Two-colour Three-pulse Spectrally Resolved Nonlinear Spectroscopy for Studies of Dynamics in Semiconductor Si Quantum Dots

We demonstrate that a two-colour three-pulsenonlinear spectroscopy can be used to study the dynamics of excited carriers inSi quantum dot structures embedded in SiN. Decays of the transverse optical phonon population and the transverse acoustic phonon population are measured and discussed. A simple theoretical modelis also used to support interpretation of our experimental observations

Coherent Diffractive Imaging Using Table-top High Harmonic Generation

Coherent diffractive imaging (CDI) is a lensless microscopy technique in which the structure of a specimen of interest is probed using a coherent short-wavelength light source. CDI has been widely used in nanotechnology and structural biology to capture high resolution images of non-crystalline objects. In this paper, we review the theoretical and experimental aspects of coherent diffractive imaging using a focused narrow-bandwidth table-top high harmonic source. The review begins with an outline of generation and characterization of the high harmonic source. Theoretical description of coherent diffractive imaging technique is then summarized. The review concludes with our recent results in imaging using a single harmonic beam selected by employing XUV focusing mirrors. These achievements provide a promising technique for the non-crystallographic structural determination of membrane proteins using a table-top extreme ultraviolet source

Safety and efficacy of fluoxetine on functional outcome after acute stroke (AFFINITY): a randomised, double-blind, placebo-controlled trial

Background Trials of fluoxetine for recovery after stroke report conflicting results. The Assessment oF FluoxetINe In sTroke recoverY (AFFINITY) trial aimed to show if daily oral fluoxetine for 6 months after stroke improves functional outcome in an ethnically diverse population. Methods AFFINITY was a randomised, parallel-group, double-blind, placebo-controlled trial done in 43 hospital stroke units in Australia (n=29), New Zealand (four), and Vietnam (ten). Eligible patients were adults (aged ≥18 years) with a clinical diagnosis of acute stroke in the previous 2–15 days, brain imaging consistent with ischaemic or haemorrhagic stroke, and a persisting neurological deficit that produced a modified Rankin Scale (mRS) score of 1 or more. Patients were randomly assigned 1:1 via a web-based system using a minimisation algorithm to once daily, oral fluoxetine 20 mg capsules or matching placebo for 6 months. Patients, carers, investigators, and outcome assessors were masked to the treatment allocation. The primary outcome was functional status, measured by the mRS, at 6 months. The primary analysis was an ordinal logistic regression of the mRS at 6 months, adjusted for minimisation variables. Primary and safety analyses were done according to the patient's treatment allocation. The trial is registered with the Australian New Zealand Clinical Trials Registry, ACTRN12611000774921. Findings Between Jan 11, 2013, and June 30, 2019, 1280 patients were recruited in Australia (n=532), New Zealand (n=42), and Vietnam (n=706), of whom 642 were randomly assigned to fluoxetine and 638 were randomly assigned to placebo. Mean duration of trial treatment was 167 days (SD 48·1). At 6 months, mRS data were available in 624 (97%) patients in the fluoxetine group and 632 (99%) in the placebo group. The distribution of mRS categories was similar in the fluoxetine and placebo groups (adjusted common odds ratio 0·94, 95% CI 0·76–1·15; p=0·53). Compared with patients in the placebo group, patients in the fluoxetine group had more falls (20 [3%] vs seven [1%]; p=0·018), bone fractures (19 [3%] vs six [1%]; p=0·014), and epileptic seizures (ten [2%] vs two [<1%]; p=0·038) at 6 months. Interpretation Oral fluoxetine 20 mg daily for 6 months after acute stroke did not improve functional outcome and increased the risk of falls, bone fractures, and epileptic seizures. These results do not support the use of fluoxetine to improve functional outcome after stroke

Phase-matched high order harmonic generation and applications

This dissertation presents an experimental study of High Harmonic Generation (HHG) using ultrafast laser pulses to produce radiation in the extreme ultraviolet. Two novel schemes which provided an additional phase for the fundamental and harmonic fields were used to enhance the quality of the HHG source including the conversion efficiency and the coherence. The interplay between the single-atom response and the macroscopic response, especially the role of macroscopic propagation effects on the HHG process, were investigated. The HHG source was applied to study rotational coherence dynamics of molecules and to implement coherent diffractive imaging in the extreme ultraviolet region

Intensity dependent spectral features in high harmonic generation

We study the influence of the driving laser intensity on the spectral features of high harmonic generation in a semi-infinite gas cell. The effects of the harmonic dipole phase and the dispersion phase mismatches induced by the ionized medium during the harmonic generation process are revealed and the interplay between the macroscopic response and the single-atom response is discussed. We consider the conditions for generation of a narrow bandwidth, bright, and highly coherent high harmonic source

Phase-matched high harmonic generation for the study of rotational coherence molecular dynamics

We report the observation of periodic modulations in the high order harmonic radiation from diatomic molecules in a semi-infinitive gas cell when a preceding femtosecond laser beam, which is off-axis to the high-harmonic generation beam, modifies the phase-matching condition through the field-free alignment of the molecules. The observed modulations of the high harmonic radiation versus the time delay between the pulses result from periodic changes in the nonlinear refractive index associated with rotational Raman coherence. This opens up a new potential technique for studying rotational coherence dynamics in the ground states of molecules

Generation of extreme ultraviolet radiation with a Bessel-Gaussian beam

The generation of few high-order harmonics in the extreme ultraviolet is enhanced by focusing the fundamental femtosecond laser beam with a combination of lens and axicon in an infinite gas cell. We show that this combination leads to an improvement in the phase-matched generation of harmonics in the cutoff region, with a higher photon flux and a better spatial beam profile. A high atom density through the use of a high gas pressure can be used and the absorption limit of the harmonic generation is obtained for an interaction length of a few millimeters

High harmonic generation for study of rotational Raman coherence

The modulation of the intensity of phase-matched high-harmonic radiation from field-free aligned diatomic molecules due to changes of the nonlinear refractive index is used to determine rotational coherence in the ground state of molecules