And years later to find out if you were correct.

I like the idea of trying this to accelerate a probe to high speed. But then it is Newton in the captain’s chair.

But there are now numerous projects investigating concepts related to laser powered sailcraft Many of these involve nanospacecraft (chips).
I don’t see what good they would do, but the interest does seem widespread, and prelim studies are being funded. Check out the centauri-dreams.org website.

I must be missing something.

I do know there is a method of using lasers to decelerate upon arrival, you can look it up it in Matloff and Mallove’s “Starflight Handbook”. Again, it violates no physical law, but it does seem rather cumbersome, it employs a sort of Schmidt Cassegrain set of sails in a Rube Goldberg, double reflection arrangement. At any rate, it could always be just a fly-by mission. A return trip, or a stop is not really necessary.

And of course, optical lasers may not necessarily be the tech used. There are other regions of the spectrum…

If I have time I will try and do some calculations…

And most of the proposals require that the payload be exceedingly small. How could a small payload ever send data back across lightyears once it got to its destination?

The sail would need to be exceedingly thin and lightweight – but space is not empty- at relativistic speeds pebbles, dust and even the stray hydrogen atoms would quickly erode it away.

Could you illuminate it uniformly enough to avoid tearing it apart?

The more intense the laser is on the sail, the less time you need to accelerate it to the speed you want- but there is an upper limit to the intensity the sail can withstand- no matter how reflective it is, if the intensity reaches the point that it has a real chance of causing multiphoton ionization (MPI) then your sail will quickly turn into plasma. MPI- lets say the photons you are sending have low energy- no single photon has the energy to ionize the atoms in your sail… but you turn up the intensity to the point where there is a good chance that an atom in the sail will be able to absorb multiple photons at the same time… at some point you will reach the point that probability of ionization is high… at which point your sail vaporizes.

If your transmitter is in space then you have Newton’s 3rd law to contend with- your transmitter will experience a recoil force as it beams photons out in one direction. if its floating in space how do you keep it in place?

If your transmitter is on earth, then the atmosphere would cause you no end of problems as well as restricting your maximum intensity even further… so building it on a large airless body would make the most sense…

Targeting and beam control would be very challenging, but since we are already assuming advanced technology and engineering I won’t say its impossible…

But what would be the purpose? You wont get any data from the payload when its lightyears away (the starshot initiative proposal I saw was to send a payload that was exceedingly small, like a microchip) so what is the point of such a monumental endeavor?