L13 Diffraction

Question 1

define diffraction

Answer 1

when light passes an aperture/slit the light waves bend and spread at the edges of the opening

• can happen for any EM wave
• ability of a wave to propagate around corners

Question 2

explain diffraction at single slit

Answer 2

when monochromatic light passes thru slit

• no diffraction: central focused vertical light band (brightest, constructive interference)
• diffraction: parallel rays bend at edge of slit, spreading through opening
• happens best when wvl = gap

Question 3

diffraction pattern factors with different apertures

Answer 3

1. size
   large: less, no diffraction
   small: more diffraction
2. shape

Question 4

how does diffraction affect resolution

Answer 4

when light passes through an optical system, the image point suffers some diffraction effects and does not form a perfect point image.
-spread out point image = airy’s disc
airy’s disc dependent on size of aperture
-large: little diffraction, little airy’s disc, resolvable
-small: increased diffraction, increased airy’s disc, unable to resolve

Question 5

define rayleigh’s criterion

Answer 5

• two objects are resolved when the maximum intensity of the central pattern of one object falls on the first minimum of the other
• patterns overlap less, resolvable

Question 6

resolution

Answer 6

• limited by diffraction, larger apertures give best resolution
• when limited by aberrations, smaller apertures counter aberrations but resolution limited by diffraction