In Young's Double Slit Experiment (YDSE), light from two coherent sources interferes to form a pattern on a screen.

• Fringe Width ($\beta$): The separation between two consecutive bright (or dark) fringes. $\beta =\frac{\lambda D}{d}$ where $\lambda$ is the wavelength, $D$ is the distance to the screen, and $d$ is the distance between the two slits.