Showing papers on "Stray light published in 1982"

Probing the Solar Wind Acceleration Region Using Spectroscopic Techniques

Abstract: Measurements of the intensities and profiles of UV and EUV spectral lines can provide a powerful tool for probing the physical conditions in the solar corona out to 8R ⊙ and beyond. We discuss here how measurements of spectral line radiation in conjunction with measurements of the white light K-corona can provide information on electron, proton and ion temperatures and velocity distribution functions; densities; chemical abundances and mass flow velocities. Because of the fundamental importance of such information, we provide a comprehensive review of the formation of coronal resonance line radiation, with particular emphasis on the H I Lα line, and discuss observational considerations such as requirements for rejection of stray light and effects of emission from the geocorona and interplanetary dust. Finally, we summarize some results of coronal H I Lα and white light observations acquired on sounding rocket flights.

Polarization and Depolarization in the Fiber-Optic Gyroscope

Abstract: From the scattering matrix of a general N-mode fiberoptic ring interferometer conditions are derived for gyro operation with stable zero point and stable scale factor. The discussion includes reciprocity, polarization filtering, stray light suppression, polarization adjustment and control, birefringence effects in optical fibers, nonreciprocity by magnetic field, polarization-holding fibers, and polarization scrambling by a depolarizer.

Apparatus for detecting foreign matters on a planar substrate

Abstract: An apparatus for detecting foreign matter present on a planar substrate comprises apparatus for scanning the surface of the substrate with an oblique incident light beam, apparatus for photo-electrically detecting the scattered light generator in the trajectory of the light beam scanning on the substrate, and apparatus for eliminating stray light unnecessary for the foreign matter detection

Heterochromatic stray light in UV absorption spectrometry: a new test method.

Abstract: A new method of estimating the amount of heterochromatic stray light in UV spectrophotometers is described. The method uses the same solution filters with sharp UV absorption edges as ASTM Test Method E387, but one measures the apparent absorbance of a 10-mm path-length cell in the sample beam relative to a 5-mm cell in the reference beam. Scanning toward shorter wavelengths, one records an apparent absorbance maximum which is a direct measure of the stray light. This method was found to be in satisfactory agreement with the ASTM method in comparative tests of several spectrophotometers at different wavelengths between 200 and 390 nm, using KC1, KI, Nal, acetone, and NaNO(2) solution filters. The new method proved to be simpler, the main advantage being that the apparent absorbance maximum occurs at considerably lower scale values than the corresponding absorbance plateau measured by the ASTM method. This reduces the need for successive attenuations of the reference beam every time the spectrophotometer runs off scale. In many instances the new method required no attenuation at all.

Stray light measurement and compensation

Abstract: Methods for stray light measurement and compensation in spectrophotometers are disclosed In one exemplary embodiment, stray light is determined as a convolution of a selected detected radiant power spectrum and a monochromator slit function Such a stray light measurement may be made with or without the sample in an optical path between a source and detector within the spectrophotometer When made with the sample in the optical path, the resulting stray light measurement may be used to compensate sample absorbance or transmittance measurements In accordance with another embodiment of the present invention, sample absorbance or transmittance may be compensated in a method including measuring sample detected radiant power at a wavelength outside an interval of significant detected radiant power within which a sample measurement compensated for stray is desired

Monochromator with concave grating

Abstract: A constant deviation monochromator with a holographically formed concave grating and entrance and exit slits positioned on opposite sides of the plane including the Rowland circle of the grating, wherein the grating has been formed by using two coherent light sources positioned on the same side of the Rowland plane, whereby aberrations and stray light are substantially reduced.

Multi-wavelength spectrometer

Abstract: PURPOSE:To eliminate the replacement of filters by arranging them on individual image detectors adapted to simultaneously detect spectra scattered according to the wavelength, as shited perpendicular to the scattered surface. CONSTITUTION:A light coming from a slit 21 is separated into spectra lambdal...lambdan with a grating and a prism. They irradiate image detectors 3, the output of which is processed with an amplifier 4, a scanner 5, an A/D converter 7, a memory 8 and the like to obtain data. The image detector 3 is composed of a plurality of detectors 31-33 and shifted perpendicular to the spectral surface (at the right angle to AA'' in the drawing) and with both ends overlapping, cut filters 36-38 are inserted into the front of the photo detection surface of the detectors as required. This enables simultaneous measurement of multiple wavelength elminating complicated replacement of the filters thereby providing a spectrometer minimizing the mixing of stray light and light of higher order.

Calcite 2 × 2 optical bypass switch controlled by liquid-crystal cells

Abstract: Three blocks of birefringent calcite and two 6-V twisted nematic liquid-crystal cells have been used to make a 2 x 2 optical bypass switch for series-type fiber-optic networks. Optical cross-talk levels of -32 dB have been obtained in both states. The insertion loss was 3 dB in a nonoptimized switch.

Universal spectrophotometer for determining the efficiency of optical components and systems.

Abstract: An instrument has been developed to measure the absolute reflectance or transmittance of optical elements or systems. Contrary to existing spectrophotometers, it is not limited by the size or by the optical power of the element to be analyzed.

Multiple wavelength spectroscope device

Abstract: PURPOSE:To enhance light measuring accuracy by a simple improvement, by providing a light shielding plate, which shields the straight input of dispersed light, for at least one light receiving element in an image forming region of the dispersed light, detecting the amount of stray light, and correcting the amount of the stray light with respect to the measured values of the light from other light emitting elements. CONSTITUTION:The light, which is inputted to an incident slit 1 from a light source, is dispersed on a photodiode array 4 and an image is formed. The photodiode array 4 is arranged on a Rowland circle, and the light is dispersed sequentially from a short wavelength side between l0 and ln. When diffracted light in the range of l1-ln is inputted to the photodiode array 4, the light is reflected and scattered on the surface of each of photodiodes 61-6n. The light is further reflected by a light receiving window 7 and inputted again. At this time, the scattered and astrayed light is distributed to the photodiode 60 on the short wavelength side, and the largest effect is received. Since the direct propgressing light is not inputted to the photodiode 60, only the astray light is detected. The same amount of the astray light is inputted to the neighboring photodiode 6a. When the detected astray signal of the photodiode 60 is subtracted from the detected signal of the photodiode 6a, the effect of the astray light of the photodiode 6a is mostly eliminated.

Improvement to monochromator spectral calibration using a tungsten strip lamp

Abstract: A simple and inexpensive procedure is described to correct for stray light background in absolute spectral calibration of a grating monochromator by means of a tungsten strip lamp. The method permits extension of the calibration towards both lower and higher wavelengths than otherwise accessible.

Reflection-free metallic film

Abstract: A metallic anti-reflection film is described which consists of a relatively thick, i.e. light-impervious metal layer and on which there is at least one thin second metallic layer. The second metallic layer on one or else on both sides of the thick metal layer appropriately consists of chromium oxide. The anti-reflection film described facilitates production, especially when it is used for stray light diaphragms or annular slits in optical instruments such as endoscopes or microscopes.

Atomic absorption spectrophotometer providing background correction using the Zeeman effect

Abstract: An atomic absorption spectrophotometer having a source, e.g., a hollow cathode lamp, of spectral radiation of a selected narrow band of wavelengths optically directed along an axis through an electrothermic sample atomizer and a field stop to a photoelectric detector. The sample atomizer is subjected to a substantially unipolar AC electromagnetic field having flux lines directed transversely to said axis to effect Zeeman splitting of the radiation into two orthogonally polarized components π and σ. Disposed in the optical path between the atomizer and detector is a stationary beam-splitting polarizer prism oriented so as to transmit the σ polarized component and block the π component. Mirrors are used exclusively in the optical systems so as to minimize the effect of dispersion and stray light. An electromagnet, used to generate the electromagnetic field, is connected to the AC power line in series with the diode and has a small capacitor connected across its coils. This causes the magnetic field at the sample atomizer to vary sinusoidally from a maximum value of one polarity to a very small value of the opposite polarity. The polarizer prism is of unique design in which one polarization passes through undeviated on the optical axis while the other is diverted to one side on the other. The ray passing through the prism along the optical axis is uniquely depolarized upon exiting. A field stop is located between the prism and the atomizer and restricts the field of view of the prism to an angle less than or equal to its restricted field of view, excludes blackbody radiation of the furnace, and limits the aperture at the source.

Specular UV reflectance measurements for cavity radiometer design.

Abstract: Specular reflectance measurements were made on a black paint used in a solar constant monitoring cavity radiometer. Interference filters peaking at 180, 200, and 220 nm were used in conjunction with a deuterium lamp source and a silicon photodiode detector. Results showed that the black paint was specular for light incident 60° from normal and it reflected ~8% of the light at these wavelengths. We conclude that the high absorptance of the radiometer calculated for visible wavelengths should remain valid down to ~190-nm UV wavelengths.

Connector for optical fiber

Abstract: PURPOSE:To prevent the inclusion of dust and stray light by providing a hole of a diameter larger than that of a hole which is closed in a bottom part and has a photodetector in the bottom part to said hole, and fitting an optical fiber plug therein in a manner as to abut on its level differing part CONSTITUTION:A fiber holder 2 is fixed by means of screws 3 to a substrate mounted with a photodetector 7 A fiber plug 6 is fitted into a recess 2B' of a diameter larger than that of the hole 2A of the holder 2, and its leading end is abutted on a level differing part Thereby, the inclusion of dust and stray light is prevented

Spectrograph instrumental profiles - dependence on dispersion

Abstract: Spectrograph instrumental profiles (including stray light far away from the central peak) have been measured in blue and red light for the three cameras in the coude spectrograph of the 1.52-m telescope at Observatoire de Haute-Provence. The different dispersions 0.7, 1.2, and 2.0 nm mm-1 are obtained using the same ruled diffraction grating. On a linear distance scale in the focal plane the profiles are rather similar down to a 10-3 intensity level, but on a wavelength scale the profiles improve with increasing dispersion, indicating the presence of a stray light component other than that caused by diffraction by grating irregularities. The effects of these instrumental profiles on observed spectra are illustrated by numerical convolutions with the solar spectrum.

Illumination method for non-image-forming part

Abstract: PURPOSE:To prevent stray light due to reflection of a photoreceptor, by using a filter in which a peak of spectral transmission distribution is in existing near the wave length of the peak of spectral sensitivity distribution of the photoreceptor, in the removal of unnecessary charge of non-working part of the photoreceptor. CONSTITUTION:Light of lamps 7A, 7B is incident to a non-working part N of a photoreceptor 1 respectively via openings 10A, 6A or 10B, 6B. Filters 11A, 11B fitted to the openings 6A, 6B are filters which have a peak of spectral transmission distribution near the wave length of the peak of spectral sensitivity distribution of the photoreceptor. Thus, the peak of the spectral distribution of light radiating the non-working part N is closed relating to the wave length with the peak of the spectral sensitivity distribution of the photoreceptor, and illuminated light can be absorbed efficiently to the photoreceptor 1 at the non- working section N. Then, stray light due to reflection of the photoreceptor can be prevented.

BRDF Measurementsof Sunshield and Baffle Materialsfor the

Abstract: SUMMARY Measurements of the far-infrared bidirectional reflectance distribution func-tions (BRDF) of four samples of Martin Black coating and one sample of gold coatedaluminum from the telescope to be flown on the Infrared Astronomy Satellite (IRAS)are presented. At incidence angles near 35°, Martin Black is a diffuse reflector atwavelengths as long as 36 _m. The gold coated aluminum sample from the IRAS sun-shield has a visible grain which causes a strong diffraction enhancement of the BRDFat large nonspecular angles. This enhancement from the sunshield will increase thestray light level inside the telescope.INTRODUCTIONA nonspecular reflectometer (NSR), recently constructed at Ames Research Centerin support of the Shuttle Infrared Telescope Facility (SIRTF), was used to measurethe bidirectional reflectance distribution function (BRDF) of four light bafflescoated with Martin Black and one sample of sunshade material from the telescope ofthe Infrared Astronomy Satellite (IRAS). Stray light rejection is very important inthe design and operation of space telescopes such as SIRTF, IRAS, and COBE (CosmicBackground Explorer), because they must often point toward astronomical objectswhose direction is not far from that of bright, extended sources. Knowledge of theBRDF of certain critical surfaces is required to calculate the amount of stray lightreaching the telescope focal plane and to thus evaluate off-axis rejection charac-teristics. The samples and angles described here were selected by the IRAS Projectand are specific to the IRAS telescope; however, their far-infrared reflectancecharacteristics are similar to those of several other optical black coatings thathave been measured. The sunshield material performs as a surprisingly good infraredreflection grating.INSTRUMENTATIONAlthough the NSR has been described before (ref. I), it will be brieflydescribed again to define terms and angles. The instrument is a far-infraredgoniometer-photometer utilizing bandpass transmission filters (ref. 2) with spectralresolutions between 3% and 22%. Additional short-wave blocking is provided by along-wave pass interference filter designed by Whitcomb and Keene (ref. 3). Themajor components of the NSR are shown in figure i where, for convenience, thedetector (a Ga:Ge bolometer) has been shown to rotate. The angle of reflection orscattering 8s is continuously variable between ±i0° and ±90°. When a gold coatedmirror replaces the black substrate, the aperture of the blackbody source is

Compact strip illuminator for photocopier - has light guide plates with fluorescent coating to enhance illumination

Abstract: The light guide plates (10) collect light from several fluorescent tube lamps (11 etc) spaced along the plates with the light emitted from the ends (16) of the plates and directed at the scanning slit. The backs of the plates are mirrored and a fluorescent coating enhances the illumination. The plates can be bent into an enclosed shape to contain the lamps and to prevent stray light from entering the copier. The light is transmitted along the plates by total reflection and provides an intense, uniform illumination for the slit.