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Your search keyword '"Xu, M. H."' showing total 4 results
Start Over Author "Xu, M. H." Topic proton beams
4 results on '"Xu, M. H."'

1. Effects of laser prepulse on proton generation: active manipulation of the distribution of laser accelerated proton beams.

Author

Batani, D., Redaelli, R., Dezulian, R., Lundh, O., Lindau, F., Persson, A., Osvay, K., Wahlström, C.-G., Carroll, D. C., McKenna, P., Bandyopadhyay, S., Pepler, D., Neely, D., Kar, S., Simpson, P. T., Markey, K., Zepf, M., Xu, M. H., and Li, Y. T.

Subjects
PROTON beams, LASER beams, LASERS, PROTONS, SHOCK wave diffraction
Abstract

Laser pre-pulse is a major issue in experiments on laser-generation of protons, often limiting the performances of laser sources. In this paper, we show how we can actively use a low intensity prepulse (<1013 W/cm2, ns duration) to manipulate the proton beam direction or spatial energy distribution. The prepulse is focused onto the front surface of a thin foil before the arrival of the high intensity pulse (≈1019 W/cm2, ps duration). Under oblique high-intensity irradiation and for low prepulse intensities, the proton beam is directed away from the target normal. Deviation is towards the laser forward direction, with an angle that increases with the level and duration of the ASE pedestal. Also, for a given laser pulse, beam deviation increases with proton energy. The observations are discussed in terms of Target Normal Sheath Acceleration, in combination with a laser-controllable shock wave locally deforming the target surface. Results obtained with an annular intensity distribution of the prepulse show smooth proton beams with a sharp circular boundary at all energies. Potential mechanisms to explain the observations are discussed. [ABSTRACT FROM AUTHOR]

Published
2008
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2. Angle-dependent modulated spectral peaks of proton beams generated in ultrashort intense laser-solid interactions.

Author

Su, L. N., Hu, Z. D., Zheng, Y., Liu, M., Li, Y. T., Wang, W. M., Sheng, Z. M., Yuan, X. H., Xu, M. H., Shen, Z. W., Fan, H. T., Chen, L. M., Lu, X., Ma, J. L., Wang, X., Wang, Z. H., Wei, Z. Y., and Zhang, J.

Subjects
ELECTRONIC modulation, PROTON beams, ULTRASHORT laser pulses, ALUMINUM foil, SPECTROMETERS
Abstract

Proton acceleration from 4 im thick aluminum foils irradiated by 30-TW Ti:sapphire laser pulses is investigated using an angle-resolved proton energy spectrometer. We find that a modulated spectral peak at ~0.82 MeV is presented at 2.5° off the target normal direction. The divergence angle of the modulated zone is 3.8°. Two-dimensional particle-in-cell simulations reveal that self-generated toroidal magnetic field at the rear surface of the target foil is responsible for the modulated spectral feature. The field deflects the low energy protons, resulting in the modulated energy spectrum with certain peaks. [ABSTRACT FROM AUTHOR]

Published
2014
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3. Enhancement of ion generation in femtosecond ultraintense laser-foil interactions by defocusing.

Author

Xu, M. H., Li, Y. T., Carroll, D. C., Foster, P. S., Hawkes, S., Kar, S., Liu, F., Markey, K., McKenna, P., Streeter, M. J. V., Spindloe, C., Sheng, Z. M., Wahlström, C.-G., Zepf, M., Zheng, J., Zhang, J., and Neely, D.

Subjects
*FEMTOSECOND lasers research, *PROTON beams, *ULTRASHORT laser pulses, *PROTONS, *IONS
Abstract

A simple method to enhance ion generation with femtosecond ultraintense lasers is demonstrated experimentally by defocusing laser beams on target surface. When the laser is optimally defocused, we find that the population of medium and low energy protons from ultra-thin foils is increased significantly while the proton cutoff energy is almost unchanged. In this way, the total proton yield can be enhanced by more than 1 order, even though the peak laser intensity drops. The depression of the amplified spontaneous emission (ASE) effect and the population increase of moderate-energy electrons are believed to be the main reasons for the effective enhancement. [ABSTRACT FROM AUTHOR]

Published
2012
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4. Effects of shock waves on spatial distribution of proton beams in ultrashort laser-foil interactions.

Author

Xu, M. H., Li, Y. T., Yuan, X. H., Yu, Q. Z., Wang, S. J., Zhao, W., Wen, X. L., Wang, G. C., Jiao, C. Y., He, Y. L., Zhang, S. G., Wang, X. X., Huang, W. Z., Gu, Y. Q., and Zhang, J.

Subjects
*PROTON beams, *SHOCK waves, *ULTRASHORT laser pulses, *HYDRODYNAMICS, *PLASMA lasers, *ELECTRIC fields, *ION bombardment, *METAL foils
Abstract

The characteristics of proton beam generated in the interaction of an ultrashort laser pulse with a large prepulse with solid foils are experimentally investigated. It is found that the proton beam emitted from the rear surface is not well collimated, and a “ring-like” structure with some “burst-like” angular modulation is presented in the spatial distribution. The divergence of the proton beam reduces significantly when the laser intensity is decreased. The “burst-like” modulation gradually fades out for the thicker target. It is believed that the large divergence angle and the modulated ring structure are caused by the shock wave induced by the large laser prepulse. A one-dimensional hydrodynamic code, MED103, is used to simulate the behavior of the shock wave produced by the prepulse. The simulation indicates that the rear surface of the foil target is significantly modified by the shock wave, consequently resulting in the experimental observations. [ABSTRACT FROM AUTHOR]

Published
2006
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