Ultrafast and intense laser interaction with gases and solids

A dedicated laboratory has been built in DCU to study the interaction between ultra-short, intense laser radiation with both solid and gaseous materials. A commercial laser system with high intensity (3 mJ), and short temporal dura- tion ( 32 fs) has been installed and characterised as part of this project. A static, single shot Nomarski interferometer has been developed and by exploiting the non- linear response of an optical filter, the pulse width of the laser has been measured. The interaction of high intensity laser radiation with solid materials was also investigated. Experiments using a wire probe to characterise a silicon laser produced plasma were performed. The emission of ions and electrons within the laser plasma as well as the angular distribution of both species has been measured and the effects of laser intensity, laser wavelength and laser polarisation are investigated. In a complementary experiment, the expansion dynamics of the laser plasma are studied with space resolved Langmuir probe measurements. These results are analysed and presented in the context of double layer formations within the plasma plume. A Wiley-McLaren spectrometer has been built to study the interaction of high intensity laser light with gas jets. The design and construction of the spectrometer is detailed as well as its characterisation. The effects of polarisation are studied with molecular nitrogen as a gas target

Student difficulties regarding symbolic and graphical representations of vector fields

The ability to switch between various representations is an invaluable problem-solving skill in physics. In addition, research has shown that using multiple representations can greatly enhance a person’s understanding of mathematical and physical concepts. This paper describes a study of student difficulties regarding interpreting, constructing, and switching between representations of vector fields, using both qualitative and quantitative methods. We first identified to what extent students are fluent with the use of field vector plots, field line diagrams, and symbolic expressions of vector fields by conducting individual student interviews and analyzing in-class student activities. Based on those findings, we designed the Vector Field Representations test, a free response assessment tool that has been given to 196 second- and third-year physics, mathematics, and engineering students from four different universities. From the obtained results we gained a comprehensive overview of typical errors that students make when switching between vector field representations. In addition, the study allowed us to determine the relative prevalence of the observed difficulties. Although the results varied greatly between institutions, a general trend revealed that many students struggle with vector addition, fail to recognize the field line density as an indication of the magnitude of the field, confuse characteristics of field lines and equipotential lines, and do not choose the appropriate coordinate system when writing out mathematical expressions of vector fields

Intensity-dependent near-threshold ionization of Kr in the vacuum-uv

In this work, we present measurements of the intensity-dependent photoelectron spectrum of Kr irradiated by the FLASH FEL tuned to a photon energy of 25.8 eV. Intensity dependent photoelectron spectra were obtained with the aid of a Velocity Map Imaging (VMI) spectrometer. As the FEL photon energy is close to threshold, two photon sequential double ionization is favoured. The number of open channels is kept to a minimum and leading to a simple description of the process