Accurate wavelength calibration method for flat-field grating spectrometers

A portable spectrometer prototype is built to study wavelength calibration for flat-field grating spectrometers. An accurate calibration method called parameter fitting is presented. Both optical and structural parameters of the spectrometer are included in the wavelength calibration model, which accurately describes the relationship between wavelength and pixel position. Along with higher calibration accuracy, the proposed calibration method can provide information about errors in the installation of the optical components, which will be helpful for spectrometer alignment.     

Method of calibration of leak detectors over the entire effective range

A method for calibrating leak detectors that makes it possible to reproduce a sufficiently large number of calibration points over the entire effective range of the device using only two leaks is described. Because calibration is discrete, a situation that is appropriate to the relationship between the flows of both leaks, it is possible to regulate the flow of the test gas from the leaks into an analytic chamber. Translated from Izmeritel'naya Tekhnika, No. 6, pp. 23–24, June, 1998.     

A method of calibrating voltage measuring transformers over an extended frequency range

The principle of the construction of a means for calibrating measuring voltage transformers, which enables the transformer ratios of measuring voltage transformers to be determined over a extended frequency range is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 2, pp. 46–48, February, 2006.     

Accurate and precise wavelength calibration for wide bandwidth array spectrometers

Calibrating the wavelength scale of an array spectrometer typically involves measurements of lines at well-known wavelengths from a calibration lamp such as a mercury-argon source. This process is relatively straightforward when the lines are well separated, relative to the bandwidth of the spectrometer. When the spectrometer's bandwidth is large, compared with the distance between calibration wavelengths, it becomes increasingly difficult to accurately locate lines in the calibration spectrum. Even calibrations for instruments with a modest bandwidth of 12 nm can be difficult. Here we present results from a simple approach to improve the accuracy of wavelength calibration for an instrument with a large bandwidth (12 nm, center-to-center pixel spacing 3.3 nm). A monochromator has been used to filter the source so that each calibration line can be measured separately. For ten spectrometers, we were able to achieve accuracy better than 0.12 nm, or 0.09 nm on average; this is less than 3% of the pixel spacing. We anticipate this approach will be useful for improving the accuracy of measurements on array spectrometers and particularly in transferring multivariate calibrations between instruments.     

Multi-functional apparatus for the measurement of wavelength and the spectra of light sources over a broad spectral range

A multifunctional apparatus used for the study and certification of the wavelength of light sources is described. The wavelength range of interest is from O.5– 4.0 pm. The instrument is capable of characterizing the radiation from spectral lamps, as well as gas and semiconductor lasers. An error analysis is presented for the measurement of wavelength using a Fabry-Perot interferometer.Translated from Izmeritel'naya Tekhnika, No. 3, pp. 29–31, March, 1995.     

A semi-analytical solution to Brownian coagulation of fractal aggregates valid for the entire particle size range

Brownian coagulation is an important particle growth mechanism in a number of aerosol processes. Analytical solution to Brownian coagulation has been an interesting subject in aerosol population dynamics field because it can provide deep insight into the nature of the coagulation process. In the case of spherical particles, analytical solutions have been derived for all different particle size regimes. For fractal aggregates that can represent the morphology of many important industrial aerosol products and combustion soot particles, however, analytical solutions have been reported only for the free-molecule and continuum regimes. In this work, a semi-analytical solution to the Brownian coagulation of fractal aggregates valid for the entire particle size range is presented using the method of moments based on the assumption of log-normal particle size distribution. The new solution is validated by limiting-case analyses as well as by comparison with a more accurate numerical solution. The characteristics of the Brownian coagulation of fractal aggregates in the transition regime are discussed using the new solution.     

Investigation of the wavelength accuracy of brewer spectrophotometers

The wavelength accuracy of the Brewer spectrophotometer in the 280-360-nm spectral range is improved by a new grating-drive mechanism and a new dispersion function derived from the Brewer geometry. With the new mechanism, the reproducibility of wavelength settings for spectral emission lines is better than 0.3 pm (0.0003 nm) and, with a thermally compensated version, the effect of temperature is less than 0.4 pm K(-1). The new dispersion function fits spectral line positions better than the standard function and is less prone to extrapolation error. Applying the new function to data from four new and ten standard drives shows that the new drives perform as well as the best of the standard ones and much better than the majority.     

Simple method for antireflection coating ZnSe in the 20 microm wavelength range

We present a simple, inexpensive, and effective method of applying antireflection coatings to zinc selenide windows designed to operate in the thermal infrared wavelength region.     

Foamy-dielectric lens transmission lines for millimeter and submillimeter wavelength range

The principles of the construction of transmission lines based on lenses made of a material with a nearly unity refractive index (foamy-dielectric lens transmission line, FDLTL) are formulated. The transmission characteristics of two FDLTL variants for 3-mm wavelength band have been studied. It is shown that FDLTLs possess low damping and feature wave propagation in a single-mode regime.     

Matrix form for the instrument line shape of Fourier-transform spectrometers yielding a fast integration algorithm to theoretical spectra

The instrument line shape (ILS) of a Fourier-transform spectrometer is expressed in a matrix form. For all line shape effects that scale with wavenumber, the ILS matrix is shown to be transposed in the spectral and interferogram domains. The novel representation of the ILS matrix in the interferogram domain yields an insightful physical interpretation of the underlying process producing self-apodization. Working in the interferogram domain circumvents the problem of taking into account the effects of finite optical path difference and permits a proper discretization of the equations. A fast algorithm in O(N log2 N), based on the fractional Fourier transform, is introduced that permits the application of a constant resolving power line shape to theoretical spectra or forward models. The ILS integration formalism is validated with experimental data.     

A diffraction trap for neutrons in the Ångström wavelength range

The penetration depth of thermal neutrons (λ∼1 Å) upon the Bragg backscattering in a bent crystal is estimated. It is demonstrated that neutrons incident onto the crystal at an angle close to the edge of the Bragg reflection curve can be accumulated inside and then (after 1–100 μs) ejected from the crystal.     

Pulsed 5-GW resonance relativistic BWT for a decimeter wavelength range

The results of numerical modeling and experimental investigation of a high-power, resonance relativistic backward wave tube are presented. By using the working TM₀₁ mode reflections from the ends of the electrodynamic system, optimum conditions for the electron beam interaction with both the (−1)st harmonic of the backward electromagnetic wave and the main harmonic of the concurrent wave are achieved. A single mode generation with 5 GW output power and a 30% efficiency was obtained in experiments at a frequency of 3.6 GHz. The working frequency can be controlled within 15% (at the half maximum power level) by changing the slow-wave structure period at the constant electron beam parameters.     

The use of crystal phosphors based on rare-earth elements to determine the spectral resolution and to calibrate the wavelength scale of luminescence spectrometers

The results of an investigation of the crystal phosphor Y₂O₂S:Er,Yb to determine the possibility of using it to measure the spectral resolution and to calibrate the wavelength scale of luminescence spectrometers are presented. The luminescence spectrum of the crystal phosphor was measured on three spectrofluorescence instruments when excited by a laser with λ_max = 960 nm and with ultraviolet excitation with λ_max = 383 nm, the optical arrangements of which differ considerably in the radiation recording channel. The difference in the wavelength positions of the maxima of the spectra of the neon lamp used for calibration and of the crystal phosphor investigated is estimated.