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Herein, it is demonstrated that ultrashort spatially structured beams can sculpt a sample of gas‐phase molecules like a 4D material to produce a spatial pattern of aligned molecules whose shape and temporal evolution allow to restore the spatial light information on a time‐delayed reading pulse. To do so, the spatial phase and amplitude information of ultrashort light beams are encoded into rotational coherences of molecules by exploiting the interplay between spin angular momentum and orbital angular momentum. The field‐free molecular alignment resulting from the interaction leads to an inhomogeneous spatial structuring of the sample allowing to transfer the encoded information into a time‐delayed probe beam. The demonstration is conducted in CO2$\left(\text{CO}\right)_{2}$ molecules. Besides applications in terms of THz bandwidth buffer memory, the strategy features interesting prospects for establishing versatile optical processing of orbital angular momentum (OAM) fields, for studying various molecular processes, or for designing new photonic devices enabling to impart superpositions of OAM modes to light beams. [ABSTRACT FROM AUTHOR]

Raman-induced polarization spectroscopy (RIPS) experiments combined with homodyne detection have been conducted with a femtosecond laser at room temperature and low pressure (p<2 atm) in CO[sub 2]-N[sub 2] mixtures as well as in air (O[sub 2]-N[sub 2] mixtures). Each molecule of the mixture produces its own time-dependent signal, measured as a series of recurring transients. Macroscopic interference is observed when transients of both molecules overlap in the time domain. This interference leads to a large modification of the signal, which is well reproduced by calculations. The total signal recorded in CO[sub 2]-N[sub 2] or O[sub 2]-N[sub 2] mixtures of known concentration is analyzed in order to measure the polarizability anisotropy ratio of the two components at 800 nm. The ratio measured in an O[sub 2]-N[sub 2] (air) mixture is compared with values of previous works. The knowledge of the ratio for CO[sub 2]/N[sub 2] allows us to determine the concentration of CO[sub 2]-N[sub 2] unknown gas mixtures. The method is presented as a relevant technique for concentration measurements in the picosecond time domain. The accuracy of the measurements and the influence of macroscopic interference in the results are discussed. The present work can be easily extended to other gas mixtures and a broad concentration range. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The article focuses on the study of Jian Wu and colleagues on the use of gas-phase molecules to overcome the switching time of liquid-crystal displays (LCDs). The researchers used a transient electric field to orientate the molecules. It says that ultrafast image capture can be attained by integrating a reading pulse of long duration with two-dimensional amplitude and phase characterization. It shows that molecular gas samples can be used as memory buffer to achieve ultrafast optical imaging.

The applicability of several femtosecond time resolved non-linear coherent techniques such as Raman induced polarization spectroscopy (RIPS), degenerate four-wave mixing (DFWM) and coherent anti-Stokes Raman spectroscopy (CARS) for molecular spectroscopy is presented. All methods rely on the initial coherent excitation of molecular states producing wavepackets, whose time evolution is then measured. In the case of RIPS and DFWM only pure rotational transitions are involved, whereas in CARS vibrational states can be excited. First the methodology of concentration and temperature measurements using RIPS in gas mixtures involving N2, CO2, O2, and N2O is shown. In addition some applications are given for the two closely related techniques DFWM and CARS. DFWM is suitable to extract the rotational constants of molecules to a high accuracy as is demonstrated by measurements on CO2 and pyrimidine, which is a biological building block. CARS can be used to study higher order molecular constants and to sensitively determine temperature in, e.g., H2 up to 2000 K. Finally, CARS is applied for the investigation of pressure dependent lineshape models, which are important for the temperature evaluation from spectroscopic data. To cite this article: B. Lavorel et al., C. R. Physique 5 (2004). [Copyright &y& Elsevier]