Question

A typical small helium-neon laser (λ=632.8μm) has a continuous output power of 3.00mW and a beam diameter of 2.00mm.

a. What is the average value of the electric field's amplitude within the beam?

b. How many photons are emitted each second by the laser?

Answer 1

b)

The energy of a photon is given by the equation E = hc/λ,

where E is the energy,

Planck's constant h = 6.63 x 10^-34

speed of light c = 3 x 10⁸ m/s and λ is the wavelength of the light (in metres).
given λ=632.8x10^-6 m

then the energy of one photon is

E=hc/λ

=(1.989x10^-25)/(632.8x10^-6)

E=3.14x10^-22 J

3mW=0.003 j/s

So the photons are emitted each second by the laser is

=(0.003)/(3.14x10^-22)

=9.5x10¹⁸

a)
average value =E(Δx)

diameter =0.02m

=(3.14x10^-22)x(0.02)

=6.28x10^-24