Rami Arieli: "The Laser Adventure"

Rami Arieli: "The Laser Adventure" Chapter 1.2.2 page 4

Example 1.2: Numerical Calculation of Power Density

Calculate the power density of radiation per unit area at a distance of 2 meters, from an incandescent lamp rated 100 [W], compared to a Helium-Neon laser of 1 [mW]. The laser beam diameter at the laser output is 2 [mm], and its divergence is 1 [mrad].

Solution to example 1.2:

Light from incandescent lamp is radiated to all directions, so it is distributed on a surface of a sphere with a radius of 2 [m]. The surface area is: p R², so the power density at a distance of 2 [m] is:

Compared to the incandescent lamp, the laser beam diameter at a distance of 2 [m] increased to 4 [mm] (see drawing below):

R = 2.1 [mm] = 0.2 [cm]

The power density of the laser radiation is:

!!! When calculating radiation power in the visible spectrum (used for illumination), the low efficiency of the incandescent lamp must be considered (A 100 [W] lamp emits only 1-3 [W] of visible radiation, and all the rest is in the infrared spectrum).

At a distance of 2 [m] from the radiation source, the power density of the laser radiation is 4 times higher than from the lamp, although the power from the lamp is 5 times the original power of the laser.