Optical Properties Flashcards
what are transparent, translucent and opaque materials, respectively?
transparent: see through
translucent: let light through
opaque: doesn’t let any light through
what are optical properties?
a materials response to exposure to electromagnetic radiation especially to visible light
what are the 2 things light can behave as?
a particle or a wave
what is a photon
a quantum unit of light
what do the variable “E”, “v”, “h” and “c” represent respectively
energy of a photon, frequency, planck’s constant, speed of light in a vaccum
radiations are packets of energy known as what?
photons
if light is transmitted, what will happen to the electron cloud?
the cloud will distort in shape
which is greater, the velocity of light in a material or vacuum
vacuum
if we add large ions to glass, what happen to the speed of light through the glass
it will decrease
if phi(0)>phi(c), what is the case
light is totally internally reflected
how do you determine the critical angle
its when phi(2) is 90deg
why are fiber optic materials cladded in low n material
so that the light will be totally internally reflected
what can be said about the size of the distance between energy states in metals
its very small
what does the small size of the energy gap in metals mean in terms of absorption
it means almost any frequency of light can be absorbed by metals
true or false, almost all light coming into a metal is absorbed within 0.1 micrometers of the surface
true
what types of materials can electrons be absorbed by
metals and small band gap materials
what types of materials can nuclei be absorbed by
all
what is the energy lost in absorbtion light by metals lost as?
the remaining energy is lost as phonons
why are metals reflective
because the energy lost by a descending electron is the same as the incident one
when an electron transitions from excited state, what is emitted
a photon
what does the color of reflected light depend on
the wavelength
true or false, metals are more transparent to very high energy radiation, like X-rays and gamma-rays
true
what can be said about an amorphous polymer in terms of scattering of light
very little to no scattering
If a polymer is transparent, what can be said about its strucutre
it will be an amorphous polymer
what can be said about an semi-crystalline polymer in terms of scattering of light
they scatter light a little
where does scattering of light occurs
at boundaries
highly crystalline polymers will be what
opaque
if a polymer goes from being amorphous to drawn what can be said about its optical properties
it becoming increasing crystalline, therefore it will become increasingly opaque
for non-metals, what has to be the case for light to be absorbed
hv
if a semiconductor appears as metallic, what does this mean?
the visible photons were all reflected
what it the relationship between the impurities and the aborption
more impurities=more absorption
how does an increase in impurities cause an increase in absorbtion
impurities divide up the band gap to allow transitions with less energy than Egap
how is the color of nonmetals determined
by the sum of the frequencies of the 1. transmitted light and 2. the remitted light from the electron transitions
how can an image become blurred
if the transmitted light is scattered internally
what are 3 factors that cause scattering?
- grain boundaries
- pores in ceramics
- different phases in materials
what is luminescence
the reemission of light by a material. material absorbs light at one frequency and reemits it as another
how is phosphorescence achieved
if the resting time in the trapped state is relatively long (>10^-8 seconds)
what is photo luminescence?
as electrons fall back to their ground states, UV light is emitted
how are colored lamps made?
by lining the inside of the tube with a material that only absorbs UV and re-emits visible light
how can we dictate the color of these “colored lamps”
by doping with various metal cations
what is cathodoluminescense
- the inside of a tube is coated with a phosphor material.
- the phosphur is bombarded with electrons
- the electrons in phospur are excited to higher levels
- visible light is emitted as electrons drop to lower ground states
what does the color of light depend on in cathodoluminescense
the composition of the phoshur
what can be said about the direction of the light that is emitted in cathodoluminescense
its random in phase and direction
how is total internal refraction made possible in fiber optic cables
by a specific difference in the indicies of refraction of the cladding and the core
what is the problem with the step index design
the different light rays travel different distances and reach the end at different times, limiting data communication
what design of index was created to rectify the problem
the graded-index
how is this design achieved
by parabolic doping
how does the graded-index design fix the problem
becuase the rays travelling in the outer regions are going through lesser indicies of refraction therefore they travel faster (according to V=C/n), making them arrive at the same time
if the emitted light has the same energy and phase as the incident light, what is this called
coherent
