Question #3264

A laser delivers pulses of 2mJ at wavelength 633 nm with a pulse duration of

200 ps. (hint E=h.c/l, with h=6.6 x10-34 J.s and c=3x108 m/s and 1 eV=1.6

x10-19 J)

i) How far do they travel in 1s? (5marks)

ii) What is the photon energy in eV?(10marks)

iii) How many photons are delivered per pulse?10 marks)

200 ps. (hint E=h.c/l, with h=6.6 x10-34 J.s and c=3x108 m/s and 1 eV=1.6

x10-19 J)

i) How far do they travel in 1s? (5marks)

ii) What is the photon energy in eV?(10marks)

iii) How many photons are delivered per pulse?10 marks)

Expert's answer

i) S=c*t=3*10^{8}*1=3*10^{8} meters.

ii) eV=1.6*10^{-19} J → J=10^{19}/1.6 eV= 0.625*10^{19} eV=625*10^{16} eV → E=2*10^{-3}*10^{16}=2*10^{13} eV

iii) energy of 1 photon is E_{1} = hc/λ=6.6*10^{-34} *3*10^{8}/633*10^{-9 }= 31.2*10^{-20} J

Thus

n = E/E_{1} = 2*10^{-3}/31.2*10^{-20} = 6.4*31.2*10^{15} particles.

ii) eV=1.6*10

iii) energy of 1 photon is E

Thus

n = E/E

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