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Summer school of Photonics Flashcards | StudBud
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Summer school of Photonics
Summer school of Photonics
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Questions
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Answers
1
What kind of nonlinear mechanism causes a giant optical nonlinearity of nematic liquid crystals?
Density change
Reorientation of LC molecules under a low frequency external electric field
Light-induced molecular reorientation in presence of an intense opt. field
A temperature rise as a result of light absorption
2
The alignment film in liquid crystal cell is:
A transparent layer that forces molecules to align in specific direction
A film that transmits the light of a certain linear polarization
A layer which is not necessary in liquid crystal cells
A transparent and conductive layer to reorient molecules by electric field
3
Where in the Mach-Zehnder interferometer does the interference occure?
After the pinhole
Only at the second half-reflecting mirrors
On the whole path after the half-reflecting mirror
After dividing the laser beam
4
What kind of nonlinear mechanism is characterized by the fastest response time?
Photorefractive
Electronic
Molecular orientation
Thermal
5
What is the difference between FDM and SLA (resin) 3D printers:
SLA printer uses liquid resin and FDM uses solid plastic like ABS or PLA
SLA can print whole layer while FDM printer needs to extrude molten plastic
FDM can print with both resin and ABS plastic / SLA prints only using resin
FDM printer does not need any support material even for complex shapes
6
What is needed in the Mach-Zehnder interferometer set-up?
Four half-reflecting mirrors
Three half-reflecting mirrors and one reflecting mirror
Two half-reflecting mirrors and two reflecting mirrors
Two half-reflecting mirror and two reflecting mirrors
7
Which type of polarizer is a calcite crystal?
Birefringent
Calcite is not used as a polarizer
Reflective
Absorptive
8
How is the transition temperature from the nematic to the isotropic phase called?
clearing temperature
nematic temperature
isotropic temperature
liquid crystal temperature
9
Regularly repeating features in diffraction grating for visible light are separated by a distance of the order of
1 mm
10-12 m
10-6 m
10-9m
10
What advantages has Blue Phase compared to nematics in display applications?
Symmetrical viewing angle and higher thermal stability
Higher refresh rate and lower voltage threshold
Higher contrast ratio and no need to use optical filters (Red, Green, Blue)
No blur effect and higher voltage threshold
11
What symmetry has a unit cell in BPI (without an electric field)?
Tetragonal
Orthorhombic
Cubic
Hexagonal
12
Can a half-wave plate be used to attenuate a linearly polarized laser beam?
No, it cannot. The only way is to use absorptive filters.
Yes, it can if it is followed by a polarizer.
Yes, it can if is followed by a quater-wave plate.
Yes, it can if it is placed behind a quarter-wave plate.
13
Nonlinear optics is related to
The propagation of light in free space
The properties of optical media that modify the original optical field
A specific property of light
Diffraction and interference of light
14
What will happen if an electromagnetic wave passes through a material with a negative refractive index?
The angle of refraction will be on the opposite side of the normal
The Universe will collapse
Light will be absorbed completely by this material
It is impossible because light cannot propagate in such materials
15
What advantages has Blue Phase compared to nematics in display applications?
Symmetrical viewing angle and higher thermal stability
Higher contrast ratio and no need to use optical filters (Red, Green, Blue)
Higher refresh rate and lower voltage threshold
No blur effect and higher voltage threshold
16
What is the difference in optical properties between the chiral nematic (N*) phase and Blue Phases (BPs)?
BPs are optically isotropic for all wavelengths but N* phase is anisotropic
BPs reflect only blue light. N* phase reflects different wavelengths
BPs always reflect circ. pol. light with opposite handedness than in N*
Spectra reflected from sample in N* phase have wider widths than for BPs
17
A Kerr-type of nonlinear refractive index change model assumes that:
A refractive index is independent of light intensity
A refractive index change is linearly proportional to light intensity
Δn~I2 (where Δn is change in refractive index and I is light intensity)
A change in refractive index is proportonal to the root of light intensity
18
What is the interference?
The direction of the propagating wave
Making diverging wavefront after the pinhole
Result of combining two laser beams
The process caused by solitons in liquid crystals
19
Unpolarized light of 4 W/m
2
is passing through a polarizer. What is the intensity of light transmitted by the polarizer?
4 W/m2
0 W/m2
2 W/m2
1 W/m2
20
What is the main advantage of two-photon polymerization (2PP) 3D printing?
Fast printing speed
High resolution
Low cost
Compatibility with a wide range of materials
21
About which nature of light does the interference be a proof?
bipolar
birefringent
quantum
wave
22
What is the role of photosensitive materials in two-photon polymerization (2PP) 3D printing?
To provide structural reinforcement to the printed object
Photosensitive resin can work as immersion oil – minimizing mismatch of RI
To enhance the color and aesthetics of the printed object
To absorb the laser energy and initiate polymerization
23
Which is the most ordered liquid crystal phase among those listed below?
nematic
twisted nematic
isotropic
smectic
24
What allows you to switch the polarizing microscope into the conoscopic mode?
another two polarizers
twisted nematic (TN)
half wave plate
Bertrand lens
25
What type of software is needed to create and print designed structure:
Slicer – changes 3D objects into series of commands controlling 3D printer
Mapper – generates series of points to properly calibrate 3D printer
Bootloader – controller managing printing process (like GRUB or Arduino)
CAD – allows to create 3D objects (OpenScad or Fusion 360)
26
How do we call a liquid crystal cell with a vertical alignment of the molecules between glass plates?
homeotropic (HT)
planar
homogenous (HG)
twisted nematic (TN)
27
How can we watch a stereoscopic movie at the cinema?
We can wear glasses with strong lenses to distort the light beam
It is impossible because the light is too fast
We can wear glasses with polarizing filters to generate stereoscopic image
We need to blink our eyes at the rate of 20Hz to see a stereoscopic image
28
In what city is Warsaw University of Technology located?
Wałbrzych
Wrocław
Wąbrzeźno
Warszawa
29
How many Blue Phases can exist between the chiral nematic phase and the isotropic (max. number)?
4
1
3
2
30
What is not a basic 3D shape in OpenScad program:
cube( )
sphere( )
cylinder( )
pyramid( )
31
At which angle do we place planar LC cell between two crossed polarizers to get max. intensity of light in transmission?
45 degrees between molecular orientation direction and polarizer axis
with long molecular axis along polarizer axis
to make angle of 90 degrees between director and polarizer axis
it does not matter
32
In which optical material light has the lowest velocity?
In the vacuum, because light needs any medium to propagate
In diamond (it has the highest refractive index from all listed materials)
In quartz
In the air, as the refractive index is equal to 1.
33
Which experimental technique is sufficient to fully characterize the optical properties of Blue Phase Liquid Crystals?
Conoscopy (Kossel diagrams)
Polarized Optical Microscopy
All three from above are essential
Spectroscopy
34
How did you enjoy the summer school of Photonics on a scale of 1-4?
1
3
4
2
35
What is the pinhole?
The glass plate with photographic emulsion
The half-reflecting mirror
Tiny hole, after that the light beam diffracts
Parallel plane glass plate, at which the light interferes
