Explore chapters and articles related to this topic
Attosecond Laser Generation
Published in Hitendra K. Malik, Laser-Matter Interaction for Radiation and Energy, 2021
Due to diverse applications, the field of ultrafast laser physics has attracted considerable interest not only in chemical and atomic physics, but also in various areas of fundamental and applied science (Krausz and Ivanov 2009; Li et al. 2016). Because of the very small size of the molecule and its fast movement, we require a special variety of light to detect the molecular level's activities. The solution to capture the motion at the molecular level is an ultrafast laser light, called an attosecond laser. The dynamics of electrons in atoms and molecules can be recorded on the timescale of an attosecond (10−18 s) by pump-probe experiments, because of the very precise measurement of time delay between attosecond pulse and its driving laser pulse synchronized with the attosecond laser pulse, which serves to an abundance of pump (Uiberacker et al. 2007; Goulielmakis et al. 2010). In a visible wavelength regime, the optical period of light fields is of the order of a few femtoseconds; therefore, the attosecond science is essentially appropriate for the fundamental interpretation of light matter interaction. The generation of attosecond laser pulse during high-order harmonics (HOHs) has enabled its progress (Sansone et al. 2006; Goulielmakis et al. 2008; Ferrari et al. 2010). The major limitation of conventional laser-based HOHs is low conversion efficiency, which gives rise to low photon flux for the photon energy and attosecond pulse in the extreme ultraviolet regime.
Modeling of Post-Breakdown Phenomena
Published in Leon J. Radziemski, David A. Cremers, Laser-Induced Plasmas and Applications, 2020
Regardless of the details of the initiation process, the atmosphere adjacent to vapor plasma is heated, thereby enabling the gases, which were initially transparent to the laser radiation when cold, to start absorbing the laser radiation. Once a critical number of electrons are liberated, the heated gas layer absorbs strongly and rapidly heats to plasma conditions, following the same heating history as the vapor. As the atmosphere begins to absorb a significant fraction of the laser energy, a self-perpetuating absorption process commences that results in plasma propagation into the surrounding atmosphere; subsequent layers of gas experience the same ingestion process—heating initially by energy transfer from the plasma until laser absorption is initiated in the gas, then rapidly heating by laser absorption to produce a strongly absorbing plasma. The dominant energy-transfer mechanism usually changes as the plasma evolves, transforming from conduction to radiation as the plasma becomes optically thick in the extreme ultraviolet. By creating absorbing gas layers in front of it, the plasma changes from its initial confined vapor state to a fully developed propagating absorption wave in the gas; it absorbs most of the laser energy in its advancing front, thereby shielding the bulk of the plasma from further direct interaction with the laser radiation. The absorption wave propagates up the laser beam until the irradiation is either terminated or reduced to irradiance levels that can
Gas-Filled Detectors: Geiger-Müller Counters
Published in Douglas S. McGregor, J. Kenneth Shultis, Radiation Detection, 2020
Douglas S. McGregor, J. Kenneth Shultis
When a gas ion comes into contact with the cathode wall, the absorption of an electron leaves the now neutralized atom in an excited state. This physical state occurs because of the differences in ionization energies between the gas atoms and the cathode atoms. Typically, a noble gas atom de-excites by releasing a photon with an energy comparable to the atom ionization energy. For example, the minimum ionization energy for Ar is 15.6 eV, corresponding to a photon wavelength of 78.47 nm and classified as belonging to the extreme ultraviolet (EUV) region of the electromagnetic spectrum. Almost all transition metals have minimum ionization energies ranging between 5–10 eV, as can be seen from Fig. 11.4. Consequently, if the EUV photon strikes the wall, a photoelectron may be ejected, thereby triggering another Townsend avalanche. Due to competing processes, the actual photo-efficiency for these UV photons is actually very small, on the order of 10−4 per photon [Korff 1946]. However, the number of electron-ion pairs produced for a single event and in the subsequent discharge usually produces many more than 104 electron-ion pairs per event so that there is an appreciable probability that a photoelectron is emitted from the cathode wall because of the absorption in the wall of a UV photon.
Non-linear propagation effects of intense femtosecond pulses on below bandgap harmonics in solids
Published in Journal of Modern Optics, 2023
M. Hussain, G. O. Williams, T. Imran, M. Fajardo
The microscopic origin of high harmonic generation (HHG) in wide bandgap crystalline and amorphous solids have been reported and offering a promising route for new all-solid-state extreme-ultraviolet sources [1–3]. The non-linear optical response of solids can be manipulated by either tailoring the electronic structures [4,5] or by the propagation of intense driving field in thin solids [6]. The non-linear propagation effects can play a vital role in the generation of harmonics in solids in terms of the shifting of driving wavelengths which can imprint on the harmonics. The non-linear propagation effects of the intense femtosecond pulses in gases and plasma induce the red-shifted harmonics [7,8]. Recently, we have demonstrated non-linear propagation effects on harmonics in semiconductors such as silicon (Si) and ZnO. We have observed the spectral blueshifts in the generated harmonics which is attributed to the strong photoionization of the valence band through non-linear beam propagation [6].
Observation of direct power deposition of ICRF in EAST plasma boundary
Published in Radiation Effects and Defects in Solids, 2021
X. L. Li, Y. L. Li, G. S. Xu, H. Zhang, J. Xu, A. Li, C. J. Xiao, S. T. Mao, R. R. Liang, L. Zhang, W. Gao, X. J. Zhang
Multiple diagnostics had been developed on EAST tokamak for key parameter measurements for equilibrium profile reconstruction and fluctuation transport (14), including Langmuir probe (15), Thomson Scattering (16), magnetic measurement (17), radiation spectra (18), microwave diagnostics (19–22), neutron flux measurement, etc. The diagnostics used on EAST involved in this paper are summarized as follows: average collected ion parallel energy () is measured by Retarding Field Analyzer (RFA), floating potential and electron temperature is measured by Divertor Langmuir Probes (LP) (15), the temperature of the first wall is measured by Infrared camera (IR) (23), CIII impurity intensity is obtained by the Filterscope. Furthermore, radiation power is measured by Absolute extreme ultraviolet (AXUV) photodiodes (24). Finally, impurity intensity in core plasma is given by Fast extreme ultraviolet (EUV) spectrometer (25). The toroidal overall arrangement of each diagnostic and antennas of ICRF system is shown in Figure 1 and the poloidal cross-section of EAST showing other related diagnostics can be seen in Figure 2.
Spectrum modification of XUV radiation in the presence of a delayed weak control field
Published in Journal of Modern Optics, 2019
Khuong Ba Dinh, Khoa Anh Tran, Peter Hannaford, Lap Van Dao
High harmonic generation (HHG) is an extreme nonlinear optical process for the generation of coherent extreme ultraviolet (XUV) pulses on ultrashort time scales (1,2). The high order harmonics are emitted in a series of attosecond bursts with high spatial and temporal coherence. In terms of non-pertubative optics, a classical or quantum treatment through the time-dependent Schrödinger equation can be used to describe a simple picture of the high harmonic generation process (1–4). In the semi-classical three-step model, the intense laser field modifies the potential barrier so that the initially bound electron is ionized into the continuum. The free electron is then accelerated away from the ion core. When the electric field reverses its direction, the free electron is controlled and accelerated toward the parent ion. Under certain conditions the electron will recombine with the parent ion, emitting its kinetic energy plus the binding energy in the form of electromagnetic radiation (1–4). The process of recombination of the free electron and the parent ion in HHG can be used to study atomic and molecular structural dynamics and opens new directions for studies in atomic and molecular physics (5–8).