Search

We describe an imaging technique that we have applied to laser-induced plasma parameter analysis. Time-resolved spectra, that were also spatially resolved in one dimension along the axis of plasma expansion, were obtained using a time gated intensified charge-coupled device (ICCD) coupled to a stigmatic spectrometer. Plasma parameters such as electron temperature, density and plume velocity were extracted directly from the image analysis which has been automated using a new MATLAB™ code. This technique permits rapid and ready characterization of laser plasma plumes in the early stage of the plasma expansion (following the passing of the plasma heating laser pulse). In this work we present and discuss its application to the analysis of a laser-produced Li plasma.

Electron bunch lengths and time jitters have been measured with sub-ps resolution at the TESLA Test Facility at DESY. Synchrotron radiation emitted from a dipole magnet reflects the longitudinal charge distribution of the electron bunch and can also be used as a timing reference of the radiation pulses produced by the free-electron laser. For sub-ps time resolution, dispersion effects of the spectrally broad-band synchrotron radiation have to be suppressed. The phase stability of the FEL pulses with respect to the radio-frequency master oscillator has been studied with a streak camera operating in synchroscan mode.

Two-color above threshold ionization of helium and xenon has been used to analyze the synchronization between individual pulses of the femtosecond extreme ultraviolet (XUV) free electron laser in Hamburg and an independent intense 120 fs mode-locked Ti:sapphire laser. Characteristic sidebands appear in the photoelectron spectra when the two pulses overlap spatially and temporally. The cross-correlation curve points to a 250 fs rms jitter between the two sources at the experiment. A more precise determination of the temporal fluctuation between the XUV and infrared pulses is obtained through the analysis of the single-shot sideband intensities.

We describe an experimental system designed for single-shot photoelectron spectroscopy on free atoms and molecules at the Free Electron Laser in Hamburg (FLASH at DESY). The combination of the extreme ultra-violet (EUV) Free Electron Laser and a temporally synchronized optical fs laser (Ti:Sapphire) enables a variety of two-color pump-probe experiments. The spectral, temporal and spatial characteristics of both the EUV FEL and the optical laser pulses, the experimental procedure to control their overlap as well as the performance of an electron spectrometer used to obtain single-shot photoelectron spectra are discussed. As an illustration of the capabilities of this set-up, some results on two-photon two-color ionization of rare gases are presented.

We report results from a study of the integrated column density and expansion dynamics of ground-state-selected Ba+ions in a laser–plasma plume using a new experimental system—VPIF (vacuum-ultraviolet photoabsorption imaging facility). The ions are tracked by recording the attenuation of a pulsed and collimated vacuum ultraviolet beam, tuned to the 5p–6dinner-shell resonance of singly ionized barium, as the expanding plasma plume moves across it. The attenuated beam is allowed to fall on a CCD array where the spatial distribution of the absorption is recorded. Time-resolved ion velocity and integrated column density maps are readily extracted from the photoionization images.

The interaction of two counterpropagating laser-produced plasmas was studied using simultaneous imaging and spectroscopic techniques. Spectrally filtered time-gated intensified charge coupled device imaging was used to obtain information about the spatial dynamics and temporal evolution of the collision process, while time-resolved imaging spectroscopy was used to determine the spatial and temporal distributions of electron temperature and density within the interaction region. We examine specifically the interaction of plasmas whose parameters match those typically used in pulsed laser deposition of thin films. These low temperature plasmas are highly collisional leading to the creation of a pronounced stagnation layer in the interaction region.