Imaging Flashcards
What do fine/sharp features require?
They require the contribution of high frequency sinusoids in the Fourier spectrum.
Huygen’s principle:
Every point on a particular wavefront cna b considered a new source of small spherical wavelets.As the wavelets propagate outward, the curve that runs tangent to these wavelts dfines the new wavefront.
What is a wavefront?
A wavefront can be defined as the line or curve that connects the points of constant phase in a wave.
What is an infinite plane wave?
A wavefront that is completely straight. This is theoretically impossible, but it is a good approximation of i.e the light coming from distant star. An infinite wave plane will continue to produce infinite plane waves as it propagates forward.
Define diffraction:
When we pass an infinite wave past a barrier (a hole) we break the symmetry of the Huygen wavelets near the edges. As a result, waves diffract (ben) as they pass through small openings. Smaller openings diffract waves at larger angles.
How small does a hole need to be to cause diffraction?
Diffraction becomes appreciable when the opening get to be approximately the same size or smaller than the wavelength of the wave passing through it.
When are two sources said to be coherent?
If they maintain a constant phase between each other.
What do you need to create a sustained and stable interference pattern?
Two sources with the same wavelength that are coherent.
What happen as we increase the number of sources (slits)?
We will de-cohere more quickly as we move away from perfect constructive interference and the bands thus sharpen into narrower peaks.
What happen when you have a sinusoidal grating making the slits?
The resulting diffraction pattern has one zero-order and first order peaks.
How do you calculate NA?
NA = n (index of refraction) multiplid by th maximum acceptance angle of the lens.
Why do we use Formamide for hybridization during FISH?
Formamide reduces the free energy of binding of nucleic acids strands to allow hybridization to take place at lower temperatures without a loss in specificity, thus improving structural preservation ofth tissue.
What is an antifade agent?
An antifade agent is a substance used in microscopy to slow down the photobleaching of fluorescent dyes and labels. Photobleaching occurs when fluorescent molecules lose their ability to fluoresce due to damage by photons during the imaging process.
