Peak Power Beam Research Articles

Target depth estimation by frequency interference matching for a deep vertical array

A vertical line array can be deployed in deep water below the critical depth, i.e., the depth where the sound speed equals the sound speed at the surface, to take advantage of the lower ambient noise level, relative to above the critical depth for target detection. The depth of a source can be estimated exploring the interference between the direct and reflected signals described by Lloyd’s mirror theory. Existing methods for source-depth estimation assume either a source transmitting a pulsed signal or a source traveling a straight line at a constant depth. For the latter, the source depth can be estimated after collecting observations over a sufficiently large domain of ranges. A method is proposed here that can estimate the source depth using a short snapshot of the random broad band signal, and can thus estimate the source depth semi-instantaneously, even as the source changes course and/or depth. An incoherent matched beam processing method is used matching the peak beam power measured from data as a function of frequency with a replica peak beam power spectrum for a hypothesized source depth. The performance of the proposed method is evaluated using simulated data and validated with experimental data from the South China Sea.

Spatial beam self-cleaning and supercontinuum generation with Yb-doped multimode graded-index fiber taper based on accelerating self-imaging and dissipative landscape.

We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index profile when 1064 nm pulsed beams propagate from wider (122 µm) into smaller (37 µm) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm. By taper cut-back, we observed that the dissipative landscape, i.e., a non-monotonic variation of the average beam power along the MMF, leads to modal transitions of self-cleaned beams along the taper length.

Multi-terawatt femtosecond laser system of visible range based on a photochemical XeF(C-A) amplifier

AbstractThis paper reports on the creation of a THL-100 multi-terawatt hybrid laser system based on a Start-480M titanium-sapphire starting complex and photochemical XeF(C-A) amplifier with a 25-cm aperture. The complex produces 50-fs radiation pulses of energy up to 5 mJ at a second harmonic wavelength of 475 nm. The active medium of the amplifier is created in a XeF2/N2 mixture under vacuum-ultraviolet radiation of electron beam-excited xenon. The results of first experiments on femtosecond pulse amplification in the active medium of the XeF(C-A) amplifier are presented to demonstrate that a laser beam peak power of 14 TW has been attained.

Nd:YAG Laser Welding of Stainless Steel 304 for Photonics Device Packaging

Although pulsed Nd:YAG laser welding has been widely used in microelectronics and photonics packaging industry, a full understanding of various phenomena involved is still a matter of trials and speculations. In this research, an ultra compact pulsed Nd:YAG laser with wavelength of 1.064μm has been used to produce a spot weld on stainless steel 304. The principal objective of this research is to examine the effects of laser welding parameters such as laser beam peak powers, pulse durations, incident angles, focus point positions and number of shots on the weld dimensions: penetration depth and bead width. The ratio of the penetration depth to the bead width is considered as one of the most critical parameters to determine the weld quality. It is found that the penetration depth and bead width increase when the laser beam peak power, pulse duration and number of shot increase. In contrast, the penetration depth decreases when the laser beam defocus position and incident angle increase. This is due to the reduction of the laser beam intensity causing by the widening of the laser spot size. These experimental results provide a reference on an optimal laser welding operations for a reliable photonics device packaging. The results obtained shows that stainless steel 304 is suitable to be used as a base material for photonics device packaging employing Nd:YAG laser welding technique.

A Reliable Nd:YAG Laser Welded Stainless Steel 304 for Photonics Device Packaging Application

An ultra compact pulsed Nd:YAG laser with laser beam peak power of 3.5kW and 6.5ms pulse duration is employed to produce a butt joint and lap joint for both spot and seam welding on a stainless steel 304 specimen. The strength test of the weld joints is conducted by pulling the joint materials using INSTRON Series IX/s Automated Materials Tester System. From the experimental results, it is found that a butt joint produces much stronger attachment than a lap joint. The stronger attachment is contributed by a larger volume of welded stainless steel 304 at the joint interfaces. However, the strength of a lap joint can be increased by producing a deeper weld penetration depth. It is done by controlling the laser beam parameters such as laser peak power and pulse duration. It is inferred that the commercial welding material, InvarTM, provides more robust joint than stainless steel 304. It is also concluded that the welded stainless steel 304 cannot attain the strength and elastic modulus of the stainless steel 304 itself. However, the stainless steel 304 is a good welding material for photonics device packaging by using pulsed Nd:YAG laser welding technique.

Experimental Investigation of a Novel Circuit for Millimeter-Wave TWTs

A novel folded waveguide circuit that features thick iron pole pieces with hollow centers was built as part of a periodic-permanent-magnet-focused W-band single-stage test-vehicle traveling-wave tube (TWT). These hollow centers, which comprise part of the slow wave circuit, increase the rms axial field and significantly reduce the unwanted transverse field imbalance. For this TWT, a tetrode gun that creates an ultralaminar 20-kV 0.25-A nominal electron beam was used. It was demonstrated that this gun and magnetic structure can provide greater than 97% beam transmission for peak beam power levels as high as 9.25 kW (25 kV, 0.37 A). The unplated circuit, operating around 91 GHz on the edge of a passband, exhibits between 10 dB and 12 dB gain that compares favorably with results of device modeling utilizing the 3D particle-in-cell code Magic3D. Using a feedback approach to characterize large-signal operation, the tube generated 40 W of regenerative oscillator power. Design-optimized versions of this circuit show promise of enabling W-band TWT amplifiers that provide up to 300 W of peak RF output power

Atmospheric propagation of gradient-shaped and spinning femtosecond light pulses

The multiple filamentation of high power, ultrashort laser pulses is investigated for special waveforms exhibiting either sharp intensity gradients or vortex shapes having an angular orbital momentum. First, theoretical estimates are established on the basis of a (2+1)-dimensional model discarding temporal dependences, in order to evaluate the number of filaments and their onset distance with respect to the peak beam power or with the topological charge of optical vortices. Numerical simulations are next performed from this model and they confirm the theoretical expectations, at least qualitatively. These are shown to hold in (3+1)-dimensional geometry involving time variations, through direct numerical integrations of the propagation equations.

Laser accelerated ions and electron transport in ultra-intense laser matter interaction

Since their discovery, laser accelerated ion beams have been the subject of great interest. The ion beam peak power and beam emittance is unmatched by any conventionally accelerated ion beam. Due to the unique quality, a wealth of applications has been proposed, and the first experiments confirmed their prospects. Laser ion acceleration is strongly linked to the generation and transport of hot electrons by the interaction of ultra-intense laser light with matter. Comparing ion acceleration experiments at laser systems with different beam parameters and using targets of varying thickness, material and temperature, some insight on the underlying physics can be obtained. The paper will present experimental results obtained at different laser systems, first beam quality measurement on laser accelerated heavy ions, and ion beam source size measurements at different laser parameters. Using structured targets, we compare information obtained from micro patterned ion beams about the accelerating electron sheath, and the influence of magnetic fields on the electron transport inside conducting targets.

Preliminary Research Results for the Generation and Diagnostics of High Power Ion Beams on FLASH II Accelerator

The preliminary experimental results of the generation and diagnostics of high-power ion beams of FLASH II accelerator are reported. The high-power ion beams presently are being produced in a pinched diode. The method for enhancing the ratio of ion to electron current is to increase the electron residing time by pinching the electron flow. Furthermore, electron beam pinching can be combined with electron reflexing to achieve ion beams with even higher efficiency and intensity. The anode plasma is generated by anode foil bombarded with electron and anode foil surface flashover. In recent experiments on FLASH II accelerator, ion beams have been produced with a current of 160 kA and an energy of 500 keV corresponding to an ion beam peak power of about 80 GW. The ion number and current of high power ion beams were determined by monitoring delayed radioactivity from nuclear reactions induced in a 12C target by the proton beams. The prompt γ-rays and diode bremsstrahlung x-rays were measured with a PIN semi-conductor detector and a plastic scintillator detector. The current density distribution of ion beam were measured with a biased ion collector array. The ion beams were also recorded with a CR-39 detector.

A Magnetic Residual Ion Removal System with In-Line Ion Dumps for the ITER Neutral Beam Injection System

An alternative residual ion removal concept for the ITER neutral beam system is presented. It consists of magnetic deflection of the residual ions to in-line ion dumps. The target plates are hit from one side and form a 0.5-m-wide opening to the beam. First calculations show that for the most severe case of a 3-mrad beam, the maximum power load can be kept below 15 MW/m2, using a different horizontal focal length. However, this different beamlet optic increases the beam peak power density changing the plasma deposition profile and increasing the shine-through power during low-density operation. First calculations showed that using a passive screening, the additional stray field created by the magnet could be kept below the required 1 gauss within the neutralizer. The overall beamline transmission increases by ~10% (i.e., an additional 1.7-MW injected power for each beamline for a 3-mrad beam) due to the open structure of the magnet and the ion dumps. Furthermore, the concept offers a larger operating window regarding beam alignment, divergence, steering, and transmission, and it avoids creating accelerated secondary electrons.

Effects of thermal shocks on the release of radioisotopes and on molten metal target vessels

The ISOLDE pulsed proton beam peak power amounts to 500 MW during the 2.4 μs proton pulse. The fraction of the proton pulse energy deposited in the target material is at the origin of severe thermal shocks. Quantitative measurement of their effect on the release of radioelements from ISOLDE targets was obtained by comparison of release profiles measured under different proton beam settings. The thermal shock induced in liquids (Pb, Sn, La) lead to mechanical failure of ISOLDE molten metal target vessels. Failure analysis is presented and discussed in the light of the response of mercury samples submitted to the ISOLDE beam and monitored by high-speed optical systems.

The operation of a uniformly insulated extraction applied-B ion diode

We present the first experimental results of a uniformly insulated extraction applied-B ion diode. The diode typically attained beam generating efficiencies of 70% at the time of peak beam power. This is a significant improvement over previous extraction applied-B ion diodes, demonstrating the importance of uniform insulation as suggested by theory [J. Appl. Phys. 59, 2685 (1986)]. Furthermore, we found that the beam current is nearly independent of the ion-emitting area down to a minimum area. At the minimum area, the beam current density was enhanced by 150 times the monopolar Child–Langmuir value. This data supports a recently proposed theory [Phys. Rev. Lett. 59, 2295 (1987)] that predicts large enhancements due to the electron diamagnetic effect on the virtual cathode.

Line-Source E-Beam Crystallization of Silicon-on-Insulator Films

ABSTRACTSilicon-on-insulator films have been formed using a 20 mm by 1 mm line-source electron beam, with sample sweep speeds of 100–500 cm/sec and peak beam power densities up to 75 kW/cm2. Films were formed over 1 and 2 μm thick SiO2 isolating layers on 4°C diameter Si<100> wafers, with stripe openings of 5 to 100 μ width for seeding the crystallization from the substrate. Films consisted of Si layers from 0.4 to 1.0 μm thickness, with a capping layer of 2 μm SiO2. By sweeping the beam parallel to the long axis of the seed openings, smooth, oriented films were obtained, with low-angle grain boundaries confined to midway between seed openings. Best results were obtained for ≲ 50 μm spacing between seed openings.

Electronic Cell-Volume Analysis by Use of the AMAC I Transducer

Abstract A new potential-sensing transducer has been developed that produces short 5- to 10-µs pulses suitable for rapid cell counting and pulse height volume analysis rates. The use of a bridge circuit, where potential-sensing rather than current-carrying electrodes are connected to a differential amplifier with a high common-mode rejection ratio, permitted accurate determination of both pulse width and shapes from the short pulses generated with the transducer. A new sample injection subsystem permits small samples of constant volume to be continuously mixed at a variable rate with a constant flow of diluent. The counting rate can be optimized to 250,000 cells per minute at a 2% coincidence level. Polystyrene latex spheres produced pulses having the five basic shapes predicted by Grover et al. [Biophys. J. 9, 1398 (1969)]. Human erythrocytes produced, in addition to these shapes, a sixth, castle-shaped pulse, presumably caused by rotation or distortion of the erythrocyte as it passes through the orifice. A shape factor has been calculated from the latter pulses. The electronic cell-volume pulses from the tranducer trigger an pulsed-ion laser. The 5-W peak power beam is focused through the orifice. Illumination of the cells with this intense but economical light source permits the combined measurement of electronic cell volume, fluorescence, and light scattering.

Generation of High Intensity Beams of Nanosecond Pulse Duration by Electron Linacs

Acceleration of electron beams with a very short pulse duration and high peak intensity is achieved in electron linacs. As pulse generators for very short pulse duration, a coaxial line-type pulser, a hard-tube pulser and a pulse sharpener are newly developed which can produce pulses of about 5 nanoseconds in pulse duration and about a few thousands volts in amplitude in 50-ohm load. In Tohoku linac, peak intensity of 1.3 amperes is obtained with pulse duration of 7 nanoseconds and energy of 75 MeV, while in Mitsubishi linac, 2.0 amperes, 10 nanoseconds and 6.4 MeV, respectively. Their results agree with Leiss theory. As a parameter of transient beam loading, the ratios of the energy contained in a pulsed beam to the stored energy in the accelerating structure and of the peak beam power to the peak input RF power are presented.

Long-Pulse Radio Frequency Separator Test Facility

This paper discusses a long-pulse, line-type modulator facility which has been built to operate either one or two SLAC-type klystrons for long-pulse RF particle separator studies. The modulator is capable of driving two klystrons to a peak beam power of 80 MW, 250 kW average, for 50μs pulses or one klystron to a peak beam power of 40 MW, 125 kW average. The modulator has two 25 μs pulse-forming networks which can be operated individually to drive a single klystron or in parallel to drive two klystrons from a common pulse transformer. In addition, test results for long-pulse operation of the SLAC-type klystron are presented.