A two crystal arrangement to fight efficiency saturation in cross-polarized wave generation.

We describe a method that overcomes the observed saturation effect in cross polarized wave (XPW) generation. The previously reported internal efficiencies for XPW generation are known to be limited to around 15% whatever the length of the nonlinear medium and/or the input intensity values are. At the opposite, the theoretical limit had been estimated to be close to 25%. Here we show that using two thin BaF(2) crystals separated at optimum distance the saturation level of XPW generation efficiency can be drastically increased. An internal efficiency of 30% is demonstrated experimentally using two BaF(2) crystals.

[A case of lycanthropy with deadly violence]. / A propos d'une observation de lycanthropie avec violences mortelles.

After a short historical review of the contemporary medical literature, the authors analyze a new and original observation of lycanthropy. He is a 28 years old man, imprisoned for deadly violence, who has been showing, for many years, the belief of being transformed into a werewolf during depersonalization episodes when he presents a lycanthropic behaviour. Our observation is closer to hysteria and mythomania on an antisocial personality, although it seems difficult to place the mental pathology of this alcoholic recidivist delinquent into a nosographical frame.

[The administrative control of involuntary commitment at the department of Gironde 150 years following promulgation of the law of 30 June 1838]. / Le contrôle administratif de l'internement d'office dans le département de la Gironde 150 ans après la promulgation de la loi du 30 juin 1838.

The authors take initially stock of compulsory commitments and voluntary confinements (both types of commitment) in Gironde during 1985-1987. They note a rate of more important commitment for 100,000 inhabitants in urban zone, in particular for the voluntary confinements. The urgent procedure of compulsory commitment remains, in 1987, three time more used than the ordinary procedure. Psychiatric expertise of control on prefectoral requisition are frequently carried out before, as well as after the compulsory commitment (visits residence or in the particular hospital for the insane). 55 observations concerning medical checks at home are analyzed in the field of the origin and reasons for descriptions to the D.D.A.S.S. of Gironde as well as the diagnosis of the examined persons. The authors note finally that almost all the patients have a discontinuance of their compulsory commitment to the profit of another mode of placement during the hospitalization. They conclude that, applied and controlled well, the law of 30 june 1838 makes it possible to reconcile the protection of the public order, the care of the insane and the respect of individual freedom.

Small atomic displacements recorded in bismuth by the optical reflectivity of femtosecond laser-pulse excitations.

Subtle atomic motion in a Bi crystal excited by a 35 fs-laser pulse has been recovered from the transient reflectivity of an optical probe measured with an accuracy of 10(-5). Analysis shows that a novel effect reported here-an initial negative drop in reflectivity-relates to a delicate coherent displacement of atoms by the polarization force during the pulse. We also show that reflectivity oscillations with a frequency coinciding with that of cold Bi are related to optical phonons excited by the electron temperature gradient through electron-phonon coupling.

Nonlinear mirror based on cross-polarized wave generation.

We present a new type of nonlinear mirror based on the generation of a cross-polarized wave through a nonresonant electronic third-order process. It is characterized by a reflection coefficient that depends on the input intensity. Its behavior results from the interference between the nonlinearly generated cross-polarized wave and a pi/2 phase-retarded wave. This setup has a lot of advantages: it does not require any phase matching, it is achromatic and suitable for femtosecond pulses, linear losses are easily adjustable, and the overall behavior is predictable. The device has been experimentally tested using BaF2 and YVO4 crystals.

Comment on "Generation of 10(11) contrast 50 TW laser pulses".

We argue for a different physical interpretation of the results given in the recent Letter by Chvykov et al. [Opt. Lett.31, 1456 (2006)] in which a double nonlinear crystal scheme for cross-polarized wave generation is analyzed. We discuss the most important factors that explain the origin of the two-crystal scheme's increased efficiency, namely, the Kerr lensing effect and a Gouy phase shift. The position and orientation of the second crystal relative to the first one are unambiguously defined; related effects are illustrated by already published works on the subject.

Electronic nonlinear optical susceptibilities of silicate glasses.

Femtosecond techniques have been used to measure the electronic contribution to the nonlinear susceptibility of several standard glasses. The relation between their nonlinear efficiency and the content of network-modifying cations has been determined.

Polarization rotation induced by cascaded third-order processes.

Intensity-dependent polarization rotation that results from the simultaneous action of two third-order processes, self-phase modulation and four-wave mixing, is observed. The effect is recorded along the fourfold axis of a YVO(4) crystal. The angle of rotation is proportional to the square of the input intensity-crystal length product. This is to the authors' knowledge the first experimental evidence showing that intensity-dependent polarization rotation can be related to the real part of cubic susceptibility.

Cross-polarized wave generation by effective cubic nonlinear optical interaction.

A new cubic nonlinear optical effect in which a linearly polarized wave propagating in a single quadratic medium is converted into a wave that is cross polarized to the input wave is observed in BBO crystal. The effect is explained by cascading of two different second-order processes: second-harmonic generation and difference frequency mixing.