A typical helium-neon laser found in supermarket checkout scanners emits 633-nm-

Question

A typical helium-neon laser found in supermarket checkout scanners emits 633-nm-wavelength light in a 1.5-mm-diameter beam with a power of 1.4 mW . The intensity of the beam is 792.2 Watts/m^2. Damage caused to human eyes by laser light is dependent on the frequency of the laser, as well as the exposure time. For red laser light, a typical value for the amount of energy per square meter that would cause damge is 10J/m2. How long could someone stare directly at this supermarket checkout laser before damage occurs?

Explanation / Answer

I ( intensity) = 792.2 W/m2

E ( energy) per unit area = 10 J/ m2

I = power / area ( P = E / t(time)

I= E/ t*A ( A = 1m2)

792.2 = 10 / t *1

t = 10/ 792.2 = 0.0126 s

or t= 12.6 ms

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