TODD HAMMOND

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When intense light interacts with an atomic gas, recollision between an ionizing electron and its parent ion creates high-order harmonics of the fundamental laser frequency. This sub-cycle effect generates coherent soft X-rays and attosecond pulses, and provides a means to image molecular orbitals. Recently, high harmonics have been generated from bulk(More)
We present a simple and quick, yet accurate method to measure the dispersion of high finesse optical cavities. By exciting the cavity with a femtosecond frequency comb and measuring the resonance condition as a function of optical frequency, the cavity's dispersion can be determined with minimal uncertainty. Measurement results are presented from an(More)
A general technique for analyzing complicated gas discharges has been developed and applied to the Hg + Ar (fluorescent lamp) discharge. The theoretical model includes electron excitation and deexcitation, two-state ionization through a saturated metastable level, and proper treatment of the self-absorption of the resonance radiation. The analysis yields(More)
A beam with an angular-dependant phase Φ = ℓϕ about the beam axis carries an orbital angular momentum of ℓℏ per photon. Such beams are exploited to provide superresolution in microscopy. Creating extreme ultraviolet or soft-x-ray beams with controllable orbital angular momentum is a critical step towards extending superresolution to much higher spatial(More)
High harmonic generation, which produces a coherent burst of radiation every half cycle of the driving field, has been combined with ultrafast wavefront rotation to create a series of spatially separated attosecond pulses, called the attosecond lighthouse. By adding a coherent second harmonic beam with polarization parallel to the fundamental, we decrease(More)
The band structure of matter determines its properties. In solids, it is typically mapped with angle-resolved photoemission spectroscopy, in which the momentum and the energy of incoherent electrons are independently measured. Sometimes, however, photoelectrons are difficult or impossible to detect. Here we demonstrate an all-optical technique to(More)
The Hg 2537-A intensity from Hg + Ar discharges was measured as an independent function of mercury vapor pressure (as influenced by a cold spot temperature) at various constant currents and tube radii with ~4-Torr argon. As a function of mercury pressure, the intensity rises to a peak (which defines an optimum mercury cold spot temperature) and then(More)
Optical vortices, which carry orbital angular momentum (OAM), can be flexibly produced and measured with infrared and visible light. Their application is an important research topic for super-resolution imaging, optical communications and quantum optics. However, only a few methods can produce OAM beams in the extreme ultraviolet (XUV) or X-ray, and(More)
The intensity of the Hg 2573-A radiation from Hg + Ar discharges was measured as an independent function of mercury pressure (0.2-50 mTorr), ac current (50-2100 mA) and tube radius (0.79 cm and 1.27 cm) at a constant Ar pressure of ~4 Torr. For various constant mercury pressures, the Hg 2537-A intensity initially rises linearly with increasing current, but(More)
A simple theoretical model of visible light emission from xenon flashlamps is presented. The continuum light emission is calculated from the rate of electron-ion recombination in the xenon plasma, which is treated as a greybody in thermal equilibrium. The effect of radiation reabsorption is calculated in terms of the temperature-dependent greybody(More)