Question

A laser that emits pulses of UV lasting 2.95 ns has a beam diameter of 4.05 mm. If each burst contains an energy of 4.60 J, what is the length in space of each pulse?

What is the average energy per unit volume (the energy density) in one of these pulses?

Answer 1

This question knowing the distance equation , that the speed of light is approximately 3.00*10⁸ m/s, and the volume of a cylinder.

Step 1) To be able to find the length of the laser pulse, first convert the 2.95 ns to SI units:

Step 2) Then use that time and the speed of light in the distance equation in order to find the length in space of the pulse:

So the length of the pulse is 0.885 m.

Step 3) To find the energy density of the pulse, the volume of a cylonder is needed (since the energy is already given):

Step 4) To use that equation, get the radius of the beam by taking half of the diameter:

Step 5) To keep consistent units, change the radius to use SI units:

Step 6) Then find the volume of the beam, using that for the radius, and the 0.885 m for the height that was initially found:

Step 7) And then find the energy density, using the equation :

So the energy density of the laser pulse is about .