6. Wave optics. Microscopy.

Question 1

What are wave optics? Explain the most important paramaters and relate them in a formula.

Answer 1

If light propagates through a slit comparable or smaller than its wavelength, then its wave properties must be taken into account.

Most important parameters: λ = c * T = c/f

• period = T
• frequency = f = 1/T
• velocity = v, c
• wavelength = λ

Question 2

Define lateral magnification. What is the largest magnification used in practice for light microscopes?

Answer 2

Lateral magnification: **M = M * M **

of the microscope is the product of the magnification powers of the 2 lenses (objective and eyepiece)..

Largest magnification: M = 2500

Question 3

Explain the resolving power of the light microscope and the refering Abbe’s formula

Answer 3

Resolving power:

system with the ability to produce images with angular resolution = diffraction-limited

At least the first order diffraction maxima must be collected in order to achieve sharp vision.

Abbé’s formula: d = (0.61 * λ) / (n * sin α)

diffraction limit = smallest resolvable distance

• d = distance
• λ = wavelength
• n = refractive index of medium
• α = angle between optical axis and bounding light ray

Question 4

Explain the concept of diffraction. What is an Airy disk?

Answer 4

Interference of 2 waves leads to interference patterns.

• Constructive interference = amplification (contains information)
• Destructive interference = cancellation

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Airy disk:

because of diffraction: image of a point object = Airy disk

illustrates intensities of * order maxima: intensities decrease as m increases

⇒ principal maxima m=0, first order maxima m=1, etc.