Efficient picosecond x-ray pulse generation from plasmas in the radiation dominated regime (original) (raw)
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X-ray sources based on subpicosecond-laser-produced plasmas
Journal of X-Ray Science and Technology, 1994
The production of an efficient user friendly ultrafast x-ray source requires an understanding of the role of the various factors which aflbct the x-ray emission. Here we examine several issues which control the source brightness and the pulse duration. Picosecond timeresolved, high spectral resolution spectroscopy is used to study plasmas produced by a subpicosecond laser pulse with intensity between 1016 W/cm 2 and 5 × 10 TM W/cm 2.
Absolute keV X-ray yields from intense, ultrashort laser driven solid plasmas
Optics Communications, 1998
Absolute yields of characteristic X-ray emission from solids irradiated by picosecond laser pulses are measured in a novel manner using a simple solid state detector. The crucial role of photon statistics in estimating X-ray yields is pointed out. We have obtained an efficiency of 1.0 × 10 -9 for energy conversion into the K X-ray of aluminium at 3.0 × 10 13 W cm -2. The spectral resolution of the detector enables the measurement of the energy shift of the characteristic X-rays signifying the existence of highly charged ions.
Picosecond soft-x-ray source from subpicosecond laser-produced plasmas
Journal of The Optical Society of America B-optical Physics - J OPT SOC AM B-OPT PHYSICS, 1996
Short-pulse high-intensity laser-plasma interactions are investigated experimentally with temporally and spectrally resolved soft-x-ray diagnostics. We demonstrate that, by adjustment of the incident laser flux, the pulse width of the laser-produced x rays emitted from solid targets may be varied to as short as the picosecond time scale. Bright, picosecond, broadband emission characteristic of a short-scale-length high-density plasma is produced only when a high laser contrast (1010) is used. The results are found to be in qualitative agreement with both the predictions of a simple model of radiation from a collisionally dominated atomic system and the results obtained from a numerical simulation. 52.40.Nk.
Quantum Electronics, 2000
The effect of intensity, length, and wavelength of an ultrashort laser pulse on the formation of a hot electron component in a dense laser-produced plasma was first investigated in a single experiment. For a pulse length of 1 ps (or 200 fs, but with an energy contrast ratio of $ 20), it was shown that the principal mechanism of generation of hot electrons is the resonance absorption of laser radiation and that the temperature of hot electrons depends on the laser pulse intensity I and the wavelength l as T h $ (I l 2) 1a3. The homogenisation of the nanostructures of porous silicon due to a poor contrast ratio or a long duration (1 ps) of the laser pulse lowers the yield of hard x-ray radiation compared to the case of high-contrast 200-fs pulses.
Bright picosecond x-rays from intense sub-picosecond laser-plasma interactions
1995
Short-pulse, high-intensity laser-plasma interactions are investigated experimentally with temporally and spectrally resolved soft x-ray diagnostics. The emitted x-ray spectra from solid targets of various Z are characterized for a range of laser intensities (I~100 ps, characteristic of a long-scale-length, low-density plasma. Bright, picosecond, continuum emission, characteristic of a short-scalelength, high-density plasma, is produced only when a high laser contrast (1010) is used. It is demonstrated experimentally that the pulsewidth of laser-produced x-ray radiation may be varied down to the picosecond time-scale by adjusting the incident ultrashort-pulse laser flux. This controls the peak electron temperature relative to the ionization potential, corresponding to the emitted x-ray photon energy of interest. The results are found to be consistent with the predictions of a hydrodynamics code coupled to an average atom model only if non-local thermodynamic equilibrium (NLTE) is as...
Petawatt, picosecond laser pulses offer rich opportunities in generating synchrotron x-rays. This paper concentrates on the regimes accessible with the PETAL laser, which is a part of the Laser Megajoule (LMJ) facility. We explore two physically distinct scenarios through Particle-in-Cell simulations. The first one realizes in a dense plasma, such that the period of electron Langmuir oscillations is much shorter than the pulse duration. Hallmarks of this regime are longitudinal breakup (" self-modulation ") of the picosecond-scale laser pulse and excitation of a rapidly evolving broken plasma wake. It is found that electron beams with a charge of several tens of nC can be obtained, with a quasi-Maxwellian energy distribution extending to a few-GeV level. In the second scenario, at lower plasma densities, the pulse is shorter than the electron plasma period. The pulse blows out plasma electrons, creating a single accelerating cavity, while injection on the density downramp creates a nC quasi-monoenergetic electron bunch within the cavity. This bunch accelerates without degradation beyond 1 GeV. The x-ray sources in the self-modulated regime offer a high number of photons (∼10^12) with the slowly decaying energy spectra extending beyond 60 keV. In turn, quasimonoenergetic character of the electron beam in the blowout regime results in the synchrotron-like spectra with the critical energy around 10 MeV and a number of photons > 10^9. Yet, much smaller source duration and transverse size increase the x-ray brilliance by more than an order of magnitude against the self-modulated case, also favoring high spatial and temporal resolution in x-ray imaging. In all explored cases, accelerated electrons emit synchrotron x-rays of high brilliance, B > 10^20 photons/s/mm^2/mrad^2/0.1%BW. Synchrotron sources driven by picosecond kilojoule lasers may thus find an application in x-ray diagnostics on such facilities such as the LMJ or National Ignition Facility (NIF).
Relativistic plasma nanophotonics for ultrahigh energy density physics
Nature Photonics, 2013
The heating of dense matter to extreme temperatures motivates the development of powerful lasers 1-4 . However, the barrier the critical electron density imposes to light penetration into ionized materials results in the deposition of most of the laser energy into a thin surface layer at typically only 0.1% of solid density. Here, we demonstrate that trapping of femtosecond laser pulses of relativistic intensity deep within ordered nanowire arrays can volumetrically heat dense matter into a new ultrahot plasma regime. Electron densities nearly 100 times greater than the typical critical density and multi-keV temperatures are achieved using laser pulses of only 0.5 J energy. We obtained extraordinarily high degrees of ionization (for example, 52 times ionized Au) and gigabar pressures only exceeded in the central hot spot of highly compressed thermonuclear fusion plasmas. Scaling to higher laser intensities promises to create plasmas with temperatures and pressures approaching those in the centre of the Sun.
Enhancement of x-ray line emission from plasmas produced by short high-intensity laser double pulses
Physical Review E, 2002
Femtosecond laser-produced plasmas are bright ultrafast line x-ray sources potentially suitable for different applications including material science and biology. The conversion efficiency of the laser energy incident onto a solid target into the x-ray emission is significantly enhanced when a laser prepulse precedes the main pulse. The details of x-ray line emission from solid targets irradiated by a pair of ultrashort laser pulses are investigated both theoretically and experimentally. Insight into spatial and temporal characteristics of the line x-ray source is provided by numerical simulations and a simplified analytical model. Optimal time separation of the laser pulses is searched for in order to reach the maximum conversion of laser energy into the emission of selected x-ray lines. We deduced how the optimal pulse separation scales with laser and target parameters.