MESBP coupled CF-LIBS approach for quantitative elemental analysis of multi-element samples.

Laser-produced plasmas (LPPs) engulf exotic and complex conditions ranging in temperature, density, pressure, magnetic and electric fields, charge states, charged particle kinetics, and gas-phase reactions, based on the irradiation conditions, target geometries, and the background cover gas. The application potential of the LPP is so diverse that it generates considerable interest for both basic and applied research areas. Although most of the traditional characterization techniques developed for other plasma sources can be used to characterize the LPPs, care must be taken to interpret the results because of their small size, transient nature, and inhomogeneities. The existence of the large spatiotemporal density and temperature gradients often necessitates non-uniform weighted averaging over distance and time. Among the various plasma characterization tools, optical-based diagnostic tools play a key role in the accurate measurements of LPP parameters. The optical toolbox contains optical probing methods (Thomson scattering, shadowgraphy, Schlieren, interferometry, velocimetry, and deflectometry), optical spectroscopy (emission, absorption, and fluorescence), and passive and active imaging. Each technique is useful for measuring a specific property, and its use is limited to a certain time span during the LPP evolution because of the sensitivity issues related to the selected measuring tool. Therefore, multiple diagnostic tools are essential for a comprehensive insight into the entire plasma behavior. In recent times, the improvements in performance in the lasers and detector systems expanded the capability of the aforementioned passive and active diagnostics tools. This review provides an overview of optical diagnostic tools frequently employed for the characterization of the LPPs and emphasizes techniques, associated assumptions, and challenges.

Under high power, Nd: YAG 532nm, ns pulsed laser spectral narrowing of an amplified spontaneous emission (ASE) from ZnO nanostructures in rhodamine 6G has been studied. The dependence of emission intensity on excitation power, particle density of ZnO nanostructures, and silica as scatterers show a distinct threshold. The Full width half maximum (FWHM) substantially reduces from 46 nm to 3.16 nm at high excitation power and ZnO-silica scatterer inclusion.

As a major development in recent decades, thin films of carbon nanotubes (CNT) have emerged as a promising material suitable for many novel devices because of their exceptional electrical, optical and mechanical properties. The main goal of this work is to develop CNT based films and analyze its structure and morphology. Instead of preparing directly from carbon atoms, we have prepared films on amorphous substrates by thermal evaporation of commercially available multiwalled CNT powder from Sigma-Aldrich. Optical and structural properties were investigated through absorption, Raman and FTIR spectroscopy and high resolution Scanning Electron Microscopy and Atomic Force Microscopy. We have studied the optical damage of the prepared films using a pulsed Nd: YAG Laser. The films withstand an optical power in excess of ∼107 Wcm−2 under pulsed laser irradiation.

Here we explore ways of converting laser radiation into coherent electromagnetic radiation using laser-driven plasma waves. Several schemes are presented, including colliding laser pulses in magnetized plasma and utilizing ultra-short electron bunches from laser wakefield accelerators to produce intense single-cycle pulses through coherent transition radiation and few-cycle coherent synchrotron radiation in undulators and plasma channels. These sources rely on high current electron bunches with femtosecond durations, which can result in radiation over a broad range of frequencies from 1 to 10 5 THz.

The laser–plasma wakefield accelerator is a compact source of high brightness, ultra-short duration electron bunches. Self-injection occurs when electrons from the background plasma gain sufficient momentum at the back of the bubble-shaped accelerating structure to experience sustained acceleration. The shortest duration and highest brightness electron bunches result from self-injection close to the threshold for injection. Here we show that in this case injection is due to the localized charge density build-up in the sheath crossing region at the rear of the bubble, which has the effect of increasing the accelerating potential to above a critical value. Bunch duration is determined by the dwell time above this critical value, which explains why single or multiple ultra-short electron bunches with little dark current are formed in the first bubble. We confirm experimentally, using coherent optical transition radiation measurements, that single or multiple bunches with femtosecond duration and peak currents of several kiloAmpere, and femtosecond intervals between bunches, emerge from the accelerator.

The laser-plasma wakefield accelerator is a novel ultra-compact particle accelerator. A very intense laser pulse focused onto plasma can excites plasma density waves. Electrons surfing these waves can be accelerated to very high energies with unprecedented accelerating gradients in excess of 1 GV/cm. While accelerating, electrons undergo transverse betatron oscillations and emit synchrotron-like x-ray radiation into a narrow on-axis cone, which is enhanced when electrons interact with the electromagnetic field of the laser. In this case, the laser can resonantly drive the electron motion, lading to direct laser acceleration. This occurs when the betatron frequency matches the Doppler down-shifted frequency of the laser. As a consequence, the number of photons emitted is strongly enhanced and the critical photon energy is increases to 100' s of keV.

Stimulated Raman backscattering in plasma is potentially an efficient method of amplifying laser pulses to reach exawatt powers because plasma is fully broken down and withstands extremely high electric fields. Plasma also has unique nonlinear optical properties that allow simultaneous compression of optical pulses to ultra-short durations. However, current measured efficiencies are limited to several percent. Here we investigate Raman amplification of short duration seed pulses with different chirp rates using a chirped pump pulse in a preformed plasma waveguide. We identify electron trapping and wavebreaking as the main saturation mechanisms, which lead to spectral broadening and gain saturation when the seed reaches several millijoules for durations of 10’s – 100’s fs for 250 ps, 800 nm chirped pump pulses. We show that this prevents access to the nonlinear regime and limits the efficiency and interpret the experimental results using slowly-varying-amplitude, current-averaged particle-in-cell simulations. We also propose methods for achieving higher efficiencies.

Electron beams from laser-plasma wakefield accelerators have low transverse emittance, comparable to those from conventional radio frequency accelerators, which highlights their potential for applications, many of which will require the use of quadrupole magnets for optimal electron beam transport. We report on characterizing electron bunches where double bunches are observed under certain conditions. In particular, we present pepper-pot measurements of the transverse emittance of 120-200 MeV laser wakefield electron bunches after propagation through a triplet of permanent quadrupole magnets. It is shown that the normalized emittance at source can be as low as 1 pi mm mrad (resolution limited), growing by about five times after propagation through the quadrupoles due to beam energy spread. The inherent energy-dependence of the magnets also enables detection of double electron bunches that could otherwise remain unresolved, providing insight into the self-injection of multiple bunches. The combination of quadrupoles and pepper-pot, in addition, acts as a diagnostic for the alignment of the magnetic triplet.

Narrow band undulator radiation tuneable over the wavelength range of 150–260 nm has been produced by short electron bunches from a 2 mm long laser plasma wakefield accelerator based on a 20 TW femtosecond laser system. The number of photons measured is up to 9 × 106 per shot for a 100 period undulator, with a mean peak brilliance of 1 × 1018 photons/s/mrad2/mm2/0.1% bandwidth. Simulations estimate that the driving electron bunch r.m.s. duration is as short as 3 fs when the electron beam has energy of 120–130 MeV with the radiation pulse duration in the range of 50–100 fs.

Research on terahertz wave transmission through plasma is significant for researches on plasma itself and transmission discipline of terahertz wave through plasma. It is possible for plasma with suitable density to be an available stealth outerwear for plane or missile in THz waveband. In this paper, plasma is gotten by ionizing inert gases such as argon and helium gases with pulsed high alternating voltage. With electro-optic pump-probe measurement, THz transmission phenomena through plasma have been studied. The experiments show that some parts of THz frequency components have been cut off by plasma, and with the density of plasma rising, the starting frequency of THz prohibited by plasma is going higher. Experiments also provide an assistant scheme for plasma diagnose with terahertz technique.

Compton side-scattering has been used to simultaneously downshift the energy of keV to MeV energy range photons while attenuating their flux to enable single-shot, spectrally resolved, measurements of high flux X-ray sources to be undertaken. To demonstrate the technique a 1 mm thick pixelated cadmium telluride detector has been used to measure spectra of Compton side-scattered radiation from a Cobalt-60 laboratory source and a high flux, high peak brilliance X-ray source of betatron radiation from a laser-plasma wakefield accelerator.

Stimulated Raman backscattering is used as a non-destructive method to determine the density of plasma media at localized positions in space and time. By colliding two counter-propagating, ultra-short laser pulses with a spectral bandwidth larger than twice the plasma frequency, amplification occurs at the Stokes wavelengths, which results in regions of gain and loss separated by twice the plasma frequency, from which the plasma density can be deduced. By varying the relative delay between the laser pulses, and therefore the position and timing of the interaction, the spatio-temporal distribution of the plasma density can be mapped out.

Gas-filled capillary discharge waveguides are a commonly employed medium in laser-plasma interaction applications, such as the laser wakefield accelerator, because they can simultaneously guide high-power laser pulses while acting as the medium for acceleration. In this paper, the production of both straight and linearly tapered capillaries using a femtosecond laser micromachining technique is presented. A tapered capillary is shown to possess a smooth variation in diameter (from 305 mu m to 183 mu m) along its entire 40 mm length, which would lead to a longitudinal plasma density gradient, thereby dramatically improving the laser-plasma interaction efficiency in applications. Efficient guiding with up to 82% energy transmission of the fundamental Gaussian mode of a low intensity, 50 fs duration laser pulse is shown for both types of capillary waveguide.

Gas-filled capillary discharge waveguides are commonly used as media for plasma wakefield accelerators. We show that effective waveguides can be manufactured using a femtosecond laser micromachining technique to produce a linearly tapered plasma density, which enables the energy of the accelerator to be enhanced significantly. A laser guiding efficiency in excess of 82% at sub-relativistic intensities has been demonstrated in a 40 mm long capillary with a diameter tapering from 320 μm to 270 μm, which gives rise to an on-axis, time-averaged plasma density that varies from 1.0 × 1018 cm−3 to 1.6 × 1018 cm−3.

Summary form only given. Research on terahertz wave transmission through plasma is significant for researches on plasma itself and transmission discipline of terahertz wave through plasma. It is possible for plasma with suitable density to be an available stealth outerwear for plane or missile in THz waveband. In this paper, plasma is gotten by ionizing inert gases such as argon and helium gases with pulsed high alternating voltage. With electro-optic pump-probe measurement, THz transmission phenomena through plasma have been studied. The experiments show that some parts of THz frequency components have been cut off by plasma, and with the density of plasma rising, the starting frequency of THz prohibited by plasma is going higher. Experiments also provide an assistant scheme for plasma diagnose with terahertz technique.

The development, understanding and application of laser-driven particle accelerators require accurate measurements of the beam properties, in particular emittance, energy spread and bunch length. Here we report measurements and simulations showing that laser wakefield accelerators can produce beams of quality comparable to conventional linear accelerators.

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