Zhen Zhang

14 Questions 6 Answers 0 Followers

Questions related from Zhen Zhang

What does negative group velocity dispersion mean?

A two-color femtosecond laser is transmitted in the air and a positive group velocity dispersion occurs. Negative group velocity dispersion is introduced when a-BBO crystal is added to the optical...

01 January 1970 420 4 View

Why does the beam shape at the focus is a Lorentz distribution rather than a Gaussian distribution?

" For most THz applications, and especially for nonlinear spectroscopy, Gaussian-shaped beam profiles are desired in order to achieve localized, well-controlled high electric field values....

01 January 1970 9,386 1 View

What does this four peaks mean in the proess of photoionization?

I saw a setup from a phd thesis saying that this was used for terahertz generation from laser induced plasma. I see four peaks in this picture, so what physical quantities do these four peaks...

01 January 1970 3,782 3 View

What is the relationship between air pressure and refractive index?

More recently, Manceau et al. demonstrated the THz polarization control via the accurate control of the surrounding gas pressure of two color filaments. The change of gas pressure will induce a...

01 January 1970 8,933 4 View

Why does the plsama can affect the second energy peak formation along filament?

"Interestingly, the ring structure at the trailing part of the pulse converges with propagation, thus creating the second(weak) maximum in the dependence of the filament energy on the distance...

01 January 1970 6,886 0 View

Why high-order nonlinear effect is more important for terahertz generation by four-wave maxing model?

There are currently two mainstream theories when describing the generation mechanism of terahertz waves. One is an ionized photocurrent model, and the other is a four-wave mixing model. The...

01 January 1970 3,215 1 View

What is the difference between external focusing , geometrical focusing and self-focusing?

"Beyond this point, with shorter focal length lenses, the diameter of the self-focal zone can no longer increase because the geometrical focal diameter becomes smaller. That is to say, external...

01 January 1970 8,645 2 View

Can plasma absorb THz waves？

One sentence from reference say: “ Unlike nonlinear crystals, a lack of phonon modes in plasma prevents THz absorption, resulting in broadband THz radiation with no spectral gap”。 Can we...

01 January 1970 1,949 2 View

The terahertz radiation has a maximum when the relative phase is zero, but why does the author say that this comes from the ionization current model?

"The electrons ionized from water molecules are regarded as quasi-free electrons, and therefore the THz wave generation process in water resembles this process in air. Phenomenologically, the...

01 January 1970 8,053 0 View

What is the physical mechanism for narrowing the bandwidth of the terahertz spectrum?

"An example of these effects is shown in Figure 11, where the focusing conditions are varied to demonstrate changes in the output THz waveforms and corresponding power spectra as the...

01 January 1970 3,856 0 View

Who have the phd thesis on the spectrum of THz radiation from fs laser induced air plasma?

Who have the phd thesis on the spectrum of terahertz radiation from fs laser induced air plasma? If you have one, can you tell me the title of the thesis? Thank you for your kindly help!

01 January 1970 5,444 2 View

Can we use the theory of energy level transitions to explain the process of terahertz radiation generation?

The femtosecond laser ionizes the air to form a plasma from which terahertz waves can be radiated. The current mainstream models describing the mechanisms generated by terahertz waves are ionized...

01 January 1970 8,985 1 View

Which factors can change the phase of the THz waveform from fs laser induced filament ?

The femtosecond laser ionized air can form a filament of a length of centimeter, and broadband THz wave can be radiated from the filament. The plasma density at both ends of the filament is...

01 January 1970 9,678 1 View

What are the main factors determining the peak frequency of the terahertz spectrum?

The femtosecond laser can form a plasma in the air, and broadband terahertz radiation is formed in the plasma due to the oscillation of positive and negative charges. We know that there are two...

01 January 1970 6,209 3 View