Question

8. A laser beam with wavelength of 9
micrometer on the earth is focused by a
lens of diameter, d = 2 m on the crater on
the moon surface. The distance. D of the
moon is 4x10^8 m. What is the diameter
of the spot on the moon? Neglect the
atmospheric effects.​

Answer 1

Answer:

Light diffracts as it moves through space, bending around obstacles, interfering constructively and destructively. While this can be used as a spectroscopic tool—a diffraction grating disperses light according to wavelength, for example, and is used to produce spectra—diffraction also limits the detail we can obtain in images. Figure 1a shows the effect of passing light through a small circular aperture. Instead of a bright spot with sharp edges, a spot with a fuzzy edge surrounded by circles of light is obtained. This pattern is caused by diffraction similar to that produced by a single slit. Light from different parts of the circular aperture interferes constructively and destructively. The effect is most noticeable when the aperture is small, but the effect is there for large apertures, too.

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