Rami Arieli: "The Laser Adventure"

Rami Arieli: "The Laser Adventure" Chapter 1.2.2 page 2

Divergence Angle
Divergence Angle is the full angle of opening of the beam. (Some books use half of this angle as divergence angle).
The relation between radians and degrees is given by: 360⁰= 2p Radians
1 Radian = 57.3⁰
1 milli-Radian = 1 mrad = 0.057⁰

Using the relation between minutes and degrees: 1⁰=60’, we get:

1 mrad = 0.057*60’@ 3.5’

Since laser radiation divergence is of the order of milli-radians, the beam is almost parrallel, and laser radiation can be send over long distances.
We shall see in chapter 9, how a laser beam was sent to the moon, and returned to Earth to measure the distance between Earth and the moon with accuracy of tens of centimeters.