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Thermal Radiation. Quantum Nature of Light.

Problem 5.262

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

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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