van der Mj Marnix Wiel

Linear and Nonlinear FEL-SEW Spectroscopic Characterization of Nanometer-Thick Films

The conditions of the existence and transformations of surface electromagnetic waves (SEWs) on metals (surface plasmons) and dielectrics (phonon-polaritons) are discussed. Interferometric SEW experiments provide the possibility for the direct determination of the real and imaginary parts of the dielectric constants at the frequencies in the tuning range of a free electron laser (FEL) without any preliminary models. The important role of the outstanding facilities of FEL—namely, the broad tuning range, high power, narrow bandwidth of emission, and well-collimated beam—in SEW experiments is outlined. It is demonstrated by the examples of the infrared absorption spectra of a Langmuir-Blodgett film on metal, of a metal oxide film, and of polymeric films of nanometer thicknesses on metals. Free surfaces of single-crystal CaF2 and the thin polymeric film were studied by an interferometric experiment for the optical constant determination. Nonlinear spectroscopic applications of the SEW-FEL technique to studies of a second harmonic generation (SHG)—the frequency dependence of efficiency, the angle dependence of SHG, and the influence of a thin-film deposition on a quartz surface—are described.

Front-to-end simulations of the design of a laser wakefield accelerator with external injection

We report the design of a laser wakefield accelerator (LWA) with external injection by a rf photogun and acceleration by a linear wakefield in a capillary discharge channel. The design process is complex due to the large number of intricately coupled free parameters. To alleviate this problem, we performed front-to-end simulations of the complete system. The tool we used was the general particle-tracking code, extended with a module representing the linear wakefield by a two-dimensional traveling wave with appropriate wavelength and amplitude. Given the limitations of existing technology for the longest discharge plasma wavelength (∼50μm) and shortest electron bunch length (∼100μm), we studied the regime in which the wakefield acts as slicer and buncher, while rejecting a large fraction of the injected bunch. The optimized parameters for the injected bunch are 10pC, 300fs at 6.7MeV, to be injected into a 70mm long channel at a plasma density of 7×1023m−3. A linear wakefield is generated by a 2TW laser foc...

Parameter study of acceleration of externally injected electrons in the linear laser wakefield regime

A parameter study for laser wakefield acceleration is presented, in which externally injected electrons are accelerated in low amplitude plasma waves, represented by an analytical two-dimensional description. Results have been obtained for plasma densities up to 2.6×1024m−3, plasma lengths up to 300mm, laser intensities up to 3.5×1021W∕m2, and injection of Gaussian model bunches at energies up to 12MeV. For the range of parameters studied, effects of laser depletion and the influence of the electron bunch on the plasma can be ignored. In the parameter space, a region is identified where final energies of over 100MeV are reached, at an energy spread of less than 5% and a rms emittance of a few micrometers.

Linear and nonlinear FEL–SEW spectroscopic characterization of nanometer-thick films

The conditions of the existence and transformations of surface electromagnetic waves (SEWs) on metals (surface plasmons) and dielectrics (phonon–polaritons) are discussed. Interferometric SEW experiments provide the possibility for the direct determination of the real and imaginary parts of the dielectric constants e at the frequencies in the tuning range of a free electron laser (FEL) without any preliminary e models. The important role of the outstanding facilities of the FEL, namely the broad tuning range, high power, narrow bandwidth of emission, well-collimated beam, in SEW experiments is outlined. It is demonstrated by the examples of the infrared absorption spectra of a Langmuir–Blodgett film on metal, of a metal oxide film and of polymeric films of nanometer thickness on metals. The free surfaces of some single crystals (CaF2, LiNbO3) and thin polymeric films were studied by an interferometric experiment for the optical constant determination. The nonlinear spectroscopy applications of the SEW–FEL technique to studies of a second harmonic generation (SHG) are described (the frequency dependence of efficiency, the angle dependence of SHG, and the influence of a thin film deposition on a quartz surface).

Mid-IR FEL user facility FELIX

The user facility FELIX (free electron laser for infrared experiments) was built to provide the scienti® c community with an intense tunable source for the mid-IR. After a construction and commissioning phase, the facility became operational in the beginning of 1994 and now delivers more than 3000 hours of beam time per year, 80% of which is meant for users from several disciplines such as physics, chemistry, biomedicine, etc. The spectral range covered extends presently from 2000 to 100 cm2 1, and an extension to 30 cm2 1 is planned for the near future. At a particular setting of the accelerator, the wavelength is scanned by changing the undulator gap. This way the wavelength can be continuously varied over a factor of 2 to 4 in about a minute. It can be controlled from within LABVIEW, a programming environment often used by users for data acquisition and control of their experimental setup.The relative merit of the use of the free electron laser for infrared experiments (FELIX) for spectroscopy is discussed and illustrated with some examples.