26 August 2021
Europe/Prague timezone

TEST Questions

1) Which of the following processes is not fundamental in achieving laser amplification?

a - Absorption

b - Spontaneous emission

c - Stimulated emission

d - Fast non-radiative relaxation


2) In what type of media can we observe effects related to the second-order nonlinear polarization like sum and difference frequency generation or parametric processes?

a - Isotropic

b- Transparent

c - Non-centrosymmetric

d - Optically active


3) In the condition of full charge collection, which is the main parameter affecting the ion recombination in the air:

 a - Ion species

b - The beam dose rate

c - Temperature or pressure of the ionizing medium

d - The distance between the beam exit and the irradiation point


4) Interaction of femtosecond laser with underdense plasma has been successfully used for electron acceleration up to energies of few GeV. In laser-plasma acceleration, the most efficient electron acceleration mechanism is the so-called bubble regime which provides stability of the acceleration process. The distance that the trapped electrons travel until they outrun the wave is known as the dephasing length and is given by   

    
is the critical electron density.

In addition, the maximum attainable energy in the absence of energy-boosting mechanisms, such as direct laser acceleration, plasma taper, laser pulse negative chirp, is given by 

A 30 fs, 810 nm laser pulse containing an energy of 10 J is focused to a spot size 20 µm at the entrance of a 6 mm long gas jet with a plasma density of  2 x 1018 cm-3. What would be the maximum attainable energy of this accelerator, and at what length of plasma this acceleration can be achieved?

  1. 1.5 GeV, 4.97 mm
  2. 4.2 GeV, 3.78 mm
  3. 7.8 GeV, 5.78 mm
  4. 3.5 GeV, 1.7 mm

5) Which of the following processes has a de-focusing effect?

a - Ponderomotorive force

b - Relativistic motion of electrons in laser field

c - Thermal expansion of laser-heated plasma

d - Gas/plasma ionization by a laser


6) A laser pulse of frequency w0 impinges into a homogeneous plasma such w0 > wpe  (the plasma frequency). Which of the following statements is correct?

a - regardless of the laser intensity, the pulse will always be transmitted with 100 %

b - if the intensity is low enough, the majority of the pulse will be transmitted

c - regardless of the laser intensity, the pulse will always be reflected

d - if the intensity is low enough, the majority of the pulse will  be reflected


7) Which statement is describing the field of plasma optics :

a - plasma optics is a field where optical elements are made by plasma instead of solid materials

b - plasma optics describes a technique of machining solid optical elements

c - plasma optics uses optical properties to create plasmas

d - plasma optics is not sensitive to the plasma properties


8) What is the most important motivation for fuel compression in ICF?

a - It allows reducing the driver power

b - It allows reducing the released fusion energy

c - It allows producing the energy gain

d - It allows reducing the burning time


9) The alternative ignition concepts are based on the principle of decoupling the implosion and heating stages of the ignition process. What is the principal motivation for that choice?

a - To reduce the risk of parametric instabilities and hot electron generation

b - To reduce the overall laser energy and to increase the target gain

c - To increase the target mass and the released energy

d - To reduce constraints on the target fabrication


10) National Ignition Facility at the Lawrence Livermore National Laboratory delivers laser energy of about 2 MJ. What is currently the largest fusion energy yield that has been attained in the experiments at this facility?

a - 30 kJ

b - 130 kJ

c - 1.3 MJ

d - 13 MJ


11) High energy density is characterized by pressures of ~1 Mbar and above. Calculate the pressure in the Sun’s core, assuming an ideal gas made of hydrogen with a density of ~160 times the density of water and a temperature of 15 MK (hint: 1 bar ~ 1 atm ~ 105 Pa):

a - ~2 bar

b - ~2 Mbar

c - ~2 Gbar

d - ~200 Gbar


12)


13) A semiconductor has a band structure, as given in the sketch below. In which band and at which point does one find the least effective mass?

a - Band 1, X valley, 

b - Band 1, Γ valley,      

c - Band 2, Γ valley,       

d - Band 4,  Γ valley.

 


14) Photocatalytic efficiency is intimately related to the photosystem used and its ultrafast dynamics. A popular strategy to improve the photosensitizer efficacy is to connect them to semiconductors. These photosystems hybrid systems enable:

a - Longer charge-separated state, absorption in the UV range, and a larger redox window

b - Longer charge-separated state, absorption in the visible range, and a smaller redox window

c - Shorter charge-separated state, absorption in the visible range, and a large redox window

d - Shorter charge separated state, absorption in the visible range, and a smaller redox window


15)  Which, out of the following,  is detrimental to Radiation Pressure Acceleration in ultrathin foils?

a - Enhanced laser contrast

b - Relativistic transparency

c - Target compression

d - Circular polarization


16) Which are the main advantages of Laser Wakefield Electron Acceleration over conventional radiofrequency acceleration?

a - Compactness and fs electron beam time duration

b - Electron Beam Quality

c - Electrical Efficiency

d - Higher achievable maximum electron beam energy