This experiment was first demonstrated by A. L. Schawlow(1).
In this experiment you measure the laser wavelength with a simple ruler (!) …
Schawlow is the scientist who received the Nobel price for the invention of the idea of the laser.
Objective: To calculate the wavelength of laser light using a simple ruler as a diffraction grating.
Theory: In this interference experiment, a simple ruler will serve as a grating.
The experimental set up is shown in Figure 1:
i = Angle between the laser beam and the perpendicular to the ruler.
qm = Angle between the perpendicular to the ruler and the reflected beam.
d = Smallest distance between neighboring marks on the ruler.
L = Distance from the ruler (where the laser beam hits) to the screen.
a = Grazing angle between the ruler and the original direction of the laser beam (very small angle, between 2-60).