a) A laser produces light pulses of energy 5 J and duration 2 × 10⁻⁹ s. If the beam is circular in cross section and of diameter 2 mm, calculate the intensity (the power per unit area) of a laser pulse.
b) State one significant difference in the nature of the light emitted by a laser from that emitted by an ordinary light bulb.
c) The wavelength of the laser is 400 nm. Light can be seen either as a wave or a particle (a photon). The energy E of a photon of light is given by E = hf, where f is the frequency of the light and h is Planck's constant. Calculate the number of photons in a single pulse from the laser.
Planck's constant h = 6.6 × 10⁻³⁴ Js
speed of light c = 3.0 × 10⁸ ms⁻¹
d) Calculate the volume of a single pulse of light from the laser, and hence the density of photons in the laser pulse.
e) If the photons in the pulse were equally spaced, rather like ball bearings packed uniformly in a box, what would be the volume occupied by a single photon?
f) If the volume occupied by a photon was a cube, what would be the length of a side of the cube?