Multiple Light Spots Before Beam Expander in Michelson Interferometer

Before the beam expander in a Michelson interferometer experiment, several light spots may be observed on the screen due to the interference of multiple beams.

In the Michelson interferometer, the incoming light is divided into two beams by the beam splitter. One beam travels directly towards the screen, while the other beam is reflected off a mirror and then reaches the screen. These two beams interfere with each other when they recombine at the screen, resulting in an interference pattern.

The interference pattern consists of bright and dark fringes. However, before reaching the beam expander, the beams may have slightly different path lengths or angles, causing them to interfere at different points on the screen. This leads to the observation of multiple light spots instead of a clear interference pattern.

The purpose of the beam expander is to expand the beams, making them parallel and collimated, which helps in obtaining a well-defined interference pattern with distinct fringes. By adjusting the beam expander, the multiple light spots observed before can be reduced, and a more precise interference pattern can be achieved for accurate analysis.