A 1.5-mW helium-neon laser beam delivers a spot of light 5 mm in diameter across a room 15 m wid

To find the beam divergence angle, we can use the formula for the angle of a triangle with given

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A $1.5-\mathrm{mW}$ helium-neon laser beam delivers a spot of light $5 \mathrm{mm}$ in diameter across a room $15 \mathrm{m}$ wide. The beam radiates from a small circular area of diameter $0.5 \mathrm{mm}$ at the output mirror of the laser. Assume that the beam irradiance is constant across the diverging beam. a. What is the beam divergence angle of this laser? b. Into what solid angle is the laser sending its beam? c. What is the irradiance at the spot on the wall $15 \mathrm{m}$ from the laser? d. What is the radiance of the laser?

          A $1.5-\mathrm{mW}$ helium-neon laser beam delivers a spot of light $5 \mathrm{mm}$ in diameter across a room $15 \mathrm{m}$ wide. The beam radiates from a small circular area of diameter $0.5 \mathrm{mm}$ at the output mirror of the laser. Assume that the beam irradiance is constant across the diverging beam. 
a. What is the beam divergence angle of this laser?
b. Into what solid angle is the laser sending its beam?
c. What is the irradiance at the spot on the wall $15 \mathrm{m}$ from the laser?
d. What is the radiance of the laser?

Added by Jennifer W.

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