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Thermal Radiation. Quantum Nature of Light.

Problem 5.262

A laser emits a light pulse of duration τ=0.13 ms\tau=0.13 \mathrm{~ms} and energy E=10E=10 J. Find the mean pressure exerted by such a light pulse when it is focussed into a spot of diameter d=10μmd=10 \mu \mathrm{m} on a surface perpendicular to the beam and possessing a reflection coefficient ρ=0.50\rho=0.50

Reveal Answer
⟨p⟩=4(1+ρ)E/πd2cτ≈50 atm. \langle p\rangle=4(1+\rho) E / \pi d^{2} c \tau \approx 50 \text { atm. }
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