High-accuracy transmission measurements at an optical wavelength of 633 nm and mechanical measurements of the thickness of a 13-mu-m thick silicon-crystal film have been used to calculate the absorption and extinction coefficients of silicon at 633 nm. The results are 3105 +/- 62 cm-1 and 0.01564 +/- 0.00031, respectively. These results are about 15% less than current handbook data for the same quantities, but are in good agreement with a recent fit to one set of data described in the literature.

A breadboard photometer was constructed that demonstrates a precision of 2 times 10 to the 4th power in the laboratory and scintillation-limited performance when used with an 0.5 m aperture telescope. Because the detectors and preamps are not cooled, only stars with m sub v approx. less than 4 are bright enough to allow the photometer to attain a precision of 1 times 10 to the 3rd power for three minute observations with an 0.5 m aperature telescope. Cooling the telescope should allow much fainter stars to be observed. Increasing the aperture of the telescope will allow higher precision and the observation of fainter stars.

The photometric method of searching for planets around stars depends on observing the decrease in light flux produced by the transit of a planet across the stellar disk. The magnitude of this reduction is proportional to the ratio of the planet’s area to that of the star. For the solar system, the decrease in light amounts to 0.01 per cent for terrestrial-sized planets. To overcome the effects of scintillation and variable extinction in the Earth’s atmosphere, it will be necessary to operate the photometric system on a space platform. The photometric method works only for planets whose orbital plane is near our line of sight. Thus many stars must be monitored to insure that some stars with appropriately-oriented orbital planes are observed. If every solar-type star has a planetary system similar to our solar system, then a photometer that monitors 1000 stars with the requisite precision should detect at least 10 transits per year of observation. Thus a 3-year observation period should allow meaningful statements to be made about the frequency of solar-type planetary systems. A state-of-the-art photometer is being developed to test components and concepts. The goal is the development of a photometer that can routinely measure the relative brightness of stars to a precision of 1 part in 100,000. Such precision should be achievable using “quantum perfect” detectors. Results of field tests of a prototype photometer are promising.

An intercomparison has been conducted among three independent scales of spectral irradiance: two source-based and one detector-based. Specifically, a radiometer composed of a silicon photodiode, an interference filter, and an integrating sphere was characterized and calibrated against an absolute silicon detector standard at 600 nm using a cw dye laser. This radiometer was then used to measure the spectral irradiance at 600 nm from spectral irradiance lamps calibrated against a gold-point blackbody, and the spectral irradiance at the same wavelength from the NBS electron storage ring, SURF-II. Intercomparisons of this type are an important check of the agreement between these independent radiometric techniques. It was found that the detector scale indicated a spectral irradiance at 600 nm that was 0.76% lower than predicted by the gold-point blackbody scale and 0.25% higher than predicted by the electron storage ring scale. This result implies agreement within the overall quadrature uncertainties of ±0.25% for the detector scale, ±0.84% for the gold-point blackbody scale, and ±0.60% for the electron storage ring scale.

The theory of photodiodes and their application to radiometric measurements is reviewed. Some suggestions concerning photodiode detectors for use in stellar radiometric measurements are given. Quantum efficiency, linear response characteristics, and noise current values of silicon photodiodes are considered.

A new high-accuracy dye-laser-based system useful for measuring the spectral transmittance of filters or the spectral response of optical detectors has recently been developed at NBS. This paper describes the system and discusses the results of measurements made for purposes of comparison with a high-accuracy spectrophotometer also developed at NBS.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text A. Russell Schaefer and Robert D. Saunders, "Intercomparison between silicon and blackbody-based radiometry using a silicon photodiode/filter radiometer," Appl. Opt. 23, 2224-2226 (1984) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

A method of determining the absolute beam current in the NBS electron storage ring SURF-II by electron counting is described. Recent improvements and the present implementation of the technique are discussed, along with the results of an intercomparison with the NBS spectral irradiance scale.

An explanation is put forth for the observed nonlinearity in the red spectral region of the response of silicon photodiodes. Experiments are described to support the explanation; and the results, implications, and precautions indicated for the use of these diodes are given. Correlation of nonlinearity with spatial nonuniformity of response is demonstrated.

The uncertainty in the number of stored electrons was the major component of the absolute uncertainty (except at the shortest wavelengths) in the photon flux from SURF-II. A highly linear silicon diode with spectral sensitivity from 200 nm to 1150 nm, and a quartz window and lens which collect 70 mrad of radiation are used as a beam current monitor. The combination of the diode (selected ones known to be linear to within 0.2% over nine decades), the wide band width and collection angle (providing a sensitivity of 0.2 pA per electron) is the foundation for the improvement in measurement accuracy. The high sensitivity is used to detect incremental changes in detector output as the number of stored electrons is reduced one by one for stored currents from 104 electrons to zero. The diode linearity is used to scale the current up to 5 × 109 electrons (45 mA). The use of these linear diodes (with in situ calibration), at SURF and other storage rings, to determine the linearity of photon detectors which are sensitive to any radiation emitted by that storage ring will be discussed.

Mechanisms limiting the internal quantum efficiency in various types of oxide-passivated silicon photodiodes are discussed. It is argued that unit internal quantum efficiency is achievable in metallurgical junction, oxide-n+-p-p+ photodiodes, if it is achievable in the inversion layer of induced junction diodes of the same type. Measurements of the variation in response of the latter type of photodiode under both oxide bias and reverse bias are described. The results indicate that 100% collection of the minority carriers generated in the inversion layer is achieved for sufficiently low flux levels. Implantation in the oxide of Na+ ions to augment the trapped positive charge increases the maximum flux level at which 100% collection is observed.

A project is described in which the synchrotron radiation output from the NBS storage ring known as SURF II, is measured using a well characterized silicon based radiometer. This device consists of a silicon photodiode coupled with two interference filters to restrict the spectral response to a finite and convenient spectral region for the measurement. Considerations required for the characterization of the radiometer will be discussed. The absolute radiant flux from the storage ring is also calculable from various machine parameters. A measurement of the number of circulating electrons will be derived from electron counting techniques at low levels. This will yield an important intercomparison between the synchrotron flux measurements determined in two entirely different ways.

The possibility of interpolating the internal quantum efficiency of silicon photodiodes using a model with three adjustable parameters is investigated. The three parameters are determined from self-calibration measurements at 351, 476, and 800 nm. The internal quantum efficiency is then interpolated to 407 and 677 nm using the model. The calculated results are compared with direct measurements referenced to an electrical substitution radiometer. A difference of 0.6% was observed at 407 nm. This is probably significant, arising from inadequacies in the internal quantum efficiency model and possibly from volume recombination that is not accounted for by the self-calibration procedure. An insignificant (>0.1%) difference was observed at 677 nm.