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We point out the breakdown of two approximations widely used to describe decoherence in open quantum systems, the secular and Markov approximations. We probe their limits by studying the influence of pressure on the alignment revivals (echoes) created in properly chosen gas mixtures (HCl and CO2, pure and diluted in He) by one (two) intense and short laser pulse(s). Experiments, as well as predictions using molecular dynamics simulations, consistently demonstrate in some of the aforementioned systems the break-down of these approximations at very short times (

We exploit gas-phase molecules as light-matter interface to store an orbital angular momentum (OAM) or a superposition of OAM states (OAM-based photonic qubits) carried by ultrashort laser pulses. The interplay between spin angular momentum and OAM is exploited to encode the amplitude and spatial phase information of light beams into rotational coherences of molecules. This last is restored on-demand over tens of picoseconds with a reading beam by taking advantage of field-free molecular alignment. The underlying mechanism at the origin of the storage can be interpreted by the spatial structuring of the molecular sample induced by the field. The excitation indeed produces an inhomogeneous spatial distribution of molecular alignment (amplitude & orientation) whose periodical revivals associated with the quantum beatings of the rotational wavepacket enables to restore the spatial beam structure on-demand. The strategy is successfully demonstrated in CO2 molecules at room temperature. Besides applicability as storage medium with THz bandwidth application, the use of molecules as light-matter interface opens new functionalities in terms of optical processing and versatile control of OAM fields.

A phase-matching free pulse retrieval technique based on plasma-induced defocusing in a rare gas is presented. Based on a pump-probe setup, this technique uses a moderately intense pump laser pulse for ionizing the medium, creating in turn an ultrafast defocusing lens. While a coronagraph blocks out the probe pulse in absence of ionization, the plasma lens leads to increase the probe beam size in the far field. By measuring the spectrum of the probe propagating around the coronagraph as a function of the pump-probe delay π, a bi-dimensional trace (ω,π) is obtained. This enables to fully characterize the temporal and spectral characteristics of the probe pulse through a method that is free of phase matching constraints. Demonstrated both in the near-infrared (800 nm) and in the ultraviolet (266 nm), the present technique is potentially suited for characterizing pulses in the whole transparency region of the used gas, i.e., from the deep-ultraviolet to the far-infrared.