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P. Roth

Publications and source records attributed to P. Roth.

3 recordsLinked to original sources

Chiral Electron Momentum Distribution upon Strong-Field Ionization of Atoms

We present a scheme to synthesize a three-dimensional laser field that produces a chiral electron momentum distribution upon strong-field ionization of atoms. Our approach employs two orthogonally propagating two-color laser beams. This results in a time-dependent three-dimensional electric field vector of the combined light field which varies for different positions within the focal volume. For each position, we conduct a simulation of the corresponding electron momentum distribution that includes non-adiabatic dynamics and Coulomb interaction after tunneling. For suitable laser parameters, only a small region of the focal volume contributes to the final momentum distribution. Thus, integrating over all position coordinates, a specific chiral laser field dominates. This leads to a volume-averaged electron momentum distribution, which is chiral, as well. This work will serve as a benchmark for future strong-field experiments aiming at the synthetization of well-defined, three-dimensional laser fields.

physics.atom-ph

Protecting quantum modes in optical fibres

Polarization-preserving fibers maintain the two polarization states of an orthogonal basis. Quantum communication, however, requires sending at least two nonorthogonal states and these cannot both be preserved. We present a new scheme that allows for using polarization encoding in a fiber not only in the discrete, but also in the continuous-variable regime. For the example of a helically twisted photonic-crystal fibre, we experimentally demonstrate that using appropriate nonorthogonal modes, the polarization-preserving fiber does not fully scramble these modes over the full Poincar\'e sphere, but that the output polarization will stay on a great circle; that is, within a one-dimensional protected subspace, which can be parametrized by a single variable. This will allow for more efficient measurements of quantum excitations in nonorthogonal modes.

quant-ph

Strong circular dichroism in twisted single-ring hollow-core photonic crystal fiber

We report a series of experimental, analytical and numerical studies demonstrating strong circular dichroism in helically twisted hollow-core single-ring photonic crystal fiber (SR-PCF), formed by spinning the preform during fiber drawing. In the SR-PCFs studied, the hollow core is surrounded by a single ring of non-touching capillaries. Coupling between these capillaries results in the formation of helical Bloch modes carrying orbital angular momentum. In the twisted fiber, strong circular birefringence appears in the ring, so that when a core mode with a certain circular polarization state (say LC) phase-matches to the ring, the other (RC) is strongly dephased. If in addition the orbital angular momentum is the same in core and ring, and the polarization states are non-orthogonal (e.g., slightly elliptical), the LC core mode will experience high loss while the RC mode is efficiently transmitted. The result is a single-circular-polarization SR-PCF that acts as a circular polarizer over a certain wavelength range. Such fibers have many potential applications, for example, for generating circularly polarized light in gas-filled SR-PCF and realizing polarizing elements in the deep and vacuum ultraviolet.

physics.optics