The nearly parallel beam of a laser with wavelength λ = 10μm and output power of P = 10 W has a beam diameter of d = 3 cm. It is focused by a lens with f = 20 cm. a) How large is the beam waist w0 in the focal plane? b) The intensity distribution in this plane is I(r) = I0 × exp[−(r/w0) 2] . What is the value of I0? c) Assume that 10% of the laser power can be used for evaporating material from a steel sheet with thickness t = 1 mm placed in the focal plane. How long will it take for the laser beam to produce a hole through the steel sheet, if the evaporation heat is 6 × 106 J/Kg
a] Beam waist in the focal plane can be determined using Rayleigh's diffraction limit criteria.
this is the beam waist in the focal plane.
b] The intensity at this point is:
c] Power used up for evaporation = 10% of 10 W = 1 W
Radius of the hole =
thickness of the hole = 1 mm = 1 x 10-3 m
so, volume of the hole =
density of steel = 8050 kg/m3
therefore, mass of the steel evaporated = density x volume = 1.67295 x 10-7 kg
Energy required = mass x evaporation heat = 1.67295 x 10-7 x 6 x 106 = 1.00377 J
time = Energy / Power = 1.00377/1 = 1.00377s
this is how long it will take for the laser beam to produce the hole.
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