Question

A laser pulse has an energy of 21 J and a beam radius of 2 mm. The pulse duration is 15 ns and the energy density is uniformly distributed within the pulse.

(a) What is the spatial length of the pulse?

m

(b) What is the energy density within the pulse?

kJ/m^{3}

(c) Find the rms values of the electric and magnetic fields in the
pulse.

*E*_{0} = MV/m

*B*_{0} = T

Answer #1

U= 21 J and r = 2*10^-3 m , t = 15*10^-9 s ,

c = 3*10^8 m/s

so now

a) spatial length of the pulse L = c*t = 3*10^8* 15*10^-9 =
**4.5 m**

b)

the energy density within the pulse is u = U/LA = 21 /( 4.5*pi*(2*10^-3)^2) =371361.534 J

or **371.361 kJ/m^3**

c)the intensity of beam is I = u*c = 371361.534*3*10^8 = 1.1140846e14 W/m^2

Erms = sqrt(2u/epsilon) = sqrt(2*371361.534 /(8.85*10^-12))

=**289.695548 M V/m**

Brms = Erms/c =289695548/ ( 3*10^8)

**=0.965651827 T answer**

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