phase retrieval I

Question 1

at least two unknowns, sometimes third unknown

Answer 1

attenuation and phase
* Scattering

Question 2

Two propagation distances – a direct solution

Answer 2

Transport of Intensity Equation (TIE):

Question 3

Phase retrieval in the near field

Answer 3

Using two images at different distances, the phase and intensity can be solved

Can be difficult to align images exactly
* For cone beam, magnification has to be taken into account

Question 4

Propagation based phase retrieval @synchrotron

Answer 4

+ no optical elements
+ nearly no constraints on spectral width
- highly coherent beam (small source size)
- high resolution detector

Question 5

Phase-Contrast Methods

Answer 5

CDI
Ptychography
crystal interferometer
analyzer based imaging
grating based imaging
propagation based imaging

Question 6

In X-ray imaging the phase gives information about

Answer 6

weakly absorbing objects

Question 7

In astronomical imaging, the phase gives the

Answer 7

aberration induced by the atmosphere

Question 8

In X-ray crystallography the phase gives information about the

Answer 8

position of (Thomson-) scattering objects (electron densities) in space

Question 9

Classical X-ray microscopy setup diasdv

Answer 9

• resolution limited by lens size D
  and sample-to-lens distance z0
• no large lenses for X-rays available

Question 10

Lenseless Imaging

Answer 10

+ resolution increases linearly with detector size D
- requires iFT (Phase Problem)
- decreasing intensity for larger angles

Question 11

Coherent Diffractive Imaging (CDI) known as

Answer 11

Also known as lensless imaging

Question 12

Error reduction iterative algorithm known as

Answer 12

Gerchberg-Saxton
alternates between updating the phase in the spatial domain and the Fourier domain until convergence.

Question 13

principles of ptychography and CDI:

Answer 13

Principles:

Ptychography: In ptychography, the sample is illuminated with a partially coherent light source. The illumination spot is scanned across the sample, and overlapping diffraction patterns are recorded. Phase retrieval algorithms are used to reconstruct the phase and amplitude of the sample from the intensity measurements.
CDI: Coherent Diffractive Imaging involves analyzing the diffraction patterns produced when coherent waves interact with an object. The intensity distribution of these diffraction patterns is used to recover the phase information through iterative algorithms.

Question 14

analyzer based imaging

Answer 14

These analyzers consist of single crystals that can diffract X-rays at specific angles, allowing only X-rays with a narrow energy range to pass through.

Question 15

analyzer based imaging
for every pixel
1) shift in position →
2) change in height →
3) change in area →
4) change in width →
of rocking curve is analyzed

Answer 15

for every pixel
1) shift in position → differential phase
2) change in height → attenuation
3) change in area → attenuation
4) change in width → scattering
of rocking curve is analyzed

Question 16

crystal interferometer working principle

Answer 16

uses the properties of crystal materials to create interference patterns between two or more beams of light or other electromagnetic radiation. This interference allows for the measurement of various properties of the radiation, such as phase shifts, wavelength differences, and other characteristics.

Question 17

Crystal interferometer adv disadv

Answer 17

+ high phase sensitivity
+ good image quality
+ not too much restictions for beam quality

• Si crystals act as monochromator
• only for small samples

Question 18

near / far field methods

Answer 18

near: Propagation based imaging
far: CDI-ptychography

Question 19

allready used pre- / clinical method

Answer 19

propagation based imaging

Question 20

Sort the steps of the iterations in error reduction algo

Answer 20

Fourier transform image in source plane (START: guess initial phase)

Apply Fourier constraint (set amplitude to measured)

Inverse Fourier transform image

Apply spacial constraint

Repeat until convergence

Question 21

How can we interpret changes in the intensity distribution of a rocking curve?

Broadening of the peak:

Shift of the peak position:

Change of peak height / total area under curve:

Answer 21

Broadening of the peak: Scattering

Shift of the peak position: Phase shift

Change of peak height / total area under curve: Attenuation

Question 22

why do we need a high intensity beam for a crystal interferometer?

Answer 22

The (Si) crystals act as monochromator.