Papers by Anatoly Maksimchuk
Bulletin of the American Physical Society, 2016
PLASMAS GROUP TEAM-Presented here are data from a two-beam pump-probe experiment. We used synchro... more PLASMAS GROUP TEAM-Presented here are data from a two-beam pump-probe experiment. We used synchrotron-like X-rays created by betatron oscillations to probe a thin metal foil that is pumped by the secondary laser beam. The Hercules Ti:Sapphire laser facility was operated with a pulse duration of 34 fs and a power of 80 TW split. A 75-25 beam splitter was used to drive a laser wakefield accelerator and heat the secondary target. We observed opacity changes around the K-edge of thin aluminum foil as it was heated by an ultrafast pump laser. To understand how the opacity is changing with heating and expansion of the plasma, the delay between the two laser paths was adjusted on a femtosecond time scale from 50 to 400 fs. Experimental data for aluminum shows variation in opacity around the K-edge with changes in the probe delay. The transmitted synchrotron-like spectrum was measured using single photon counting on an X-ray CCD camera and was available on a shot-by-shot basis. The success of this work demonstrates a practical application for X-rays produced from betatron oscillations in a wakefield accelerator.
AIP Conference Proceedings, 2006
The acceleration of protons to therapeutic energies of over 200 MeV by short‐pulse, high‐intensit... more The acceleration of protons to therapeutic energies of over 200 MeV by short‐pulse, high‐intensity lasers requires very high temporal intensity contrast. We describe improvements to the contrast ratio of the laser pulse produced by a multi‐terawatt chirped pulsed amplification (CPA) Ti:sapphire laser for the application of proton acceleration. The modified cross‐polarized wave generation (XPW) technique has been implemented on the Hercules laser at the University of Michigan to reject the low‐intensity amplified spontaneous emission (ASE) preceding the main laser pulse. We demonstrate that by using two BaF2 crystals, the XPW technique yields a 10−11 contrast ratio between the main peak and the ASE for a 50 TW laser system which can be maintained up to 500 TW. Such contrast may be sufficient for a preplasma‐free interaction of 225 TW laser pulses with sub‐micron thick foils at an intensity of ∼1022 W/cm2. Particle‐in‐cell (PIC) simulations were conducted under the anticipated experimental conditions: 6.75 ...
日本物理学会講演概要集, Aug 21, 2007
2005 Quantum Electronics and Laser Science Conference
ABSTRACT
ABSTRACT Recent experimental results of laser wakefield acceleration (LWFA) of electrons and thei... more ABSTRACT Recent experimental results of laser wakefield acceleration (LWFA) of electrons and their subsequent radiation generation driven by the HERCULES laser with up to 200TW are presented. In LWFA, the plasma ``bubble'' structure forces trapped, off-axis electrons to undergo transverse oscillatory motion during acceleration, resulting in synchrotron-like betatron radiation in the keV X-ray regime. Measurements indicate that the beam source size can be as small as 1 micron and that the radiation exhibits spatial coherence, allowing phase-contrast imaging. Data from Cu K-α generated using an identical geometry are presented to give yield and source size comparisons. Alternatively, the high energy (>200 MeV) electron beam can be subsequently converted via Bremsstrahlung into low-divergence beams of high-energy photons and positrons. These photons are spectrally resolved using a Compton scattering-based, high-energy (30-80 MeV) photon spectrometer. All of these subsequent beams are presumed to retain the short-pulse characteristic of the electron beam, resulting in high peak flux, making the source an excellent candidate for ultrafast pump-probe applications in the keV and MeV photon range.
In recent experimental campaigns and computational surveys, high harmonic generation (HHG) has fo... more In recent experimental campaigns and computational surveys, high harmonic generation (HHG) has found applications as a diagnostic tool, revealing information regarding pre-plasma scale-length and in extension laser contrast [1], in addition to many applications such as a direct means by which to produce trains of attosecond pulses [2]: via filtering lower-ordered multiples of the fundamental frequency. Additional flexibility and utility may be derived by pre-shaping the target-area of the material undergoing irradiation on the micron scale, as the results of 2D PIC simulations carried out at the University of Michigan's High Field Science group imply. Specifically, micron-scale parabolic and spherically concave target geometries are investigated in regard to their ability to collimate and further refocus the reflected harmonic beam, respectively. Additionally, results are summarized from experimental investigations carried out at the same research facility with ultrafast, ultra-relativistic, and high-contrast pulses regarding the effect of the target's preplasma scale-length on the efficacy of the resultant reflected beam's harmonic content. [1] F. Dollar, et al.,
Laser Wakefield Acceleration in the bubble regime can be used to accelerate electrons to GeV ener... more Laser Wakefield Acceleration in the bubble regime can be used to accelerate electrons to GeV energies while simultaneously wiggling them to produce a synchotron like x-ray radiation. Using HERCULES, a 100TW TiSapphire laser, 30fs pulses are focused onto a 5mm He gas jet to accelerate electrons in the bubble regime. The betatron x-rays produced by the transverse motion of the accelerated electrons are focused onto a detector by a spherically curved quartz, and other crystals. This result shows the feasibility of dynamic studies of crystal diffraction, with femtosecond level accuracy, using pump probe techniques.
High Field Interactions and Short Wavelength Generation
Short-pulse high-intensity lasers interacting with solid targets make possible the study of a new... more Short-pulse high-intensity lasers interacting with solid targets make possible the study of a new class of plasmas.1 They are unique because during the ultrashort laser pulse relatively little expansion occurs and the density scale length remains much less than the laser wavelength. This makes possible the deposition of a significant amount of the laser energy at densities much greater than the critical density, which is then efficiently converted into heat, ionization, and subsequently x ray emission, either through de-excitation or recombination. The x-ray pulse will be extremely bright because of the high density, the small dimensions of the laser spot size, and the ultrashort x-ray pulse width. The latter is due to rapid cooling by expansion and diffusion, which results from the steep temperature and density gradients, and the high collision rates at high density. These bright compact ultrashort- pulse x-rays have applications in time-resolved diffraction, holography, spectrosco...
AIP Conference Proceedings, 1995
Short-pulse, high-intensity laser-plasma interactions are investigated experimentally with tempor... more 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 < 5 x 1017 W/cm 2) and pulse widths (r~ ~ 400 fs). With low contrast (105), the x-ray spectrum in the ,~ = 40-100/~ spectral region is dominated by line emission, and the x-ray pulse duration is found to be long, r~ > 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 (10 l~ is used. It is demonstrated experimentally that the pulsewidth of laser-produced x-ray radiation may be varied down to the picosecond timescale 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 assumed.
called betatron radiation. Using HERCULES, a 100TW TiSapphire laser, 30fs pulses were focused ont... more called betatron radiation. Using HERCULES, a 100TW TiSapphire laser, 30fs pulses were focused onto a gas jet to accelerate electrons in the bubble regime. The spatially coherent betatron radiation produced by the transverse motion of the accelerated electrons was used for phase contrast imaging of custom fabricated samples. The fabricated samples were built to contain edges for phase contrast, while keeping the material thickness constant in order to eliminate signal variation from x-ray absorption. Two detectors were implemented to produce images at different x-ray energies. Direct detection on an x-ray CCD was used in the lower energy regime (1keV-15keV), while a fiber-coupled scintillator was used to image the higher energy x-rays (3keV-60keV). Additionally, phase contrast imaging in both self-injection and ionization-induced injection cases was compared.
SPIE Proceedings, 1997
ABSTRACT
Plasma Physics Reports, 2004
This paper reviews the many recent advances at the Center for Ultrafast Optical Science (CUOS) at... more This paper reviews the many recent advances at the Center for Ultrafast Optical Science (CUOS) at the University of Michigan in multi-MeV ion beam generation from the interaction of short laser pulses focused onto thin foil targets at intensities ranging from 10 17 to 10 19 W/cm 2. Ion beam characteristics were studied by changing the laser intensity, laser wavelength, target material, and by depositing a well-absorbed coating. We manipulated the proton beam divergence using shaped targets and observed nuclear transformation induced by high-energy protons and deuterons. Qualitative theoretical approaches and fully relativistic two-dimensional particle-in-cell simulations modeled energetic ion generation. Comparison with experiments sheds light on ion energy spectra for multi-species plasma, the dependences of ion-energy on preplasma scale length and solid density plasma thickness, and laser-triggered isotope yield. Theoretical predictions are also made with the aim of studying ion generation for high-power lasers with the energies expected in the near future, and for the relativistic intensity table-top laser, a prototype of which is already in operation at CUOS in the limits of severalcycle pulse duration and a single-wavelength spot size.
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Papers by Anatoly Maksimchuk