The high-resolution time-of-flight spectrometer TOFTOF

The TOFTOF spectrometer is a multi-disc chopper time-of-flight spectrometer for cold neutrons at the research neutron source Heinz Maier-Leibnitz (FRM II). After five reactor cycles of routine operation the characteristics of the instrument are reported in this article. The spectrometer features an excellent signal to background ratio due to its remote position in the neutron guide hall, an elaborated shielding concept and an s-shaped curved primary neutron guide which acts i.a. as a neutron velocity filter. The spectrometer is fed with neutrons from the undermoderated cold neutron source of the FRM II leading to a total neutron flux of 10¹⁰n/cm²/s in the continuous white beam at the sample position distributed over a continuous and particularly broad wavelength spectrum. A high energy resolution is achieved by the use of high speed chopper discs made of carbon-fiber-reinforced plastic. In the combination of intensity, resolution and signal to background ratio the spectrometer offers new scientific prospects in the fields of inelastic and quasielastic neutron scattering.     

Multiple-fluorophore-specie detection with a tapered Fabry-Perot fluorescence spectrometer

A novel fluorescence spectrometer and method for the simultaneous detection of multiple-fluorophore species in a no-moving-parts, instantaneous manner is described. In the reported embodiment of the instrument, a tapered Fabry-Perot filter is used to spatially encode the fluorescence spectrum from a multiple-dye-containing test sample. Using a pseudoinverse reconstruction algorithm, we spectrally decode the particle concentration for each dye specie in the test sample. Experimental results are reported along with a theoretical treatment of the method.     

A large high-resolution sodium iodide spectrometer

The new NaI detector system for high-energy gamma-ray detection at The Svedberg Laboratory is presented together with results from test experiments. The system has high efficiency, good energy resolution and rejects cosmic radiation efficiently. For example, the resolution is 1.6% at 22.6 MeV, the best value obtained so far for a NaI detector in this size category.     

Field-deployable, high-resolution, time-of-flight aerosol mass spectrometer

The development of a new high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) is reported. The high-resolution capabilities of this instrument allow the direct separation of most ions from inorganic and organic species at the same nominal m/z, the quantification of several types of organic fragments (CxHy, CxHyOz, CxHyNp, CxHyOzNp), and the direct identification of organic nitrogen and organosulfur content. This real-time instrument is field-deployable, and its high time resolution (0.5 Hz has been demonstrated) makes it well-suited for studies in which time resolution is critical, such as aircraft studies. The instrument has two ion optical modes: a single-reflection configuration offers higher sensitivity and lower resolving power (up to approximately 2100 at m/z 200), and a two-reflectron configuration yields higher resolving power (up to approximately 4300 at m/z 200) with lower sensitivity. The instrument also allows the determination of the size distributions of all ions. One-minute detection limits for submicrometer aerosol are <0.04 microg m(-3) for all species in the high-sensitivity mode and <0.4 microg m(-3) in the high-resolution mode. Examples of ambient aerosol data are presented from the SOAR-1 study in Riverside, CA, in which the spectra of ambient organic species are dominated by CxHy and CxHyOz fragments, and different organic and inorganic fragments at the same nominal m/z show different size distributions. Data are also presented from the MIRAGE C-130 aircraft study near Mexico City, showing high correlation with independent measurements of surrogate aerosol mass concentration.     

Gain measurements of Fabry-Perot InP/InGaAsP lasers using an ultrahigh-resolution spectrometer

Measurements of the optical gain in a semiconductor laser using a 20 MHz resolution optical spectrum analyzer are presented for what is believed to be the first time. The high resolution allows for accurate gain measurements close to the lasing threshold. This is demonstrated by gain measurements on a bulk InGaAsP 1.5 microm Fabry-Perot laser. Combined with direct measurement of transparency carrier density values, parameters were determined for characterizing the gain at a range of wavelengths and temperatures. The necessity of the use of a logarithmic gain model is shown.     

Deriving wavelength spectra from fringe images from a fixed-gap single-etalon Fabry-Perot spectrometer

A new method is described for inferring wavelength spectra from two-dimensional images of Fabry-Perot interference fringes. This new method addresses the practical difficulties that have been previously encountered in determining the fringe image's center, magnification, and distortions accurately enough to fully exploit the spectral resolution provided by the etalon. The method proceeds in two steps. First, the instrument's mapping of image position to interference order is characterized by use of images of a scene illuminated uniformly by a highly monochromatic laser. Then this information is applied to resample two-dimensional images of unknown radiation sources down to sets of one or more one-dimensional wavelength spectra. Discrete cross-correlation techniques are used at both stages of anal-     

Superconducting magnetic system of a 400-MHz high-resolution NMR spectrometer

Translated from Izmeritel'naya Tekhnika, No. 11, pp. 53–54, November, 1989.     

Phase compensation of a separation scanned, all-sky imaging Fabry-Perot spectrometer for auroral studies

We describe a new all-sky imaging spectrometer using a separation scanned Fabry-Perot étalon. It is intended for ground-based mapping of upper atmospheric wind and temperature fields in the auroral zone. Its major advantage is that recorded spectra are not distorted by spatial and temporal brightness fluctuations in the aurora. We present a discussion of previous approaches to field widening a Fabry-Perot spectrometer, then describe the principles underlying our method. This enables comparisons with the throughput and the response to brightness fluctuations provided by previous instruments. We also describe our instrument's optical layout, its calibration, and data analysis.     

Design of a high-resolution extreme-ultraviolet imaging spectrometer with aberration-corrected concave gratings

A high-resolution extreme-ultraviolet imaging spectrometer is designed for the Japanese solar mission Solar-B. A spherical varied-line-space (SVLS) grating and a toroidal uniform-line-space (TULS) grating are chosen as candidates for use in the spectrometer to yield high spectral and spatial resolution within the spectral range 25-29 nm. The spectral image-focusing properties and the mechanical tolerances for fabrication and alignment are compared for the two types of grating. The SVLS design is found to be superior to the TULS design for off-plane spectral images and in ease of fabrication and optical alignment.     

Analytical description of a Fabry-Perot spectrometer. 8: Optimum operation with equidistant equal-noise sampling

The optimum parameters of operation for a Fabry-Perot spectrometer used in the equidistant equal-noise sampling method have been calculated. The results, expressed in terms of normalized halfwidths at half-height, are: etalon (a*) = 0.078 (0.095), linewidth (dg*) = 0.13 (0.19), and aperture (f*) = 0.10 (0.19) for temperature (wind) determinations. The etalon widths correspond to rather low reflectivities, namely, 0.62 and 0.56. The critical number of samples, required for unambiguous determinations of a measured profile, are found to be equal to 8 and 12. The usefulness of the equal-noise method in absorption measurements is discussed.     

Dual Fabry-Perot spectrometer measurements of daytime thermospheric temperature and wind velocity: data analysis procedures

Daytime thermospheric temperatures and wind velocities have been inferred from dual Fabry-Perot spectrometer observations of the atomic oxygen emission line at lambda630 nm, and this paper details the analysis procedures applied to the recorded spectra. Numerical simulation of the recorded spectra was used to examine the limitations imposed by analysis assumptions and by the influence of atmospheric molecular oxygen and water vapor absorption lines near lambda630 nm. The observational and analysis procedures provide a reliable ground-based means of monitoring the thermal and dynamical state of the neutral thermosphere during the daytime.     

Electro-optic lightning detector

The design, alignment, calibration, and field deployment of a solid-state lightning detector is described. The primary sensing component of the detector is a potassium dihydrogen phosphate electro-optic crystal that is attached in series to a flat-plate aluminum antenna; the antenna is exposed to the ambient thundercloud electric field. A semiconductor laser diode (lambda = 685 nm), polarizing optics, and the crystal are arranged in a Pockels cell configuration. Lightning-caused electric field changes are related to small changes in the transmission of laser light through the optical cell. Several hundred lightning electric field change excursions were recorded during five thunderstorms that occurred in the summer of 1998 at the NASA Marshall Space Flight Center in northern Alabama.     

Electro-optic heterodyne interferometer

We propose a new configuration for using a triangle-wave signal to drive the electro-optic modulator in an electro-optic heterodyne interferometer system. The new configuration is adapted to measure the phase retardation of a wave plate and the optical rotation angle of a chiral medium. By adding optic elements, the second-harmonic component amplitude of the interferometer photodetector output signal became proportional to the phase retardation or optical rotation angle of the samples being tested.