How many photons does a 3.2 mw helium-neon laser (λ = 633 nm) emit in 1 second? how many photons does a 3.2 helium-neon laser ( = 633) emit in 1 second? 7.6*1018 2.5*1018 5.1*1016 1.0*1016?

Answer is: 1.0*10 ¹⁶.

P (power of laser) = 3,2 mW = 0,0032 W.

λ (wavelength) = 633 nm = 633 · 10⁻⁹m = 6,33·10⁻⁷m.

P = n·h·c:λ ⇒ n = n=P· λ/h · c.

c - speed of light 3⋅10 ⁸ m/s.

h - Planck's constant - 6.63⋅10 ⁻³⁴J· s.

n - number of photons emited.

n = 0,0032W · 6,33·10⁻⁷m / 6.63⋅10⁻³⁴J·s · 3⋅10⁸ m/s

n = 1·10¹⁶ 1/s.