Charles L. Bennett

Imaging Fourier transform spectrometer

The operating principles of an Imaging Fourier Transform Spectrometer (IFTS) are discussed. The advantages and disadvantages of such instruments with respect to alternative imaging spectrometers are discussed. The primary advantages of the IFTS are the capacity to acquire more than an order of magnitude more spectral channels than alternative systems with more than an order of magnitude greater etendue than for alternative systems. The primary disadvantage of IFTS, or FTS is general, is the sensitivity to temporal fluctuations, either random or periodic. Data from the IRIFTS (ir IFTS) prototype instrument, sensitive in the infrared, are presented having a spectral sensitivity of 0.01 absorbance units per pixel, a spectral resolution of 6 cm-1 over the range 0 to 7899 cm-1, and a spatial resolution of 2.5 mr.

Livermore Imaging Fourier Transform Infrared Spectrometer (LIFTIRS)

Lawrence Livermore National Laboratory is currently operating a hyperspectral imager, the Livermore Imaging Fourier Transform Infrared Spectrometer. This instrument is capable of operating throughout the infrared spectrum from 3 to 12.5 micrometers with controllable spectral resolution. In this presentation we report on its operating characteristics, current capabilities, data throughput, and calibration issues.

Hyperspectral imaging in the infrared using LIFTIRS

In this article, recent characterization measurements made with LIFTIRS, the Livermore imaging Fourier transform infrared spectrometer, are presented. A discussion is also presented of the relative merits of the various alternative designs for imaging spectrometers.

Measurement of DT neutron‐induced activity in glass‐microshell laser fusion targets

Laser fusion targets consisting of DT gas contained in Teflon‐coated glass microshells produce 14.1‐MeV neutrons that can interact with the 28Si nuclei in the glass to produce radioactive 28Al. Using a very efficient collection‐detection scheme that could detect the decay of 10% of the 28Al created, we identified these nuclei by their 1.78‐MeV γ ray, which decayed with a 2.2‐min half‐life. From the number of 28Al nuclei created and the neutron yield the compressed glass areal density was found to be 0.0059 g/cm2.

Evaporative cooling of highly charged ions in EBIT: An experimental realization

Both the total number and trapping lifetime of near‐neon‐like gold ions held in an electron beam ion trap have been greatly increased by a process of ‘evaporative cooling.’ A continuous flow of low‐charge‐state ions into the trap cools the high‐charge‐state ions in the trap. Preliminary experimental results using titanium ions as a coolant are presented.

Experiments to support the development of techniques for hyperspectral mine detection

Under the sponsorship of the DARPA Hyperspectral Mine Detection program, a series of both non-imaging and imaging experiments have been conducted to explore the physical basis of buried object detection in the visible through thermal infrared. Initially, non-imaging experiments were performed at several geographic locations. Potential spectral observables for detection of buried mines in the thermal portion of the infrared were found through these measurements. Following these measurements with point spectrometers, a series of hyperspectral imaging measurements was conducted during the summer of 1995 using the SMIFTS instrument from the University of Hawaii and the LIFTIRS instrument from Lawrence Livermore National Laboratory. The SMIFTS instrument (spatially modulated imaging Fourier transform spectrometer) acquires hyperspectral image cubes in the short-wave and mid-wave infrared and LIFTIRS (Livermore imaging Fourier transform infrared spectrometer) acquires hyperspectral image cubes in the long-wave infrared. Both instruments were optimized through calibration to maximize their signal to noise ratio and remove residual sensor pattern. The experiments were designed to both explore further the physics of disturbed soil detection in the infrared and acquire image data to support the development of detection algorithms. These experiments were supported by extensive ground truth, physical sampling and laboratory analysis. Promising detection observables have been found in the long-wave infrared portion of the spectrum. These spectral signatures have been seen in all geographical locations and are supported by geological theory. Data taken by the hyperspectral imaging sensors have been directly input to detection algorithms to demonstrate mine detection techniques. In this paper, both the non-imaging and imaging measurements made to date will be summarized.

Infrared hyperspectral imaging results from vapor plume experiments

In this article, recent measurements made with LIFTIRS, the Livermore Imaging Fourier Transform Infrared Spectrometer, are presented. The experience gained with this instrument has produced a variety of insights into the tradeoffs between signal to noise ratio (SNR), spectral resolution, and temporal resolution for time multiplexed Fourier transform imaging spectrometers. This experience has also clarified the practical advantages and disadvantages of Fourier transform hyperspectral imaging spectrometers regarding adaptation to varying measurement requirements on SNR versus spectral resolution, spatial resolution, and temporal resolution.

Effect of jitter on an imaging FTIR spectrometer

Line of sight (LOS) jitter produces temporal modulations of the signals which are detected in the focal plane of a temporally modulated imaging Fourier Transform Spectrometer. A theoretical treatment of LOS jitter effects is given, and is compared with the results of measurements with LIFTIRS (the Livermore Imaging Fourier Transform InfraRed Spectrometer). The identification, isolation, quantification and removal of jitter artifacts in hyperspectral imaging data by means of principal components analysis is discussed. The theoretical distribution of eigenvalues expected from principal components analysis is used to determine the level of significance of spatially coherent instrumental artifacts in general, including jitter as a representative example. It is concluded that an imaging FTIR spectrometer is much less seriously impacted by a given LOS jitter level than a non imaging FTIR spectrometer.

EBIT: Electron beam ion trap

An electron Beam Ion Trap (EBIT) has been built as an instrument for in situ studies of atomic physics. Based on the EBIS concept, EBIT incorporates several novel features including ion cooling using light ions and plasma instability control using a short trap length. To understand the operation of EBIT, measurements have been made of the electron beam behavior. The radius of the beam is observed to follow Herrmann Theory during compression. The electron beam displays an energy dispersion that is larger than theory. However, this energy dispersion is only about 15% of the electron temperature in the trap due to the adiabatic compression of the beam.

Dielectronic recombination measurements of highly‐charged heliumlike and neonlike ions using an electron beam ion trap

The electron beam ion trap (EBIT) at LLNL is a unique device designed to measure the interactions of electrons with highly‐charged ions. We describe three methods used at EBIT to directly measure the dielectronic recombination (DR) process: (1) The intensity of the stabilizing X rays is measured as a function of electron beam energy; (2) The ions remaining in a particular ionization state are counted after the electron beam has been held at a fixed electron energy for a fixed time; and (3) High‐resolution spectroscopy is used to resolve individual DR satellite lines. In our discussions, we concentrate on the KLL resonances of the heliumlike target ions (V21+ to Ba54+), and the LMM resonances of the neonlike target ions (Xe44+ to Th80+).