Optics, Waves and Lasers

what is normal light with reference to polarisation

"Normal" light is a random mix of polarisations, due to incoherent reflection from microscopic material boundaries Usually make linear polarised light using Polaroid or (better, but more expensively) crystal filters

what is a crest and what is a trough?

- A crest is the point on a wave with the maximum value or upward displacement( Amplitude) - A trough is the point on a wave with the minimum or downwards displacement( Amplitude)

What is a mechanical wave?

- A disturbance that travels through a medium. - As the wave travels through the medium, the particles that make up the medium undergo displacement of various kinds, depending of the nature of the wave

how are line emission spectra to be produced?

- If an electron is in an excited state it can return to a lower energy level. When it does this, it loses energy. - amount of energy it loses is equal to the difference in the energy levels it moves between. (This energy is released as a photon.) I.e of electron moves form w4 to w2, the energy of the photon, E=hf=W_{4}-W_{2}. As the energy levels have different values, each of the possible electron transitions within an atom will produce a photon with a different energy. This means that each electron transition will produce a photon of a different frequency and hence a different colour. This causes line emission spectra to be produced A long thin black rectangle with 5 very thin, vertical, different coloured lines spread unevenly across it. Because different types of atoms have different energy levels, the photons produced will be different and so the line spectra for different elements will be different. Line spectra can be used to identify elements.

what is light as an EM wave?

- Light is a propagating wave(traveling wave ) of coupled oscillating electric (E) and magnetic (B) fields. - The wave travels (and transmits energy & momentum) perpendicular to both the E and B fields

when are line spectra produced

- Line spectra are produced when electrons move from one definite energy level inside an atom to another - When atoms lose electrons they are moving to the ionization level and so do not produce line spectra..

different levels in the structure of an atom.

- The lowest energy level is called the ground state. - If an electron gains energy it can move to a higher energy level. It is now in an excited state. - If the electron gains enough energy to completely remove it from the atom it is said to be in an ionization state.

what is the speed of propagation/ wave speed?

- The speed at which a disturbance propagates through a medium. - use v for the wave speed - the wave speed is NOT the same as the speed at which particles moves when they are disturbed by a medium.

What is the difference between a the motion of a transverse wave through a medium and the motion of the particles in a medium? Take a rope for example.

- Wave travels with constant speed along the length of the rope - Motion of the particles is simple harmonic motion and transverse to the length of the string.

what can be said about the focal length of a converging and diverging lens.

- converging lens always has a positive f - diverging lens has a negative f. The signs associated with magnification also work the same way for lenses and mirrors. - A positive magnification corresponds to an upright image - while a negative magnification corresponds to an inverted image

what is black body radiation and what emit it, give some examples.

-A blackbody refers to an opaque(not transparent) object that emits thermal radiation. - some examples arestars, the sun, incandescent filament light bulbs - A perfect/ideal blackbody is one that absorbs all incoming light and does not reflect any. At room temperature, such an object would appear to be perfectly black (hence the term blackbody)

what is the 1) angular frequency 2) The period of a wave

1) ω = 2πf 2) T = 1/f = 1/ 2πf

what does the photon show?

1)Light also has a particle nature, the photo. 2) photons in many atomic models in physics, are particles which transmit light. In other words, light is carried over space by photons 3)the light that reaches our eyes, for example, consists only of real photons, which carry both information and energy. However, all electromagnetic fields contain not only real photons, but also virtual photons, which can be thought of as "imprints on the quantum vacuum

thin lens/curved mirror equation

1/f = 1/S + 1/s'

what is the lens maker formula

1/f =(n -1)(1/R1 - 1/R2)

what are absorption bands?

A connected series of closely spaced or overlapping absorption lines. absorbtion lines are line of finite width in the absorption spectrum. absorption spectrum is the detailed dependence on wavelength of the intensity of radiation absorbed by a given medium.

(EM) A general wave can be "decomposed" into a ?

A general wave can be "decomposed" into a sum of different frequencies, meaning that different parts of a wavepacket may travel through the material at different speeds and the wavepacket may disperse: the phase and group velocities capture two important aspects of how this general dispersion relation works.

what is polarisation in waves?

A light wave that is vibrating in more than one plane is referred to as unpolarized light. Polarized light waves are light waves in which the vibrations occur in a single plane. The process of transforming unpolarized light into polarized light is known as polarization.

A mirror produces a virtual image at what distances?

A mirror produces a virtual image at the same distance "inside" the mirror as the object was "outside"

Linear Polarisation?

A plane electromagnetic wave is said to be linearly polarized. The transverse electric field wave is accompanied by a magnetic field wave

what does a polarising material(polariser) do?

A polariser allows the transmission of light in one plane due to the molecular alignments inside the material.

Difference between a real and a virtual image?

A real image of a point on an object is a ray convergence point which photons from the object actually get to - so an unlensed light-sensitive device placed there would interact with the photons and record an image.

A liquid is in a channel, lets say water in a canal. There ia a flat board at the end of the canal. someone takes a flat board pushes it forwards and then backwards. What would happen?

A wave disturbance travels down the canal. The displacements of the water have both longitudinal and transverse components. As each wave passes , each particle of the liquid surface moves in a circle.

Note that for light, E∝ω and p∝k ,so a ω vs. k plot is just a

A ω vs. k plot is just a just a rescaling of E vs. p (Energy vs momentum)

As light travels from one medium to another what happens to the frequency and the wavelength of the light.

As you go from one medium to another, the frequency stays the same, but the wavelength changes. The speed of the wave traveling from one medium to another changes, and that change is proportional to the change in wavelength. As you go from one medium to another, the refractive index, n, for that medium changes. That change in the refractive index dictates the change in the speed of the wave traveling through that medium, and thus the waves wavelength

what is Birefringence?

Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive).

What is Chromatic aberration?

Chromatic aberration occurs because real lenses don't focus all frequencies to the same point, due to dispersion or light rays of different frequencies are refracted by different amounts if the refract- ing material is dispersive (which in practice it always is), in a refraction-based light focusing system the different frequencies will focus at different points. This results in a blurry image and is called chromatic aberration Achromatic lenses counteract this by combining two lens materials, with opposing dispersion relations. Not perfect.

circular polarisation?

Circularly polarized light consists of two perpendicular electromagnetic plane waves of equal amplitude and 90° difference in phase.

what is the difference between a concave and convex lens?

Concave and convex are two basic types of lenses. A convex lens focuses light rays, whereas a concave lens causes the light rays to diverge.

what is transverse polarisation?

E and B vectors perpendicular to propagation(travel) and to each other

The energy and momentum of photons in light waves can be represented by( with factors of 2π)

E= h(bar)ω ω=2πν p= h(bar)k k=2π/λ k being the wavenumber h(bar) = h/2π

The energy and momentum of photons in light waves can be represented by?

E= hf P = h/λ where, h is planks constant(6.62607004 × 10-34 Joule-seconds.)

What exactly is an ELECTRON VOLT as opposed to a VOLT?

Electonvolt (symbol: eV) is a unit of ENERGY. One eV is equal to the amount of energy one electron acquires by accelerating (from rest) through a potential difference of one volt. It is usually used as a measure of particle energies although it is not an SI (System International) unit. The SI unit for energy is the JOULE. 1 eV = 1.602 x 10-19 joule. Volt is the SI unit of ELECTRIC POTENTIAL, potential difference or e.m.f. (electro motive force) defined as the difference of potential between two points on a conductor carrying a constant current of one ampere when the power dissipated between the points is one watt. It is named after Alessandro Volta (1745-1827)

For optically anisotropic materials, refractive index is dependent on ? and an example of one.

For optically anisotropic materials, refractive index is dependent on orientations of ray travel and polarisation! Obvious kind of anisotropy is a boundary: the surface of a pond or a plate of glass, for example. The relative orientations of the beam direction and the normal vector to the surface lead to different amounts of reflection depending on whether the polarisation vector is in the plane containing the ray and the normal, or perpendicular to it.

On average, light slows down in transparent materials: the slow-down factor n = v/c is the refractive index. why have is used "On average" here?

I say "on average", because in the simplest picture the photons are still travelling at the same speed in the gaps between atoms, but they have to periodically waste some travel time on interactions with the electron clouds around those atoms - the mix of speed-of-light travel and interaction times gives an effective wave speed which is a bit reduced from that in vacuum. This picture is also quite useful for inferring that typically a denser material (i.e. higher mass or number of molecules per unit volume) will produce more interactions per unit length, and hence a higher n for the same chemical composition. It also implies to some extent that different materials may have different "natural" refractive indices: chlorofluourocarbon gases and diamond respectively have high refractive indices com- pared to most materials of similar density, due to their electron structure and crystal structure respectively.

what is the difference between a converging and diverging lens?

If the light rays converge (as in a converging lens), then they will converge to a point. This point is known as the focal point of the converging lens. If the light rays diverge (as in a diverging lens), then the diverging rays can be traced backwards until they intersect at a point( a negative focal length)

Quickly difference between specular reflection and diffuse reflection

If the surface is (microscopically) flat over an extended distance, get coherent specular reflection, e.g. mirror A (microscopically) bumpy surface reflects adjacent rays in very different directions, loses coherence: diffuse reflection

how would create an image from a photographic film because If I just hold up a photographic film in front of an object, every point on the film receives photons from every point on the object: this doesn't form a coherent image =(

If we put a system in-between the object and the image plane (we will deal here with mirrors and refracting boundaries, but it could be something weird like gravitational lensing) then we can modify the ray paths to make them reintersect and form an image.

where is total internal reflection important?

Important in optical fibres, diamond cutting, optical instruments, mirages. .

In light that hasn't been specially filtered, each photon will have a random?

In light that hasn't been specially filtered, each photon will have a random polarisation vector (except that it's always perpendicular to the light ray direction).

what is a wave packet?

In physics, a wave packet (or wave train) is a short "burst" or "envelope" of localized wave action that travels as a unit. basically a section of a wave

what is a quantum vacuum?

In quantum field theory, the quantum vacuum state (also called the quantum vacuum or vacuum state) is the quantum state with the lowest possible energy. Generally, it contains no physical particles. Zero-point field is sometimes used as a synonym for the vacuum state of an individual quantized field..

what is an isotropic material, and what effect would an isotopic materials have on the polarisation direction?

Isotopic material - looks the same in all directions/ symmetrical The polarisation direction is not very important.

A string is under tension, if someone was to move the end of it up and down repeatedly what would occur.

It would create a transverse wave on the string. As each wave passes, each particle moves up and then down , transversely(perpendicularly) to the motion itself.

Differences between lenses and mirrors?

Light reflects from a mirror. Light goes through, and is refracted by, a lens. Lenses have two focal points, one on either side of the lens. A concave mirror converges light to a focal point. For lenses, light converges to a point for a convex lens. A convex mirror diverges light, as does a concave lens . Any lens that is thicker in the center than the ends is a convex lens. Any lens thicker at the ends than in the center is a concave lens.

How is the speed of light effected in materials compared to a vacuum? and what are the equations for this?

Light travels at speed c in vacuum. But not in transparent materials: slow-down by a factor n, the refractive index. vphase = c/n so, n = c/v

Give examples of Circular polarisation in nature

Not a lot of circular polarisation in nature, but "structural colour", e.g. chiral beetle carapaces, is a great example: Firefly glow is also circularly polarised. . . with different senses of rotation on each side of the body!

What is quantum theory?

Quantum theory is the theoretical basis of modern physics that explains the nature and behavior of matter and energy on the atomic and subatomic level. The nature and behavior of matter and energy at that level is sometimes referred to a

for a straight line what does R equal

R = ∞

How are rainbows formed?

Rainbows are formed by a mix of total internal reflection and dispersion. Double rainbows formed by double reflection in the droplet, hence a second spectrum inversion remember the shorter the wavelength the more bending they experience,

How do you form an image?

Rays are emitted in all directions by each point on the surface of an object. Forming an image means putting lots of those rays back together again so that all the rays from each point on the object pass back through a single point somewhere else(focal point) - and to be a useful image, each point on the object must map to a different image point!

what is specular reflection(regular reflection)?

Reflection from a "specular" smooth surface mostly linearly polarises light with E in the plane of the material because the E field excites the material's electrons or Light reflects from a smooth surface at the same angle as it hits the surface. For a smooth surface, reflected light rays travel in the same direction. This is called specular reflection or Specular reflection, also known as regular reflection, is the mirror-like reflection of waves, such as light, from a surface. In this process, each incident ray is reflected, with the reflected ray having the same angle to the surface normal as the incident ray

what is the angle reflected from a flat surface?

Reflection from a flat surface is very simple: just θ1 =θ2!

what is diffuse reflection?

Reflection from such a rough surface is called diffuse reflection and it appears matte(dull/ lustreless) Consequently, the outgoing rays are reflected at many different angles and the image is disrupted. The angle of incidence equals the angle of reflection at the point that the light ray strikes the surface.

Examples of Electron energy level transitions(when electrons are excited so they "jump" to a higher energy level or return to a lower energy level)

Spontaneous: sodium street lamps, light-emitting diodes (LEDs) Stimulated: lasers Fluorescence: delayed transitions

What is synchrotron radiation?

Synchrotron radiation is the electromagnetic radiation emitted when charged particles are accelerated radially. (Bending charged particles) i.e., when they are subject to an acceleration perpendicular to their velocity or Synchrotron radiation is the name given to the radiation which occurs when charged particles are accelerated in a curved path or orbit.

In any wave, a wavelength takes period T = ?

T = 1/f

what is the emission spectrum?

The detailed dependence on wavelength of the intensity of radiation emitted by a given radiator(Any source of radiant energy.)

What is a transverse wave and give some examples.

The displacements of the medium are transverse(perpendicular) to the direction of travel on the wave along the medium. ( imaging shaking a sting) Light and other types of electromagnetic radiation are transverse waves. An oscillating string and Seismic S-waves are also examples of transverse waves. In transverse waves, the vibrations are at right angles to the direction of travel.

Can an electron travel between energy levels?

The electron can gain the energy it needs by absorbing light. If the electron jumps from the second energy level down to the first energy level, it must give off some energy by emitting light. The atom absorbs or emits light in discrete packets called photons, and each photon has a definite energy.

how is the energy in a EM wave divided ?

The energy held in an EM wave is evenly divided between the E and B fields, but the force experienced by an electron is only equal if it moves at the speed of light.

EM wave interactions with normal matter are hence completely dominated by the ? Field and why?

The energy held in an EM wave is evenly divided between the E and B fields, but the force experienced by an electron is only equal if it moves at the speed of light. The force due to the magnetic field is v/c times smaller than that due to the E field, which is a very tiny fraction for normal matter. EM wave interactions with normal matter are hence completely dominated by the E field, and so we say that the E field direction is the polarisation vector of the photon

Similarities between lenses and mirrors

The equations we used for mirrors all work for lenses. A convex lens acts a lot like a concave mirror. Both converge parallel rays to a focal point, have positive focal lengths, and form images with similar characteristics. A concave lens acts a lot like a convex mirror. Both diverge parallel rays away from a focal point, have negative focal lengths, and form only virtual, smaller images.

what is the focal length

The focal length of the lens is the distance between the lens and the image sensor when the subject is in focus

How does a mirror work, and what type of reflection is required?

The key factor is a smooth surface, because rough surfaces scatter light instead of reflecting it. When photons — rays of light — coming from an object (your smiling face, for example) strike the smooth surface of a mirror, they bounce back at the same angle. Your eyes see these reflected photons as a mirror image

What is a longitudinal wave and give some examples.

The particles in the medium travel forward and back along the same direction of the wave (imagine a slinky attached to something, then pull it back and then let it go back to its original position multiple times) Sound waves, Pressure waves and Seismic P-waves (generated by explosion and earthquake) are all examples of longitudinal waves. In longitudinal waves, the vibrations are along the same direction as the direction of travel.

what is the difference between wavenumber and wavelength?

The wavelength of a wave is the length where the shape of the wave starts to repeat itself. Wavenumber is defined as the number of wavelengths in a given distance. There are two main wavenumber measurements. First one is the number of wavelengths per 2π meters. This is widely used in physics and mathematical models of the wave as well as quantum mechanics. This wavenumber is denoted using "k" and it is also known as the angular wavenumber.

what are the two types of image that can be seen?

There are two types of image that can be seen. A real image is the image formed where the light rays are focussed. A virtual image is one from which the light rays appear to come but don't actually come from that image like in a mirror.

what is the dispersion of wight light(simple)?

This is an example of refraction. When white light passes through a prism, it is dispersed and the different colours of the spectrum separate. Dispersion causes rainbows. - each spectral colour has a different refractive index - blue light has a greater refractive index in a given medium than red light - blue light refracts (bends) more than red light so basically the Each color from the original beam of light has its own particular wavelength(colour), which are each slowed down differently in the medium(glass in this case). The amount of refraction increases as the wavelength of light decreases. Shorter wavelengths of light (violet and blue) are slowed more and experience more bending compared to longer wavelengths (orange and red).

difference between a half wave plate and a quarter wave plate

Two common types of waveplates are the half-wave plate, which shifts the polarization direction of linearly polarized light and the quarter-wave plate, which converts linearly polarized light into circularly polarized light and vice versa. A quarter-wave plate can be used to produce elliptical polarization as well.

what is the difference between real and a virtual image?

Virtual 1.Doesn't form on a screen 2.Always erect 3.Ray's of light seem to be coming from the same origin Real 1.Forms on a screen 2.Always inverted 3.Ray's of light meet at the same place

what is there visual light spectrum

Visible spectrum from red → blue is λ ∈ 700-400 nm Most object colours are a mix of continuous spectrum + discrete emission/absorption bands

What do and don't waves transport from one region to another.

Waves transport energy, but NOT matter, from one region to another. "Doing the wave" at a sports stadium is an example of a mechanical wave. The disturbance propagates through the crowd, but there is no transport of matter( no one moves seats)

What are sinusoidal waves?

Waves with simple harmonic motion. Any periodic wave can be represented as a combination of sinusoidal waves.

What happens when a sinusoidal wave passes through a medium?

When a sinusoidal wave passes through a medium , every particle in the medium undergoes simple harmonic motion with the SAME frequency.

When transitioning from high to low n (i.e. leaving a material) the normal angle increases. ( basically the larger the difference between the refractive indexes , the larger the angle.) Hence?

When transitioning from high to low n (i.e. leaving a material) the normal angle increases. Hence there is a critical angle beyond which the outgoing ray does not leave at all. This leads to the phenomenon of total internal reflection

Unlike solid objects, two waves can share a point in space. what is the term for when two waves occupy the same point?

When two waves occupy the same point, superposition occurs. Constructive interference is when two waves superimpose and the resulting wave has a higher amplitude than the previous waves. Destructive interference is when two waves superimpose and cancel each other out, leading to a lower amplitude.

what is the angle of incidence, reflection and refraction?

angle of incidence - the angle at which the wave hits the medium( always to the normal) angle of reflection - the angle at which the wave reflects off medium( always to the normal) the angle at which the wave refracts into the medium ( always to the normal)

what is an anisotropic material, and what effect would an anisotopic materials have on the polarisation direction?

anisotropic material - the material is not symmetric The mismatch between the polarisation direction and the special directions of the material can be important.

So light can either reflect or refract at a boundary?

both from low- to high-n and vice versa: which happens when? Both! But the intensity varies with incidence angle

what is circular polarisation? and the equation

circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electric field of the wave has a constant magnitude but its direction rotates with time at a steady rate in a plane perpendicular to the direction of the wave. the formula Looks complicated, but just overlay two linear polarised waves, relatively rotated by 90◦ and out of phase by π/2: E(t) = E0 [cos(ωt)x(with^over the x) + sin(ωt)y(with^over the y)] So, polarisation angle θ = tan−1(Ey/Ex) = ωt So θ varies constantly with time: circular polarisation! this Can be created using a quarter-wave plate

difference between a positive/ negative focal length and a magnification grater/ less than 0

converging(concave) lens always has a positive f - diverging lens has a negative f. The signs associated with magnification also work the same way for lenses and mirrors. - A positive magnification corresponds to an upright image - while a negative magnification corresponds to an inverted image

A liquid or gas is in a tube whit a rigid wall at the right end and a movable piston at the left end. If the pistons started to move in a single back and forth motion what would happen?

displacement and pressure fluctuations travel down the length of the medium. As each wave passes, the particles will travel forward and back parallel to the motion of the wave itself.

how would you know a lens wouldn't focus?(goes to infinity)

if 1/f = 0

what happens to light at a materials interface?

light changes direction at material interfaces

For a telescope total angular magnification is given by?

m = -f1/f2

what is the magnification formula

m = y'/y = -s'/s

formula for angular magnification

m = Θ'/Θ ≈ dmin/f (where dmin ∼ 25cm is the "near point" of human vision)

what is the speed of light in a vacuum?

n vacuum, light speed is c(3x10^8ms^-1), the universe speed limit.

what is snells law equation?

n1 sinθ1 = n2sinθ2 where n1 <n2 ⇒ reduces normal angle & vice versa

Does the Polarisation axis does have to be fixed?

no Polarisation axis does not have to be fixed. E vector can rotate around the direction of travel!

are EM waves normally polarised?

no, EM waves are transverse-polarised. Electromagnetic waves consist of perpendicular oscillating electric and magnetic fields, perpendicular to the direction of propagation, which make EM waves transverse. The plane of vibration of the EM wave is the one containing the oscillating electric field vector and the direction of propagation

what is the phase velocity with non-trivial dispersion? ann what is non-trivial dispersion?

non-trivial dispersion is where the angular frequency ω and wavenumber k are not linearly related. in non-dispersive(non-trivial dispersion) materials the local gradient to the dispersion relation, Vgroup = dω/dk is

What do polymer/crystal structures do to electron movement?

polymer/crystal structure restricts electron movement to 1 Dimension

what is the critical angle formula?

sinθc = n2/n1

what does superimpose mean?

superimpose: To place an object over another object

what is phase velocity and the equations for it

the speed of propagation of a sine wave or a sinusoidal component of a complex wave, equal to the product of its wavelength(λ) and frequency(f). vphase = λ/T = λf = ω/K

unpolarised ligt has oscillations (of then light's electric field) in?

unpolarised ligt has oscillations (of then light's electric field) in every plane perpendicular to its direction of travel

Plane mirrors and convex mirrors only produce ?

virtual images Only a concave mirror is capable of producing a real image and this only occurs if the object is located a distance greater than a focal length from the mirror's surface.