We can say that the components of ANY light oscillate perpendicular
to the direction of propagation ... left and right, up and down, upper left
and lower right, upper right and lower left, etc. ... any direction ACROSS
the direction of propagation, just not forward and backward.
If the light is polarized, then the Ɛ-field (electrostatic) component of
the wave can only oscillate in the polarized direction ... say, left and
right across the direction of propagation. (The magnetic component
is always perpendicular to the electrostatic component. So if the
polarizer is left/right, then the magnetic component is up/down.)
Any light that doesn't oscillate in the direction selected by the polarizer
gets absorbed in the polarizer, and doesn't come out the other side.
That's why when you pass light through a polarizer, it comes out dimmer
than it went in.
LASER light is always naturally polarized before it comes out of the diode
or whatever is generating it. That's another advantage of laser light.
