A pulsed laser emits photons at a frequency of toward a photodetector

PHYSICS · Multi-part · A Level · Physics · Waves · Waves

Problem

A pulsed laser emits photons at a frequency of

5.00\times10^{14}\,\text{Hz}

toward a photodetector. Before reaching the detector, the pulse passes perpendicularly through a

4.00\,\text{mm}

-thick fused-silica window (index of refraction

n_{\text{fs}}=1.46

) and then travels an additional

2.00\,\text{m}

through air (index of refraction

n_{\text{air}}=1.0003

). Assume the laser pulse is sufficiently short that dispersion can be neglected. (a) Calculate the speed of the photons while they are inside (i) fused silica and (ii) air. (b) Determine the wavelength of the photons inside the fused-silica window. (c) Compute the extra time delay introduced by the presence of the fused-silica window relative to the time the pulse would have required to traverse the same

4.00\,\text{mm}

distance in air. (d) Discuss whether the energy of an individual photon changes while it is inside the fused-silica window. Justify your answer using appropriate physical arguments.

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