Figure 2. (a) Experimental set-up. The laser pulse hits the thin foil target at the front side exactly opposite to a micro-dot. Protons from the dot are accelerated within the central, homogeneous field region of the TNSA field and analysed with a Thomson spectrometer. The ions can be detected either with CR39 track detection plastics or an online imaging system (micro channel plate (MCP)). A second laser, which hits the target on the back side concentrically with respect to the first, is used for the cleaning of the target from residual contamination layer protons. (b) and (c) Microstructured target foils. (b) A 5 µ m titanium foil carries polymer (PMMA) dots of 0 . 2 µ m thickness, 20 × 20 µ m 2 extent and 80 µ m separation. The dots were ‘carved out’ from a polymer layer with the help of a femtosecond laser system. (c) Lithography targets. Round dots of 0 . 2 µ m thickness and 10 µ m diameter with 80 µ m separation were generated on the back side of a 5 µ m titanium foil via lithography with a pulsed excimer laser. The second technique allows for a more flexible fabrication of micro-dots, which are, however, considerably more sensitive to laser ablation than those produced with the femtosecond system.
The spectrometer becomes uniquely valuable for quantitative analysis of laser-accelerated particles if detectors with single par- ticle sensitivity are used, such as an absolutely calibrated multichannel-plate (MCP) coupled to a phosphor screen (see Sec- tion 3.3). If this is imaged onto a CCD camera chip, a relation can be established between registered counts on the camera image and the impact of a single ion onto the MCP. This affords parameter measurement of ion yields from a single laser shot with high dy- namic range as well as spatial and spectral resolution. Such capa- bility would be highly bene ﬁ cial for understanding relevant plasma dynamics and particle acceleration mechanisms. Although stan- dard Thomson spectrometers are very useful, in recent years several modi ﬁ cations have been introduced to allow a more comprehensive analysis of the ion acceleration phenomena. The construction of a Thomson spectrometer which employs micro- channel-plate (MCP) detection (with single particle sensitivity) enables: temporally gated  and spatially resolved  detection of accelerated ions (at the detector plane); the simultaneous measurement of ion and electron spectra along the same obser- vation direction ; precise measurement of the proton/ion tra- jectories and its applicability for proton de ﬂ ectometry [52,53] and tomography of the ion source [54,55]. A Thomson spectrometer that combines MCP detection with a tunable magnetic ﬁ eld has also been developed . Additionally, complementary ion and XUV spectrometers for laser e plasma diagnosis have been developed  for qualitative analysis of the ion emission and XUV spectra which can provide detailed information about the plasma condi- tions, and possible correlations between the energetic proton emission and the XUV plasma emission.
We propose a cascaded ion acceleration scheme using laser-irradiated microtubes, by which both the energy and the quality of an injected proton beam can be en- hanced. Irradiated by short intense laser pulses, a micro- tube will be ionized instantaneously and its electrons will be quickly blown away as shown in Fig. 1(a). Due to the expansion of electrons a radial charge-separation electric ﬁeld will be generated, which is inward inside the micro- tube as illustrated in Fig. 1(b). So it can play a unique role in the focusing of ion beams . While the lag- behind ions will form a positively charged hollow cylin- der, which brings out a strong axial electric ﬁeld outward along the axis as displayed in Fig. 1(c). It was proved that this axial electric ﬁeld can be utilized to generate a well-collimated quasi-monoenergetic proton beam, whose divergence angle is less than 1 degree and energy spread ∆E/E ∼ 10%. However, the energy of generated pro- tons is only about a few MeV , which greatly limits its applications. By controlling the arrival time of an inject- ed pre-accelerated proton beam in Fig. 1(a), we will show that this proton beam can be eﬃciently gained energy af- ter it passes through the laser-irradiated microtube. We demonstrate that this cascaded ion acceleration scheme works well with the injected protonbeams of energies up to 100 MeV. More importantly, both the divergence and energy spread of the injected proton beam can be maintained at a low level, or even be suppressed. There-
A numerical model was developed to investigate how the size of the laser focus and the separation of the laser foci in the case of two beams may be expected to influence the resulting proton beam distribution. The model (an earlier version of which is described in Ref. 23) calculates how the evolving fast electron density distribution on a grid corre- sponding to the target rear surface maps into the beam of protons accelerated by TNSA. Fast electrons produced at the target front side in a given laser focus are assumed to be bal- listically transported through the target in a beam with a fixed divergence angle. Transport phenomena such as colli- sions and self-generated fields are not accounted for, but are expected to have a limited effect in relatively thin targets. 24 Recirculation or refluxing of fast electrons within the foil is also neglected. It was validated in simulations that refluxing for a 35 fs-duration laser pulse will occur essentially only for target thicknesses of more than 3 lm. The rear-surface fast electron sheath dynamics, field-ionization of hydrogen, and the direction of projection of the resulting protons are calcu- lated. Unlike more computationally intensive 3D Particle-in- Cell (PIC) modelling, this simpler approach enables a range of parametric scans to be performed relatively quickly, to explore the expected changes to the proton beam profile.
The interaction of high intensity lasers with opaque plasma has been widely investigated as a source of multi- MeV ions. Irradiation of micron thick foils at high laser intensity produces sheath ﬁelds that can accelerate protons [ 1, 2 ] . However, these beams characteristically have a thermal spectrum. Limiting the energy spread of these beams, especially reducing low energy parasitic ions, is a key objective in this ﬁeld. Schemes to reduce the energy spread of sheath accelerated beams often rely on spatially localising the protons within a mixed species foil. This was demonstrated by manufacturing targets with the required ion species localised on the target rear surface [3–5]. A similar effect can be achieved by pre-expanding the foil , so that protons can be separated from a trailing lower charge-to-mass ratio host ion species.
on laser and target parameters). The manipulation of lasergeneratedprotonbeams gives new challenges due to the high bunch charge and short pulse nature of the beams, requiring innovative approaches to enable beam control - recently a technique employing electric fields triggered by a second laser pulse on a separate target, has been used for focusing selectively a portion of the beam spectrum . However, the inherent large divergence and energy spread can make it hard to utilise the full flux of the proton beam for applications and indeed for further transport and beam manipulation. Here we demonstrate a novel target configuration which, without the need for an auxiliary laser pulse, exploits the self-charging of the target to improve the collimation of the entire proton beam, while conserving the characteristic high laminarity required for radiography applications . This approach also allows the control of chromatic properties of the beam and creation of achromatic electrostatic lenses, by exploiting the strong temporal variation of the target potential. Hence this technique allows the full flux of the proton beam to be used in many demanding applications in science, medicine and industry .
wave plate used for adjusting the linear polarization direction, a beam expander (M ≈ ×3), and after reflection on mirrors 1, 2 and 3, illuminated a reflective phase only SLM, a Hamamatsu X10468-03 liquid crystal on silicon (LCoS) device with 800 × 600 pixels and dielectric coating for 1064 nm wavelength (reflectivity η > 95%), oriented at < 10 degree angle of incidence. A flipping mirror, placed after lens 1, reflected the beam to a charge-coupled device (CCD) camera-based laser profiler (Spiricon) to observe the reconstructed annular beam patterns when it was flipped into beam line. A 4f-optical system was formed from A to D to remove the unwanted 0-th order beam . The beam then entered a scanning galvanometer with f = 100 mm flat field f-theta lens (Nutfield) producing an agile focusing system. Substrates were mounted on a precision 5-axis (x, y, z, p, q) motion control system (Aerotech) allowing accurate positioning of the substrate surface at the laser focus. The spectral bandwidth, ∆𝜆 < 0.3 nm, was relatively narrow and important in eliminating chromatic dispersion of the SLM [11, 18].
and longitudinal instabilities (such as the Weibel et al., 1959), two-stream (Hao et al., 2009), and resistive filamenta- tion instabilities (Gremillet et al., 2002)), and to self- generated magnetic fields (Bell & Kingham, 2003). Upon reaching the target rear side, a small population of the highest energy electrons escape, but the remainder form a sheath layer with a large electric field, which evolves spatially and temporally. The field strength, on the order of TV / m, is large enough to ionize atoms on the target rear surface and accelerate them to multi-MeV / nucleon energies. Since the ions originate due to the action of the sheath field, the prop- erties of the ion beam are a direct consequence of this field evolution, which in turn is directly affected by the fast elec- tron propagation inside the target. Measurement of the ion beam properties can thus provide a diagnostic of fast electron beam transport within the solid.
I × . Furthermore, our simulation results show that the required laser intensity increases much slower than the increase of the target density. The target is tested with different target densities and target parameters, indicating its robustness in the performance. The proposed new target based upon interactive laser and target shaping provides a possible guidance for future target design. The current design is different from the normal cone target by which only laser or electron focusing effects are considered. Our design actually includes both laser focusing and target shaping process simultaneously. Our studies try to transfer the pursuit of getting high power laser facility to ingenious target design. By such idea, it is possible to obtain ion acceleration beyond 200MeV by current laser plasma conditions, which meets the quality requirements of protonbeams for cancer therapy.
B-field is a common feature in particle-in-cell (PIC) simulations; however the existence of a proton-focusing region of the B-field is a novel feature for these experimental parameters. This produces a broad spectral peak in the target normal spectrum. The measured signal at the peak is much higher than it is in the thicker target spectra at the same energy—the spectral modification also enhances the proton flux. Theoretical studies of underdense targets at higher intensities ( I ≈ 10 22 W cm −2 ) have indicated that proton-focusing B-fields can be formed [17, 18], although it has not been clear until now whether this could be realized or be significant at lower intensities (I ≈ 10 19 W cm −2 ) with planar solid foils. This is the first report of indications that there is a new regime of magnetically influenced TNSA in which highly non-Maxwellian spectra naturally occur.
With the current laser parameters, the target normal sheath acceleration (TNSA) has been the typical mechanism found in experiments for laser-driven ion acceleration 10,11 . How to generate protonbeams with modulated spectral distributions by TNSA mechanism has been investigated by many groups in the last decade. In the interaction of a 20-TW/0.8 ps laser with a hydrogen-desorbed palladium foil target, Hegelich et al. obtained a spectrally modulated C 5+ ion beam by removing the contaminants on the target rear surface 12 . Schwoerer et al. reported quasi-monoenergetic protons emitted in the target normal direction from microstructured targets with a 10 TW Ti: sapphire laser 13 . Toncian et al. used ultrafast laser-driven micro lens to focus MeV protons with specific energies, generating modulated protonbeams 14 .
Simulations of the temporal proﬁles are shown in Fig. 2. Pulse durations, determined by the total thickness of all the shaping crystals, are shown to be 40 ps by using four shaping crystals (Fig. 2(a)) and 80 ps by using ﬁve shaping crystals (Fig. 2(b)). The rise and fall time is 2.1 ps, preset by the duration of input pulses. Although sub-pulses are divided with equal intensity, modulation is clearly observed, due to the phase interference among sub-pulses. More shaping crystals  or longer input pulse duration  can be used to produce a truly ﬂat-top proﬁle. However, any slight phase variation from the change in crystal thickness will have a dramatic impact on the proﬁle, causing instability. Therefore, a tradeoﬀ must be made between the stability and the ripple. Simulations show that an approximate 40% peak-to- peak modulation in the lasershaping pulses would be the best choice to ensure that the temporal proﬁle is nearly immune to any phase variation of all the sub-pulses. Fortunately, the subsequent measurement has almost smeared out the ripple, due to the ﬁnite response time in the detector, and ultrashort ﬂat-top ps electrical pulses could still be generated.
8 The idea for Run 2 is to split the plasma into two sections: a self-modulator and an accelerator. The proton bunch modulates (until saturation is reached) into a micro-bunch train in the self- modulator. A short electron bunch (σ ∼ 100 fs) is injected into the stable wakefields (driven by the microbunch train) in the accelerator plasma. First simulation results  indicate that the majority of the witness bunch can preserve its quality (emittance, relative energy spread) if: 1) the electron bunch beam loads the wakefields and 2) its front contributes to creating a blow-out region in which its back can experience a linear focusing force.
simultaneously in separate audio channels to allow for the measurement of RT. RT measurements were calculated in Audacity® by measuring the time delay between the speech offset in the stimulus to the start of the participant’s oral response. The difference in these two time points was calculated for each sentence trial and averaged across a block of ten sentences for each condition. RTs were measured for 19 participants as the time between offset of the sentence stimuli to the onset of the participant’s oral response. This was done using the “SoundFinder” function in Audacity® and manually adjusted by two trained scorers. This function divides an audio file by placing region labels for areas of sound that are separated by silence. Manual adjustment was required because of the noise offset in the stimuli, which occurred after the speech offset. The final RT was an average of the two scorers for each spectral condition within the three background conditions. In addition, RTs associated with trials that a participant either a) did not respond during the trial or b) repeated none of the sentence keywords correctly were excluded from the analysis in order to ensure that only trials that involved some
The data acquisition system designed and constructed for the experiments discussed in this thesis is shown schematically in fig. A3.1. The system consisted of an Apple 3 microcomputer and an external analog input u n i t . Through the analog input unit, the computer was able to select any one of five analog inputs, have the voltage level appearing at the selected input converted to a 12 bit binary word, and read the binary word into memory for processing and/or storage. The unit was also able, on command from the computer, to trigger a probe laser frequency scan.
irradiance, the temperature as well as the number density were found to rise to a level of 1000mj irradiance of laser and to saturate later on. The temperature’s saturation along with the number density which was over the 1000mj radiance level is thought to occur due to the effect of shielding of plasma, In other word, it means absorption and/or reflection laser photons mode by the plume of plasma.
With the application of laser technology in underwater, the evolution properties of laserbeams propagating in oceanic turbulence have been investigated. In recent years, the propagation properties of various laserbeams in oceanic turbulence have been illustrated and analyzed, including the scintillation index of laser beam , mutual coherence function of laser beam , astigmatic stochastic electromagnetic beam , partially coherent flat-topped vortex hollow beam , partially coherent annular beam , Gaussian Schell-model vortex beam , stochastic electromagnetic vortex beam , flat-topped vortex hollow beam , partially coherent Hermite-Gaussian linear array beam , partially coherent four-petal Gaussian vortex beam , Gaussian array beam [28–30], partially coherent cylindrical vector beam , chirped Gaussian pulsed beam , Lorentz beam  and partially coherent four-petal Gaussian beam . To the best of our knowledge, there has been no report on the propagation analysis of partially coherent Lorentz beams propagating in oceanic turbulence. In this paper, based on the derived equations, the average intensity of beams propagating in oceanic turbulence has been analyzed, and influences of oceanic turbulence have been given.
Laser forming is thermo mechanical process in which a sheet metal is formed in to a desired shape without using external force. No direct contact with the work piece, so it is a non contact type process. The aim of this study is to form “V” shaped component through straight line laser forming. Experimental set up for straight line laser forming has been developed. A parametric study has been carried out to study effect of process parameters i.e. thickness of sheet metal, feed and no. of pass. DOE has been performed to optimize process parameters. Also ANOVA method is used to evaluate most dominant factor to affect the bending angle and temperature difference.
In this letter, we show that the normal three-wave stimu- lated Brillouin scattering occurring from the pump field, which prematurely depletes the pump laser before interaction with the seed, can be preferentially damped by the introduc- tion of collisional effects in the code without affecting the driven process, which occurs as a result of the beating of the pump and seed frequencies together. As a result, the energy available for transfer between the beams is maximised and a notable reduction in the amount of seed pre-pulse produced is observed. We also report on the fact that when such colli- sional effects are accounted for an increase in the plasma ion temperature leads to damping of both of these Brillouin scat- tering processes resulting in complete eradication of the Brillouin instability. The first results from OSIRIS simula- tions of the effects of collisional processes and the effect of varying the plasma electron/ion temperature ratio on this energy transfer method through the Brillouin process are presented.
cifically, G(2.63) and G(3.16) are predicted to prepare the resultant outgoing beams in a state not representable by duality. In the interest of eliminating potential systematic sources of experimental error, the respective resultant beams for all three gratings and for the NG control are maintained at the same power level for the complete set of trials. With this constraint of equivalent power, duality necessarily imposes a fundamental physical equivalence of the four resultant beams. Duality also forbids a net transfer for these or any other beams upon coupling with an independently generated beam. Nevertheless, when the four resultant beams are respectively coupled with Φ R ,