Slide 1
A narrow opening can spread a wave
A wave passing through a narrow opening spreads into the region beyond it. This diffraction becomes pronounced when the opening is comparable to the wavelength.
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Sound bends around everyday obstacles more noticeably than visible light because audible wavelengths are much larger. The relevant comparison is obstacle size divided by wavelength, rather than a different set of wave rules.
Slide 2
Waves from parts of the slit interfere
Different parts of an illuminated slit contribute waves to the outgoing pattern. Their phases combine to create brighter and darker directions.
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A single slit produces a broad central bright region and weaker side regions. Those features arise from the spread of path differences across the aperture, even without a second separate slit.
Slide 3
A narrower opening produces a wider spread
Reducing an opening’s width increases the angular spread of its diffraction pattern. A smaller aperture does not always make a sharper image.
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In a camera, stopping down can first reduce lens aberrations and increase depth of field. Eventually diffraction becomes important, creating a tradeoff between different causes of image blur.
Slide 4
Aperture and wavelength limit distinguishable detail
A finite aperture limits how closely two sources can be distinguished. Larger apertures or shorter wavelengths can improve the diffraction-limited resolution.
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The exact criterion depends on aperture shape and what counts as distinguishable. Practical instruments may perform worse because of vibration, detector sampling, atmospheric distortion or imperfections in their optics.
Slide 5
A grating uses interference to separate wavelengths
A diffraction grating has many regularly spaced features. Their interference sends different wavelengths into different directions for measurement.
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A spectrometer can use that separation to estimate a light source’s wavelength content. Calibration is still necessary: angles must be connected to wavelength, and overlapping diffraction orders may need to be separated.