Complete Characterization of Light Waves using Attosecond Pulses

The most direct way to probe the strength of an electric field, is to measure the force that exerts to a charged particle. For a time varying field, charge placement within an interval substantially shorter than the characteristic period of variation of the field is essential for sampling its temporal evolution. Employing such a scheme to track the field variation of light waves that changes its direction 1015 times per second, charge release shall be confined within a fraction of a femtosecond. In this thesis, the complete characterization of a light pulse is demonstrated experimentally for the first time by probing its field variation using a 250 attosecond electron burst. Such an ultrafast charge probe, can be generated by the impulsive ionization of atoms, using an XUV attosecond pulse precisely synchronized with the light waveform to be characterized. The technique allows access to the instantaneous value of the electric field of IR, visible, or UV light and thereby opens the door for the synthesis of controlled, extremely broadband and arbitrarily shaped light waveforms. The above experiments, are presented along with critical pertinent developments on the generation of few-cycle phase-controlled light waveforms and their subsequent exploitation, for the generation of isolated XUV attosecond pulses. Precisely characterized and controlled light fields and XUV attosecond pulses employed in combination, hold the promise for probe and control of elementary processes evolving on an attosecond time scale

A dispersionless transmission grating based michelson interferometer for the characterization of harmonics

A new Michelson type interferometer, based on a transmission grating beam splitter, is presented and studied in detail. It posses dispersionless characteristics and flat spectral response, over the UV- XUV spectral range. Three variant configurations of the interferometer are examined, using ray tracing techniques. It was found that when certain imaging conditions are preserved, the interferometer exhibits extremely low dispersion and therefore its applicable for the temporal characterization of harmonics, and harmonic superpositions. Further, the interferometer is experimentally employed for the temporal characterization, of the third harmonic of a Ti:Saph laser. The results obtained, are coincide with those acquired with a conventional Michelson interferometer, as well as with the general conclusions of the ray tracing calculation

Real-time observation of valence electron motion

The superposition of quantum states drives motion on the atomic and subatomic scales, with the energy spacing of the states dictating the speed of the motion. In the case of electrons residing in the outer (valence) shells of atoms and molecules which are separated by electronvolt energies, this means that valence electron motion occurs on a subfemtosecond to few-femtosecond timescale (1 fs = 10(-15) s). In the absence of complete measurements, the motion can be characterized in terms of a complex quantity, the density matrix. Here we report an attosecond pump-probe measurement of the density matrix of valence electrons in atomic krypton ions. We generate the ions with a controlled few-cycle laser field and then probe them through the spectrally resolved absorption of an attosecond extreme-ultraviolet pulse, which allows us to observe in real time the subfemtosecond motion of valence electrons over a multifemtosecond time span. We are able to completely characterize the quantum mechanical electron motion and determine its degree of coherence in the specimen of the ensemble. Although the present study uses a simple, prototypical open system, attosecond transient absorption spectroscopy should be applicable to molecules and solid-state materials to reveal the elementary electron motions that control physical, chemical and biological properties and processes