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Lecture Note #2

This document provides an overview of key concepts in optical review, including refraction and dispersion of light, light optical microscopes, resolution, depth of field, and aberrations in optical systems. It discusses how refraction causes light to change direction when passing between materials of different densities, defined by the refractive index. Snell's law describes the relationship between incident and refracted angles. Refraction by lenses can focus light, with the focal length determining convergence. Dispersion occurs as different wavelengths of light refract to different degrees when passing through materials like glass, separating light into a spectrum.

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Hatra Mulyono
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27 views10 pages

Lecture Note #2

This document provides an overview of key concepts in optical review, including refraction and dispersion of light, light optical microscopes, resolution, depth of field, and aberrations in optical systems. It discusses how refraction causes light to change direction when passing between materials of different densities, defined by the refractive index. Snell's law describes the relationship between incident and refracted angles. Refraction by lenses can focus light, with the focal length determining convergence. Dispersion occurs as different wavelengths of light refract to different degrees when passing through materials like glass, separating light into a spectrum.

Uploaded by

Hatra Mulyono
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Optical Review

1
Outline

 Refraction and dispersion of light

 Light optical microscope

 Resolution

 Depth of field

 Aberrations in optical systems


(1) Chromatic aberration
(2) Monochromatic aberration

2
Outline

 Refraction and dispersion of light

 Light optical microscope

 Resolution

 Depth of field

 Aberrations in optical systems


(1) Chromatic aberration
(2) Monochromatic aberration

3
Refraction of light
Refraction: [noun] Deflection from a straight path

4
Refraction of light

• Physical basis for many optical phenomena.

• Refraction is the change in direction of light as it


passes into another material of different density.

• Refractive index (n) in light optics is defined as


𝑐𝑐 𝑐𝑐: speed of light in vacuum
𝑛𝑛 =
𝑣𝑣 𝑣𝑣: speed of light in the substance

• The n of vacuum is defined as 1.0 (i.e., maximum


speed in vacuum); n of all other materials exceeds 1.0.

5
Refractive index (n)
Refractive Index of
Selected Media
• For most practical purposes, the
Refractive
refractive index (1.0003) of air is so Material
Index
close to that of vacuum; can be used Air 1.0003
to calculate refractive indices (n) of Water 1.333
unknown materials. Glycerin 1.473
Immersion
1.515
Oil

• Materials with higher refractive Glass 1.520


indices slow down the speed of light
Diamond 2.417
to a great degree than those with Lead
lower refractive indices. 3.910
Sulfide

6
Snell’s law

• Snell's Law describes the relationship between the


angles (with respect to the normal) of the two light
waves and the refractive indices of the two materials.

• The normal is defined as a line perpendicular


to the interface between two substances.

(higher index
of refraction)

7
Snell’s law
• If a light wave passes from a medium of lower
refractive index to one of higher refractive index, it is
bent toward the normal.
• However, if the wave travels from a medium of higher
refractive index to a medium of lower refractive index,
it is bent away from the normal.
Snell’s law

or

When the light is monochromatic,

𝑣𝑣: phase velocity of light in the respective medium


λ: wavelength of light in the respective medium
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Effect of refraction in lenses
• Because the “refracted” angle depends on the
“incident” angle, a convex lens can be used to focus
light to a point at a specified distance from the lens.

Focused

Incident Refracted

• Focal point: the point at which rays meet after refraction


• Focal length: a measure of how strongly the optical
system converges (or diverges) light 9
Dispersion

• Light with different wavelength refracts differently.

• Violet light (λ ~ 400 nm) refracts more than red light (λ


~ 700 nm).
Refraction occurs at the
“glass/air” boundary bending
the rays away from the normal
as they speed up again.
Refraction occurs at the
“air/glass” boundary
bending the rays towards the
normal as they slow down.

Each color refracted to a


Red light bends
different degree by the
less because it is
glass – the color disperse
refracted less.
into a spectrum of light.

10

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