3MT Department Winners

A few interesting publications

Here are two excellent articles related to Zach Etienne's colloquium




Selected Publications

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Doppler-free two-photon spectroscopy in the vacuum ultraviolet: helium 1(1)S-2(1)S transition
By S. D. Bergeson (et al.)
Abstract: We describe techniques for laser spectroscopy in the vacuum-UV (VUV) spectral region that combine high spectral resolution with high absolute accuracy. A nearly transform-limited nanosecond laser source at 120 nm is constructed with difference-frequency mixing. This source is used to perform the first, to our knowledge, Doppler-free VUV measurement. We measure the inherently narrow 1(1)S-2(1)S two-photon transition in atomic helium with a spectral resolution of 7 parts in 10(8) (180 MHz), the narrowest line width so far observed at such short wavelengths. Careful measurements of optical phase perturbations allow us to determine the absolute frequency of the line center to a fractional uncertainty of 1 part in 10(8). Improvements now in progress should reduce this uncertainty to 2 parts in 10(9). (C) 2000 Optical Society of America [S0740-3224(00)01009-2].
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Plasma oscillations and expansion of an ultracold neutral plasma
By S. D. Bergeson (et al.)
Abstract: We report the observation of plasma oscillations in an ultracold neutral plasma. With this collective mode we probe the electron density distribution and study the expansion of the plasma as a function of time. For classical plasma conditions, i.e.,weak Coulomb coupling, the expansion is dominated by the pressure of the electron gas and is described by a hydrodynamic model. Discrepancies between the model and observations at low temperature and high density may be due to strong coupling of the electrons.
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Creation of an ultracold neutral plasma
By S. D. Bergeson (et al.)
Abstract: We report the creation of an ultracold neutral plasma by photoionization of laser-cooled xenon atoms. The charge carrier density is as high as 2 X 10(9) cm(-3), and the temperatures of electrons and ions are as low as 100 mK and 10 mu K, respectively. Plasma behavior is evident in the trapping of electrons by the positive ion cloud when the Debye screening length becomes smaller than the size of the sample. We produce plasmas with parameters such that bath elections and ions ale strongly coupled.

Theses, Captstones, and Dissertations

Figure from thesis
Two-Photon Ionization of the Calcium 4S3D 1D2 Level in an Optical Dipole Trap (by Jared Estus Daily)
This thesis reports an optical dipole trap for atomic calcium. The dipole trap is loaded from a magneto-optical trap (MOT) of calcium atoms cooled near the Doppler limit (∼ 1 mK). The dipole trap is formed by a large-frame argon ion laser focused to 20 µm into the center of the MOT. This laser runs single-line at 488 nm with a maximum power of 10.6 watts. These parameters result in a trap of 125 mK for calcium atoms in the 4s3d 1D2 state. The 488 nm light also photo-ionizes the trapped atoms due to a near-resonant transition to the 4s4f 1F3 level. These ions leave the trap and are detected to determine the trap decay rate. By measuring this decay rate as a function of 488 nm intensity, we determine the 1F3 photo-ionization cross section at this wavelength to be approximately 230 Mb.
Figure from thesis
Optical Detection of Ultracold Neutral Calcium Plasmas (by Elizabeth Ann Cummings)
We demonstrate an optical method to detect calcium ions in an ultracold plasma. We probe the plasma with a 397 nm laser beam tuned to the Ca II 2S1/2 to 2P1/2 transition. The probe laser beam is focused to a 160 µm waist allowing fine spatial resolution. Ions are detected by measuring fluorescence using a PhotoMultiplier Tube (PMT). The signal, an average of 4000 acquisitions, has a temporal resolution of 120 ns. We present the details of this method, potential improvements, and prospects of imaging the expanding plasma ions. We also present preliminary work on spatially resolved absorption measurements, as well as additional studies.