Ian Talks Optics A-Z: PhysicsAtoZ, #2

By Ian Eress

Light is all around us, and understanding how it works has led to remarkable technologies that have shaped our world. This accessible reference book introduces the fundamentals of optics, revealing key concepts through engaging examples. It covers the behavior of light, including reflection, refraction, and diffraction. You'll learn how lenses and mirrors form images, how the eye sees, and the workings of common optical instruments. You'll also explore the mysteries of light's quantum nature and its interaction with atoms.

From the basic principles of light and its properties to recent advancements, this reference book covers it all. With clear explanations, illustrations, and practical applications, this reference book is perfect for students, and anyone interested in learning more about optics.

 

• Language: English
• Publisher: Ian Eress
• Release date: Mar 16, 2023
• ISBN: 9798215143643

Ian Eress

Born in the seventies. Average height. Black hair. Sometimes shaves. Black eyes. Nearsighted. Urban. MSc. vim > Emacs. Mac.

Book preview

Ian Talks Optics A-Z

PhysicsAtoZ, Volume 2

Ian Eress

Published by Ian Eress, 2023.

While every precaution has been taken in the preparation of this book, the publisher assumes no responsibility for errors or omissions, or for damages resulting from the use of the information contained herein.

IAN TALKS OPTICS A-Z

First edition. March 16, 2023.

Copyright © 2023 Ian Eress.

ISBN: 979-8215143643

Written by Ian Eress.

Table of Contents

A

B

C

D

E

F

G

H

I

J

K

L

M

N

O

P

Q

R

S

T

U

V

W

Y

Z

INDEX

For Caitlyn

A

Abbe number: I. The Abbe number is a measure of the dispersion of a material, or its ability to separate light into its component colors. It is defined as the ratio of the difference in the refractive index of a material for two specific wavelengths of light to the refractive index at the mean of those wavelengths.

II. In optics, the Abbe number refers to a measure of the dispersion of a material. Some key points:

• The Abbe number is defined as the inverse of the relative difference between two specific wavelengths' refractive indices. It indicates how much the refractive index changes with wavelength.

• A higher Abbe number means lower dispersion so that different wavelengths have more similar refractive indices. Lower dispersion is desirable for reduced chromatic aberration in lenses.

• The Abbe number is commonly used to compare the dispersion of different optical materials. It provides a measure of how achromatic material is in terms of having similar refractive indices for different wavelengths.

• Together with the refractive index, the Abbe number determines the optical properties of materials and how suitable they are for various applications. It is an important parameter in optics and lens design.

III. https://en.wikipedia.org/wiki/Abbe_number

Abbe prism: I. An Abbe prism is a type of prism used in optics for dispersing light into its component colors. It is named after its inventor, Ernst Abbe, a German physicist and mathematician who developed it in the late 19th century.

An Abbe prism consists of two right-angled prisms with their hypotenuses cemented together, forming a parallelogram-shaped block of glass. The angle between the two prisms is 30 degrees, although it can vary depending on the design. Light entering the prism is refracted twice, first by the surface of the first prism and then by the surface of the second prism. The angle between the incoming light and the outgoing light is dependent on the wavelength of the light, resulting in a separation of the different colors of light.

One of the advantages of an Abbe prism is that it produces a linear dispersion, which means that the angle of deviation of the different colors of light is directly proportional to their wavelength. This makes it useful in spectroscopy and other applications where precise control of the spectral dispersion is required.

Abbe prisms are commonly used in spectrographs, monochromators, and other optical instruments where spectral dispersion is needed. They are also used in some types of binoculars and spotting scopes to correct for chromatic aberration, a type of distortion that can occur when different colors of light are refracted differently by a lens or prism.

II. An Abbe prism is a type of optical prism used to deviate a light beam by a specific angle while minimizing dispersion. Some key points:

• An Abbe prism consists of two prisms made of materials with different dispersion, arranged such that dispersion is canceled out. The prisms have the same deviation angle but different refractive indices and dispersions.

• The materials for the prisms are chosen such that the ratio of their refractive index changes with wavelength is the inverse of the ratio of the refractive index changes needed to obtain the same deviation angle. This cancels dispersion.

• Abbe prisms are used when the deviation is needed but chromatic aberration and dispersion must be minimized. They allow a fixed deviation angle for different wavelengths, unlike a single-material prism.

• The Abbe prism is named after Ernst Abbe, who discovered the dispersion-canceling design. It is a key optical component that enables deviation while reducing dispersion effects.

III. https://en.wikipedia.org/wiki/Prism_(optics)

Abbe sine condition: I. The Abbe sine condition is a relationship between the object distance, image distance, and aperture of an optical system, like a lens or microscope. It was developed by Ernst Abbe, a German physicist and mathematician, in the late 19th century, and it is an important concept in the design and analysis of optical systems.

The Abbe sine condition states that for an optical system to produce a sharp, aberration-free image, the ratio of the sine of the angle of incidence of a light ray to the sine of the angle of refraction of the same ray at the image plane must be constant for all rays passing through the aperture of the system. This constant ratio is known as the numerical aperture (NA) of the system.

Mathematically, the Abbe sine condition can be expressed as:

n sin(θ) = n' sin(θ')

where n and n' are the refractive indices of the two media through which the light is passing, θ is the angle of incidence of the light ray, and θ' is the angle of refraction of the same ray at the image plane.

The Abbe sine condition is important because it ensures that light rays passing through the outer edges of the aperture are focused at the same point as those passing through the center of the aperture, producing a sharp and clear image. It is used in the design and optimization of optical systems to ensure that they meet the necessary performance requirements for a given application.

The Abbe sine condition is also related to the concept of depth of field in photography and microscopy, which is the range of distances from the lens or microscope objective that are in acceptable focus. A larger numerical aperture allows for a greater depth of field and improved resolution.

II. The Abbe sine condition refers to a constraint on a lens system to minimize chromatic aberration. Some key points:

• The Abbe sine condition states that the ratio of the sines of the angles of incidence and refraction for two wavelengths must equal the ratio of the reciprocals of the dispersions of the materials at those wavelengths.

• Satisfying the Abbe sine condition enables a lens system to have the same focal length for different wavelengths. This minimizes chromatic aberration, where the focal length depends on wavelength.

• The Abbe sine condition must hold for all interfaces in a lens system for chromatic aberration to be eliminated. It places constraints on the glasses/materials and lens curvature/thicknesses that can be used.

• The Abbe sine condition is important for achromatic and apochromatic lens design. It enables the focusing of multiple wavelengths at the same point, reducing chromatic aberration. It was derived by Ernst Abbe, relating to his work on achromatic optics.

III. https://en.wikipedia.org/wiki/Abbe_sine_condition

Aberration in optical systems: I. In optics, aberration refers to any departure from ideal optical behavior in an optical system, like a lens or mirror. Aberrations can cause distortions or other imperfections in images or other optical signals, and they can limit the performance of optical instruments.

There are several types of aberrations that can occur in optical systems. This includes:

Chromatic aberration: This occurs when different colors of light are refracted differently by a lens, resulting in color fringes around objects in the image. Chromatic aberration can be reduced by using lenses made from materials with different dispersive properties, or by combining lenses of different shapes and materials.

Spherical aberration: This occurs when light rays passing through the outer edges of a spherical lens are refracted differently than those passing through the center, causing a blurring or distortion of the image. Spherical aberration can be reduced by using aspherical lenses or by carefully designing the shape of the lens.

Coma: This occurs when light rays passing through the edges of a lens are not focused to the same point as those passing through the center, causing distortion in the image. Coma can be reduced by using a lens with a smaller aperture or by using a lens with a specially designed shape.

Astigmatism: This occurs when the curvature of a lens or mirror is different in different directions, causing distortion in the image. Astigmatism can be reduced by using a lens with a cylindrical shape or by using a combination of lenses with different shapes and orientations.

Distortion: This occurs when straight lines in the object appear curved or distorted in the image. Distortion can be reduced by using a lens with a carefully designed shape or by using image processing techniques to correct the distortion.

Aberrations can be minimized through careful design and manufacturing of optical systems, but they can never be completely eliminated. The choice of optical materials, the design of lens shapes, and the quality of manufacturing all play a role in minimizing aberrations and optimizing the performance of optical instruments.

II. Aberrations refer to defects in optical systems that cause images to be distorted or blurred. Some key points:

• Common aberrations include spherical aberration, chromatic aberration, coma, astigmatism, field curvature, and distortion. They are caused by the inability of a lens to focus all light perfectly.

• Spherical aberration occurs when parallel light rays at different distances from the axis focus at different points. Chromatic aberration is caused by dispersion, with different wavelengths focusing at different points.

• Coma and astigmatism cause blurring and distortion of off-axis points. Field curvature and distortion warp and compress the image.

• Reducing aberrations is a key goal in optical design. A combination of lens shapes/materials and positioning is used to minimize aberrations and create sharp, undistorted images. Aberration correction enables higher-quality optical systems.

III.

https://en.wikipedia.org/wiki/Optical_aberration

https://www.britannica.com/technology/aberration

Absorption: I. Absorption in the context of optics refers to the process by which light is absorbed by a material, leading to a reduction in the intensity of the light. When light passes through a material, it can interact with the electrons in the material, causing them to absorb some of the energy of the light. This absorption process can occur over a wide range of wavelengths, depending on the properties of the material.

The degree of absorption of light by a material depends on several factors. This includes the wavelength of the light, the thickness of the material, and the properties of the material itself. Different materials have different absorption spectra, which describe the wavelengths of light that are absorbed most strongly by the material.

Absorption can have several effects on the behavior of light, depending on the application. In some cases, absorption can be used intentionally to filter out certain wavelengths of light, like in optical filters. In other cases, absorption can lead to a loss of energy or signal, which can limit the performance of an optical system.

One important application of absorption in optics is in the design of solar cells, which convert light into electrical energy. Solar cells use materials that have strong absorption in the visible and near-infrared regions of the spectrum, allowing them to convert a wide range of wavelengths into electrical energy.

Absorption can also play a role in the behavior of light in the atmosphere, like in the absorption of sunlight by gases in the Earth's atmosphere. This absorption can lead to phenomena like atmospheric scattering and the greenhouse effect, which have important implications for climate and weather.

II. Absorption refers to the capture of light by a material, leading to loss of light energy. Some key points:

• Light absorption happens when photons interact with electrons in atoms/molecules and are absorbed, increasing the energy of the electrons. The absorbed photons are lost and the light is attenuated.

• The absorption of a material depends on the wavelengths of light and the electronic structure of the material. Materials absorb light at wavelengths that can excite their electrons to higher energy states.

• Strong absorption leads to less light transmission, while weak absorption results in more transmission. Absorption affects the color/brightness of materials and is important in applications like sunscreens, colored glass, and photovoltaics.

• Light absorption is complementary to transmission and reflection. Less absorption means more transmission and/or reflection. Understanding absorption requires considering how materials interact with electromagnetic radiation at the atomic/molecular scale.

III. https://en.wikipedia.org/wiki/Absorption_spectroscopy

Absorption spectrum: I. An absorption spectrum is a plot of the amount of light absorbed by a material as a function of the wavelength or frequency of the light. It is a graphical representation of the absorption properties of a material, and it provides information about the wavelengths at which the material absorbs light most strongly.

The absorption spectrum of a material is determined by the interactions between the incoming light and the electrons in the material. When light passes through a material, it can interact with the electrons in the material, causing them to absorb some of the energy of the light. The energy of the absorbed light is related to the frequency or wavelength of the light, and the amount of light absorbed depends on the properties of the material and the frequency of the light.

Different materials have different absorption spectra, depending on their chemical composition and structure. For example, materials that contain metal ions sometimes have absorption spectra that include characteristic absorption bands, which are related to the electronic transitions of the metal ions. Organic molecules also have characteristic absorption spectra, which are related to the chemical bonds and functional groups in the molecules.

The absorption spectrum of a material can be measured using a variety of techniques, like spectrophotometry or absorption spectroscopy. These techniques involve shining light of different wavelengths or frequencies through the material and measuring the amount of light that is absorbed in each wavelength or frequency. The resulting absorption spectrum can then be used to identify the material and characterize its optical properties.

Absorption spectra have many practical applications in optics. This includes the design of optical filters, the characterization of materials in scientific research, and the analysis of atmospheric absorption in remote sensing and environmental monitoring.

II. An absorption spectrum refers to the range of wavelengths absorbed by a material. Some key points:

• A material's absorption spectrum depends on its electronic structure. Light is absorbed in wavelengths that can excite electrons to higher energy states, which depend on the electron energy levels of the material.

• The absorption spectrum determines how a material absorbs light of different wavelengths. Strong absorption at a wavelength means that wavelength is strongly absorbed by the material, while minimal absorption means little light is absorbed in that wavelength.

• Absorption spectra are sometimes used to characterize materials and identify substances. The distinct absorption lines and bands can be like fingerprints, allowing the identification of unknown materials. Studying absorption spectra reveals properties of a material's electronic and molecular structure.

• Absorption spectra are related to emission spectra, which show the wavelengths a material emits. The wavelengths a material absorbs correspond to the wavelengths it can emit. Absorption and emission spectra provide complementary information about optical interactions with a material.

III.

https://en.wikipedia.org/wiki/Absorption_spectroscopy

https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/bohr-model-hydrogen/a/spectroscopy-interaction-of-light-and-matter

Active laser medium: I. An active laser medium is a material that can amplify light by stimulated emission of radiation. It is a key component in the operation of a laser, which is a device that produces a coherent beam of light through the process of stimulated emission.

The active laser medium can be made up of a variety of materials, like gases, liquids, or solids, depending on the specific application. In general, the active laser medium must have certain properties to function effectively in a laser. These include a high degree of transparency to the laser wavelength, a high gain coefficient (which is related to the rate of stimulated emission), and a long fluorescence lifetime (which is related to the persistence of the excited state).

When the active laser medium is excited by an external energy source, like a flash lamp or another laser, the electrons in the material are raised to a higher energy level. As these excited electrons relax back to their ground state, they can emit photons through either spontaneous or stimulated emission. In stimulated emission, the emitted photons have the same wavelength and phase as the incident photons, leading to a process of amplification.

The properties of the active laser medium, like its gain coefficient and fluorescence lifetime, determine the efficiency and performance of the laser. In order to achieve optimal laser performance, the active laser medium must be carefully selected and optimized for the specific application. For example, certain types of lasers are used in medical applications, while others are used in industrial manufacturing or scientific research.

Examples of active laser media include gases like helium-neon (HeNe) and carbon dioxide (CO2), solids like ruby, Nd:YAG (neodymium-doped yttrium aluminum garnet), and semiconductor materials like gallium arsenide (GaAs).

II. An active laser medium refers to the material that amplifies light in a laser. Some key points:

• The active laser medium contains ions/atoms/molecules that can be stimulated to emit light. When pumped with energy, it amplifies light at specific wavelengths corresponding to energy transitions in the medium.

• Common active laser media include helium-neon gas, ruby crystal, Nd:YAG crystal, and diode. The medium is chosen based on the desired laser wavelength/properties. Gaseous and solid media are used.

• The active laser medium must absorb pump energy and undergo stimulated emission at a particular wavelength. It enables light amplification, oscillation, and coherence in lasers. The properties of the medium determine the laser's wavelength, power, and other characteristics.

• The active laser medium is a key component of lasers. It facilitates stimulated emission and light amplification at specific wavelengths. The medium's properties are crucial in determining a laser's output and performance. Different media are used for different laser types and applications.

III.

https://en.wikipedia.org/wiki/Laser

https://www.britannica.com/technology/laser

Airy disk: I. In optics, the Airy disk refers to the pattern of light produced by a point source of light when viewed through a circular aperture, like the aperture in a telescope or camera lens. The Airy disk is named after the British astronomer Sir George Airy, who first described the phenomenon in 1835.

When a point source of light is viewed through a circular aperture, like the pupil of the eye or the aperture of a telescope, the light waves are diffracted as they pass through the aperture. This diffraction causes the light to spread out into a pattern of bright and dark rings, with the brightest spot at the center. The size and shape of the pattern depend on the size of the aperture and the wavelength of the light.

The central bright spot of the Airy disk is sometimes referred to as the Airy core or Airy spot. The size of the Airy disk is determined by the diameter of the circular aperture and the wavelength of the light, and it can be calculated using the formula:

θ = 1.22 * λ/D

where θ is the angular size of the Airy disk, λ is the wavelength of the light, and D is the diameter of the aperture.

The Airy disk is important in optics because it limits the resolving power of optical instruments, like telescopes and microscopes. When two point sources of light are close together, their Airy disks can overlap. This makes it difficult to distinguish between them. The ability of an optical instrument to separate two closely spaced point sources is determined by the angular resolution, which is related to the size of the Airy disk.

Overall, the Airy disk is an important concept in optics that helps to explain the behavior of light when it passes through circular apertures. By understanding the properties of the Airy disk, researchers can design and optimize optical instruments for a variety of applications.

II. The Airy disk refers to the central diffraction pattern of a point light source passing through a circular aperture. Some key points:

• The Airy disk is caused by diffraction, which spreads out the light from a point source. It consists of a central bright region surrounded by dimmer rings.

• The size of the Airy disk depends on the wavelength of light and aperture size. A larger aperture or shorter wavelength leads to a smaller Airy disk.

• The Airy disk limits the sharpness of imaging systems. Two-point sources appear as separate objects if their Airy disks do not overlap. The disk size thus determines the optical resolution.

• The Airy disk is important in understanding and limiting diffraction and image sharpness in optical systems. It represents the diffraction pattern of a point source, with implications for resolving power and system design. The disk's characteristics depend on optical parameters like wavelength and aperture size.

III.

https://en.wikipedia.org/wiki/Airy_disk

https://www.britannica.com/technology/Airy-disk

Albedo: I. In optics, albedo refers to the fraction of light or radiation that is reflected by a surface or object, as opposed to being absorbed or transmitted. The term is sometimes used in the context of solar radiation, where it's essential in determining the energy balance of the Earth's climate system.

The albedo of a surface is determined by the properties of the surface. This includes its color, texture, and composition. Surfaces that are lighter in color, smoother, and more reflective tend to have higher albedo values, while darker, rougher, and more absorptive surfaces have lower albedo values.

The albedo of different surfaces can vary widely. For example, snow and ice have high albedo values, reflecting much of the incoming solar radiation back into space, while forests and oceans have lower albedo values, absorbing more of the solar radiation. The Earth's overall albedo is around 0.3, meaning that about 30% of the incoming solar radiation is reflected back into space, while the remaining 70% is absorbed by the Earth's surface and atmosphere.

The concept of albedo is important in many areas of science. This includes climate science, astronomy, and remote sensing. For example, in climate science, the albedo of different surfaces is an important factor in determining the Earth's energy balance and the amount of solar radiation absorbed by the planet. In astronomy, the albedo of planets and moons can provide information about their composition and surface properties. In remote sensing, the measurement of albedo can be used to study changes in land use, vegetation cover, and snow and ice cover over time.

Overall, albedo is an important concept in optics and related fields, providing insight into the properties of surfaces and their interaction with light and radiation.

II. Albedo refers to the ratio of reflected to incident light for a surface. Some key points:

• Albedo depends on the material and wavelength of light. It ranges from 0 (no reflection) to 1 (complete reflection). A higher albedo means more light is reflected.

• A surface's albedo determines how much light it reflects versus absorbs. Surfaces with a high albedo, like snow, reflect the most light, while those with low albedo, like asphalt, absorb the most light.

• Albedo is important for applications like radiometry and climate modeling. It affects how much light is absorbed/reflected by a surface and influences heating. Measuring surface albedo helps determine energy balances and temperatures.

• The albedo can change depending on properties like surface roughness. Fresh snow has a higher albedo than old snow. Albedo is a key optical property that depends on material and wavelength, influencing the interaction between light and matter. It is crucial for understanding reflection, absorption, and energy flows.

III.

https://en.wikipedia.org/wiki/Albedo

https://www.britannica.com/science/albedo

Alexander's band: I. In optics, Alexander's band refers to the dark band that is sometimes visible between the primary and secondary rainbows in a double rainbow. The band is named after Alexander of Aphrodisias, a Greek philosopher who first described the phenomenon in the 3rd century AD.

When light passes through water droplets,