurface features of Mars.

Not lasers. But radar is routinely used to study Venus.

By sending probes as we are presently doing is the way to go, laser nah.