Question

How can I find the force of a laser given wavelength and power? Is it just momentum or momentum multiplied by number of phtons or something else?

Answer 1

Let be the power of Laser light and be the wavelength.

Then momentum of each photon-

and energy of each photon-

now since power is P so it means total energy emitted by laser=P joule per second

So total number of photons emitted per second by the laser source-

So total momentum carried by n photons per second

                   

                  

                  

When laser strikes a surface(suppose normally) then all photons gives their momentum to the surface.

Since total momentum per second is equal to the applied force so radiation force produced by this beam will be equal to the momentum carried by n photons per second i.e.-