Role of the ionization potential in nonequilibrium metals driven to absorption saturation.

A composite metallic foil (Al/Mg/Al) has been exposed to intense sub-100 fs free electron laser (FEL) pulses and driven to ultrafast massive photoionization. The resulting nonequilibrium state of matter has been monitored through absorption spectroscopy across the L(2,3) edge of Mg as a function of the FEL fluence. The raw spectroscopic data indicate that at about 100J/cm(2) the main absorption channels of the sample, i.e., Mg (2p→free) and oxidized Al (valence→free), are almost saturated. The spectral behavior of the induced transparency has been interpreted with an analytical approach based on an effective ionization potential of the generated solid-density plasma.

Four-wave mixing experiments with extreme ultraviolet transient gratings.

Four-wave mixing (FWM) processes, based on third-order nonlinear light-matter interactions, can combine ultrafast time resolution with energy and wavevector selectivity, and enable the exploration of dynamics inaccessible by linear methods. The coherent and multi-wave nature of the FWM approach has been crucial in the development of advanced technologies, such as silicon photonics, subwavelength imaging and quantum communications. All these technologies operate at optical wavelengths, which limits the spatial resolution and does not allow the probing of excitations with energy in the electronvolt range. Extension to shorter wavelengths--that is, the extreme ultraviolet and soft-X-ray ranges--would allow the spatial resolution to be improved and the excitation energy range to be expanded, as well as enabling elemental selectivity to be achieved by exploiting core resonances. So far, FWM applications at such wavelengths have been prevented by the absence of coherent sources of sufficient brightness and of suitable experimental set-ups. Here we show how transient gratings, generated by the interference of coherent extreme-ultraviolet pulses delivered by the FERMI free-electron laser, can be used to stimulate FWM processes at suboptical wavelengths. Furthermore, we have demonstrated the possibility of observing the time evolution of the FWM signal, which shows the dynamics of coherent excitations as molecular vibrations. This result opens the way to FWM with nanometre spatial resolution and elemental selectivity, which, for example, would enable the investigation of charge-transfer dynamics. The theoretical possibility of realizing these applications has already stimulated ongoing developments of free-electron lasers: our results show that FWM at suboptical wavelengths is feasible, and we hope that they will enable advances in present and future photon sources.

Psychopathology factors in first-episode affective and non-affective psychotic disorders.

BACKGROUND: Since the onset, prevalence, and course of specific psychopathological features rarely have been analyzed simultaneously from the start of dissimilar psychotic illnesses, we compared symptom-clusters in first-episode DSM-IV affective and non-affective psychotic disorders. METHODS: Subjects (N=377) from the McLean-Harvard First Episode Project hospitalized for first-lifetime primary psychotic illnesses were followed prospectively for 2 years to verify stable DSM-IV diagnoses. We ascertained initial symptoms from baseline SCID and clinical assessments, applying AMDP and Bonn psychopathology schemes systematically to describe a broad range of features. Final consensus diagnoses were based on intake and follow-up SCID assessments, family interviews, and medical records. Factor-analytic methods defined first-episode symptom-clusters (Factors), and multiple-regression modeling related identified factors to initial DSM-IV diagnoses and to later categories (affective, non-affective, or schizoaffective disorders). RESULTS: Psychopathological features were accommodated by four factors: I represented mania with psychosis; II a mixed depressive-agitated state; III an excited-hallucinatory-delusional state; IV a disorganized-catatonic-autistic state. Each factor was associated with characteristic prodromal symptoms. Factors I and III associated with DSM-IV mania, II with major depression or bipolar mixed-state, III negatively with delusional disorder, IV with major depression and negatively with mania. Factors I and II predicted later affective diagnoses; absence of Factor I features predicted non-affective diagnoses, and no Factor predicted later schizoaffective diagnoses. CONCLUSION: The findings contribute to descriptive categorizations of psychopathology from onset of dissimilar psychotic illnesses. This approach was effective in identifying and subtyping affective psychotic disorders early in their clinical evolution, but non-affective and schizoaffective conditions appear to be more complex and unstable.