Precise and accurate measurements of strong-field photoionisation and a transferrable laser intensity calibration standard

Ionization of atoms and molecules in strong laser fields is a fundamental process in many fields of research, especially in the emerging field of attosecond science. So far, demonstrably accurate data have only been acquired for atomic hydrogen (H), a species that is accessible to few investigators. Here we present measurements of the ionization yield for argon, krypton, and xenon with percentlevel accuracy, calibrated using H, in a laser regime widely used in attosecond science. We derive a transferrable calibration standard for laser peak intensity, accurate to 1.3%, that is based on a simple reference curve. In addition, our measurements provide a much-needed benchmark for testing models of ionisation in noble-gas atoms, such as the widely employed single-active electron approximation.Comment: Article: 5 pages, 2 figures, submitted to PRL (manuscript number LZ14457). Supplementary information: 7 pages, 6 figures, appended to end of main Articl

Experimental ionization of atomic hydrogen with few-cycle pulses

We present the first experimental data on strong-field ionization of atomic hydrogen by few-cycle laser pulses. We obtain quantitative agreement at the 10% level between the data and an {\it ab initio} simulation over a wide range of laser intensities and electron energies

Migration experiences, employment status and psychological distress among Somali immigrants: a mixed-method international study

Background: The discourse about mental health problems among migrants and refugees tends to focus on adverse pre-migration experiences; there is less investigation of the environmental conditions in which refugee migrants live, and the contrasts between these situations in different countries. This cross-national study of two samples of Somali refugees living in London (UK) and Minneapolis, Minnesota, (USA) helps to fill a gap in the literature, and is unusual in being able to compare information collected in the same way in two cities in different countries. Methods: There were two parts to the study, focus groups to gather in-depth qualitative data and a survey of health status and quantifiable demographic and material factors. Three of the focus groups involved nineteen Somali professionals and five groups included twenty-eight lay Somalis who were living in London and Minneapolis. The quantitative survey was done with 189 Somali respondents, also living in London and Minneapolis. We used the MINI International Neuropsychiatric Interview (MINI) to assess ICD-10 and Results: The overall qualitative and quantitative results suggested that challenges to masculinity, thwarted aspirations, devalued refugee identity, unemployment, legal uncertainties and longer duration of stay in the host country account for poor psychological well-being and psychiatric disorders among this group. Conclusion: The use of a mixed-methods approach in this international study was essential since the quantitative and qualitative data provide different layers and depth of meaning and complement each other to provide a fuller picture of complex and multi-faceted life situations of refugees and asylum seekers. The comparison between the UK and US suggests that greater flexibility of access to labour markets for this refugee group might help to promote opportunities for better integration and mental well-being