0000000000087592
AUTHOR
G. Karras
Interpretation of negative birefringence observed in strong-field optical pump-probe experiments: High-order Kerr and plasma grating effects
The analysis of negative birefringence optically induced in major air components (Loriot et al., [1, 2]) is revisited in light of the recently reported plasma grating-induced phase-shift effect predicted for strong field pump-probe experiments (Wahlstrand and Milchberg, [3]). The nonlinear birefrin- gence induced by a short and intense laser pulse in argon is measured by femtosecond time-resolved polarimetry. The experiments are performed with degenerate colors, where the pump and probe beam share the same spectrum, or with two different colors and non-overlapping spectra. The in- terpretation of the experimental results is substantiated using a numerical 3D+1 model accounting for nonlinear…
Business cycle volatility and country size: evidence for a sample of OECD countries
The main purpose of this paper is to investigate the relationship between business cycle volatility and country size using quarterly data for a sample of OECD countries over 1960-2000. The results suggest very strongly that the relationship between country size and business cycle volatility is negative and statistically significant. This finding is very robust, suggesting that country size does matter, at least for the severity of cyclical fluctuations.
Business Cycles Synchronization in the EMU
This article asks whether the business cycles of the EU countries have become more or less synchronized after the introduction of the euro. Our findings show that all countries in our EU sample are better synchronized with the EMU-wide economy in the post-EMU period than they were before the euro. We also show that this increase in synchronization is present in all components of aggregate demand, as well as two supply-side variables, but it is more pronounced in the trade components (imports and, particularly, exports). It is also shown that the increase in trade within the EMU area is at least partly responsible for the increase in cyclical synchronization.
Optical kerr effect in the strong field regime
The optical Kerr response of hydrogen atom submitted to a strong and short near infrared laser pulse excitation is studied by solving the full 3D time-dependent Schro¨dinger equation. The nonlinear polarization evaluated at the driving field frequency is compared to the canonical expression derived from perturbation theory. A discrepancy between the two models is observed at large intensity affecting the nonlinear propagation of short and intense laser pulses.
Using molecular alignment to track ultrafast collisional relaxation
Field-free molecular alignment has been used in order to track the collisional relaxation occurring in a molecular gas. CO${}_{2}$ molecules were initially irradiated by a short linearly polarized laser pulse resulting in the increase of their rotational energy. The evolution of the subsequent ultrafast relaxation process was optically probed after irradiating the sample with a second, weaker, short pulse leading to the alignment of the preheated molecules. Using classical molecular dynamic simulations, we were able to quantitatively reproduce the experimental shapes and amplitudes of the recorded revival transients for a time interval extending from 25 to 500 ps until thermalization of the…
Orientation and Alignment Echoes
We present one of the simplest classical systems featuring the echo phenomenon---a collection of randomly oriented free rotors with dispersed rotational velocities. Following excitation by a pair of time-delayed impulsive kicks, the mean orientation or alignment of the ensemble exhibits multiple echoes and fractional echoes. We elucidate the mechanism of the echo formation by the kick-induced filamentation of phase space, and provide the first experimental demonstration of classical alignment echoes in a thermal gas of ${\mathrm{CO}}_{2}$ molecules excited by a pair of femtosecond laser pulses.
Are the New EU Countries Ready for the EURO? A Comparison of Costs and Benefits
This paper examines the main macroeconomic determinants of costs and benefits of adopting the euro for the new EU member countries, and compares them to those of the older members. We show that these cost and benefit factors exhibit substantial variability across the countries considered. Our findings suggest that, in terms of price stability, the position of the new members is overall better than some EMU countries, such as Portugal and Greece. At the same time, we identify countries (such as Slovenia, Cyprus, and Hungary) whose business cycle is already well synchronized with EMU's, but also countries (such as Latvia and Estonia) with lower synchronization, and countries (such as Romania,…
Harmonic Generation and Nonlinear Propagation: When Secondary Radiations Have Primary Consequences
In this Letter, it is experimentally and theoretically shown that weak odd harmonics generated during the propagation of an infrared ultrashort ultraintense pulse unexpectedly modify the nonlinear properties of the medium and lead to a strong modification of the propagation dynamics. This result is in contrast with all current state-of-the-art propagation model predictions, in which secondary radiations, such as third harmonic, are expected to have a negligible action upon the fundamental pulse propagation. By analyzing full three-dimensional ab initio quantum calculations describing the microscopic atomic optical response, we have identified a fundamental mechanism resulting from interfere…
Is the Middle-East an Optimum Currency Area? A Comparison of Costs and Benefits
This paper examines the macroeconomic costs and benefits of adopting a common currency for 13 Middle Eastern countries. Economic theory suggests that the main benefit is enhanced price stability, while the main cost is higher business-cycle volatility if the member country’s output is not sufficiently correlated with the area’s, as a whole. Using data from 1980–2005, the paper finds that the estimated cost and benefit measures exhibit substantial variability across the countries and are sometimes positively correlated. Moreover, focusing on the results for the last decade, it seems that many Middle Eastern countries (such as Bahrain, Kuwait, Libya, Oman, Qatar, Saudi Arabia, Syria and Unite…
Polarization shaping for unidirectional rotational motion of molecules.
Control of the orientation of the angular momentum of linear molecules is demonstrated by means of laser polarization shaping. For this purpose, we combine two orthogonally polarized and partially time-overlapped femtosecond laser pulses so as to produce a spinning linear polarization which in turn induces unidirectional rotation of N2 molecules. The evolution of the rotational response is probed by a third laser beam that can be either linearly or circularly polarized. The physical observable is the frequency shift imparted to the probe beam as a manifestation of the angular Doppler effect. Our experimental results are confirmed by theoretical computations, which allow one to gain a deep p…