Anthony R. Valenzuela

High harmonic generation in relativistic laser–plasma interaction

High harmonics generated due to the scattering of relativistic electrons from high intensity laser light is studied. The experiments are carried out with an Nd:Glass laser system with a peak intensity of 2×1018 W cm−2 in underdense plasma. It is shown that, at high intensities, when the normalized electric field approaches unity, in addition to the conventional atomic harmonics from bound electrons there is significant contribution to the harmonic spectrum from free electrons. The characteristic signatures of this are found to be the emission of even order harmonics, linear dependence on the electron density, significant amount of harmonics even with circular polarization and a much smaller spatial region over which these harmonics are produced as compared to the atomic case. Imaging of the harmonic beam shows that it is emitted in a narrow cone with a divergence of 2 to 3 degrees.

High-harmonic generation in plasmas from relativistic laser-electron scattering

Results are presented on the generation of high harmonics through the scattering of relativistic electrons from high-intensity laser light. The characteristic signatures of this process are found to be the emission of even-order harmonics, linear dependence on the electron density, significant amount of harmonics with circular polarization, and small spatial extent of the source. The harmonics are emitted as a forward-directed beam with a divergence of 2°–3°. The measured spatial profile of the harmonics is in excellent agreement with calculations that assume that relativistic electrons play a significant part in the scattering process.

High-harmonic generation in plasmas by relativistic Thomson scattering

Results are presented on the generation of high harmonics due to the scattering of relativistic electrons from high-intensity laser light. The experiments are carried out with a Nd:glass laser system with a peak intensity of 1019 W cm-2 in underdense He, N2 and Ar plasma. It is shown that, at high intensities when the normalized electric field approaches unity, in addition to the conventional atomic harmonics from bound electrons, there is significant contribution to the harmonic spectrum from free electrons. The characteristic signatures of this are found to be the emission of even-order harmonics, a linear dependence on the electron density, a significant amount of harmonics even with circular polarization and a much smaller spatial region over which these harmonics are produced as compared to the atomic case. Imaging of the harmonic beam shows that it is emitted in a narrow cone with a divergence of 2-3°. The measured spatial profile of the harmonics is shown to be in excellent agreement with calculations, which assume that electrons with relativistic energies play a significant part in the scattering process.

Developments in Relativistic Nonlinear Optics

We report recent results of experiments and simulations in the regime of peak laser intensities above 1019 W/cm2, including the following topics: (1) electron and proton acceleration to energies in excess of 10 MeV in well collimated beams; (2) use of laser chirp to control the growth of plasma waves and acceleration of electrons by the Raman instability; (3) all optical injection and acceleration of electrons; (4) relativistic self-focusing by means of the mutual index of refraction of two overlapping laser pulses; (5) creation of a radioisotope by the reaction 10B(d,n)11C; (6) high-order harmonic generation from relativistic free electrons in an underdense plasma.

Generation of ultrashort pulses of electrons, X‐rays and optical pulses by relativistically strong light

We report recent results of experiments in which relativistic optical effects play an important role, at peak laser intensities above 1019 W/cm2. These effects are leading to novel radiation sources, all with femtosecond pulse durations: (1) the generation of optical photons by means of pulse compression via relativistic cross‐phase modulation, (2) ponderomotive deflection of laser accelerated electron beams, and (3) the generation of well‐collimated keV‐energy x‐ray beams by means of either Thomson scattering or betatron oscillations in ion channels.

Vacuum scattering technique for wakefield electron beam diagnostic and conditioning measurements

We report the theoretical prediction and experimental verification of polarization independence of direct laser scattering of free electrons in vacuum. Simulations show multi-MeV electron scattering is possible. The focal volume requirement for independence is derived.

High harmonic generation by relativistic Thomson scattering

We discuss the first experimental observation of high-order harmonic generation via Compton scattering of a high-intensity laser beam from a laser-driven beam of megavolt-energy electrons. Novel scaling laws governing these processes are also derived theoretically.