Rms Duration Research Articles

Generation and Characterization of Intense Ultralow-Emittance Electron Beams for Compact X-Ray Free-Electron Lasers.

The transverse emittance of the electron beam is a fundamental parameter in linac-based x-ray free-electron lasers (FELs). We present results of emittance measurements carried out at SwissFEL, a compact x-ray FEL facility at the Paul Scherrer Institute in Switzerland, including a description of the novel high-resolution measurement techniques and the optimization procedure. We obtained slice emittance values at the undulator entrance down to 200nm for an electron beam with a charge of 200pC and an rms duration of 30-40fs. Furthermore, we achieved slice emittances as low as 100nm for 10pC beams with few fs duration. These values set new standards for electron linear accelerators. The quality, verification, and control of our electron beams allowed us to generate high-power FEL radiation for a wavelength as short as 0.1nm using an electron beam with an energy of only 6GeV. The emittance values demonstrated at SwissFEL would allow producing hard x-ray FEL pulses with even lower-energy beams, thus paving the way for even more compact and cost-effective FEL facilities.

The dynamics of a dolphin’s biosonar signals while performing target discrimination tasks

An experiment was conducted to determine if a blindfolded echolocating dolphin modified its biosonar signals depending on the targets it was investigating in a target shape discrimination task. Biosonar signals were measured with a specially designed bite-plate apparatus with a dowel extending from the bite plate to support the hydrophone. The detected signals were digitized and stored on a modified SoundTrap (Ocean Instrument New Zealand) attached to the dowel. The dolphin engaged in a matching-to-sample task: he first examined a sample target and then swam to a different area of the pool to examine three alternative targets, one of which matched the sample. The animal’s task was to point to the matched target. The characteristic of each emitted signal was determined by calculating the peak frequency, center frequency, rms bandwidth, and rms duration. A specific target set was used for each session of 15-18 trials; some sets were unfamiliar to the dolphin. Considerable amount of variations in the signal parameters were observed across trials and sessions, but our statistical analyses suggested the variations were not based on target identity, thereby leading us to conclude that the clicks emitted by the dolphin did not differ with the target set.

Comparing the biosonar signals of free swimming dolphins with those of a stationary dolphin in a net pen

The biosonar signals of two free-swimming Atlantic bottlenose dolphins performing a complex sonar search for a bottom target in San Diego Bay were compared with the biosonar signals of a dolphin performing a target discrimination task in a net pen. A bite-plate device that the dolphins carried supported a hydrophone that extended directly in front of the dolphin. A biosonar measuring tootbox (BMT) attached to the bite plate measured the outgoing biosonar signals while the dolphins conducted sonar searches. Both of the free-swimming dolphins used different biosonar search strategy in solving the problem and their biosonar signals reflect the difference in strategy. The dolphin stationed in a hoop in the pen while echolocating on a target 6 m away and reported if the indentation on a spherical target was directed toward it. The signals were parameterized by determining the peak-to-peak source levels, source energy flux density, peaked frequency, center frequency, rms bandwidth, rms duration, and the Q of the signals. Some of the characteristics of the r signals were similar for the free-swimming and stationary dolphins while some were significantly different suggesting biosonar signals used by free-swimming animals may be different than signals used by captive dolphins in restrictive environments.

Duration of the 2011 Tohoku earthquake ground motions

We compared several different duration measures for the 2011 M9.0 Tohoku earthquake sequence, because empirical duration models are of great interest for purposes of correlation with structural damage, and the Tohoku mainshock was remarkable for its long duration. Among the three considered definitions, RMS duration (McCann and Shah, Bull Seism Soc Am 69: 1253–1265, 1979) is best able to predict the duration within which pulses or groups of pulses of energy arrive; it is particularly suitable for the Tohoku mainshock, for which source complexity caused time-series with multiple-phase arrivals. Two other considered definitions, both of which tend to underestimate the observed duration, are: (i) duration defined by random vibration theory (RVT); and (ii) the significant duration as defined by the interval between 5 and 75 % or 95 % of the integral of the square of the ground acceleration (known as “Arias intensity” (Arias 1970)) or velocity (known as “energy integral” (Anderson 2004)). In the Tohoku mainshock, significant amplitudes precede the 5 % of the Arias intensity marker; we need to use 0.3 % of the maximum of the accumulated energy as the lower bound marker to appropriately estimate the duration using the significant duration definition. The RVT duration (used in stochastic simulations) can be estimated easily from the 5–75 % of the Arias intensity (significant duration) definition as the two measures give very similar durations. Overall, the significant duration of ground motions observed during the 2011 M9.0 Tohoku earthquake increases with distance as 0.19R cd for the horizontal components or 0.33R cd for the vertical component, where R cd is the closest distance to the fault plane. By comparison, the duration of four aftershocks (M4.5–7.7) increases with distance as ~0.10R hypo where R hypo is the hypocentral distance. For the mainshock, the distance-dependent slope term is greater, presumably due to the large fault plane size.

Dynamics of biosonar signals of free swimming dolphins searching for bottom targets

Measuring on-axis biosonar signals from a free swimming dolphin performing a sonar task is extremely difficult without having a special device that the animals carry. A bite-plate device which had a hydrophone directly in front of the dolphin at a fixed location along the beam axis of the biosonar beam was constructed as a part of the Navy Marine Mammal Research Program in San Diego. A data acquisition and storage unit was a part of the Biosonar Measurement Toolbox (BMT) and hung below the bite plate. The outgoing signal was measured by the omnidirectional hydrophone while two disk hydrophones measured the echoes. The device was used with two Atlantic bottlenose dolphins (Tursiops truncatus) as the animals conducted biosonar searches for specific objects on the ocean bottom. The outgoing signals were parameterized into the following, peak-to-peak source levels, source energy flux density, center frequency, rms bandwidth, rms duration, and interclick intervals. The parameters were analyzed with both a cluster analysis and a principle component analysis to determine the grouping of the parameters and the relationship between parameters. Both dolphins used different biosonar search strategy in solving the problem and their biosonar signals reflect the difference in strategy.

Water equivalent path length measurement in proton radiotherapy using time resolved diode dosimetry

To verify water equivalent path length (WEPL) before treatment in proton radiotherapy using time resolved in vivo diode dosimetry. Using a passively scattered range modulated proton beam, the output of a diode driving a fast current-to-voltage amplifier is recorded at a number of depths in a water tank. At each depth, a burst of overlapping single proton pulses is observed. The rms duration of the burst is computed and the resulting data set is fitted with a cubic polynomial. When the diode is subsequently set to an arbitrary depth and the polynomial is used as a calibration curve, the "unknown" depth is determined within 0.3 mm rms. A diode or a diode array, placed (for instance) in the rectum in conjunction with a rectal balloon, can potentially determine the WEPL at that point, just prior to treatment, with submillimeter accuracy, allowing the beam energy to be adjusted. The associated unwanted dose is about 0.2% of a typical single fraction treatment dose.

New spectral image compression method based on an optimal phase coding and the RMSduration principle

By using only phase information, this paper describes a new spectral lossy compressionmethod which can: reduce required memories; adaptively retrieve original images by usingonly spectral phase information; increase the peak-to-correlation energy (PCE) at theoutput of the correlator; and be easily employed in major encryption techniques. Toincrease the compression ratio of the proposed method, an optimal phase codingbased on ‘a fading grid’ is performed. In fact, a variable number of quantizationbits has been used to quantize phase information depending on the importanceof the spectral phases. The phase information could be classified according tothe concept of ‘RMS duration’. Many simulations have been carried out. Ourexperimental results corroborate the performance of the proposed new method.

Exploiting root-mean-square time-frequency structure for multiple-image optical compression and encryption

We report on an algorithm to compress and encrypt simultaneously multiple images (target images). This method, which is based upon a specific spectral multiplexing (fusion without overlapping) of the multiple images, aims to achieve a single encrypted image, at the output plane of our system, that contains all information needed to reconstruct the target images. For that purpose, we divide the Fourier plane of the image to transmit into two types of area, i.e., specific and common areas to each target image. A segmentation criterion taking into account the rms duration of each target image spectrum is proposed. This approach, which consists of merging the input target images together (in the Fourier plane) allows us to reduce the information to be stored and/or transmitted (compression) and induce noise on the output image (encryption). To achieve a good encryption level, a first key image (containing biometric information and providing the intellectual property of the target images) is used. A second encryption key is inserted in the Fourier plane to ensure a relevant phase distribution of the different merged spectra. We also discuss how the encoding information can be optimized by minimizing the number of bits required to encode each pixel.

PRODUCTION OF FEMTOSECOND PULSES AND MICRON BEAM SPOTS FOR HIGH BRIGHTNESS ELECTRON BEAM APPLICATIONS

Current and future applications of high brightness electron beams, which include advanced accelerators and beam-radiation interactions require both transverse and longitudinal beam sizes on the order of tens of microns. Ultra-high density beams may be produced at moderate energy (50 MeV) by compression and subsequent strong focusing of low emittance, photoinjector sources. We describe the implementation of this method used at the PLEIADES inverse-Compton scattering (ICS) x-ray source at LLNL in which the photoinjector-generated beam has been compressed to 300 fsec rms duration using the velocity bunching technique and focused to 20 μm rms size using an extremely high gradient, permanent magnet quadrupole focusing system.

The Relationship Between the Variance of Energy Estimates and the Uncertainty Parameter

The relationship between the uncertainty (4π times the product of rms duration, Dt, and rms bandwidth, Df) and the variance of energy estimates of random transients is examined. If a transient can be modeled with the product model, it is shown that for many cases the normalized error in the energy estimate, as measured by the uncertainty, is approximately the same as the normalized error determined from the more exact statistical duration and bandwidth. The uncertainty is a quantitative measure of the expected energy estimate errors. If the transient has a significant random component, a small uncertainty parameter implies a large error in the energy estimate. Attempts to resolve a time/frequency spectrum near the uncertainty limits of a transient with a significant random component will result in large errors in the spectral estimates.

The Variance of Energy Estimates for the Product Model

A product model, in which{x(t)}, is the product of a slowly varying random window,{w(t)}, and a stationary random process,{g(t)}, is defined. A single realization of the process will be defined asx(t). This is slightly different from the usual definition of the product model where the window is typically defined as deterministic. An estimate of the energy (the zero order temporal moment, only in special cases is this physical energy) of the random process,{x(t)}, is defined asm0=∫∞∞|x(t)|2dt=∫−∞∞|w(t)g(t)|2dtRelationships for the mean and variance of the energy estimates,m0, are then developed. It is shown that for many cases the uncertainty (4πtimes the product of rms duration,Dt, and rms bandwidth,Df) is approximately the inverse of the normalized variance of the energy. The uncertainty is a quantitative measure of the expected error in the energy estimate. If a transient has a significant random component, a small uncertainty parameter implies large error in the energy estimate. Attempts to resolve a time/frequency spectrum near the uncertainty limits of a transient with a significant random component will result in large errors in the spectral estimates.

Fourier limited micro-pulses in the OK-4/Duke storage ring FEL

The Super-modes are Fourier limited FEL micro-pulses predicted by Dattoli and Renieri in 1980. The OK-4 FEL at Duke, operating in the wavelength range from 193.7 nm to 730 nm, was the first to observe the Super-modes in a storage ring FEL in 1996. Since 1996, the up-graded diagnostics and improved control of the RF frequency allowed generation of Super-modes on a regular basis and systematic study of them. The Gaussian FEL micro-pulses with 1.3 ps RMS duration and Fourier limited RMS linewidth were generated in 1998–1999. In this paper we present the results of our studies and the comparison with theoretical predictions. We also present practical criteria for operating SR FELs with Super-modes.

Influence of phase self-modulation on the temporal characteristics of ultrashort pulses emitted by solid-state lasers

The kinetics of changes in the temporal profile and frequency modulation of pulses under conditions of phase self-modulation and allowing for the width of the gain profile was analyzed using a model which postulates that the fluctuation pattern of the radiation emitted by a passively mode-locked solid-state laser has the form of an intensity peak against a background which is constant over the resonator period. The rms duration and the half-height duration of the largest peak were compared and the fraction of the pulse energy in the largest peak was studied to analyze the degree of deformation of the pulse temporal profile. It was found that, for moderate values of the phase self-modulation parameters, ultrashort pulses with a small fraction of energy in the side satellites and almost linear chirp in the central peak can be generated by tuning the system to the second threshold in a train of giant pulses. For large phase self-modulation parameters, this can be achieved by using a spectrum-limiting filter in the resonator.

Influence of optical losses on the dynamics of nonlinear propagation of pulses in single-mode fiber waveguides

The results are reported of numerical experiments on nonlinear dynamics of ultrashort pulses in fiber waveguides. The quantitative criteria for a structural instability of solitons in such waveguides are derived. A study is made of the influence of the optical losses on the dynamics of formation and decay of bound soliton states in fiber waveguides. It is shown that the main contribution to the rms duration of a multisoliton pulse does not come from a narrow central peak but from the pedestal of the pulse, which gives rise to additional difficulties in the development of high-transmission-rate fiber-optic communication lines utilizing solitons.

Sample-whitened matched filters

A sample-whitened matched filter (SWMF) for a channel with intersymbol interference and additive white Gaussian noise is defined as a linear filter with the properties that its output samples are a sufficient statistic for the MAP estimation of the transmitted sequence and have uncorrelated noise components. These filters are shown to exist for ali realistic channels and the complete set of SWMF's for any channel is determined. It is shown that for nonpathological channels there is a unique SWMF which minimizes the amount of intersymbol interference defined as the discrete-time analog to the rms duration of a continuous-time signal. Finally, the theory is extended to more general modulation systems including pulse position modulation and frequency position modulation.