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Showing papers by "Dino A. Jaroszynski published in 1997"


Journal ArticleDOI
TL;DR: It is demonstrated that superradiance (SR) is a general feature of free-electron-laser (FEL) devices, incuding high gain amplifiers as well as low gain oscillators, and that SR pulses and spiking, due to synchrotron instabilities, have the same origin.
Abstract: We demonstrate that superradiance (SR) is a general feature of free-electron-laser (FEL) devices, incuding high gain amplifiers as well as low gain oscillators, and that SR pulses and spiking, due to synchrotron instabilities, have the same origin. In particular, we present a direct observation of SR from an FEL oscillator. The ultrashort SR pulses are characterized by a peak intensity and pulse duration which depend, respectively, on the square and the inverse square root of the electron current. The spectral brightness, $B$, defined as the ratio between the efficiency and the relative rms spectral width, is constant and equal to $0.86$.

54 citations


Journal ArticleDOI
TL;DR: In this paper, self-amplified spontaneous emission emitted by a relativistic electron beam passing through an undulator for the first time in the mid-infrared was analyzed.
Abstract: We have produced and analyzed self-amplified spontaneous emission emitted by a relativistic electron beam passing through an undulator for the first time in the mid-infrared. The spectral behavior of the line exhibits an unexpected growth at the start-up of the process.

33 citations


Journal ArticleDOI
01 Jul 1997
TL;DR: In this paper, a short-pulse free-electron laser (FEL) oscillator with superradiance has been experimentally studied, and the authors have measured the efficiency, optical pulse energy, pulse duration and spectral width as functions of electron beam current and cavity loss for the optimum cavity length detuning.
Abstract: Superradiance has been experimentally studied, in a short-pulse free-electron laser (FEL) oscillator. Superradiance is the optimal way of extracting optical radiation from an FEL and can be characterised by the following scale laws: peak optical power P, scales as the square of electron charge, Q, (P, proportional to Q(2)); the optical pulse duration, sigma(z), scales as the inverse of the square root of the charge, (sigma(z) proportional to 1/root Q); the efficiency, eta, scales as the inverse of optical pulse length (eta proportional to 1/sigma(z) proportional to root Q), which also implies that the relative spectral brightness defined by eta/(sigma(lambda)/lambda) remains constant and close to 0.86. To characterise the properties of the superradiant emission, we have measured the efficiency, optical pulse energy, pulse duration and spectral width as functions of electron beam current and cavity loss for the optimum cavity length detuning. The efficiency has been deduced from measurements of electron beam energy spectra. The optical pulse duration has been determined from second-order autocorrelation measurements and the optical spectra determined using a grating spectrometer. We show that the superradiance in the oscillator has properties similar to that in a high-gain amplifier and discuss the links with spikes created by synchrotron instabilities.

7 citations


Proceedings ArticleDOI
01 Jun 1997
TL;DR: In this paper, the authors show that SR in the oscillator has analogous properties to that in a high gain amplifier and discuss the relevance of these analogies to the X-ray FEL starting from self-amplifie.
Abstract: Superradiance (SR) in the short pulse free-electron laser (FEL oscillator is the optimal way of extracting optical radiation from an electron beam SR is characterized by a peak intracavity optical power, P, scaling as the square of the electron charge, Q, (P∝Q2), an optical pulse duration, σz, scaling inversely with the square root of the charge, (σ2∝Q−1/2) and an efficiency, η, scaling with the inverse of optical pulse length (η∝1/σz∝Q1/2) The latter scaling also implies that the relative spectral brightness, η/(σλ/λ), is constant and close to ∛/2 Similar scaling of the peak power, temporal width, energy and efficiency with the cavity quality factor also exist The efficiency in SR emission is enhanced above the usual natural efficiency, η=1/2Nu, for the weakly saturated CW FEL, where Nu is the number of undulator periods We show that SR in the oscillator has analogous properties to that in a high gain amplifier and discuss the relevance of these analogies to the X-ray FEL starting from self-amplifie

4 citations


Journal ArticleDOI
01 Oct 1997
TL;DR: In this article, room temperature pump-probe transmission experiments have been performed on arsenic-rich InAs/InAs/sub 1-x/Sb/sub x/ strained layer superlattices (SLS) using a picosecond far-infrared free electron laser.
Abstract: Room temperature pump-probe transmission experiments have been performed on arsenic-rich InAs/InAs/sub 1-x/Sb/sub x/ strained layer superlattices (SLS) using a picosecond far-infrared free electron laser. With excitation frequencies well above the fundamental bandgap, near 10 /spl mu/m, large excited carrier concentrations were obtained, allowing the density dependence of the recombination rate to be determined directly. The results have been interpreted in terms of an 8/spl times/8 (k.p) SLS energy band calculation, including the full dispersion for both k in-plane and k parallel to the growth direction. A comparison with identical measurements on epilayers of InSb, of comparable room temperature bandgap, shows that Auger processes have been substantially suppressed in the superlattices, In the non-degenerate regime, where the Auger lifetime scales as /spl tau//sub aug//sup -1/=C/sub 1/N/sub e//sup 2/ a value of C/sub 1/ between 10 and 100 times smaller is obtained for the SLS structures.

3 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the temporal overlap between single-frequency micropulses in a two-color free-electron laser and found that the average separation appears to be related to the slippage length between the electrons and light when passing through the undulator.
Abstract: By using sum-frequency generation in a Michelson arrangement, we have directly measured the temporal overlap between single-frequency micropulses in a two-color free-electron laser. As expected, the average separation appears to be related to the slippage length between the electrons and light when passing through the undulator. The two colors are then partly simultaneous, although there is not necessarily two-frequency bunching in the electron beam.

3 citations


Journal ArticleDOI
TL;DR: In this article, a spectral analysis of the self-amplified spontaneous emission (SASE) was carried out in the start-up regime of SASE, far from the saturation level.
Abstract: A solution has been proposed about ten years ago to reach the X-ray range: the principle is to operate the FEL in the Self-Amplified Spontaneous Emission (SASE) configuration. In the high gain regime, the spontaneous emission is amplified along the undulator in a single pass configuration and without optical cavity. We report here the observation of SASE at the shortest wavelength, the mid-infrared range. A spectral analysis of the SASE has been carried-out in the start-up regime of SASE, far from the saturation level.