Required Laser Intensity Research Articles

Superposition of nuclear states in multi-lambda systems using x-ray laser pulses

Nuclear-state population transfer in the multi-lambda systems with N = 5 that interact with four x-ray laser pulses are investigated theoretically. By using the coincident pulses and stimulated Raman adiabatic passage (STIRAP) techniques, the population transfer from one initially populated ground state to an arbitrary coherent superposition of other ground states. Since the frequency of currently available x-ray lasers is lower than the gamma rays, in this method, x-ray laser pulses with different frequencies are interacting with the accelerated nuclei. We employ the Morris-Shore transformation to reduce the five-states system to two separate three-state and two-state linkage. The required laser intensities were calculated, which satisfy the conditions of coincident pulses and multi-lambda STIRAP techniques. Considering the spontaneous emission from excited states, the master equation has to be used for numerical study, and it is shown that an arbitrary superposition of final ground states can be obtained. Also, it is observed that by increasing the number of coincident pulses, the population of ground states gets closer to the ideal situation.

Spectrally resolved ion imaging from laser produced plasmas using CR-39 detectors

Intense laser-produced plasmas generate bright, ultrashort bursts of accelerated ions. Reducing the required laser intensity and increasing the repetition rate of the laser to generate high energy ions is important, and mesoscopic particle targets are an attractive option to address this issue. Newer experimental strategies to measure ion energies and their angular distribution are needed in studies of such systems. In this paper, we outline a method to simultaneously measure these quantities using a single CR39 film. Although CR-39 detectors are known for ion imaging or spectroscopy, combining these specially for lower ion energies and applications to low-intensity laser experiments is not common. The paradigm chosen in our study is to consider the spatial distribution of nuclear tracks on a CR-39 sheet, while simultaneously separating them by their track diameter. Our method achieves an energy resolution of about 100 keV and a spatial resolution of tens of micrometers. In addition, ion species other than protons, i.e., carbon and oxygen, can also be imaged in an energy-resolved manner.

Effect of laser polarization and target location on acceleration of electrons generated during ionization of gases by a laser pulse

We investigate the effect of the target position, laser polarization, and focusing on the energy spread and the angle of emittance for the acceleration of electrons generated during the ionization of rarefied gases, neon ions Ne8+, krypton ions Kr32+, and argon ions Ar16+ by a laser pulse. The electrons generated from the ions at the position after laser focus interact with the laser pulse for a longer duration and gain more energy than those electrons generated from the ions at the position before laser focus. There are two peaks in the energy spectrum for linear polarization and only one peak for circular polarization. The energy spectrum peak is sharper for circular polarization than that for linear polarization. The energy gained by the electrons increases with the laser spot size due to the increase in the laser energy. The spectrum of the angle of emittance for electrons shows the sharpest peak at the lowest angle for linear polarization for ions at the position after laser focus. The circular polarization is good to obtain quasi-monoenergetic electron beams and linearly polarized laser pulse is good to generate collimated electron beams. The required laser intensity to ionize electrons from the ions Ne8+, Kr32+, and Ar16+ increases and the electron energy peaks are at higher energies and scattering angles are at lower values for these gases, in their respective orders.

Novel target design for a laser-driven aneutronic fusion reactor

This paper discusses the suitability of proton sources and the appropriate targets for lithium-proton and boron-proton fusion reactions. Protons are emitted by a hydrogen-based source that is exposed to an intense laser beam. The protons are sent onto lithium or boron targets where fusion reactions are triggered. A comparison is made between solid, liquid and gaseous proton sources and the required laser intensity. Furthermore, the main characteristics of the lithium and boron targets are assessed. It is shown that a hybrid target made of lithium and boron offers opportunities to considerably enhance the fusion yield.

Characterization of plasma emission in the 1-6 nm band from laser-irradiated cryogenic xenon targets

We present measurements from laser-produced plasmas generated using cryogenic Xe targets and quantify the emission characteristics in the soft x-ray region (1 to 6 nm). The system is based on a LN2-cooled rotating drum, which allows for a high repetition rate, and Nd:YAG laser systems with energies up to 325 mJ on-target with pulse lengths of 130 ps, 600 ps, or 6.5 ns. High resolution spectra are measured using a grazing incidence spectrometer, and we present the first quantitative conversion efficiency (CE) measurements for Xe in this range. Data show CE values up to ∼1% at 6 nm and ∼0.08% at 1.5 nm (for 2% bandwidth and 2π solid angle), and there are lower limits on the required laser intensities and energies on target to achieve these efficiencies. In addition, the emission spot size is directly measured at 2 nm (620 eV) using a point-projection slit imaging method, with optimized emission spot sizes of ∼20 μm.

Brightness of femtosecond nonequilibrium photoemission in metallic photocathodes at wavelengths near the photoemission threshold

The operation of photoemission electron sources with wavelengths near the photoemission threshold has been shown to dramatically decrease the minimum achievable photocathode emittance, but at the cost of significantly reduced quantum efficiency (QE). In this work, we show that for femtosecond laser and electron pulses, the increase in required laser intensities due to the low QE drives the photocathode electronic distribution far from static equilibrium. We adapt an existing dynamic model of the electron occupation under high intensity laser illumination to predict the time-dependent effects of the nonequilibrium electron distribution on the QE, mean transverse energy (MTE), and emission brightness of metal photocathodes. We find that multiphoton photoemission dramatically alters the MTE as compared to thermal equilibrium models, causing the MTE to no longer be a monotonic function of photon excess energy.

Nuclear-state engineering in tripod systems using x-ray laser pulses

Coherent superposition of nuclear states in tripod systems using three x-ray laser pulses is investigated theoretically. The laser pulses transfer the population from one ground state to an arbitrary superposition of other ground states using coincident pulses and stimulated Raman adiabatic passage techniques. The short wavelengths needed in the frame of the nuclei are achieved by envisaging an accelerated nucleus interacting with three x-ray laser pulses. This study exploits the Morris-shore transformation to reduce the tripod system into a coupled three-state $\mathrm{\ensuremath{\Lambda}}$-like system and a noncoupled state. We calculated the required laser intensities which satisfy the conditions of coincident pulses and adiabatic passage techniques. Considering the spontaneous emission from excited state $|4\ensuremath{\rangle}$ and unstable ground states $(|2\ensuremath{\rangle},|3\ensuremath{\rangle})$ to other states, we have used a master equation for numerical study, and the final fidelity of desired states with respect to the tolerance of laser intensities is studied numerically.

Investigating and Modeling the Effect of Laser Intensity and Nonlinear Regime of the Fiber on the Optical Link

AbstractUnderstanding the nonlinear characteristics of the optical link is essential to exploit it effectively. Even though various expensive experimental investigations have been conducted in the literature, this paper presents a simulation model to understand the nonlinear relationship that exists between the laser intensity, the nonlinear regime of the fiber and the error probability. Firstly, an analysis model is introduced to observe the numerical relevance between the aforesaid parameters. The analysis results are graphically portrayed to determine the relevance effectively. Secondly, an optical-neural model is adopted based on the feed-forward neural network architecture to relate the parameters mathematically, without hard technical constraints. The model is experimented for the fair estimation of the required laser intensity, which achieves the least desired error probability, when the nonlinear regime of the fiber is known.

Proton acceleration in a slow wakefield

We propose and analyze a mechanism to accelerate protons in a low-phase-velocity wakefield. The wakefield is shock-excited by the interaction of two counter-propagating laser pulses in a plasma density gradient. The laser pulses consist of a forward-propagating short pulse (less than a plasma period) and a counter-propagating long pulse. The beating of these pulses generates a slow forward-propagating wakefield that can trap and accelerate protons. The trapping and acceleration is accomplished by appropriately tapering both the plasma density and the amplitude of the backward-propagating pulse. An example is presented in which the trapping and accelerating wakefield has a phase velocity varying from Vph≈0 to ≈0.15 c (∼10 MeV proton energy) over a distance of ∼1 cm. The required laser intensities, pulse durations, pulse energies, and plasma densities are relatively modest. Instabilities such as the Raman instability are mitigated because of the large plasma density gradients. Numerical solutions of the wakefield equation and simulations using turboWAVE are carried out to support our model.

Shortcut to adiabatic population transfer in quantum three-level systems: Effective two-level problems and feasible counterdiabatic driving

Shortcut to adiabaticity in various quantum systems has attracted much attention with the wide applications in quantum information processing and quantum control. In this paper, we concentrate on stimulated Raman shortcut-to-adiabatic passage in quantum three-level systems. To implement counter-diabatic driving but without additional coupling, we first reduce the quantum three-level systems to effective two-level problems at large intermediate-level detuning, or on resonance, apply counter-diabatic driving along with the unitary transformation, and eventually modify the pump and Stokes pulses for achieving fast and high-fidelity population transfer. The required laser intensity and stability against parameter variation are further discussed, to demonstrate the advantage of shortcuts to adiabaticity.

Nuclear-state population transfer by a train of coincident pulses

Population transfer of three-level $\mathrm{\ensuremath{\Lambda}}$-like nuclei interacting with x-ray free electron lasers (XFEL) via a train of coincident pulses has been investigated theoretically. This study uses copropagating beams in which the frequency of the pump laser is different from that of the Stokes laser. We calculate the required laser intensities for each step which satisfy the condition of coincident-pulse technique in different nuclei. By employing the master equation and considering the effect of spontaneous emission, we show that complete nuclear population transfer occurs by choosing the appropriate number of pulse pairs. It is shown that the effect of laser intensity fluctuation is suppressed by increasing the number of pulse pairs. In this scheme, after each step, the populations of system are in stable states and the time delays between the neighboring pulses do not affect the transmission efficiency.

Multistage coupling of independent laser-plasma accelerators.

Laser-plasma accelerators (LPAs) are capable of accelerating charged particles to very high energies in very compact structures. In theory, therefore, they offer advantages over conventional, large-scale particle accelerators. However, the energy gain in a single-stage LPA can be limited by laser diffraction, dephasing, electron-beam loading and laser-energy depletion. The problem of laser diffraction can be addressed by using laser-pulse guiding and preformed plasma waveguides to maintain the required laser intensity over distances of many Rayleigh lengths; dephasing can be mitigated by longitudinal tailoring of the plasma density; and beam loading can be controlled by proper shaping of the electron beam. To increase the beam energy further, it is necessary to tackle the problem of the depletion of laser energy, by sequencing the accelerator into stages, each powered by a separate laser pulse. Here, we present results from an experiment that demonstrates such staging. Two LPA stages were coupled over a short distance (as is needed to preserve the average acceleration gradient) by a plasma mirror. Stable electron beams from a first LPA were focused to a twenty-micrometre radius--by a discharge capillary-based active plasma lens--into a second LPA, such that the beams interacted with the wakefield excited by a separate laser. Staged acceleration by the wakefield of the second stage is detected via an energy gain of 100 megaelectronvolts for a subset of the electron beam. Changing the arrival time of the electron beam with respect to the second-stage laser pulse allowed us to reconstruct the temporal wakefield structure and to determine the plasma density. Our results indicate that the fundamental limitation to energy gain presented by laser depletion can be overcome by using staged acceleration, suggesting a way of reaching the electron energies required for collider applications.

The Study of Refractive Indices of Liquid Crystal Mixtures

In the present study the ordinary refractive indices of Nematic liquid crystal (LC), Cholesteric liquid crystal and their mixtures were measured by multiple wavelength refractometer in the visible range with temperature range from 20°C to 80°C. As the wavelength increases, the refractive indices may decrease. As the temperature increases, the refractive index may decrease. The ordinary refractive index decreases or increases depending on the crossover temperature of the Liquid Crystal employed. The wavelength- and the temperature-dependent refractive indices are fundamentally interesting and practically important for optimizing the display performances and other photonic devices employing LCs.We also tried to investigate factors affecting the temperature gradient of ordinary refractive index (dno/dT).Liquid crystal should exhibit a large temperature gradient refractive index to reduce the required laser intensity for triggering the nonlinear optical effects. The two crucial parameters for achieving large dno/dT are high birefringence and low clearing point. However, these two requirements are often conflicting each other. The temperature at which dno/dT = 0 is called the cross-over temperature To. If Tc, the clearing temperature of liquid crystal material is much higher than the room temperature then the cross-over temperature would be relatively high and dno / dT < 0 at room temperature. From all the investigations it is observed that the values of refractive index change with temperature, wavelengths as well as with the mixture. Some of the liquid crystal mixtures show excellent index matching property.

Nonlinear Laser Driven Donut Wakefields for Positron and Electron Acceleration

We show analytically and through three-dimensional particle-in-cell simulations that nonlinear wakefields driven by Laguerre-Gaussian laser pulses can lead to hollow electron self-injection and positron acceleration. We find that higher order lasers can drive donut shaped blowout wakefields with strong positron accelerating gradients comparable to those of a spherical bubble. Corresponding positron focusing forces can be more than an order of magnitude stronger than electron focusing forces in a spherical bubble. Required laser intensities and energies to reach the nonlinear donut shaped blowout are within state-of-the-art experimental conditions.

Radiation-reaction trapping of electrons in extreme laser fields.

A radiation-reaction trapping (RRT) of electrons is revealed in the near-QED regime of laser-plasma interaction. Electrons quivering in laser pulse experience radiation reaction (RR) recoil force by radiating photons. When the laser field reaches the threshold, the RR force becomes significant enough to compensate for the expelling laser ponderomotive force. Then electrons are trapped inside the laser pulse instead of being scattered off transversely and form a dense plasma bunch. The mechanism is demonstrated both by full three-dimensional particle-in-cell simulations using the QED photonic approach and numerical test-particle modeling based on the classical Landau-Lifshitz formula of RR force. Furthermore, the proposed analysis shows that the threshold of laser field amplitude for RRT is approximately the cubic root of laser wavelength over classical electron radius. Because of the pinching effect of the trapped electron bunch, the required laser intensity for RRT can be further reduced.

Sympathetic electromagnetically-induced-transparency laser cooling of motional modes in an ion chain.

We use electromagnetically-induced-transparency laser cooling to cool motional modes of a linear ion chain. As a demonstration, we apply electromagnetically-induced-transparency cooling on 24Mg+ ions to cool the axial modes of a 9Be+-24Mg+ ion pair and a 9Be+-24Mg+-24Mg+-9Be+ ion chain, thereby sympathetically cooling the 9Be+ ions. Compared to previous implementations of conventional Raman sideband cooling, we achieve approximately an order-of-magnitude reduction in the duration required to cool the modes to near the ground state and significant reduction in required laser intensity.

GeV electron beams from a centimetre-scale accelerator

Gigaelectron volt (GeV) electron accelerators are essential to synchrotron radiation facilities and free-electron lasers, and as modules for high-energy particle physics. Radiofrequency-based accelerators are limited to relatively low accelerating fields (10–50 MV m−1), requiring tens to hundreds of metres to reach the multi-GeV beam energies needed to drive radiation sources, and many kilometres to generate particle energies of interest to high-energy physics. Laser-wakefield accelerators1,2 produce electric fields of the order 10–100 GV m−1 enabling compact devices. Previously, the required laser intensity was not maintained over the distance needed to reach GeV energies, and hence acceleration was limited to the 100 MeV scale3,4,5. Contrary to predictions that petawatt-class lasers would be needed to reach GeV energies6,7, here we demonstrate production of a high-quality electron beam with 1 GeV energy by channelling a 40 TW peak-power laser pulse in a 3.3-cm-long gas-filled capillary discharge waveguide8,9.

A Numerical Method for Optimizing Laser Power in the Irradiation of a 3-D Triple-Layered Cylindrical Skin Structure

ABSTRACT It is of interest to research hyperthermia combined with radiation and cytotoxic drugs to enhance the killing of tumors. The crucial problem is to keep surrounding normal tissue below a temperature that will produce harm when heating the tumor tissue. In this study, we develop a numerical model for optimizing laser power in the irradiation of a 3-D triple-layered cylindrical skin structure. The method determines the required laser intensity in order to obtain prespecified temperatures at given locations on the skin surface after a prespecified laser exposure time.

Performance of semitransparent silicon strip sensors for high precision optical alignment monitoring systems

Novel semitransparent optical position sensors ("ALMY sensors") have been developed for the alignment monitoring systems of modern large-area tracking detectors. The high transmittance of up to 90% allows to align more than 10 sensors along a collimated laser beam. A position resolution of 1 /spl mu/m and an uncertainty in the deflection of the traversing laser beam of less than 3 /spl mu/rad have been achieved for sensitive areas of several square centimeters. For the thin-film amorphous silicon sensors, the required laser intensity could be minimized such that the performance is not deteriorated by aging effects.

Enhanced atom guiding in metal-coated, hollow-core optical fibers

A new-type of atom guiding structure has been analyzed. It consists of a hollow-core optical fiber (step index) which is not clad, but instead has a metal coating on its outer lateral surface. It will be shown that this structure produces the maximum evanescent field in the hollow region of the fiber and guiding can be accomplished with lower power lasers. Both the dipole and the van der Waals potentials have been combined and the resulting barrier height was maximized as a function of both Δ, the detuning, and r, the position. An optimized potential having a barrier height of 1 K has been determined by iteratively solving for the required laser intensity. The probability of atom tunneling through this barrier to the inner wall has been calculated and is expected to be unimportant. Centripetal effects due to bending of the fiber have also been estimated and are small for the barrier considered here. Compared to other structures, this new-type of guide provides bigger barriers for the same laser power and therefore, enhanced atom guiding.