The energy distribution of an ion in a radiofrequency trap interacting with a nonuniform neutral buffer gas

An ion in a radiofrequency (rf) trap sympathetically cooled by a simultaneously trapped neutral buffer gas exhibits deviations from thermal statistics caused by collision-induced coupling of the rf field to the ion motion. For a uniform density distribution of the buffer gas, the energy distribution of the ion can be described by Tsallis statistics. Moreover, runaway heating of the ion occurs if the buffer gas particles are sufficiently heavy relative to the ion. In typical experiments, however, ultracold buffer gases are confined in traps resulting in localised, non-uniform density distributions. Using a superstatistical approach, we develop an analytical model for an ion interacting with a localised buffer gas. We demonstrate theoretically that limiting collisions to the centre of the ion trap enables cooling at far greater mass ratios than achievable using a uniform buffer gas, but that an upper limit to the usable mass ratio exists even in this case. Furthermore, we analytically derive the functional form of the energy distribution for an ion interacting with a buffer gas held in a harmonic potential. The analytical distribution obtained is found to be in excellent agreement with the results of numerical simulations.     

Multispectral imaging with a confocal microendoscope

The concept of a multispectral confocal microscope for in vivo imaging is introduced. To demonstrate the concept we modified a slit-scan fluorescence confocal microendoscope incorporating a fiber-optic catheter for in vivo imaging to record multispectral images. The system was designed to examine cellular structures during optical biopsy and to exploit the diagnostic information contained within the spectral domain. Preliminary experiments were carried out in phantoms and cell cultures to demonstrate the potential of the technique.     

Oscillator strengths from line absorption in a high-temperature furnace—II. The (0,0) band of the B2σ+—X2σ+ transition in CN*

Quantitative high-resolution absorption spectroscopy was applied to the (0,0) violet band of CN. The CN radical was prepared in a furnace at 1421°K containing pure cyanogen gas. Since the calculated CN concentration is dependent on the controversial CN heat of formation, only the relationship, f_υ = 6·84 X 10^-3exp (0·354δ), where f_υ is the excess over the initially assumed ΔH⁰_f(CN) = 100·8 kcal/mole, could be directly determined in this study with an estimated error in f_υ of ±20%. For δ = 0, our f_υ is a factor of 4·8 smaller than an average value of 0·033±0· derived from other measurements. If this latter value of f_υ is assumed, our relationship yields ΔH⁰_f(CN) = 105·3±1· kcal/mole or D₀(CN) = 7·66±0·05 eV. The rotational temperature and line widths for this band were also measured.