163 research outputs found
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Optical field ionization of atoms and ions using ultrashort laser pulses
No full textThis dissertation research is an investigation of the strong optical field ionization of atoms and ions by 120-fs, 614-run laser pulses and 130-fs, 800-nm laser pulses. The experiments have shown ionization that is enhanced above the predictions of sequential tunneling models for He{sup +2}, Ne{sup +2} and Ar{sup +2}. The ion yields for He{sup +l}, Ne{sup +l} and Ar{sup +l} agree well with the theoretical predictions of optical tunneling models. Investigation of the polarization dependence of the ionization indicates that the enhancements are consistent with a nonsequential ionization mechanism in which the linearly polarized field drives the electron wavefunction back toward the ion core and causes double ionization through inelastic e-2e scattering. These investigations have initiated a number of other studies by other groups and are of current scientific interest in the fields of high-irradiance laser-matter interactions and production of high-density plasmas. This work involved: (1) Understanding the characteristic nature of the ion yields produced by tunneling ionization through investigation of analytic solutions for tunneling at optical frequencies. (2) Extensive characterization of the pulses produced by 614-nm and 800-ran ultrashort pulse lasers. Absolute calibration of the irradiance scale produced shows the practicality of the inverse problem--measuring peak laser irradiance using ion yields. (3) Measuring the ion yields for three noble gases using linear, circular and elliptical polarizations of laser pulses at 614-nm and 800-nm. The measurements are some of the first measurements for pulse widths as low as 120-fs
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Double ionization in gases driven by optical field ionization using ultrashort laser pulses
No full textRapid optical field ionization (OFI) for atoms and ions is distinguished using ultra-short laser pulses focused to peak fields comparable to Coulomb binding values. This nonperturbative field description facilitates understanding of standard sequential ionization and distinguishes the double (or two-electron ejection) ionization process. Following our discovery of double optical field ionization in He{sup +2} at 614 nm we have extended experiments to include helium, neon and argon at an 800 nm wavelength with varying ellipticity. We compare double ionization data with predictions from the semi-classical model by Corkum. New experimental results at 800 nm use 130 femtosecond laser pulses focused to intensities of order 10{sup 16} W/cm in the extraction region of a 1 meter time-of-flight spectrometer. Gas pressures ranged from 10{sup {minus}8} to 10{sup {minus}5} torr
80 Gb/s optimised pulse source using a gain-switched laser diode in conjunction with a nonlinearly chirped grating
No full textThe authors demonstrate the generation of transforms limited short optical pulses, which display excellent spectral and temporal qualities by employing a novel technology, based on an externally injected gain-switched laser in conjunction with a non-linearly chirped grating. Using this technique, 3.5 ps optical pulses, exhibiting a time bandwidth product of 0.45, are generated, which are suitable for use in high-speed 80 Gb/s OTDM communications systems
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Advanced Compressor Designs for High Energy Petawatt Pulse Generation
No full textWe discuss compressor designs for a proposed multikilojoule, sub-picosecond beamline at the National Ignition Facility. A novel grating configuration reduces the size of the compressor chamber. Optimization of the design leads to a 4.7 x 1.4 x 0.4 m{sup 3} minimum compressor volume
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Spatial and Temporal Characterization of Femtosecond Pulses at High-Numerical Aperture Using Collinear, Background-Free, Third-Harmonic Autocorrelation
No full textWe show that a simple plane wave analysis can be used even under tight focusing conditions to predict the dependence of third-harmonic generation on the polarization state of the incident beam. Exploiting this fact, we then show that circularly polarized beams may be used to spatially characterize the beam focus and temporally characterize ultrashort pulses in high numerical aperture systems by experimentally demonstrating, for the first time, novel collinear, background-free, third-harmonic intensity autocorrelations in time and space in a high numerical aperture microscope. We also discuss the possibility of using third harmonic generation with circularly polarized beams for background-free collinear frequency resolved optical gating
Consistency and variability in the behavior of mature, isolation-reared, male rhesus macaques
No full textPulsed laser field errors: theoretical and experimental analysis of a phase error figure of merit
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Hyperdispersion Grating Arrangements for Compact Pulse Compressors and Expanders
No full textA novel, but general, arrangement of parallel sets of gratings is presented that can effectively increase the dispersion of pulse compressors and expanders by over an order of magnitude. These arrangements will dramatically reduce the footprint of the pulse compressors and expanders used in CPA
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