Stray Light Correction Research Articles

A combination of a pulsed continuum light source, a high resolution spectrometer, and a charge coupled device detector for multielement atomic absorption spectrometry

This paper presents first results of atomic absorption measurements carried out for the development of a new multielement atomic absorption spectrometer. The results were obtained in the wavelength range 283–228 nm, using a flash lamp continuum of high intensity, a newly developed, advanced high-resolution echelle spectrometer and a charge coupled device (CCD) array as radiation detector arranged in the focal plane of the spectrometer. In this measuring method, each flash exposure yields the complete information for an absorption measurement including the background absorption. Because of the simultaneous measurement of the two intensity values I 0 and I these two quantities are processed with a correlation coefficient of r = 1. Using a graphite tube furnace as an absorber, characteristic masses of 0.6 and 18 pg are achieved for the elements Cd and Pb, respectively, which exceed those of line atomic absorption with the same absorption equipment by a factor of only 2 and 1.5, respectively. Absorption measurements were carried out on saturated Hg vapour in quartz cuvettes at room temperature. Owing to the high intensity of the continuum radiation at all wavelengths, appreciable stray light components occur in the echelle spectrometer, requiring a stray light correction of the measured intensity values.

Stray-light correction in photoacoustic measurements of solid samples

An experimental correction procedure is presented which allows one to measure separately and to eliminate signal contributions produced at the walls of photoacoustic cells by the directly incident light or by the light (diffusively) reflected from the solid sample. This stray-light correction procedure is tested for an opaque and a transparent photoacoustic cell. It helps to reduce the systematic error of photoacoustic measurements considerably when the solid to be analyzed and the reference material have different reflection properties and when in quantitative thermal depth profiling a larger interval for the modulation frequency of heating is needed.

Straylight correction to doppler rotation measurements

The data published by Pierce and LoPresto (1984) are corrected for straylight. This correction increases the observed equatorial rotation velocity from 1977 to 2004 m s −1. The correction has an uncertainty of approximately 10 m s−1 because the accurate form of the straylight function is not available.

Solar luminosity fluctuations and active region photometry

view Abstract Citations (25) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar luminosity fluctuations and active region photometry Chapman, G. A. ; Herzog, A. D. ; Lawrence, J. K. ; Shelton, J. C. Abstract Monochromatic observations, obtained with a 512-element diode array, of the irradiance fluctuations of the sunspots and faculae of an active region during its disk transit in August 1982 are presented. Bolometric and stray light corrections are approximately equal in magnitude but opposite in sign, so they have not been applied. The maximum sunspot fluctuation, as a fraction of the quiet-sun irradiance, is -800 parts per million (ppm). Faculae have a maximum irradiance fluctuation of about +200 ppm near the limbs. It is found that the facular energy excess is more than 50 percent of the sunspot energy deficit, which is -5.8 x 10 to the 35th ergs. These observations show that faculae are an important element in active region energy balance. Publication: The Astrophysical Journal Pub Date: July 1984 DOI: 10.1086/184315 Bibcode: 1984ApJ...282L..99C Keywords: Astronomical Photometry; Faculae; Stellar Luminosity; Sunspots; Bolometers; Energy Budgets; Irradiance; Solar Physics full text sources ADS |

Absolute emission cross sections for the calibration of optical detection systems in the 120–250 nm range

Absolute emission cross sections have been determined for electron impact on CO, NO and N 2. For the CO(A 1ΠX 1Σ +) and N 2(a 1ΠX 1Σ g) radiation our data is in good agreement with that of other groups. For CO + (B 2Σ +X 2Σ +) the values of the emission cross sections are different from those measured previously. This discrepancy is explained in terms of an inadequate straylight correction in the former experiments. For the NO(A 2Σ +X 2Π) emission no previous σ em values are known to the authors. Furthermore the electronic transition moments of the NO(A 2Σ +X 2Π) and CO +(B 2ΣX 2Σ +) systems have been measured and are found to be independent of the internuclear distance.

Photocount statistic and correlation for a single Lorentzian

The photocount statistic and the second order correlation function was measured for a simple diffusion process. The former was fitted to the exact Bedard formula, taking straylight and 4th order dead-time corrections into account. The coherence time determined from count statistic and correlation are compared.

Scattered light - a comparison between theory and experiments during the 1973 transit of Mercury

We check the formalism used to derive stray light corrections from measured aureole intensities and correct an error in the pertinent literature. We solve the alledged problem of appropriately normalizing the spread function by treating blurring and scattering separately. We test the method by comparing stray light corrections derived from both the aureole and from intensity profiles across Mercury's disc obtained during the transit of November 10, 1973.

Relative umbral intensity of a large sunspot

Simultaneous observations of relative umbral intensities in four wavelength regions are presented. In the visual wavelength region the umbral intensities show lower values than given by most authors. By observing the same spot during different seeing conditions the method of correction for stray light is found to be consistent within the accuracy of the method. In addition, a new simple correction method is suggested.

Correction of solar observations for stray light by numerical integration, with application to Mercury's drop

A numerical method for correction of stray light in solar observations has been developed. In particular a regular sunspot, where the circular contours of penumbra and umbra are projected as ellipses, has been studied. When a specified set of values for the stray light parameters is given, and also tentative values for the relative intensities of penumbra and umbra, the integration of stray light can be performed in any point. The result will be the observable intensity if the conditions were as given by these initial values.

AUTOMATIC SCANNING SPECTROPHOTOMETER WITH PUNCH TAPE OUTPUT FOR BIO‐APPLICATIONS

Abstract— An automated scanning spectrophotometer has been constructed for the measurement of color‐vision test stimuli and various types of luminescence. Recorder and paper tape output data have been provided. Processing of the spectral information is performed on a CDC 3300 computer.Photoelectric detection is employed. An inexpensive Jarrel‐Ash 0.25 m,f/3.6 Ebert type monochromator is employed with two gratings, blazed for 300 and 600 nm, respectively.The spectral sweep range can be easily set by electromechanical registers, as can the number of sweeps required. Photon numbers are integrated by a counter over 5 nm blocks, and this procedure sets the limit of resolution. At present the spectral range is from 400 to 800 nm. By calibration against an ultraviolet‐emitting standard lamp the useful range can easily be extended downwards to 250 nm.Computer programs have been written which add several spectra when these are faint and produce a mean spectrum in the form of listed and plotted output. The mean noise level is subtracted. Subprograms have been made for the smoothing of poor spectral data where noise predominates and for the correction for stray light and grating ‘ghosts’ in the monochromator. A program has been made which performs colorimetric analyses of light sources, spectral filters, and pigmented surfaces. The dominant wavelength and the excitation purity are computed and given in CIE chromaticity coordinates and three‐stimulus values.

Stray Light in Absorption Spectrophotometry. III. A Survey of Methods for Evaluating Stray Light Levels and Stray Light Corrections

An experimental survey of the estimation of stray light levels and corrections has been carried out. The performance of methods requiring no special instrumentation has been evaluated and compared. A new method, as convenient as the currently used filters method and capable of yielding better results especially when large stray light corrections are required, has been established and tested.

Isotopes of magnesium in the solar atmosphere

We have analysed MgH A2Π-X2Σ(0.0), (1.1), (2.2), (0.1) and (1.2) absorption bands in a sunspot spectrum. By two different methods, which are almost independent of the estimated value of the correction for stray light, we have determined the solar isotopic ratios of magnesium. These ratios are equal to the terrestrial ones - 24Mg∶25Mg∶26Mg = 80∶10∶10.

Observations of stray-light and sunspot intensities during the Mercury transit of 1970 May 9

In order to test the usual method for correcting sunspot intensity measurements for stray light, we have measured, during the Mercury transit of 1970 May 9, the intensities of Mercury, a sunspot umbra, and the aureole. The direct observations result in Mercury intensities < 0.06 I ⊙ and aureole intensities <0.01 I ⊙. The stray light correction to the spot intensities has been <(0.03 ± 0.01) I ⊙. The main contribution to the stray light on the solar disc is shown to be produced by a spread-function with a half width of 10 arc sec. Consequently, for stray light corrections the range R ⩽ R ⊙ + + 20″ in the aureole has to be measured very precisely; furthermore, a remarkable fraction of the stray light in the center of an umbra originates from the surrounding penumbra.

The Photo-Electric Threshold for Mercury

In order to insure a perfectly clean surface of mercury for test, the apparatus was arranged so that carefully purified mercury flowed intermittently into a shallow iron cup and out through an overflow opening at the surface back into an electrically heated still. Direct observation showed that with such a flow the surface cleans itself of any added contamination very quickly. Also, the results for the wave-length limit were found to be independent of the rate of flow, to a rate far below that normally used, and also unaffected by the presence of gases (air, ${\mathrm{H}}_{2}$, ${\mathrm{O}}_{2}$, He and C${\mathrm{O}}_{2}$) and even of traces of water vapor in the photochamber. The photo-currents to a copper oxide receiver were measured by means of a quadrant electrometer to within about 1 percent for various Hg lines from a Cooper-Hewitt quartz mercury arc, correction being made for stray light by means of intermediate readings. This arc operated at 92-93 volts with 2.1 amp., was constant to 1 percent. Intensity measurements accurate to 1 percent were made by means of a vacuum thermopile connected to a d'Arsonval galvanometer (sensitivity ${10}^{\ensuremath{-}9}$ amp.) using a Hilger monochromator to disperse the light and making correction for stray light by taking readings between the lines. Plots of the ratio of corrected photo-current to corrected light intensity as a function of wave-length give the threshold at 2735A. The corresponding photo-electric work function is 4.52 volts. This result is free from the objections raised to those of previous observers and seems clearly to be the evaluation of an intrinsic property of mercury uncontaminated by surface impurities.