The modeling of a Gaussian beam focused by a lens in air is presented assuming its waist is located at the lens. We study the nonlinear focal shift for ultraintense light beams where the Kerr effect is unavoidable. The modeling assumes that the propagation of the beam through the lens is linear and that the Kerr effect only becomes evident near the focal region of the lens. We will show that this approximation is valid for thin focusing lenses with a Fresnel number Nω > 8.17 and a truncation parameter α > 12.76. Under this approximation, we show that for input powers below the critical power, there is a shift of the focal point and that the nonlinear focal point moves further away from the lens as the input power increases.
The development of laser driven plasma accelerators with high average power in solids requires simple and robust autofocus systems to determine, with accuracy, the focal position with respect to a rapidly refreshing target. Trial-and-error processes used in single shot experiment are not useful in this scenario. In this work we present a passive pre-alignment procedure to calibrate an autofocus setup, for fast refreshing solid target system, based on an astigmatic optical system. The calibration technique uses a hard aperture and a photodetector, located at the target position, to find the focal point with an experimental error, standard deviation, of less than 5 μm, which represents our translation stage resolution, achieved for a Rayleigh length of 35 μm. A geometrical analysis and numerical simulation have been done to demonstrate the effectiveness of the calibration technique and the accuracy of the astigmatic autofocus system. System accuracy can be improved with a better resolution of the translation stage.
Development of laser-plasma X-ray sources provides a new route to high brightness and small source size somewhere in the middle of low cost micro-focus X-rays and large scale synchrotron facilities. We explore one application of this new type of sources with emphasis on the stability of the source at high repetition rate and the advantage over similar conventional sources. In this paper we report the development and application of a micro-focus X-ray source for phase contrast imaging. The X-ray source produced at the Laser Laboratory for Acceleration and Applications (L2A2) of the University of Santiago de Compostela (USC), is made by focusing a 1 mJ, 35 fs, 1kHz pulses at 800 nm wavelength on metallic plates close to the diffraction limit. The X-ray spectra of this source are characterized by the K-α peaks which can be 'tuned' by changing the target material and a Bremsstrahlung continuum up to several tens of keV. The stability of the source is achieved by optimizing the positioning system of the metallic target which refresh and keep the surface within the small the Rayleigh length allowing the development of applications.
Non linear propagation of ultra short pulses in air is studied. By preparing an initial field distribution by an amplitude mask we can obtain a Townes soliton[1] (self similar channel of coherent radiation) in air. Experimental observation can be described accurately by the numerical integration of the Non Linear Schroedinger Equation (NLSE) and allow us to explain the origin of the remarkable stability of this soliton as a balance between diffraction and Kerr effect. We further explore on the role of coherence by revisiting the two slit Young's experiment but now in the non linear regime.
In the non-relativistic limit, the dynamics of the interaction of light with matter is described via a Hamiltonian
that does not include spin operators. However, the actual spin configuration of the interacting particles still
plays a fundamental role, via the Pauli's exclusion principle, by forcing a particular symmetry of the spatial
part of the wavefunction. In this paper we analyze the role of symmetry in the process of ionization of two and
three-electron atoms.
We report the observation of self-guided propagation of 120 fs, 0.56 mJ infrared pulse in air for distances greater
than a meter (more than thirty Rayleigh Lengths). The numerical simulations demonstrates the this localized
structure corresponds to a Townes soliton, specially stable under these conditions.
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