Rami Arieli: "The Laser Adventure" Divergence Lab., Page 2

Experimental Procedure :

This experiment is best performed in a long corridor, with the lights off.
For safety reasons, it is suggested to put the laser on the floor.

Figure 1: Measuring Beam Divergence. (Diverge1.jpg)

Place the screen, supported by the magnetic mount, directly in front of the He-Ne laser, so that the light from the laser is perpendicularly incident on the screen.
Put the He-Ne laser on the table, make sure the area where the laser beam is pointing is clear.
Place the screen at a few different positions, starting close to the laser and finishing at large distances a few meters away from the laser (the further the better).
Measure and record (on the data sheet) the distance of screen from the laser L
Measure and record (on the data sheet) the diameter of the beam D on the screen.

Determining the exact diameter of the beam is difficult, because the beam intensity is reduced with 1/(distance)², and over the beam cross section it decays almost exponentially (Gaussian shape) toward the edges.

More accurate measurement is by subtracting the laser beam diameter at the laser output (d) from the measured value (D), and call it the new value (D^*).

Draw a graph of D^* vs. L.
Calculate (on the data sheet) the slope of the graph.
Calculate (on the data sheet) the angle of divergence of the laser.
Repeat steps 1 through 6 with the Diode laser.