Question

How many photons are produced in a laser pulse of 0.533 J at 693 nm?

Answer 1

We first need to calculate the energy os a single photon of wavelength = 693 nm. This can be done using:

$E=h\cdot \frac{c}{\lambda }$

Where E is the energy, h is Planck's constant, c is the speed of light and lambda is the wavelength.

For our case:

$E=6.626x10^{-34}Js\cdot \frac{3x10^{8\frac{m}{s}}}{693x10^{-9}m}=2.87x10^{-19}J$

If our laser energy is 0.533 J, the number of photons is given by:

$n=\frac{0.533J}{2.87x10^{-19}J/photon}=1.86x10^{18}photons$