Physics laser question

Question

A HeNe laser is made up of a cylindrical beam of light with a diameter of 0.710 cm. The energy is pulsed, lasting for 2.30 ns, and each burst contains an energy of 2.00 J.

What is the length of each pulse of laser light?

What is the average energy per unit volume for each pulse? 

Answer 1

First question: Multiply the speed of light by the duration of the pulse.

L = ct = (3 x 10⁸ m/s)(2.30 x 10^-9 s) = ? m

Second question: Energy density of one pulse is

E / V = E / (Lπd²/4)

Plug in the values

E = 2.00 J

d = 0.710 x 10^-2 m

L = ? (result from first question)

and get E / V in joules/m³. You can finish from here.