Scattering Flashcards
What are the orders in a diffraction grating?
Zero order: specular reflection. First order: first angle of diffraction; is symmetric (positive and negative orders) relative to the zero order.
What are blaze wavelength and angle?
Blaze wavelength: wavelength in diffracted spectrum with highest efficiency. Blaze angle: first order diffracted angle of the blaze wavelength.
What is an echelle grating?
An echelle grating has higher groove spacing/lower groove density than other gratings; high angle of incidence means high dispersion, resolving power, and efficiency. Good for high resolution.
Which is more dispersive - prism or grating?
Definitely grating. Maximum prism dispersion is limited by refractive index.
Are the two outputs of a Mach-Zehnder interferometer the same?
No. They are separated in phase by pi.
Differences between reflective and transmissive gratings
Transmission gratings have better aberration compensation, meaning lower (better) alignment sensitivity. Transmission not as good for longer wavelengths.
What are examples of non-coherent imaging systems? What are some unique properties of non-coherent imaging systems?
Telescopes, microscopes. AKA shift-invariant.
The image formation process is linear in image intensity, meaning that imaging two items simultaneously gives you the sum.
Is generally “better” in lateral resolution than coherent imaging.
In non coherent imaging systems, the image of an object is the convolution of the object and the PSF.
What are examples of coherent imaging systems? What are some unique properties of coherent imaging systems?
OCT, radar. Coherent systems are linear in complex amplitude as a result of the fixed phase relationship between rays emerging from the object. Only coherent imaging can measure phase information from the objects.
Coherent imaging is better for edge detection because you can use negative numbers. (Incoherent phase is magnitude squared of coherent phase)
What is a point spread function?
The point spread function, also known as a impulse response function, describes the response of a focused optical imaging system to a point source. It is the spatial domain equivalent of the optical transfer function.
What is an Airy disc/pattern?
The Airy disc is a description of the PSF of an ideal focused spot of light from a perfect lens with circular aperture. The wavelength of light used affects. Angle of first minimum is given by the Rayleigh criterion
What is the mean free path for photon scattering events vs. mean path length before photon absorption in tissue?
Scattering: ~0.1mm, absorption: ~10-100mm.
Difference between SNR and CNR?
CNR is local change in intensity divided by the standard deviation of background intensity, and SNR is average background image intensity divided by its standard deviation. CNR = C * SNR.
What is the scattering cross section?
This is a ratio of total scattered power divided by the incident light intensity (power per area), and is in units of area (although it may not necessarily correspond to a physical size of target, such as in plasmons)
What information does Mie theory reveal for a spherical particle of any size?
Scattering efficiency, scattering anisotropy, and scattering cross section. If given a medium, you can also get the scattering and reduced scattering coefficient.
What is a two-fold improvement in dB?
3 dB amplitude, 6 dB intensity
