A novel description, based on the Doppler effect, is given for laser

switching by a rotating mirror. Fourier analysis yields a relation between the width of the pulse

and the angular velocity of the mirror

. It is shown that for laser emission having a Gaussian spatial amplitude profile the temporal shape of a

-switched pulse is also Gaussian. It is predicted that for different lasers

switched by mirrors rotating with the same

will depend on the wavelength of the laser. For a ruby laser, measurements are reported of

versus

for different configurations of the cavity into which vertical and horizontal slits were introduced.