Photons in a laser beam have the same energy, wavelength, polarization direction, and phase because?

all photons are alike

regardless of their emission source

all come from the same atom

the lasing material has only two quantum states

each is produced in an emission that is stimulated by another

Explanation

Lasers operate on the principle of stimulated emission, proposed by Einstein.

In stimulated emission, an incoming photon stimulates an excited atom to drop to a lower energy level, releasing a new photon.

This new photon has:

Same energy
Same wavelength
Same polarization
Same phase and direction
as the photon that stimulated it.

Because of this process, all photons in a laser beam are coherent, monochromatic, and travel in the same direction — a unique property of laser light.