Showing papers by "Dino A. Jaroszynski published in 2008"

A compact synchrotron radiation source driven by a laser-plasma wakefield accelerator

Abstract: Ultrashort light pulses are powerful tools for time-resolved studies of molecular and atomic dynamics1. They arise in the visible and infrared range from femtosecond lasers2, and at shorter wavelengths, in the ultraviolet and X-ray range, from synchrotron sources3 and free-electron lasers4. Recent progress in laser wakefield accelerators has resulted in electron beams with energies from tens of mega-electron volts (refs 5,6,7) to more than 1 GeV within a few centimetres8, with pulse durations predicted to be several femtoseconds9. The enormous progress in improving beam quality and stability5,6,7,8,10 makes them serious candidates for driving the next generation of ultracompact light sources11. Here, we demonstrate the first successful combination of a laser-plasma wakefield accelerator, producing 55–75 MeV electron bunches, with an undulator to generate visible synchrotron radiation. By demonstrating the wavelength scaling with energy, and narrow-bandwidth spectra, we show the potential for ultracompact and versatile laser-based radiation sources from the infrared to X-ray energies.

Pulse-duration dependency of femtosecond laser refractive index modification in poly(methyl methacrylate).

Abstract: Refractive index modification of pure poly(methyl methacrylate) (PMMA) is investigated as a function of pulse duration using femtosecond lasers at 800 and 387 nm wavelength. It is observed that at 800 nm, the refractive index is modified more efficiently as the pulse duration decreases below 100 fs, whereas at 387 nm, efficient index modification is accomplished with longer, 180 fs pulses. Results suggest that three- and two-photon absorption is responsible for modification of pure PMMA at 800 nm and 387 nm, respectively. Repeated irradiation with short pulses of low laser fluence allows control of the photomodification via incubation, thus reducing bulk damage.

Monoenergetic Electronic Beam Production Using Dual Collinear Laser Pulses

Abstract: The production of monoenergetic electron beams by two copropagating ultrashort laser pulses is investigated both by experiment and using particle-in-cell simulations. By proper timing between guiding and driver pulses, a high-amplitude plasma wave is generated and sustained for longer than is possible with either of the laser pulses individually, due to plasma waveguiding of the driver by the guiding pulse. The growth of the plasma wave is inferred by the measurement of monoenergetic electron beams with low divergence that are not measured by using either of the pulses individually. This scheme can be easily implemented and may allow more control of the interaction than is available to the single pulse scheme.

Quantum path contribution to high-order harmonic spectra

Abstract: Ultrashort pulses of uv and soft x-ray radiation with durations ranging from femtoseconds to attoseconds can be produced as high-order harmonics of the fundamental frequency of a laser beam focused into gas. Applications to fields such as spectroscopy and attosecond metrology require the control and characterization of spectral and spatial properties of the emitted radiation. These are determined by both single atom and macroscopic response of the interaction medium to the laser field. Here we present evidence that microscopic effects have a larger influence than previously thought, and can induce a splitting and a frequency shift of the harmonic lines. These results not only offer a direct diagnostic for high-order harmonic generation, but also enable us to better tune the parameters of the produced radiation, while giving a deeper insight into the fundamental physics underlying this nonlinear optical process.

Propagation of a Short Intense Laser Pulse in a Curved Plasma Channel

Abstract: In this paper, the propagation of a short intense laser pulse in a curved plasma channel is considered. The effects of the shape of the plasma density profile and feedback from the wakefield on the pulse envelope dynamics are studied, with particular attention being paid to the conditions for avoiding laser spot size and centroid oscillations. A possible application to laser wakefield acceleration in the nonlinear regime is discussed.

Synchrotron radiation from laser-accelerated monoenergetic electron beams

Abstract: In this paper, we report on the generation of incoherent synchrotron radiation in the visible spectral range which is produced by laser-accelerated electrons with 55-75-MeV energy as they propagate through an undulator. Simultaneous detection of electron and photon spectra allows for precise comparison between experimental results and undulator theory. First- and second-order undulator radiation was detected. The agreement between experiment and theory and the exclusion of other effects proves that the observed radiation is generated in the undulator. Beyond that, this experiment introduces laser-accelerated electrons into the radio-frequency accelerator domain of synchrotron light sources. This marks a noticeable step toward a new, compact, and brilliant short-wavelength light source.

Limits of validity of photon-in-cell simulation techniques

Abstract: A comparison is made between two reduced models for studying laser propagation in underdense plasma; namely, photon kinetic theory and the slowly varying envelope approximation. Photon kinetic theory is a wave-kinetic description of the electromagnetic field where the motion of quasiparticles in photon coordinate-wave number phase space is described by the ray-tracing equations. Numerically, the photon kinetic theory is implemented with standard particle-in-cell techniques, which results in a so-called photon-in-cell code. For all the examples presented in this paper, the slowly varying envelope approximation is accurate and therefore discrepancies indicate the failure of photon kinetic approximation for these cases. Possible remedies for this failure are discussed at the end of the paper.