Single Pulse Spectrum Research Articles

Plasma high-current generator of wideband high-power microwaves with magnetic self-insulation

A plasma maser that does not use a strong magnetic field for transporting a relativistic highcurrent electron flow is calculated within the particle-in-cell model. Tuning of the average radiation frequency from 3 to 7GHz with a single pulse spectrum width of 2 to 3GHz is demonstrated. The power of a radiation pulse with a duration up to 70 ns is from 0.5 to 0.7GW at the efficiency of 4 to 6%.

Frequency-Comb Spectrum of Periodic-Patterned Signals.

Using arbitrary periodic pulse patterns we show the enhancement of specific frequencies in a frequency comb. The envelope of a regular frequency comb originates from equally spaced, identical pulses and mimics the single pulse spectrum. We investigated spectra originating from the periodic emission of pulse trains with gaps and individual pulse heights, which are commonly observed, for example, at high-repetition-rate free electron lasers, high power lasers, and synchrotrons. The ANKA synchrotron light source was filled with defined patterns of short electron bunches generating coherent synchrotron radiation in the terahertz range. We resolved the intensities of the frequency comb around 0.258THz using the heterodyne mixing spectroscopy with a resolution of down to 1Hz and provide a comprehensive theoretical description. Adjusting the electron's revolution frequency, a gapless spectrum can be recorded, improving the resolution by up to 7 and 5 orders of magnitude compared to FTIR and recent heterodyne measurements, respectively. The results imply avenues to optimize and increase the signal-to-noise ratio of specific frequencies in the emitted synchrotron radiation spectrum to enable novel ultrahigh resolution spectroscopy and metrology applications from the terahertz to the x-ray region.

Metabolic responses during hemodialysis determined by quantitative 1H NMR spectroscopy

A large proportion of patients with end-stage renal disease have lifelong hemodialysis (HD) treatment. HD rapidly and indiscriminately removes necessary small metabolites together with uremic toxins from plasma into dialysate. To investigate metabolic responses to HD, we determined the levels of metabolites through time-course monitoring of 1H NMR spectroscopy of dialysate during HD. The dialysate sample is stable for analysis because it contains only small metabolites without proteins. It was collected non-invasively from 9 HD patients with chronic glomerular nephropathy, at 6 time points during 4h of HD in 5 sessions. Creatinine, alanine, lactate, pyruvate and valine were simultaneously quantified on a one-dimensional single-pulse spectrum with a single standard compound. The concentration of creatinine exhibited monotonous decay with time, while that of valine decreased slowly and then maintained its levels throughout an HD. Lactate, alanine and pyruvate increased at 2–3h after the initiation of HD. They exhibited remarkable responses to HD with production from the body. The time-course of change in the 4 metabolites of lactate, pyruvate, alanine, and valine had reproducible behavior unique to each patient during the HD. This finding may be applied to distinguish metabolic status in HD patients.

Study of diamond film by dynamic nuclear polarization-enhanced13C nuclear magnetic resonance spectroscopy

Three chemical vapor deposited diamond films were studied by dynamic nuclear polarization (DNP)-enhanced high-resolution solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy. Enhanced C-13 direct-poiarization spectra of diamond Films were obtained by irradiating the samples with microwaves at or near electron spin resonance Larmor frequency of carbon center free radicals. No NMR signal for sp(2) hybridized carbons could be observed. From the Curve of the DNP enhancement as a function of Frequency, it is found that the dominant DNP mechanism is the solid-state effect. The C-13 cross-polarization spectrum, which is an evidence for existence of the proton defect in the lattice of diamond films, is much broader than the C-13 single Pulse spectrum. The reason is discussed shortly.

Broadband noise filtering in random sequences of coherent pulses using the temporal Talbot effect

The exact power spectrum of the detected optical envelope of a train of random pulses after the temporal Talbot effect is computed. The input train into a Talbot device consists of a sequence of chirped Gaussian pulses whose appearance in the train is probabilistic. Dispersion provides a Talbot replica of the original train. The resulting noise spectrum shows narrow spectral windows below a broadband output noise envelope. The noise-envelope width depends on the value of the chirp, coinciding with the single-pulse spectrum only if the pulses are unchirped. The locations and width of the spectral windows depend on the values of the chirp and the temporal width of the pulses in the train. For wide pulses, high output harmonics, and low dispersive devices, these windows are cosine-squared modulated. The properties of this modulation depend only on the statistics of the appearance of the pulses. © 2004 Optical Society of America

A two-axis goniometer for sensitivity enhancement in single-crystal nuclear magnetic resonance spectroscopy

The construction of a single-crystal nuclear magnetic resonance (NMR) probe with a new two-axis geometry for the goniometer has improved the sensitivity of the NMR response from small crystals. This allows studies of the smallest crystals used so far in single-crystal NMR. The goniometer of the probe uses only two different mountings of the crystal, and the rotation axis of the goniometer is tilted 45° with respect to the direction of the magnetic field. By moving the goniometer outside the radio frequency coil, the filling factor and the probe sensitivity increase. The improved sensitivity for the probe is illustrated by the P-{H1}31 cross-polarization spectrum of a 0.088 mm3 crystal of (NH4)2HPO4 and a Rb87 single-pulse spectrum of a 0.048 mm3 crystal of RbZn2(HPO4)PO4. Moreover, the capability to determine precise parameters for the solid-state NMR interactions using the new probe is demonstrated by Na23 and Rb87 single-crystal studies of NaNO3 and RbClO4.

Pile-up effect for a counting channel with amplitude selection and imposed non-cumulative dead time

The performance of radioactivity counting systems is limited by pile-up which causes counting losses, timing uncertainties and incorrect energy selection. The counting signals are either single pulses for which amplitude distribution is observable at low count rate, or more complex signals for which the amplitude distribution is, for the superposition of rectangular pulses, the self convolution of the single-pulse spectrum. Without amplitude selection, the effect on the count rate is small. It is the same as an extending dead time equal to the width of a single pulse. However, amplitude selection reveals a more important distortion. The output count rate has been derived for a single channel analyser followed by a non-cumulative dead time. These results are confirmed by computer simulations.

A technique for single-pulse spectrum and pulse width measurements for an IR-FEL

A diagnostic system has been designed to measure the spectrum and pulse width of infrared FEL pulses. Use of an image dissector [H.A. Baldis et al., Rev. Sci. Instr. 48 (1977) 173] and a single element high speed detector with integrating sphere, allows one to obtain spectral or temporal information for each individual mu-pulse inside the pulse train. The spectral diagnostic consists of a mode matching telescope, a high resolution spectrometer, an imaging telescope and an image dissector system. The imaging telescope between the spectrograph and the image dissector provides for variable magnification (and hence resolution) of the spectrum onto the image dissector. The pulse width measurement uses single pulse autocorrelation through noncollinear optical mixing in a frequency doubling crystal [S.A. Arakelian et al., Opt. Commun. 44 (1982) 67], an imaging telescope and again an image dissector system. Here, the imaging telescope relays the image of the region in the nonlinear crystal in which second harmonic light was generated onto the image dissector. The design and implementation of these diagnostics for the 1–11 μm on the IR-FEL at Stanford University are discussed.

Spectral characteristics of CVL pumped dye lasers

We have investigated the effect of changing the resonator length on the time-averaged and single pulse spectrum of a copper vapour laser pumped GIG dye laser oscillator. The time-averaged spectrum showed a well defined spectral profile and mode structure. However the single pulse spectrum was found to vary from pulse to pulse and showed strong gain competition and spatial hole burning effects. In addition it has been shown that there is an optimum position of the output mirror for which the laser linewidth is a minimum.