Showing papers on "Stray light published in 1981"

Scanning Laser Ophthalmoscope

Abstract: An instrument is described which functions as a low light level ocular fundus camera and ophthalmoscope, and which is capable of making a wide range of quantitative measurements in the eye. Light levels for ophthalmoscopy (20 ?W/cm2 at the retina) are at least two orders of magnitude below those in current use. A focused laser bearn forms a flying spot, moved physically by scanning mirrors. This allows a 20 ?m or smaller resolution element, with only a 0.9 mm diameter area of the patient's pupil used for the entering beam. The remaining pupillary area forms the exit pupil?a critical inversion of the division of pupils necessary for systems using conventional imaging. It is this inversion which allows the low light level and the unique measurement capabilities. We discuss the constraints imposed by viewing the inside of a spheroid through a small hole in its wall, and our solutions?both optical and electronic?to these problems. We also describe electronic problems encountered in the video system, which arise from our special detection and display systems. Some specifics of the instrument's measurement capabilities are discussed.

Global auroral imaging instrumentation for the Dynamics Explorer mission.

Abstract: The instrumentation for obtaining global images of the auroral oval from the high-altitude spacecraft of the Dynamics Explorer Mission is described. It is noted that the three spin-scan auroral imaging photometers are expected to be able to effectively view the dim emissions from earth in the presence of strong stray light sources near their fields-of-view along the sunlit portion of the spacecraft orbit. A special optical design that includes an off-axis parabolic mirror as the focusing element and super-reflecting mirror surfaces is used to minimize the effects of stray light. The rotation of the spacecraft and an instrument scanning mirror provide the two-dimensional array of pixels making up an image frame. It is pointed out that the full width of the fields-of-view of the photometers corresponding to a single pixel is 0.29 deg and that the angular dimensions of a typical full frame are 30 deg x 30 deg and span 14,400 pixels.

Standards in fluorescence spectrometry

Abstract: 1 General considerations on fluorescence spectrometry.- 1.1 Introduction.- 1.2 Molecular photochemistry.- 1.3 Fluorescence instrumentation.- 1.4 Good spectroscopic practice.- 1.5 Fluorescence intensities.- 1.6 Nomenclature in fluorescence spectrometry.- 2 Monochromator wavelength calibration.- 2.1 Introduction.- 2.2 Characteristics of calibration methods.- 2.3 Use of spectral lines from the spectrometer light source.- 2.4 Use of an auxiliary light source.- 2.5 Use of narrow bandwidth fluorescence maxima of inorganic and organic solutes.- 2.6 Conclusions and recommendations.- 3 Stray light in fluorescence spectrometers.- 3.1 Origins of stray light and resultant errors.- 3.2 Stray light in grating monochromators.- 3.3 Summary and recommendations.- 4 Criteria for fluorescence spectrometer sensitivity.- 4.1 Background: inter-instrument comparisons.- 4.2 The limit of detection method.- 4.3 The signal-to-noise ratio method.- 4.4 Summary and recommendations.- 5 Inner filter effects, sample cells and their geometry in fluorescence spectrometry.- 5.1 Inner filter effects.- 5.2 Sample cells.- 5.3 Recommendations.- 6 Temperature effects and photodecomposition in fluorescence spectrometry.- 6.1 Errors caused by temperature effects.- 6.2 Countermeasures and recommendations for temperature effects.- 6.3 Errors caused by photolysis effects.- 6.4 Countermeasures and recommendations.- 7 Correction o excitation and emission spectra.- 7.1 Introduction: the need for correction procedures.- 7.2 Excitation spectra.- 7.3 Emission spectra.- 7.4 Polarization effects.- 7.5 Recommendations.- 8 The determination of quantum yields.- 8.1 Introduction.- 8.2 Primary methods of determining quantum yields.- 8.3 Secondary methods of determining quantum yields: use of fluorescence standards.- 8.4 Other methods of determining quantum yields.- 8.5 Summary and recommendations.- Appendix Corrected excitation and emission spectra.

Correlator based on an integrated optical spatial light modulator.

Abstract: The fabrication and characterization of a 17.5-M bit/sec integrated optical correlator are described. The correlator makes use of a novel programmable electrooptic spatial light modulator in conjunction with a digitally modulated surface acoustic wave.

Photometric method for determining courses of reactions

Abstract: The invention provides a photometric method of determining courses of reaction in a specimen, in which method the intensities of the transmitted light and of the stray light are measured, wherein the two intensities are measured simultaneously and the electrical signals corresponding to the transmitted light and to the stray light are combined to form one signal. The invention makes it possible to perform reliable measurement even with low levels of transmitted and stray light. The method is preferably used in determining the coagulation times of blood. Apparatus for carrying out the method is also disclosed.

First-Order Design Of Optical Baffles

Abstract: Optical systems which have stringent reouirements on stray light levels often need optical baffles. Some basic design principles and goals for baffles are Presented. Four generic optical designs and their advantages for stray light control are discussed: all reflective and all refractive reimaging and nonreimaging systems. The desirable shape and location of baffle vanes are shown, based on various design criteria. Presuming that the designer has the ability to control specular reflections from baffle surfaces, absorptive coatings which reflect specularly are preferred over those which reflect diffusely. Stray energy from edge diffraction can be controlled in a nonreimaging optical system by forcing light to undergo multiple diffractions.

Echelle and holographic gratings compared for scattering and spectral resolution

Abstract: An echelle grating with 316 grooves/mm and a 63° blaze angle is compared with a 3600-groove/mm holographic grating. The scattered light and resolution of the 10- × 20-cm gratings are photoelectrically evaluated in a 3-m spectrometer optimized to eliminate coma and baffled to minimize instrumental scattered light. Both gratings are ghost-free, but the holographic grating has substantially lower scattered light for test lines near 4000 A and yields improved stray light rejection within absorption lines. It also exhibits slightly higher resolution. The throughput of the spectrometer with the holographic grating is about 5 times higher than the equivalent combination of spectrometer, echelle grating, and predisperser.

Optical measuring cell

Abstract: PURPOSE:To increase the sensitivity and accuracy in measuring light detection, by providing the photoisolator which isolates the phototransmission section inputting are outputting the incident light and the phototransmission section introducing the detected light optically. CONSTITUTION:The cell main body 1 consisting of cylindrical glass and synthetic resin is provided with the ring shape phototransmission section 2 inputting the outputting the incident light P and the phototransmission section 3 introducing the detected light Q, and the photoisolator 4 mixing dark color material such as black color to glass or synthetic resin is provided between the phototransmission sections 2 and 3. Further, the background 4A of the detected light Q is colored with the black color. Accordingly, the incident light from the incident light window 5 of the phototransmission 2 is a stray light and goes straight to the output light window 6 without propagating and immersing to each part of the wall 1A, and a part of the incident light is introduced to the detection light window 7 of the phototransmission 3. Thus, the detected light can be measured with high sensitivity and high accuracy.

Simulation Of Stray Light In Optical Systems With The Guerap III

Abstract: The GUERAP III is a sophisticated stray light analysis computer program. It uses the Monte Carlo method with importance sampling to trace random real rays through an optical sensor model. The program is useful for calculating stray light in an existing optical sensor and for determining dominant paths of scattered light to aid in the improvement of an optical baffle. The accuracy of the program depends on the accuracy of the input data for geometry and surface scatter characteristics. The uncertainty in the random ray trace depends on the proper use of importance sampling.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Optical element for lidar system - forms extremely short length cassegrain telescope with laser emitter combined in rugged housing

Abstract: The optical element (10) is made of glass or plastics material similar to glass and has a rear mirrored surface (10a) with a recess for a receiving diode (12) which is adjustable by means of the correcting foot (14) formed by an interference filter (14) cemented to the diode cover glass (12a). The filter (14) also carries a baffle (15) for gathering stray light, which the optically active surface (12b) of the diode (12) also does at the same time. The form of the optical element is such that the light paths are always of the same length and almost completely independent of the angle of incident and the distance to the optical axis. The diode (12) is connected to the electronic circuits (13) by connectors (12c) and feeds a laser diode mounted beneath the lens, thus forming a Lidar system which can be made small and rugged and shockproof as well as impervious to surroundings.

Absorbing coatings for the far infrared

Abstract: Far-infrared optical sensors operating in the submillimeter wavelength region require baffle systems to suppress stray light. Because a high degree of rejection of the stray light is required, the baffle systems must use highly absorbent coatings. Most common optical baffle coatings are not functional at wavelengths greater than 100 μm. However, multilayer coatings have been developed that minimize front surface reflectance and maximize absorptance with a minimum required coating thickness. Data for a polyurethane binder and carbon-pigmented coating show that a multilayer coating with a thickness of approximately 5 mils has a reflectance of less than 10 percent over the wavelengths out to 300 μm.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Comparison of stray light mechanisms and performance in the Infrared Astronomy Satellite /IRAS/ and Shuttle Infrared Telescope Facility /SIRTF/ telescopes

Abstract: NASA is developing two large space-based infrared astronomy telescopes, IRAS and SIRTF. Both of these systems will be functioning in the environment of a bright thermal emitting earth and sun while concurrently having baffle surfaces radiating thermal photons which combine to produce a stray-radiation background. The APART program was used to analyze the stray radiation propagation paths of both the IRAS and SIRTF designs. The SIRTF design was found to be about 1000 times superior in its stray radiation transmission, because several design options were able to be incorporated through different mechanical and optical constraints that were different, while being generically of a similar optical design.

Stray light in fluorescence spectrometers

Abstract: Stray light may be defined [1] as light of unwanted wavelengths emerging from a grating monochromator or other dispersion device: light of the selected band-width is thus contaminated by the stray light. In general, stray radiation can arise from a variety of causes [2]: (a) Leakage of external light into the fluorescence spectrometer. (b) Reflection and scattering from walls, optical surfaces, and other instrument components. (c) Scattering of light by airborne dust. (d) Scattering within optical components such as lenses. (e) Background fluorescence of optical materials. (f) Unused orders in grating spectra.

Light reflecting sensor

Abstract: PURPOSE:To maintain invariably high coupling efficiency by using a retroreflective reflector for the light reflecting sensor consisting of a light source, waveguide, reflector, and photodetector, and making a deviation in optical path betweek incident light and reflected light less than the luminous flux with of the incident light. CONSTITUTION:The light reflecting sensor guides light from the light source 1 such as a light emitting diode to a prescribed position through the waveguide 14, and the reflected light from the retroreflective reflector 13 enters the waveguide 14 again to reach the photodetector 6 through a photocoupler 6 and is transduced into an electric signal. The reflector 13 uses a bead reflector 7 or corner cube mirror 12 to make an optical path deviation l between the incident light and reflected light mush less than the luminous flux width of the incident light, and consequently the reflected light returns to an optical fiber 14 without fall, so that even if the angle of incident varies, the coupling efficiency is held invariably high.

Spectrophotometer for Both Transmissivity and Reflectivity Measurement in the Region from the Near Infrared to the Ultraviolet

Abstract: When multiple internal reflections are taken into account, low-absorption (high-transmissivity) measurement must be corrected with the reflectivity. With this in mind, a spectrophotometer for both transmissivity and reflectivity measurement has been developed. It covers measurement from the near infrared to the ultraviolet (1.1 to 6.2 eV). Since the spectrophotometer aims at especially high transmissivity measurement, it requires low stray light, fine adjustment of the optical system and low-noise electronics. This paper discusses its principle, its performance and the method of correction for effective operation. The spectrophotometer can measure the transmissivity T from 0.0004 to 0.998 and the reflectivity R from 0.0005 to 0.998 in the spectral region from 1.1 to 5.1 eV, and T from 0.003 to 0.995 and R from 0.0008 to 0.995 in the region from 5.2 to 6.2 eV.

General Concepts And Approach On Making Stray Light Calculations Without The Use Of Large Computers

Abstract: The general configuration of a satellite telescope is used to show how simple projections of the various limiting apertures onto a chosen plane can show the obscuration and vignetting at any selected position on the focal plane. The projections also indicate what por-tions of the walls, baffles, etc. are viewed from various positions on the focal plane. Again projections taken at the angle of external sources show what portions of the interior are illuminated by these sources and the two combined give a method of estimating stray rad-iation. Since most detectors in scanning systems are AC coupled, the ability to estimate the rate of change of stray light with time is demonstrated.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Theory of a Double Monochromator Consisting of Two Concave Holographic Diffraction Gratings

Abstract: In the present paper we have discussed the basic principle and aberration properties of a Double Monochromator consisting of two concave holographic diffraction gratings. Both the gratings have a common axis and small central holes The gratings are mounted in such a way that the centre of one grating is situated near the central hole of the other grating. The source and the image points are situated at the two centres of the gratings and the spectrum is scanned by imparting translatory movement to one of the gratings along the axis of the system. Because of the on-axis configuration the system suffers from spherical aberration only. It has been found that even at high aperture the system has moderate resolution properties throughout the UV-visible region of the spectrum. Since the system consists of two holographic diffraction gratings, the stray light level will be very low. Also use of only two diffracting elements makes the system suitable for UV instruments where addition of extra reflections causes intensity problem at the final image point.

Measurement Of Transmittance And Veiling Glare Index

Abstract: Transmittance and Veiling Glare Index measurements in conjunction with the Optical Transfer Function can give a set of objective measurements for specifying and providing quantitative data on the performance of components and complete optical systems. The main application of the work described, is to directly viewed telescopic systems. Transmittance, the ratio of transmitted radiance to incident irradiance, of telescopic instruments is usually measured with a small diameter collimated beam, integrating sphere and photo multiplier detector. An alternative method in which the full aperture of the objective is filled by the incident beam will reveal any adverse effects of vignetting or variability of anti reflection coatings and is of importance in subjective/objective comparisons when the eye pupil is greater than the exit pupil of the telescopic system. The MVEE 'audit' and Standard telescopes which were developed for investigation of the application of OTF measurement to visual instruments were found to have markedly different Veiling Glare Index values when measured on a wide glare field apparatus. Subsequently a series of measurements of these telescopes, using several current techniques for the measurement of stray light, indicated the importance of unwanted radiation which came from outside the field of view and the inadequacy of routine VGI measurements with a glare field equal to the field of view of the specimen being tested. For a single measurement test it was concluded that a black spot on a wide field (>±45 degrees) was desirable; this is substantially test condition C2 of British Standard 4995. The Standard telescope, as tested above, had the lowest VGI and the Audit telescope the highest VGI of all systems tested, with a modern 10 x 60 sight having a VGI value close to the former. The final section of the paper discusses possible combined instruments for measuring all three parameters, to give the most effective utilization of apparatus.© (1981) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Stray Radiation And The Infrared Astronomical Satellite (IRAS) Telescope

Abstract: Stray light control is a major consideration in the design of infrared cryogenically cooled telescopes such as the Infrared Astronomical Satellite (IRAS). The basic design of the baffle system, and the placement, shape, and coating of the secondary support struts for the telescope subsystem are described. The intent of this paper is to highlight the stray light problems encountered while designing the system, and to illustrate how computer analysis can be a useful design aid. Scattering measurements of the primary mirror, and a full system level scatter measurement are presented. Comparisons of predicted performance with the measured results are also presented.

Heterodyne detection of ruby laser light scattered in a theta pinch plasma

Abstract: Ruby laser light scattered by a 1016 cm-3, 5 eV deuterium theta pinch plasma has been detected and its frequency and wavelength spectra measured by heterodyne techniques using a vacuum photodiode as a mixer, stray light radiation as the local oscillator and a UHF communications receiver as a frequency analyser. Scattered light came predominantly from k vectors parallel to the magnetic field. Frequency and wavelength distributions showed maxima at 680 MHz and 4*10-3 cm respectively, consistent with scattering by an ion acoustic wave corresponding to plasma temperature 8 eV. The temperature deduced from the plasma diamagnetism was 4.8 eV.

Quartz-glass chopping method of measuring solar irradiance.

Abstract: A solar irradiance photometer was launched on a pair of ESRO Centaure rockets. The instrument, a solar irradiance photometer used six wavelength channels. Three of these channels were used to measure mesospheric ozone by the occultation method. Two other channels were equipped with 214-nm Fabry-Perot filters to monitor the absorption of sunlight required for the excitation of NO γ-band fluorescence, which was measured by another instrument in the same payload. One of the 214-nm channels used a quartz lens, while the other used a glass lens. With a glass–quartz chopping technique, stray light with wavelengths longer than 300 nm could be eliminated. Since ozone is absorbing at 214 nm, these two channels were also used for measuring mesopheric ozone. By comparing the ozone measurements from the two 214-nm channels with the measurements from the three channels intended for ozone measurements, one can obtain the performance of the glass–quartz chopping method.

Falling light illuminating and observing device

Abstract: PURPOSE:To remove stray light and widen the visual field of observation by reflecting the luminous flux deviated from a falling light illuminating device by transmitting or reflecting through or from a beam splitter thereby illuminating the specimen in the falling light illuminating device branched to the falling light illuminating device and an observing device by the beam splitter. CONSTITUTION:Light from a light source 1 irradiates a specimen 5 through a condenser lens 2 and a beam splitter 3. The reflected light frofm the sample 5 is observed through the beam splitter 3, an objective lens 6, and an eyepiece lens 7. On the other hand, these are so constituted that the light from the light source transmitted through the beam splitter 3 illuminates the specimen diagonally by providing a reflection mirror 4. Hence, the visual field wider than that by conventional falling light illumination is uniformly illuminated. Thereby, stray light is reduced and the visual field of observation is widened.

Optical surface defect detector

Abstract: PURPOSE:To improve detection performance by preventing disturbance due to stray light while lessening a sensitivity deviation, by arranging optical fibers having photoelectric converting elements connected to other-side terminals, slantingly over both ends of a scanning line of a beam spot. CONSTITUTION:Optical fibers 8 penetrate through-holes 9 provided to holder 11 and end face 8' are fixed by setsecrew 14 by adjusting being sufficiently close to the scanning line of a beam spot on plane plate 3. Further right and left optical fibers 8 are arrayed in zigzag. A laser beam is projected upon plane plate 3 as shown by arrow A in the figure and its reflected light is supplied to photoelectric converting elements as the other side terminals of optical fibers 8 to regard scattering reflection of more than fixed intensity as a surface defect. Optical fibers 8 are arrayed in zigzag to reduce a sensitivity deviation and end faces 8' are set close to plane plate 3 to photodetect little stray light, so that the detection performance can be improved.

Detecting circuit for reflected light of optical fiber

Abstract: PURPOSE:To prevent the generation of a stray light pulse and disused light-reflection pulse by coupling three required optical fibers by a translucent mirror slanting at a prescribed angle and by using a light absorber, etc., while convering the coupling part with a medium having a prescribed refractive index. CONSTITUTION:Light pulses supplied from leading-in optical fiber 1 pass through optical fiber 5 whose end surface is coupled with translucent mirror 3 slanting at a prescribed angle to optical fiber 1 and bonding optical medium 9 having the same refractive index as those of fibers 1, 5 and 7 while covering and coupling with optical fiber 7 and, after being reflected partially by mirror 3, is absorbed by light absorber 8. The remaining light pulses penetrating mirror 3, on the other hand, pass through fiber 5 and are reflected at the end surface of optical fiber 4 to be measured. Those reflected pulses propagate in fiber 5 backward and, after being reflected by thin clad surfaces of fibers 5 and 7, are photodetected by way of fiber 7 with small attenuation. This constitution prevents the generation of a stray light pulse and reflected-light pulse to provide reflected-light detection with high precision.

Spectroscopic photometry device

Abstract: PURPOSE:To eliminate the influence of stray light from an ultrasonic spectroscopic element and heighten photometric accuracy, by applying an amplitude-modulated driving input signal to the ultrasonic spectroscopic element to amplitude-modulate the light which is transmitted through the element CONSTITUTION:The driving input 112 is applied to the ultrasonic spectroscopic element 104 by a high-frequency oscillator 400 The amplitude of the oscillation signal 112 is moduiated by a modulation signal 404 from a modulation signal generator 402 The frequency of the oscillation signal 112 is based on a signal 408 from a wavelength sweep generator 406 The output light 105 of the element 104 contains the stray light, which goes into a detector 106 The output of the detector 106 contains components based on the stray light 202, background light and the dark current 300 of the detector as shown by a thick line 500 in the figure The output of the detector is rectified by a synchronous rectifier 108 synchronously with the modulation signal 404 to simply remove not only the components based on the background light and the dark current 300 but also the component 202 based on the stray light This results in heightening photometric accuracy

Monochromator wavelength calibration

Abstract: The essential components of a single beam fluorescence spectrometer without facilities for spectral corrections are shown in Fig. 2.1. The instrument has two monochromators or alternative wavelengthselection devices. The excitation monochromator (M1) selects the wavelength of the light with which the sample is to be irradiateci, and the emission monochromator (M2) selects the wavelength of fluorescence (or scattered light or phosphorescence, etc.) received by the detector. M1 and M2 may be coloured or interference filters in simple instruments, but in more advanced instruments grating monochromators are normal. Some instruments incorporate doublegrating monochromators to minimize stray light levels (see Chapter 3). The monochromators may normally be scanned using motorized drive units. Scanning M1 with M2 set at a fixed wavelength generates excitation spectra and scanning M2 with M1 fixed generates fluorescence emission spectra. In view of the increasing interest in synchronous scanning methods [1] the facility to scan both monochromators simultaneously is desirable (see also Section 7.1.3). The reflection gratings used in M1 and M2 are normally blazed to give maximum efficiencies (approximately 50%) at 250–350 nm and 350–500 nm, respectively.Holographic gratings, which yield low stray-light levels (see Chapter 3) have been introduced in some instruments.