We report new detailed density profile measurements in expanding strongly-coupled neutral plasmas. Using laser-induced fluorescence techniques, we determine plasma densities in the range of 10 5 to 10 9 cm −3 with a time resolution limit as small as 7 ns. Strong-coupling in the plasma ions is inferred directly from the fluorescence signals. Evidence for strong-coupling at late times is presented, confirming a recent theoretical result. [2], and in some astrophysical settings. A new class of strongly-interacting neutral plasmas was recently demonstrated using the tools of laser-cooling and trapping [3,4,5,6,7]. These "ultracold" neutral plasmas occupy a unique position in phase space. In these plasmas it is possible to create strongly-interacting Coulomb systems at modest densities because the initial electron and ion temperatures can be in the milliKelvin range. The initial ion-ion and ion-electron interaction strength can also be selected with great precision.Recent experimental work in this field has used absorption imaging techniques to make temperature and density measurements in expanding ultracold neutral plasmas [6,7]. This work explored the 50 to 1000 ns time period after plasma formation in great detail. Correlationinduced heating was observed in the plasma ions. The ion coupling parameter, given as the ratio of nearestneighbor Coulomb energy to the kinetic energy, equilibrated just inside the strongly-coupled regime, with a coupling parameter around 2.Radio-frequency (RF) excitation techniques have also been used to determine the average ion density and the electron temperature in these systems [4,8,9]. These studies confirm theoretical predictions regarding the generally self-similar Gaussian expansion of the ions and the clamping of the electron temperature in the weaklycoupled regime.In this letter we report laser-induced-fluorescence measurements of ions in expanding strongly-coupled plasmas as a tool to study the spatial and temporal evolution of the ion temperature and density. This measurement technique has a 7 ns temporal resolution limit. We measure plasma densities as low as 10 5 cm −3 at effective plasma temperatures of 100 K. The maximum density that can be measured is limited by radiation trapping, and for spherically-symmetric systems in the milliKelvin range is limited to around 10 9 cm −3 . The temporal resolution * Present Address: Lockheed Martin Space Systems Company, Sunnyvale, CA 94089 † Electronic address: scott.bergeson@byu.edu and dynamic range of this method in ultracold plasma measurements surpass those currently seen in absorption spectroscopy, and rival the sensitivity of RF spectroscopic methods.Much of the experimental setup has been described previously [10]. We create a calcium magneto-optical trap (MOT) using the resonance transition at 423 nm. Up to 50 mW of 423 nm radiation is generated by frequency-doubling a diode laser system at 846 nm using a periodically-poled KTP crysal in a resonant build-up cavity. The 423 nm MOT light is detuned one line-width below the atom...

We extend an isothermal thermal model of ultracold neutral plasma expansion to systems without spherical symmetry, and use this model to interpret new fluorescence measurements on these plasmas. By assuming a self-similar expansion, it is possible to solve the fluid equations analytically and to include velocity effects to predict the fluorescence signals. In spite of the simplicity of this approach, the model reproduces the major features of the experimental data

We report an optical dipole trap for calcium. The trap is created by focusing a 488-nm argon-ion laser beam into a calcium magneto-optical trap. The argon-ion laser photoionizes atoms in the trap because of a nearresonance with the 4s4f 1 F 3 level. By measuring the dipole-trap decay rate as a function of argon-ion laser intensity, we determine the 1 F 3 photoionization cross section at our wavelength to be approximately 230 Mb.