scholarly journals Numerical studies on terahertz radiation generated from two-color laser pulse interaction with gas targets

2011 ◽  
Vol 29 (4) ◽  
pp. 447-452 ◽  
Author(s):  
H.W. Du ◽  
M. Chen ◽  
Z.M. Sheng ◽  
J. Zhang
Keyword(s):  
Intensity Ratio ◽  
Second Harmonic ◽  
Electromagnetic Emission ◽  
Current Theory ◽  
Particle In Cell ◽  
Neutral Gas ◽  
Ionization Model ◽  
The Difference ◽  
Gas Targets ◽  
Proper Values

AbstractBased upon the Ammosov-Delone-Krainov ionization model, it is shown that two-color laser interaction with neutral gas generates strong ionization currents, which lead to electromagnetic emission at terahertz frequency when the gas density is at proper values. The emission efficiency depends on the difference of the phases between the fundamental and its second harmonic. The intensity ratio between the two pulses also affects the emission strength. An optimum intensity ratio has been found within our parameter region. The above ionization current theory is in agreement with one-dimensional particle-in-cell simulations with field ionization included.

scholarly journals Observation and Modeling of Optical Emission Patterns and Their Transitions in a Penning Discharge

2008 ◽  
Vol 2008 ◽  
pp. 1-7 ◽  
Author(s):  
C. C. Klepper ◽  
R. C. Hazelton ◽  
F. Barakat ◽  
M. D. Keitz ◽  
J. P. Verboncoeur
Keyword(s):  
Fusion Energy ◽  
Optical Emission ◽  
Nonlinear Dependence ◽  
Sensor Technology ◽  
Gaseous Species ◽  
Optical Signals ◽  
Particle In Cell ◽  
Neutral Gas ◽  
Minority Species ◽  
Mode Transitions

A Penning discharge tube has been used as the excitation source for optical detection of gaseous species concentrations in a neutral gas. This type of diagnostic has been primarily used in magnetic fusion energy experiments for the detection of minority species in the effluent gas (e.g., for helium detection in a deuterium background). Recent innovations (US Patent no. 6351131, granted February 26, 2002) have allowed for extension of the operation range from <1 Pa to as high as 100 Pa and possibly beyond. This is done by dynamically varying the gauge magnetic field and voltage to keep the optical signals nearly constant (or at least away from a nonlinear dependence on the pressure). However, there are limitations to this approach, because the Penning discharge can manifest itself in a number of modes, each exhibiting a different spatial emission pattern. As a result, varying the discharge parameters can cause the gauge to undergo transitions between these modes, disrupting any intended monotonic dependence of the overall emission on the varied parameter and hence any predicable impact on the emission. This paper discusses some of the modes observed experimentally using video imaging of the discharge. It also presents a first successful application, a particle-in-cell (PIC) code, to simulate these modes and a mode transition. The hope is that a good understanding of the physics involved in the mode transitions may allow for methods of either avoiding or suppressing such transitions. This would aid in broadening the use of this plasma-based sensor technology.

Optimization of Carrier Distributions in Periodic Gain Structures toward Blue VCSELs

2014 ◽  
Vol 1736 ◽  
Author(s):  
Kenjo Matsui ◽  
Kosuke Horikawa ◽  
Yugo Kozuka ◽  
Kazuki Ikeyama ◽  
Daisuke Komori ◽  
...  
Keyword(s):  
Emission Intensity ◽  
Intermediate Layer ◽  
Intensity Ratio ◽  
Active Regions ◽  
Cavity Surface ◽  
Carrier Injection ◽  
Vertical Cavity Surface ◽  
The Difference ◽  
Emitting Lasers ◽  
Emission Intensity Ratio

ABSTRACTWe have fabricated light emitting diodes (LEDs) in which two active regions separated with a Mg-doped GaN intermediate layer were placed in a single pn junction toward periodic gain structures (PGS) for blue vertical-cavity surface emitting lasers (VCSELs). By current density dependence on a emission intensity ratio from two different active regions, we obtained a very stable emission intensity ratio over 1 kA/cm2. This result is also confirmed with the simulation result. Furthermore, we found that the difference of emission wavelength affect the carrier injection and the emission intensity ratio. On the basis of this result, the optimized well-balanced Mg concentration in the intermediate layer for the two identical active regions were estimated approximately 5 x 1018 cm-3.

Expansion of hot plasma with Kappa distribution in coronal flare sources

2021 ◽  
Author(s):  
Jan Benáček ◽  
Marian Karlický
Keyword(s):  
Langmuir Wave ◽  
Maxwellian Distribution ◽  
Double Layers ◽  
Kappa Distribution ◽  
One Dimensional ◽  
X Ray ◽  
Particle In Cell ◽  
Hot Plasma ◽  
The Difference ◽  
Field Lines

&lt;p&gt;We study how hot plasma that is released during a solar flare can be confined in its source and interact with surrounding colder plasma. The X-ray emission of coronal flare sources is well explained using Kappa velocity distribution. Therefore, we compare the difference in the confinement of plasma with Kappa and Maxwellian distribution. We use a 3D Particle-in-Cell code, which is large along magnetic field lines, effectively one-dimensional, but contains all electromagnetic effects. In the case with Kappa distribution, contrary to Maxwellian distribution, we found formation of several thermal fronts associated with double-layers that suppress particle fluxes. As the Kappa distribution of electrons forms an extended tail, more electrons are not confined by the first front and cause formation of multiple fronts. A beam of electrons from the hot part is formed at each front; it generates return current, Langmuir wave density depressions, and a double layer with a higher potential step than in the Maxwellian case. We compare the Kappa and Maxwellian cases and discuss how these processes could be observed.&lt;/p&gt;

Second harmonic electromagnetic emission via beam-driven Langmuir waves

2005 ◽  
Vol 12 (1) ◽  
pp. 012103-012103-15 ◽  
Author(s):  
B. Li ◽  
A. J. Willes ◽  
P. A. Robinson ◽  
I. H. Cairns
Keyword(s):  
Second Harmonic ◽  
Electromagnetic Emission ◽  
Langmuir Waves

THz emission control by tuning density profiles of neutral gas targets during intense laser-gas interaction

2012 ◽  
Vol 101 (18) ◽  
pp. 181113 ◽  
Author(s):  
Hai-Wei Du ◽  
Min Chen ◽  
Zheng-Ming Sheng ◽  
Jie Zhang ◽  
Hui-Chun Wu ◽  
...  
Keyword(s):  
Emission Control ◽  
Intense Laser ◽  
Density Profiles ◽  
Neutral Gas ◽  
Gas Targets

scholarly journals H σχέση των συναισθημάτων με την εστιαζόμενη στον εαυτό προσοχή και την ρύθμιση της συμπεριφοράς

2020 ◽  
Vol 23 (1) ◽  
pp. 37
Author(s):  
Γεωργία Παναγιώτου ◽  
Δημήτρης Αγοραστός
Keyword(s):  
Negative Emotion ◽  
Subjective Evaluation ◽  
Self Regulation ◽  
Evaluation Process ◽  
Current Theory ◽  
Current Status ◽  
Focused Attention ◽  
New Findings ◽  
The Difference ◽  
The Individual

The present study has two aims: First it summarizes current theory and research on the association between self-consciousness/self-focused attention and different aspects of emotions in both typical and clinical populations. Second, it presents some new findings which address this association. As described in the literature, in the process of achieving one’s goals the individual compares oneself with standards and regulates one’s behavior, making behavioral adjustments or changing the goal in order to minimize the difference between one’s current status and one’s goals. During this self-evaluation process, which is an inherent part of self-regulation, attention is focused on the self and can be related to either positive or negative emotions depending on the subjective evaluation regarding the likelihood of achieving one’s goals. In psychopathology this process seems to dysfunction, so that the individual is trapped in a vicious cycle of negative emotion and increased self-focused attention/selfconsciousness. Research suggests that specific emotions, or their dimensions are associated with increased self-focused attention but it remains unclear which these dimensions are and how are related to psychopathology. Τhe findings we present attempt to separate the effects of the basic affective dimensions of valence, arousal and dominance on increased self-focused attention.

scholarly journals The difference between first and second harmonic amplitudes correlates between glottal airflow and neck-surface accelerometer signals during phonation

2019 ◽  
Vol 145 (5) ◽  
pp. EL386-EL392 ◽  
Author(s):  
Daryush D. Mehta ◽  
Víctor M. Espinoza ◽  
Jarrad H. Van Stan ◽  
Matías Zañartu ◽  
Robert E. Hillman
Keyword(s):  
Second Harmonic ◽  
The Difference

scholarly journals Temporal characterization of laser-induced plasma of tungsten in air

2020 ◽  
Vol 38 (1) ◽  
pp. 14-24
Author(s):  
Eshita Mal ◽  
Rajendhar Junjuri ◽  
Manoj Kumar Gundawar ◽  
Alika Khare
Keyword(s):  
Laser Pulse ◽  
Intensity Ratio ◽  
Second Harmonic ◽  
Branching Ratio ◽  
Plasma Condition ◽  
Incident Laser ◽  
Experimental Conditions ◽  
Laser Induced Plasma ◽  
Tungsten Target ◽  
Thin Plasma

AbstractIn this manuscript, the time-resolved laser-induced breakdown spectroscopy (LIBS) on tungsten target in air and the coexistence of LTE among atoms and ions as well as the fulfillment of optically thin plasma condition are reported. The laser-induced plasma (LIP) of tungsten is generated by focusing the second harmonic of a Q-switched Nd:YAG laser of pulse width ~7 ns and repetition rate of 1 Hz on the tungsten target. The temporal evolution of LIP of tungsten is recorded at four different incident laser fluences of 60, 120, 180, and 270 J/cm2. The several atomic and singly ionized lines of tungsten are identified in LIP. For the estimation of plasma temperature via the Boltzmann plot, the transitions at 430.7, 449.4, 468.0, 484.3, 505.3, and 524.2 nm of Atomic transition of tungsten (WI) and that of the ionic transitions, First Ionic transition of Tungsten (WII) at 251.0, 272.9, and 357.2 nm are selected. The electron density is estimated using the Stark-broadened profile of WI line at 430.2 nm. The McWhirter criteria for the local thermodynamic equilibrium (LTE) condition is verified in present experimental conditions as well as the relaxation time and diffusion length are estimated to take into account the transient and inhomogeneous nature of the plasma. The optically thin plasma condition is studied by assessing the experimental intensity ratio of atomic lines and compared with that of the theoretical intensity ratio (branching ratio). The signal to noise ratio (SNR) is also obtained as a function of time with respect to laser pulse and incident laser fluence. All these observations indicate that the spectra should be recorded within the temporal window of 1–3.5 µs with respect to laser pulse where the plasma can be treated as optically thin as well as under LTE simultaneously along with the large SNR.

scholarly journals Development of a 1 TW/35 fs Ti:sapphire Laser Amplifier and Generation of Intense THz Waves Using Two-Color Laser Filamentation

Photonics ◽  
2021 ◽  
Vol 8 (8) ◽  
pp. 316
Author(s):  
Vanessa Ling Jen Phung ◽  
Keekon Kang ◽  
Seongjin Jeon ◽  
Jinju Kim ◽  
Kyungmin Roh ◽  
...  
Keyword(s):  
Laser Energy ◽  
Second Harmonic ◽  
Laser Pulses ◽  
Intense Laser ◽  
Laser Amplifier ◽  
Terahertz Waves ◽  
Regenerative Amplifier ◽  
Central Wavelength ◽  
Particle In Cell ◽  
Ti:Sapphire Laser

We developed a compact Ti:sapphire laser amplifier system in our laboratory, generating intense laser pulses with a peak power of >1 TW (terawatt), a pulse duration of 34 fs (femtosecond), a central wavelength of 800 nm, and a repetition rate of 10 Hz. The laser amplifier system consists of a mode-locked Ti:sapphire oscillator, a regenerative amplifier, and a single-side-pumped 4-pass amplifier. The chirped-pulse amplification (CPA)-based laser amplifier was found to provide an energy of 49.6 mJ after compression by gratings in air, where the pumping fluence of 1.88 J/cm2 was used. The amplified spontaneous emission (ASE) level was measured to be lower than 10−7, and ps-prepulses were in 10−4 or lower level. The developed laser amplifier system was used for the generation of intense THz (terahertz) waves by focusing the original (800 nm) and second harmonic (400 nm) laser pulses in air. The THz pulse energy was shown to be saturated in the high laser energy regime, and this phenomenon was confirmed by fully electromagnetic, relativistic, and self-consistent particle-in-cell (PIC) simulations.

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