Calibration Light Source Research Articles

The Photochemical Generation of Hydroxyl Radicals in the UV−vis/Ferrioxalate/H2O2 System

A reaction mechanism has been validated for the photochemical generation of hydroxyl radicals by ultraviolet or visible irradiation of oxalato iron(III) complexes (ferrioxalate) in the presence of hydrogen peroxide and 2-propanol as a model substrate. A kinetic simulation program incorporating the set of reactions was written to predict the behavior of this photochemical system. The program calculates the quantum yield of oxidation of 2-propanol used as a hydroxyl radical scavenger. The scavenger's oxidation product, 2-propanone, was analyzed by gas chromatog raphy after controlled exposure of the solution to a calibrated light source. The theoretical quantum yields of 2-propanol oxidation, ΦRH, agreed reasonably well with experimentally determined ΦRH values under a variety of initial reaction conditions. The value of ΦRH, which under appropriate conditions is directly proportional to the quantum yield for the generation of hydroxyl radicals, ΦOH, was considerably greater than unity in most cases (often ...

A LED light calibration source for dual-wavelength microscopy

An LED light source for dual-wavelength calibration of light microscope recording systems is described. A 1 mm 2 circular field of bi-chromatic illumination is formed by passing the crossed beams of two light emitting diodes (LEDS) through an optical diffuser and circular mask. The source is constructed using LEDs which emit light at wavelengths overlapping those of many of the dual-emission molecular probes used for measurement of calcium, pH and membrane potential. The light output can be independently varied to set the ratio of light intensities recorded at two wavelengths. Internally sampled voltages which are proportional to LED light output intensity provide an internal reference for comparison with optical recordings. The LED source is useful for obtaining the optical response of dual emission recording equipment for specific recording conditions defined by the filtering and light detection components of the system.

Development of Spaceborne Frequency-Stabilized Helium-Neon Laser.

A frequency stabilized Helium-Neon laser was developed to be launched into space and used as a calibration light source in a Fourier-transform interferometer. It is a simple Helium-Neon laser constructed with a minimum number of components and without any active resonator length controls to achieve both frequency stability and operating reliability in the space environment. Tests indicate a short-term frequency vs. temperature stability of the order of 10-8/degreeC, a frequency repeatability of 5×10-9, and an estimated reliability of 0.94 for 3 years of operation period, all of which satisfy the mission requirements.

Chemiluminescent Detection of Nonisotopic Probes

With recent advances in techniques for detecting chemiluminescent substrates, hybridization with nonisotopic rather than radiolabeled probes is becoming more common. In the Basic Protocol, nylon membranes carrying transferred nucleic acids are prepared for hybridization with biotinylated probes by UV cross-linking. This is a critical step in the procedure and the Support Protocol provides a detailed description of light-source calibration. After hybridization, the target nucleic acid is detected through a series of steps that lead to an enzyme-catalyzed light reaction. The Alternate Protocol describes chemiluminescent detection based upon antibody recognition of digoxigenin-labeled probes. For both biotinylated and digoxigenin-labeled probes, chemiluminescent detection is more sensitive than colorimetric detection and has the added advantage that the membrane can be used for multiple film exposures, then stripped and redetected with different probes.

A light-emitting diode light standard for photo- and videomicroscopy.

A light calibration system consisting of a compact light-emitting diode (LED) source with feedback control of intensity is described. The source is positioned in the focal plane of the microscope objective and produces flat-field illumination of up to 31 microW. The source can be easily used to determine the performance of microscope optics and camera response. It can also be used as a standard light source for calibration of experimental systems. Selectable light intensities are produced by controlling the LED input power via a feedback circuit consisting of a photodiode that detects output light intensity. Spectral coverage extends between 550 and 670 nm using green, yellow and red LEDs mounted side by side, which are selected individually. The LED chips are encapsulated in plastic diffusers which homogenize the light, and a flat field of illumination is obtained through a thin 1-mm-diameter aperture positioned directly over each chip. Provision is made for insertion of Ronchi rulings over the aperture to enable measurements of contrast modulation in a uniform field. The light may be pulse-modulated to assess camera response times and the device can be synchronized with video frames. Narrow bandpass interference filters can be placed between the objective lens and the LED source to produce monochromatic light without affecting the spacing of controlled light intensities since emission spectra do not shift appreciably over the range of LED powers chosen in this design. Results of tests using controlled light intensity and uniform illumination are presented.

The Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) experiment on board the Upper Atmosphere Research Satellite (UARS)

The state of solar ultraviolet irradiance measurements in 1978, when NASA requested proposals for a new generation of solar ultraviolet monitors to be flown on the Upper Atmosphere Research Satellite (UARS), is described. To overcome the radiometric uncertainties that plagued the measurements at this time, the solar ultraviolet spectral irradiance monitor (SUSIM) instrument design included in‐flight calibration light sources and multichannel photometers. Both are aimed at achieving a maximum precision of the SUSIM measurements over a long period of time, e.g., one solar cycle. The design of the SUSIM‐UARS instrument is compared with the original design specifications for the UARS instruments. Details including optical train, filters, detectors, and contamination precautions are described. Also discussed are the SUSIM‐UARS preflight calibration and characterization, as well as the results of the inflight performance of the instrument during the first 3 months of operation. Finally, flight operations, observation strategy, and data reduction schemes are outlined.

Nanosecond Calibration Light Source Using LED for Ruby-Laser Thomson Scattering Device

A nanosecond LED ligh pulse similar to the ruby laser light was used to calibrate a ruby laser Thomson scattering device. The continuous spectral region between 5500Å and 7000 Å was obtained using two different kinds of LED element. The calibration data was obtained within 1-2% fluctuation in the repeated experiments, and the uncertainty in the relative sensitivity calibration constant was below 2%. The following results were obtained using the nanosecond light source: The width of the light pulse was scarcely changed during the pulse's passage through the optics and electronics. The transmission time from entering the fiber optic system to entring the data acquisition system was determined in order to minimize the gate duration.

An instrument for the spectral radiance calibration of light sources in the VUV by means of the synchrotron radiation of the desy machine

The instrument consists out of two combined monochromators with appropriate imaging optics for the synchrotron radiation, for a tungsten ribbon lamp and for the light source to be calibrated. One brach of the instrument operates in the visible and determines the electron current of the synchrotron. The VUV branch is for the calibration of a light source by comparison with the synchrotron radiation. The improved instrument is described and results on the calibration of deuterium lamps as transfer standards are given.

A Measurement of the Fast Luminescent Decays of the MV-50 LED

The fast luminescent decay of the MV-50 GaAs doped Si light emitting diode has been studied. The MV-50 provides a fast, inexpensive, bright, and convenient light source for calibration of fast optical timing systems. A simple passive electronic module is described which allows driving the light source directly by a laboratory pulse generator.

Absolute Calibration of Light Sources in the Vacuum Ultraviolet by Means of the Synchrotron Radiation of DESY

With the synchrotron radiation of DESY (Deutsches Elektronen Synchrotron) as a primary standard light source, secondary standard light sources have been calibrated in the spectral range 1500-2700 A. By this method, the accuracy of the intensity of the calibrated lamp is about 4%.