Lasers can be constructed that produce an extremely high intensity electromagnet

Question

Lasers can be constructed that produce an extremely high intensity electromagnetic wave for a brief time—called pulsed lasers. They are used to ignite nuclear fusion, for example. Such a laser may produce an electromagnetic wave with a maximum electric field strength of 0.93× 10^11V/m for a time of 1.00 ns.

(a) What is the maximum magnetic field strength in the wave?

(b) What is the intensity of the beam?

(c) What energy does it deliver on a 2.00 mm2 area?

(d) The laser light has a wavelength of 600nm. How many photons made up the pulse?

Explanation / Answer

(a) maximum magnetic field strength = B = E/c = 0.93× 10^11/3*10^8 = 310 T

b) intensity of the beam = I = c*B^2/(2uo) = (3*10^8*310^2)/(2*4pi*10^-7) = 1.15*10^19 W/m^2

c) Energy = E = I*t*A = 1.15*10^19*10^-9*2*10^-6 = 23 kJ = 1.44*10^23 eV

d) E' = 1240/600 = 2.1 eV

No. of photons = 1.44*10^23/2.1 = 6.86*10^22 photons

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