Measuring the electron beam quality of an ultracold plasma setup

We report measurements and simulations of disorder-induced heating in ultracold neutral plasmas. Fluorescence from plasma ions is excited using a detuned probe laser beam while the plasma relaxes from its initially disordered nonequilibrium state. This method probes the wings of the ion velocity distribution. The simulations yield information on time-evolving plasma parameters that are difficult to measure directly and make it possible to connect the fluorescence signal to the rms velocity distribution. The disorder-induced heating signal can be used to estimate the electron and ion temperatures $~$100 ns after the plasma is created. This is particularly interesting for plasmas in which the electron and ion temperatures are not known.We report measurements and simulations of disorder-induced heating in ultracold neutral plasmas. Fluorescence from plasma ions is excited using a detuned probe laser beam while the plasma relaxes from its initially disordered nonequilibrium state. This method probes the wings of the ion velocity distribution. The simulations yield information on time-evolving plasma parameters that are difficult to measure directly and make it possible to connect the fluorescence signal to the rms velocity distribution. The disorder-induced heating signal can be used to estimate the electron and ion temperatures $~$100 ns after the plasma is created. This is particularly interesting for plasmas in which the electron and ion temperatures are not known.

Physical Review AFeb 11, 201134 citations

Very slow expansion of an ultracold plasma formed in a seeded supersonic molecular beam of NO

J. P. Morrison, Chris Rennick, Edward R. Grant

The double-resonant laser excitation of nitric oxide, cooled to 1 K in a seeded supersonic molecular beam, yields a gas of $\ensuremath{\approx}{10}^{12}$ molecules per cubic centimeter in a single selected Rydberg state. This population evolves to produce prompt free electrons, and a durable cold plasma of electrons and intact ${\text{NO}}^{+}$ ions. This plasma travels with the molecular beam through a field-free region to encounter a grid. The atomic weight of the expansion gas controls the beam velocity and hence the flight time from the interaction region to the grid. Monitoring electron production as the plasma traverses this grid measures its longitudinal width as a function of flight time. Comparing these widths to the width of the laser beam that defines the initial size of the illuminated volume allows us to gauge the rate of expansion of the plasma. We find that the plasma created from the evolution of a Rydberg gas of NO expands at a small but measurable rate, and that this rate of expansion accords with the Vlasov equations for an initial electron temperature of ${T}_{e}\ensuremath{\approx}7\text{ }\text{K}$.The double-resonant laser excitation of nitric oxide, cooled to 1 K in a seeded supersonic molecular beam, yields a gas of $\ensuremath{\approx}{10}^{12}$ molecules per cubic centimeter in a single selected Rydberg state. This population evolves to produce prompt free electrons, and a durable cold plasma of electrons and intact ${\text{NO}}^{+}$ ions. This plasma travels with the molecular beam through a field-free region to encounter a grid. The atomic weight of the expansion gas controls the beam velocity and hence the flight time from the interaction region to the grid. Monitoring electron production as the plasma traverses this grid measures its longitudinal width as a function of flight time. Comparing these widths to the width of the laser beam that defines the initial size of the illuminated volume allows us to gauge the rate of expansion of the plasma. We find that the plasma created from the evolution of a Rydberg gas of NO expands at a small but measurable rate, and that this rate of expansion accords with the Vlasov equations for an initial electron temperature of ${T}_{e}\ensuremath{\approx}7\text{ }\text{K}$.

arXiv:0812.4051Physical Review AJun 9, 200929 citations

Ultracold plasmas : phenomena and applications

Edgar J. D. Vredenbregt

Ultracold plasmas (UCPs) represent a marriage between the seemingly distinct fields of cold atom physics and plasma physics. In cold atom physics, dilute clouds of atoms can be trapped with laser radiation and cooled to J.1Ktemperatures. In contrast, in plasma physics the constituents generally have temperatures in the 1,000K-1O,000K range as well as much higher density. In 1999,Rolston and co-workers [1] first converted a cloud of laser-cooled atoms into a plasma by photo-ionizing the atoms just above threshold. This provides very unusual circumstances:the temperature of ions and neutrals is O.OOIK,that of electrons 10K! Such ultra-cold plasmas therefore are interesting subjects for fundamentalplasma physics studies.\nIn a recent paper [2], we argued that ultracold plasmas (UCPs) may in addition provide an entirely new way of generatinghigh-brightnesscharged-particlebeams, such as used in focused-ion beams, laser synchrotrons, and ultra-fast electron microscopy.\nHere, a low temperature T is beneficial for the intrinsic (transverse) brightness B of a\nsource since B = II(A1), where I is the current and A the cross-sectional area. I will discuss an experimental investigation of the properties of ion and electron beams extracted from ultracold plasmas, which shows that such beams indeed have low temperatures, and, as a result, high angular intensity.Ultracold plasmas (UCPs) represent a marriage between the seemingly distinct fields of cold atom physics and plasma physics. In cold atom physics, dilute clouds of atoms can be trapped with laser radiation and cooled to J.1Ktemperatures. In contrast, in plasma physics the constituents generally have temperatures in the 1,000K-1O,000K range as well as much higher density. In 1999,Rolston and co-workers [1] first converted a cloud of laser-cooled atoms into a plasma by photo-ionizing the atoms just above threshold. This provides very unusual circumstances:the temperature of ions and neutrals is O.OOIK,that of electrons 10K! Such ultra-cold plasmas therefore are interesting subjects for fundamentalplasma physics studies.\nIn a recent paper [2], we argued that ultracold plasmas (UCPs) may in addition provide an entirely new way of generatinghigh-brightnesscharged-particlebeams, such as used in focused-ion beams, laser synchrotrons, and ultra-fast electron microscopy.\nHere, a low temperature T is beneficial for the intrinsic (transverse) brightness B of a\nsource since B = II(A1), where I is the current and A the cross-sectional area. I will discuss an experimental investigation of the properties of ion and electron beams extracted from ultracold plasmas, which shows that such beams indeed have low temperatures, and, as a result, high angular intensity.

Jan 1, 20060 citations

How electron collisions shape an ultracold plasma

Edward R. Grant

Bulletin of the American Physical SocietyJun 8, 20120 citations

{\text{NO}}^{+}

ions. This plasma travels with the molecular beam through a field-free region to encounter a grid. The atomic weight of the expansion gas controls the beam velocity and hence the flight time from the interaction region to the grid. Monitoring electron production as the plasma traverses this grid measures its longitudinal width as a function of flight time. Comparing these widths to the width of the laser beam that defines the initial size of the illuminated volume allows us to gauge the rate of expansion of the plasma. We find that the plasma created from the evolution of a Rydberg gas of NO expands at a small but measurable rate, and that this rate of expansion accords with the Vlasov equations for an initial electron temperature of ${T}_{e}\ensuremath{\approx}7\text{ }\text{K}$.