It would take very little effort if you are talking about a missile. Aluminum is one of cheapest metals, and it provides high reflectivity through all the typical light frequencies, including IR.
If the missile is absorbing 10% of the incoming power and reflecting 90% away then the 50 kW becomes 5 kW. If you also spin the missile it spreads the spot over the missile's body (in a band.) Combine this with instability of the beam that in part instrument-dependent (accuracy of aiming) and in part environment-specific (air distorts light) and you end up with needing 10x more power to be effective. Do not forget about the range either; if there is a nuke coming, shooting its carrier missile in terminal phase and only a mile away is pointless.
But ultimately this is the solution, as lasers become bigger and badder. Laser guns can be already mounted in stationary installations or where there is enough power for them. They have infinite ammo, and their rate of fire is only limited by the power supplies and by cooling - which is a solvable technical problem. IR laser beams are also invisible to the naked eye, and goggles are just another thing that may fail (and will fail after seeing a small reflection of the beam.)
We will have to develop “hand held laser guns” to get around the upcoming gun bans...
We will use 3-D printers to “print” the casings/body of such weapons and use multiple refracted diode lasers along with lithium ion cell and heavy duty capacitors to get enough energy for short lethal bursts....
Feed a capacitor with lithium ion batteries and let it rip...
I think use either an infrared or ultraviolet laser wavelength....