Light and Refractive Index Flashcards
what are the goals of microscopy?
- magnification (produce a magnified image of the specimen)
- resolution (separate details in the image)
- contrast (render details visible to the detector)
electric field and magnetic field vibrate in __________ planes as they propagate forward.
perpendicular
what is specular reflection?
smooth surface maintains coherence and reflects
what is diffuse reflection?
rough surface scatters light
what are plane waves?
when waves of light spread out from their original tight circles to form straightened waves where all photons hit something at the same time
what types of images do convex and concave lenses make?
convex = real image (projected into space); converge light; projected on opposite side of object inverted
concave = virtual image (have to look through lens to see); diverge light; appears upright on same side as object
what is Snell’s law and what does it say?
n1sinθ1 = n2sinθ2
- when going from a high RI medium into a low RI medium, the ray is bent AWAY from normal
if the incident angle is greater than the critical angle, the ray will be …
internally reflected
what is dispersion?
change in RI with wavelength; lower value, the more dispersion
what is magnification?
m = q / p
p < q = object distance < image distance
what is spherical abberation?
- optical-path dependent distortion (blurry)
- rays at perimeter converge closer than center rays
- correct through correct thickness of cover glass
what is chromatic aberration?
dispersion causes wavelengths to separate (different wavelength, different RI)
what is curvature of field?
flat object perceived to be a curved object
what is image distortion?
- when magnification is not constant across field of view
- if magnification decreases with distance from the center = barrel
- if magnification increases with distance from the center = pincushion
what does Kohler illumination do?
- produces even lighting of the specimen
- reduces unwanted diffraction, light scattering, and glare from optical surfaces within microscope
what are the fundamental actions of Abbe’s Theory of Image Formation?
- diffraction that occurs by the specimen
- collection of the diffracted orders by the objective
- interference of these orders to produce the image (by eye or captured)
what causes light and dark bands?
diffracted beams of light that cause destructive (dark) and constructive (light) interference
what causes contrast?
interference between the 0th and highest order of diffracted rays in the back focal plane of the objective
finer details diffracts light over _______ angles.
larger
how is wavelength related to resolution?
shorter wavelength, greater resolution
what is numerical aperture (NA)?
- measure of the light gathering ability of a lens
- higher the NA, the better
NA = n (sinμ)
when are two object points resolved according to Rayleigh?
when the central diffraction spot of one point coincides with the first diffraction minimum of the other point in the image plane
what is empty magnification?
when an image is magnified but no additional features have been resolved (bigger but blurry)
define approximate useful magnification?
- multiply objective by eyepiece
- needs to fit between 500 x NA and 1000 x NA
what is the approximate useful magnification if the objective = 100x (NA = 1.42) and eyepiece = 10x?
magnification of objective x eyepiece = 100 x 10 = 1000
minimum = 500 x 1.42 = 710
maximum = 1000 x 1.42 = 1420
since 1000 is between 710 and 1420, its good
what is incandescence?
emission of electromagnetic radiation as a result of high temperature
what is a black-body radiator?
theoretical “perfect” radiator, emitting light over all wavelengths of EM spectrum; wavelengths of BBR only depend on temperature
what does a condenser do?
- controls contrast
- minimizes/eliminates “stray light” by reducing glare and contrast
- focuses the image of field diaphragm
- must match NA of condenser to that of the objective to achieve maximum resolution
what does an open condenser do?
decreases contrast but increases resolution
what is the most common type of condenser?
- Abbe-type (simple two-lens, inexpensive, not corrected, good for routine work)
- other type is swing out (more lenses, higher NA)
what are the three types of condensers? which one is the best?
achromat (worst) , fluorite, and apochromat (best)
how is magnification related to depth of field and wavelength?
increased magnification, increased depth of field, decreased wavelength
how is magnification related to working distance?
increased magnification, decreased working distance
what differentiates glass from other substances?
it is an organic product of fusion that has solidified without crystallization
how crystalline quartz different from amorphous glass?
- crystalline quartz = cooled slowly; breaks along straight lines
- amorphous glass = cooled rapidly; random orientation of molecules and random breakage; stronger than quartz
what are formers in glass? name an example
- compounds that, when cooled quickly after melting, will solidify w/o crystallization
- SiO2
what are fluxes in glass? name an example
- used to lower melting temperature of glass
- Na2CO3 (soda ash)
what are stabilizers in glass? name an example
- used to impart chemical resistance and strength to glass
- CaO
what are the steps of glass manufacturing?
1) raw materials
2) melting
3) forming (shaping)
4) annealing (controlled cooling in lehrs)
5) secondary processing (cut, polished, etc.)
what is the most common type of glass?
soda-lime
what is boro-silicate glass and what is it used for?
- add >5% boric acid
- provides low thermal expansion and better resistance to acid corrosion
- used in lab glassware and cookware
what is alumino-silicate glass and what is it used for?
- add greater % of aluminum
- provides greater heat tolerance than boro-silicate glass and resistant to alkalis
- used in lab glassware and cookware
what is lead-alkali-silicate (AKA leaded) glass and what is it used for?
- high RI and dispersion
- easier to shape
- used in crystal tableware, neon sign tubing, jewelry, etc.
what is silica glass and what is used for?
- made from molten quartz (costly and difficult to manufacture)
- ONLY used in specialized applications
how is flat glass made?
drawn through rollers in float process (glass flows onto bed of molten tin - makes one side fluoresce)
how is container glass made?
molding process (pressed, blown, cast, or spun into shape of mold)
how are glass fibers/fiberglass made?
drawn into filaments by rotary process similar to cotton candy makers
