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A laser outputs light of a single color with photon energy . A nonlinear crystal, which halves the wavelength of light, is placed in the path of the laser beam. What is the energy of the photons exiting the crystal?
Halving the wavelength is equivalent to doubling the frequency since for a light wave the wavelength and frequency are related by , where
is the speed of light. The energy of a photon is
, where
is Planck's constant, so the photon energy is doubled.
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A monochromatic light source is incident on a neutral density filter which decreases the light source's intensity by a factor of 3 but does not change its color. What happens to the energy of a photon in the less intense beam?
The photon energy does not change since the color of light (and therefore the frequency of the light) does not change.
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