Twyman-green specialization of michelson interferometer
Twyman-green
specialization of michelson interferometer
Twyman-Green
modified Michelson interferometer utilises a pin-hole source diaphragm and
collimating lenses. In
this way, all rays are rendered parallel to the central rays and thus all rays
describe the same path. All
modern two-beam interferometers are based on this arrangement. The mirrors M1
and M2 are arranged perpendicular to the optical axis. If
mirror M1 is kept fixed and M2 is moved slowly exactly parallel to itself, the
observer will note periodic changes in the intensity of the field being viewed,
from bright to dark for every λ/2 movement of the mirror. In
fact intensity variation is found to be sinusoidal. It
may also be noted that if one of the mirrors is even slightly inclined to the
optical axis then parallel fringes will be seen moving parallel to themselves
by just one fringe for every λ/2 (half the wavelength of the light source used)
mirror motion. Usually
it is quite difficult to count such fringes by eye. However,
photo detectors connected to high speed counters can do this job very
accurately (accuracy of one part in million being obtainable).