Fast and ultrafast multiphoton-multicolour Ionization and spectroscopy of small quantum systems

The interaction of atoms (Kr) and small molecules (CO2, CH4), with laser light emit- ted by different types of sources was investigated. Photoelectron spectroscopy was applied to study the two photon double ionization of krypton, induced by free electron laser (FEL) photons at 25.2 eV. Velocity map imaging (VMI) spectroscopy was also used to record the angular distributions of the photoelectrons for both the first and second ionization steps. The resolution of the spectrometer was high enough to allow for resolving the spin-orbit components in the photoelectron spectra. Measurements for different FEL intensities were per- formed to illustrate the intensity dependence for each spin-orbit component. The main result was the observation of an intensity dependent pattern, characteristic for each spin-orbit component. Photoabsorption measurements around the carbon and oxygen K-edges were ac- quired for neutral ’not ionized’ CO2 and CH4 molecules. Similar measurements were performed for the CO2 and CH4 photoionized plasmas. The photons used to create and subsequently probe the plasmas were emitted by a laser produced plasma (LPP) source based on the double stream gas puff target geometry. The main result, was the observation of atomic ions in the absorption spectra of the photoionized plasmas, contrary to the case of the ’not ionized’ neutral molecules. A comparative study was performed for methane irradiated by ultrafast laser pulses at 800 nm and 400 nm. Ionization and subsequent dissociation mechanisms were in- vestigated via ion spectroscopy at different laser intensities for both the fundamental (800 nm) laser field and the second harmonic (400 nm) field. The main result was the observation of different fragmentation pathways for each laser wavelength. The fragmentation pathways were also found to be dependent on the laser intensity

The Effect of Confinement Angle on Self-Colliding Aluminium Laser Plasmas Using Spectrally Resolved Fast Imaging

In this work we investigate the effect of the confinement angle on self-colliding aluminium laser produced plasmas. More specifically, we apply V-shaped channel targets of different angles (90°, 60° and 30°) and report both broadband and filtered time-resolved fast imaging measurements on the formation of such plasmas in ambient air. Based on the broadband measurements we suggest that the plasmas formed on the two inner walls of the V-shaped channel expand normally to the surface, interact with each other and possibly stagnate. The spectrally filtered fast imaging reveals the presence of a spatial distribution of different species within the plasmas and signatures of forced recombination

The 5d-6p VUV Photoabsorption Spectrum of Bi+

The photoabsorption spectrum of Bi+ was measured in the wavelength range between 37 and 60 nm, using the dual laser plasma technique in which one plasma is used as the source of vacuum ultraviolet continuum radiation and the other plasma is used as the sample of atoms and/or ions to be probed. A number of features in the Bi+ spectrum was identified with the aid of the Cowan suite of atomic codes. The 5d → 6p transitions from the ground configuration (5d106s26p2) gave rise to the most prominent features in the measured spectrum. Transitions from low-lying excited states associated with the four excited configurations, 5d106s26p6d, 5d106s26p7s, 5d106s26p7p and 5d106s6p3, were found to make small contributions to the observed spectrum in the 47–50 nm spectral region. To the best of our knowledge, for Bi+, this spectral region is rather unexplored and spectroscopic data are absent from the literature

Line plasma <i>versus</i> point plasma VUV LIBS for the detection of carbon in steel: a comparative study

Comparison of line plasma and point plasma VUV laser induced breakdown spectroscopy for the detection of carbon in steel

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