A pulsed laser produces brief bursts of light. One such laser emits pulses that

Question

A pulsed laser produces brief bursts of light. One such laser emits pulses that carry 0.400 J of energy but last only 300 fs.

a. What is the average power during one of these pulses? (in W)
b. Assuming the energy is emitted in a cylindrical beam of light 2.20 in diameter, calculate the average intensity of this laser beam. (in W/m^2)
c. What is the rms electric field in this wave? (in V/m)

I found that the answer to (a) is P_av = 1.33*10^12 W, but I can't figure out (b) or (c) from there. I tried I_av = 8.75*10^16 using I = P/A but that didn't work... thanks for the help in advance!

Explanation / Answer

a)

You found a: P_av = E/t = 1.33*10^12 W

b)

R = 1.1 mm

I = P/A

= 1.33333*10^12/(3.14*1.1*10^-3*1.1*10^-3)

= 3.51 * 10^17 W/m2

c)

I = Emax2 /(2c)

>>> Emax2 = I (2c)

               = 3.51e17 * 2*4*3.14e-7*3e8

>>>> Emax = 1.626 *10^10

>>>> Erms = 1.626 *10^10/2 = 1.15 * 10^10 N/C

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