Nanosecond Width Research Articles

Reconfigurable microwave properties in C-, L- and S-shaped nanomagnets

Dynamic responses of magnetic nanostructures exist in the GHz frequency range and therefore offer excellent opportunities to miniaturize microwave devices. Here, we have demonstrated C-, L- and S-shaped nanomagnetic structures which enable reconfigurable microwave properties. Magnetic and microwave properties have been studied utilizing micromagnetic simulations. We have obtained two different magnetic remanent states for all the samples by using a simple field initialization process. Different remanent states are associated with distinct magnetization dynamic properties which can be tuned using a magnetic field pulse of nanosecond width. Remarkably large frequency shifts have been observed between the two different magnetic remanent states. Tunable microwave properties relies on the strong dipolar field variations—the effect of which have been shown systematically in all spatial directions in strategically designed sample geometries such as single layer arrays, isolated multilayers and networks of multilayers. The results have potential implications for the realization of ultra-low-power and ultrafast microwave devices.

Controlling waveform of light pulse with light in optical fibers

We present our experimental demonstration of controlling waveform of a signal pulse by using two beams of continuous wave (CW) generated by stimulated Brillouin scattering (SBS) in optical fibers with different frequencies. Waveform of the signal pulse is modulated in an “all-optical” way according to total input power. This method is only suitable for light pulse with nanosecond width. We provide a new method for controlling light with light.

WE‐A‐134‐10: Non‐Ionizing, Non‐Invasive, Non‐Contact, and Real‐Time Tumor Detection Using Ultra‐Wideband (UWB) Radar: A Feasibility Study

Purpose: We introduce a revolutionary tumor‐detection technology using the Ultra‐Wideband (UWB) radar. The UWB is electromagnetic pulses with around nanosecond width encompassing 3.1‐10.6 GHz. The UWB is well known in radar world as a through‐the‐wall imaging technology. We investigate penetration capability of the UWB through biological tissues to detect tumors. Methods: To experimentally demonstrate UWB penetration, our setup consists of transmitter/receiver radar system to measure the reflected signal off from the aluminum plate behind the biological tissues (pig skins, cow muscles, bones, fat, and wet‐sponges (lung‐substitute)). We perform a series of two complementary measurements: 1) a tissue sample with an aluminum plate under the tissue, 2) tissue only. The two measurements are subtracted to extract only the reflected signal from the aluminum back through the tissue to the receiver. Additionally, a phantom consisting of 0.2‐cm skin, 2.0‐cm fat, 0.5‐cm muscle, and 2.4‐cm wet sponge stacked in series was used as a miniature version of a human thorax. Instead of an aluminum plate, a 20‐ml water balloon (diameter=5 cm) was placed under the phantom to mimic lung‐tumor. Results: We confirm that the UWB can penetrate through all biological tissues with varying transmission. Specifically, the 1/e (36.7%) transmission depths from air to bone, fat, skin, muscle, and wet sponge are 1.52, 1.24, 0.09, 0.24, and 1.74cm, respectively. For the phantom‐tumor experiment, the reflected signal from the water balloon was detected with a SNR of ∼2 and its amplitude was reduced to 11.1% compared to the reflected signal measured without the phantom. Conclusion: The UWB is a revolutionary technology for tumor detection with multiple advantages including non‐contact, non‐invasive, non‐ionizing, real‐time, and low cost. This technology shows great promise as a real‐time sensing and imaging technique for radiation oncology.

Integrated Optical Electric Field Sensor From 10 kHz to 18 GHz

A lithium niobate (LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> )-based integrated optical sensor with Mach-Zehnder optical waveguide interferometer and tapered antenna array was designed and fabricated for electric field detection. Experimental results reveal that this sensor has a frequency response deviation less than ±10 dB within the range of 10 kHz to 18 GHz, and its minimum detectable electric field intensity is 0.4 V/m. Moreover, a pulsed electric field with nanoseconds width and electric field intensity of 103 V/m have been detected by this sensor.

Spectroscopy Methods and Applications of the Tor Vergata Laser‐Plasma Facility Driven by GW‐Level Laser System

A review focused on plasma induced on solid target by GW‐level pulsed laser source is presented. A description of the Tor Vergata laser‐plasma source (TVLPS), at the Tor Vergata University in Rome, is given. Such a facility uses a 1 GW, tabletop, multistage Nd:YAG/Glass laser system, delivering infrared (IR) pulses with nanosecond width and 1064 nm wavelength (TEM00 mode). Its applications are discussed providing: wide analysis of IR → soft X‐ray conversion efficiency (1.3–1.55 keV); measures and modeling of line emission in soft X‐ray spectra, such as those from zinc plasma near Ne‐like Zn XXI and from barium plasma near Ni‐like Ba XXIX. Particular attention is devoted to high‐n dielectronic Rydberg satellites for finding a useful diagnostic tool for plasma conditions. Dependence of plasma spectra on laser parameters is shown. Finally, microradiography applications are presented for thin biological samples. Images permit to visualize specific structures and detect bioaccumulation sites due to contamination from pollutants.

A study of a Q-switched double-clad ytterbium-doped fiber laser with amplifying effect

A high repetition rate ytterbium-doped double-clad (YDDC) fiber laser with amplifying effect is described by using acousto-optic modulator. The characteristic of Q-switched pulses are studied with accurate control of opening gate time of modulator. The stable Q-switched pulses with tens of nanoseconds width can be observed at high repetition rate varied from 50kHz to 500kHz using this laser. The stable operation area of the Q-switched fiber laser is discussed and the analysis results agree well with that of the experiment.

Atmospheric pressure volume discharge without external preionization

The phenomenon of electric breakdown in air at atmospheric pressure without additional preionization was studied by experimental and theoretical methods. Using voltage pulses of different polarity with subnanosecond leading front and nanosecond width, volume discharge can be obtained under such conditions between electrodes of various configurations, in particular, between two point electrodes. The development of an ionization wave in nitrogen is described within the framework of a diffusion-drift approximation in a spherical geometry. The fact that the qualitative character of discharge is independent of the voltage pulse polarity is explained by the multiplication of background electrons in the high-density gas.

Characterization of a high-intensity unipolar-mode pulsed ion source with improved magnetically insulated diode

A magnetically insulated ion diode (MID) with an improved external-magnetic field system has been developed and installed onto a TEMP-6-type high-intensity pulsed ion source in order to produce a high-intensity pulsed ion beam (HIPIB) for surface modification of materials. The external-magnetic field MID is operated in unipolar mode based on dielectric high-voltage flashover, and a double coaxial pulse-forming line (PFL) powered with a Marx generator is used to form the unipolar pulse of nanosecond width. A specially designed cathode has been constructed with a forked connection to two symmetrically installed transformers to improve the effect of the magnetic field and thus increase the stability of generation and propagation of the ion beam. It was found that the efficient generation of HIPIB mainly depended on the magnetic field strength, the gas pressures in reverse and output switches of PFL, and the anode–cathode (A–K) gap of the external-magnetic field MID. A proper magnetic field strength was found with magnetic field power system at dc charging voltage of 8 kV. The proper A–K gap distance is not uniform with the value varied from 6 to 8 mm. Suitable gas pressures for reverse and output switches were about 1.2 and 2.4 atm, respectively, at a charging voltage of 40 kV to the Marx generator. The most efficient plasma generation and ion extraction led to a maximum output of HIPIB with a peak ion current density of 300 A cm−2 and a beam pulse width of 80 ns (full width at half maximum), at an accelerating pulse of 300–350 kV with a pulse width of 70 ns.

Microwave emission due to hypervelocity impacts and its correlation with mechanical destruction

Microwave emission due to hypervelocity impacts on metallic plates has been found. The targets used in the experiment are aluminum plates with various thicknesses. The projectile, a nylon cylinder with metal screw of 0.21 gm, was accelerated up to the velocity of 4 km/s; a heterodyne receiver detected the microwave at 22 GHz. The emission is a random sequence of pulses with several nanosecond width, which lasts more than 10 μs. The phenomenon seems to be dependent on the extent of target destruction through the formation of impact craters or penetration. If so, we could use the characteristics of the phenomena to better understand the mechanical destruction process. We propose several models for the cause of this microwave generation and study them on the basis of timing relation of observed events.

Characterization of a high-intensity bipolar-mode pulsed ion source for surface modification of materials

A high-intensity pulsed ion source of TEMP-type series, operating in bipolar mode, has been developed as a unique pulsed energy source to produce a high-intensity pulsed ion beam (HIPIB) for surface modification of materials. To generate the ion beam, a specially shaped bipolar pulse, consisting of a first negative pulse and a second delayed positive pulse both of nanosecond width, is formed by a double coaxial pulse-forming line (PFL) powered with a Marx generator and supplied to a magnetically insulated ion diode (MID) by a self-magnetic field. It is found that the efficient generation of a HIPIB is mainly dependent on the delay time of the bipolar pulse, adjusted by pressure ratio in the two gas switches of a PFL, and the anode–cathode (A–K) gap distance in the self-magnetic field MID. The delay time determines the effective area on the anode surface for plasma generation and the A–K gap distance ensures the stability of the process. A proper delay time and a proper A–K gap distance are obtained by a series of experimental investigations. Under delay time from 30 to 280 ns and several different A–K gap distances, the typical wave forms of the bipolar pulses at a dc charging voltage of 45 kV to Marx generator are illustrated to clarify the effects of delay time and A–K gap distance on the ion beam generation. The proper A–K gap distance is not uniform, varied from 6 to 8 mm, and the corresponding proper delay time is 250 ns. The most efficient plasma generation leads to a maximum output of HIPIB with a peak ion current density of 350 A cm−2 and a beam pulse width of 75 ns (full width at half maximum), at an accelerating pulse of 220 kV with a pulse width of 100 ns.

Measurement of the tensile strength of aluminium at a strain rate of 2×107 s-1

Laser-driven shock waves were used to measure the spall strength of pure aluminum at a strain rate of approximately 2*107 s-1. The measurement was made possible due to a novel method which uses the phenomenon of spallation as a measure of the constant pressure situation of laser-induced shock waves of nanosecond width. The authors have found a spall strength of sigma =3.0+or-0.2 GPa for pure aluminum at a strain rate of epsilon =(1.8+or-0.9)*107 s-1. Comparison of this result with those of Ek and Asay indicates a power law dependence of the spall strength on the strain rate: sigma =(1.5+or-0.2)( epsilon /106 s-1)0.22+or-0.04 GPa for epsilon >or=105 s-1. A short discussion on the variation of the spall thickness as a function of target thickness is also presented.

A Light Pulse Source of a Few Tens of a Picosecond to Nanosecond Width with Cherenkov Radiation

It was experimentally proven that Cherenkov radiation arising from intense electron pulses passing through a dielectric material could be utilized for a light source of short pulse width. A linear accelerator at ISIR, Osaka University, which can produce intense single-bunch electron pulses, was used for a Cherenkov radiation exciter. The spectral distribution and pulse shape of the Cherenkov radiation from an air radiator with these electron pulses were investigated with a fast detection system for this purpose. The spectrum showed a peak at 200 nm and a continuous band of which intensity decreased towards the longer wavelength. The minimum pulse width of the Cherenkov radiation with the single-bunch electrons was about 40 ps, and the light peak power was about 10 kW in the spectral region of 200 to 600 nm.

A Multiwire Secondary Emission Profile Monitor for Small Emittance Beams

A secondary emission monitor using two multiwire grids separated by a positively biased collector has been constructed and tested with a 1 GeV electron beam at the Orsay Linac. The monitor installed just before the electron-positron converter has 8 gold-plated-tungsten wires of 0.1 mm diameter equally spaced 0.2 mm apart in each plane. Each wire is connected with an integrator using a low-bias current operational amplifier. The wire planes and the collector are moved into the beam by a stepping motor : that allows beam-position verification. We measured narrow profiles for 1 Amp peak current pulses of 30 nanoseconds width. Profiles are displayed on a scope and allow emittance determination by the three gradient method. Such a monitor is very useful to control the electron beam position and dimensions on the converter, because the positron source dimensions are rather bigger than those of the incident beam and the geometrical acceptance of the positron Linac is limited.

Free-ion yields, electron mobilities and electron-ion recombination rate constants in liquid and solid isooctane and several other nonpolar compounds

Free-ion yields ( G fi 0) in solid isooctane were determined by a new simple method which was a combination of the electric current measurement during irradiation of very low dose of 60Co γ-rays and the continuous measurement of thermostimulated current after the irradiation by applying d.c. high voltage to the solid isooctane. Electron mobilities (μ e) in the solid isooctane were determined by the free-ion yields and the measurement of peak electric current upon the X-ray pulse irradiation of a few nanoseconds width. In the liquid phase, however, G fi 0 and μ e were also measured by the usual charge clearing method and the decay curve analysis or peak current method, respectively. The effects of temperature from 26 to – 158°C and of phase change from liquid to solid on G fi 0, μ e and b (the most probable electron-thermalization length) are compared with those for neopentane, tetramethysilane, and cyclohexane. Some values of the G fi 0, μ e and b determined in liquid and solid isooctane are as follows: in liquid G fi 0=0.13 at -101°C, μ e =1.6 cm 2 V -1 s -1 at -99°C, b=103 A at -101°C; in solid, G fi 0=0.15 at -118°C, μ e =0 cm 2 V -1 s -1 at -118°C, b=104 A at -116°C. The values of apparent activation energy of μ e obtained by the Arrhenius plot are 0.049 eV in the liquid and 0.077 eV in the solid isooctane, respectively. As the results, it is concluded that in liquid and solid isooctane localized electrons play a main role in electron transport with somewhat larger contribution of quasi-free electrons than in liquid and solid cyclohexane and that the rather larger contribution of quasi-free electrons than in cyclohexane seems to relate to the variation in G fi 0 and b value with temperature and phase change. Electron-ion recombination reaction in some organic liquids and solids is also discussed.

Ameliorations apportees aux chronometees a vernier (verniers chronotrons)

The largest time interval, that can be measured by means of the vernier chronotrons working on the principle of beat between two generators of slightly different periods, is limited by the period of the slower generator. This present paper deals with the improvements brought to the vernier chronotrons system and which permit to use this device in order to define a very great number of channels without impairing their stability and differential linearity: indeed, the method used leads to measure in a homogeneous way the time intervals larger than one period. In order to verify the basic principle, a time analyzer with 3000 channels of one nanosecond width each has been built. The measurements exhibit a stability of the order of 3 × 10 −4/°C and the first tests carried out have not allowed to detect any lack in differential or integral linearity.