# Question #0e707

Jan 19, 2018

The helium neon laser typically operates at $632.8$ $n m .$

Thus the energy contained in a single photon from the laser is:

$E = h f = h \frac{c}{\lambda} = \left(6.63 \times {10}^{- 34}\right) \frac{3 \times {10}^{8}}{632.8 \times {10}^{- 9}}$

$= 3.143 \times {10}^{- 19} J$

If the laser operates at $90$ $w a t t = 90$ $J {s}^{-} 1$ then the amount photons emitted per second will be:

Power output of laser/ Energy of photon.

$= \frac{90}{3.143 \times {10}^{- 19}} = 2.863 \times {10}^{20}$ ${s}^{-} 1$