We consider the possibility of using a thin plasma slab as an optical element to both focus and compress an intense laser pulse. By thin we mean that the focal length is larger than the lens thickness. We derive analytic formulas for the spot size and pulse length evolution of a short laser pulse propagating through a thin uniform plasma lens. The formulas are compared to simulation results from two types of particle-in-cell code. The simulations give a greater final spot size and a shorter focal length than the analytic formulas. The difference arises from spherical aberrations in the lens which lead to the generation of higher-order vacuum Gaussian modes. The simulations also show that Raman side scattering can develop. A thin lens experiment could provide unequivocal evidence of relativistic self-focusing.
14With the successful operation of three 2.3 megapixel, 120Hz readout rate, hybrid pixel array detectors 15 at the Linac Coherent Light Source (LCLS), the SLAC National Accelerator Laboratory detector group is 16 now exploring additional applications based on the same detector platform. These megapixel cameras 17 are based on the Cornell-SLAC hybrid Pixel Array Detector (CSPAD). 18The CSPAD platform is developed around the CSPAD ASIC, a 36 kilopixel device, each pixel at 19 110x110μm 2 . Important characteristics of the CSPAD (room temperature operation, 14bit on chip 20 digitization with a purely digital data interface, and scaling modularity) make it an effective choice for 21 designing detector variants that are optimized for a range of experiments and applications. 22One of the first spin-off detectors based on this proven CSPAD platform is the CSPAD-140k: a 140 23 kilopixel detector, with an active area of approximately 4x4cm 2 and four ASICs, bundled in a small, 24 inexpensive and easy-to-deploy package. Due to its versatility it has already been used successfully in 25 several experiments at the CXI, XPP and XCS instruments at LCLS. The work also describes problems 26 faced by scaling from a prototype system to a full size x-ray camera and presents the current status on 27 the improvements achieved. 28 29
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Using a variational method, we show that an effective attractive force exists between two Gaussian laser beams in a plasma because of a mutual coupling from relativistic mass corrections. The effective force can be generalized to other nonlinearities. This force can cause two laser beams to spiral around each other with a rotation period that is proportional to the Rayleigh length. These orbits are stable if the ratio of the orbit diameter to the laser spot size d(0)/W(0)=sqrt[2]. Three-dimensional particle-in-cell simulations are presented which confirm the mutual attraction.
An approach for describing the evolution of short-pulse lasers propagating through underdense plasmas is presented. This approach is based upon the use of a variational principle. The starting point is an action integral of the form S[a,a(*),straight phi]=integrald(4)x L[a,a(*),straight phi, partial differential(&mgr;)a, partial differential(&mgr;)a(*), partial differential(&mgr;)straight phi] whose Euler-Lagrange equations recover the well-known weakly nonlinear coupled equations for the envelope of the laser's vector potential a, its complex conjugate a(*), and the plasma wave wakes' (real) potential straight phi. Substituting appropriate trial functions for a, a(*), and straight phi into the action and carrying out the integrald(2)x( perpendicular) integration provides a reduced action integral. Approximate equations of motion for the trial-function parameters (e. g., amplitudes, spot sizes, phases, centroid positions, and radii of curvature), valid to the degree of accuracy of the trial functions, can then be generated by treating the parameters as a new set of dependent variables and varying the action with respect to them. Using this approach, fully three-dimensional, nonlinear envelope equations are derived in the absence of dispersive terms. The stability of these equations is analyzed, and the growth rates for hosing and symmetric spot-size self-modulation, in the short-wavelength regime (k approximately omega(p)/c) are recovered. In addition, hosing and spot-size self-modulational instabilities for longer wavelength perturbations (k<
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