Silicon Photodiode Array Research Articles

Observations of Spectroscopic Binaries with a Solid-State Detector

The recent installation of a solid-state 1024-element silicon photodiode array detector (Reticon) at the coude focus of the 2.7 m McDonald Observatory reflector has greatly extended its limits of observation for binary and multiple systems which have weak and/or broad-lined components. This detector can produce extremely high signal-to-noise ratio observations and has high quantum efficiency over the wavelength region 3000-11000Å. The observational programs of three users of this device are described below.

Phosphor converter camera for near-infrared laser-beam profile recording

A compact camera system, made up of an IR sensitive phosphor activated by a photographic flashgun and with Polaroid film recording, has been developed for use in laser beam diagnostics at 1.315 microm. Detection thresholds, phosphor camera sensitivity, linearity, saturation, and time response have been determined. Estimates are made of the performance of a phosphor combined with an electronic system based on silicon vidicons or photodiode arrays.

Noise in large-aperture self-scanned diode arrays

An equation for the random noise of self-scanned silicon photodiode arrays is developed which includes significant terms not previously considered. It is shown that, including these terms, the new 2.5-mm-high self-scanned arrays are only slightly noisier than older arrays; but because of their much greater aperture, they can detect much smaller light fluxes than the older arrays even when used with simple, inexpensive amplifiers.

Lineare Silizium-Photodioden-Matrizen mit parallelem Datenausgang als Strahlungsempfänger in der optischen Emissionsspektroskopie—II. Analytische anwendung in verbindung mit der glimmentladungslampe nach Grimm

A silicon photodiode array was placed in the focal plane of a spectrometer to detect the radiation. Three single diodes of the array, each 6.5 mm long and 19 μm wide, were connected to the three channels as described in Part I. The properties of the photodiodes were investigated with respect to their applicability in spectral analysis. Especially the spectral response, the dynamic range and the signal-to-noise ratio were of great interest. The quantum efficiency was found to be in the range from 300 to 800nm. The dynamic range, defined as the range from the noise level to the maximum permissible signal voltage extends over 5.5 decades and is a linear function of the radiative flux. The signal-to-noise ratio of systems using photodiodes depends on the wavelength of the radiation and, if high feedback resistors (≧10 11Ω) are used, reaches the same order of signal-to-noise ratio as that obtained by using a photomultiplier (EMI 9789 QB). To demonstrate the applicability of the photodiodes, the analysis of limestone was studied. The sample powder was mixed with copper powder, pressed into pellets, and the major constituents Al, C, Mg and Si were determined by means of a Grimm glow discharge lamp. The calibration curves obtained as well as the detection limits are reported. Furthermore, oxygen was determined in a series of synthetic samples using the line 777.2 nm.

Self-scanning silicon photodiode array with microcomputer control

Self-scanning silicon photodiode array with microcomputer control

Self-scanned photodiode array: high performance operation in high dispersion astronomical spectrophotometry

We have developed a multichannel spectrophotometric detector system using a 1024 element self-scanned silicon photodiode array, which is now in routine operation with the high-dispersion coudé spectrograph of the University of Texas McDonald Observatory 2.7-m telescope. We discuss operational considerations in the use of such arrays for high precision and low light level spectrophotometry. A detailed description of the system is presented. Performance of the detector as measured in the laboratory and on astronomical program objects is described, and it is shown that these arrays are highly effective detectors for high dispersion astronomical spectroscopy.

Lineare Silizium-Photodioden-Matrizen mit parallelem Datenausgang als Strahlungsempfänger in der optischen Emissionsspektroskopie—I. Messanordnung und Analysen mit Funkenstrahlungsquelle

A linear silicon photodiode array has been used which consists of 5 photodiodes each having a separate output. Because of the dimensions of a single photodiode, i.e. 3mm long and 20 μm wide, they are capable of replacing the exit slits of a spectrometer. The read out system having 3 channels is described in detail. In each channel a FET operational amplifier with a low input bias current served as a current-to-voltage converter. The signal-to-noise ratios of systems using the photodiode array and of a photomultiplier (EMI 9789 QB) respectively are compared. The dynamic range of the photodiode is linear and extends over 5 1 2 decades referred to the noise level. As an analytical example copper was determined in aluminium alloys using medium voltage spark excitation in an argon atmosphere. The limit of detection was c = 4.8 × 10 −3%, the relative standard deviation as a measure of the precision was s rel = 0.014 for concentrations above 0.08%. In part II the application of recently produced photodiode arrays on the analysis of powders with a glow discharge will be described.

Spatial Profiles of Emission from an Inductively Coupled Plasma Source Using a Self-Scanning Photodiode Array

Detailed spatial profiles of analyte emission in an inductively coupled plasma source have been measured using a self-scanning linear silicon photodiode array mounted vertically in the exit focal plane of a monochromator. These profiles were measured for both neutral atom and ion lines of several elements as a function of plasma power, central axial (nebulizer) flow rate, and coolant flow rate. The plasma has complex but characteristic emission spatial patterns; patterns that are highly dependent, at the submillimeter level, on both flow and power parameters of the plasma. These data also indicate that the spatial position of peak neutral atom line emission may depend on analyte excitation and/or ionization characteristics while the spatial position of peak ion line emission appears to be species independent for those elements studied.

A wide-range monitor system for laser beam profiles

The system described uses an array of 50 FET switches to access the elements of either a linear array of silicon photodiodes or an array of pyroelectric detectors formed on a single sheet of PVF2 plastic. Compensating capacitors are used to give 1% uniformity of response down the array. The two types of arrays are easily interchanged, giving a very flexible system. With suitable attenuation, the photodiode array can give a saturation signal-to-noise ratio of 100:1 in the range 0.4-1.1 mu m for all levels above 4 W m-2 CW or 60 mJ m-2 for 10 ns duration pulses. The pyroelectric array can give a saturation signal-to-noise ratio of 1300:1 for CW beams above 180 kW m-2 or 260:1 for 10 ns pulses above 700 J m-2 in the range 0.3-30 mu m. These figures are achieved without the prescanning usually necessary with other systems.

Characteristics of Photodiode Arrays for Spectrochemical Measurements

A rather large number of spectrochemical studies and analyses can be greatly facilitated by the simultaneous measurement of spectral information over a range of wavelengths. Of particular importance and interest to analytical spectroscopists is the development of simultaneous multielement analysis systems. The development and implementation of such analyses have been hampered by a lack of convenient and versatile multichannel spectrochemical measurement systems. New detector subsystems based on modern electronic image sensors are helping to overcome this obstacle. One type of electronic image sensor is the self-scanning linear array of silicon photodiodes. These arrays are available with densities of 1024 photodiodes per in and in lengths of up to 1 in. They are packaged in conventional dual-in-line integrated circuit packages complete with the necessary scanning circuitry. These sensors have simple and inexpensive control and measurement circuitry, and superior blooming and lag performance when compared to most other electronic image sensors. In addition, the signal integrating capability of the arrays is a flexible and powerful asset for many spectrochemical measurements. These and other operational characteristics of photodiode arrays are emphasized in this study. In addition, the measurement capability of a computer coupled photodiode array spectrometer based on a 1024 element array which is capable of simultaneously measuring over 50 nm (500 Å) of continuous spectral information anywhere from 200 to 1000 nm is illustrated.

Measurement of the 'spontaneity' of self-emulsifiable oils.

Abstract Self-emulsifiable oils are solutions of surfactants in non-polar solvents which spontaneously form emulsions when added to water. Measurement of the degree of spontaneity has remained subjective. Accordingly, a method has been devised in which a small volume of the oil solution is injected into a flowing stream of water and carried across an intense beam of parallel light from a helium-neon laser. Light scattered from the beam by the dispersed oil droplets is collected by means of fibre optics onto an array of silicon photodiodes and the amplified output is integrated as a function of time. By varying the flow rate of the water stream it is possible to estimate the time required for an emulsifying system to come to its equilibrium state of dispersion under the conditions of the experiment, the ‘spontaneity’ of emulsion formation. Under the experimental conditions employed, systems comprising solutions of phosphated nonylphenolethoxylate (PNE) and phosphated fatty alcohol ethoxylate (PFE) in n-hexane came to equilibrium between 5 and 12 s, depending on the constitution. These times could be approximately correlated with the values for spontaneity estimated by the CPAC dilution test, although this latter test is somewhat subjective. The spontaneity appears to depend on the nature of the material existing within the phase diagram and the anomalous results obtained may be accounted for by the likely presence of a complex formed at the emulsion interface between the PNE, PFE and water during the dispersion process.

Simultaneous Multielement Quantitative Spectrochemical Analysis Using a DC Arc Source and a Computer Coupled Photodiode Array Spectrometer

Abstract Self scanning linear arrays of silicon photodiodes have been utilized as multichannel detectors in a variety of spectrochemical measurements (1,2,3,4). These arrays have densities of 1000 photodiodes per inch and can be thought of as completely solid state single line image sensors. In some earlier work (3) a spectrometer based on this detector was utilized for qualitative dc arc spectrochemical analysis. In this note we report on the utilization of an improved computer coupled photodiode array spectrometer system for simultaneous multielement quantitative analysis with a dc arc source.

Application of AND and Exclusive-Or (XOR) Logic Operations to the Identification of Elemental Emission Spectra Measured Using a Photodiode Array Direct Reading Spectrometer

Direct current arc emission spectra have been measured for 35 elements over a 140 Å range in the 3240 to 3380 Å region employing a monochromator self-scanned linear silicon photodiode array detector system. Each spectrum was reduced to a binary representation by compressing the spectral intensity information such that a logic 1 and a logic 0 represented the presence and absence of spectral features. It is shown that with the application of the logic operations AND and exclusive-or (XOR) it is possible to identify uniquely each of the 35 elemental emission spectra. The feasibility of extending the procedure to multicomponent spectra is illustrated and discussed.

Characteristics and applications of self-scanning linear silicon photodiode arrays as detectors of spectral information

Characteristics and applications of self-scanning linear silicon photodiode arrays as detectors of spectral information

Solid state photodiode system matched to high-gain low-noise d.c. and lock-in amplifiers for use in multichannel emission spectrochemical analysis

Various configurations of planar silicon photodiode arrays were tested as detection devices for multichannel emission spectrometry. The electronics comprised a laboratory-built preamplifier (open loop gain 25,000) that allowed measurements with commercial high-gain low-noise d.c. and lock-in amplifiers. An a.c. noise level of 2.5 × 10 −15 A (modulating frequency = 400 Hz, frequency band pass ≈ 1 Hz) and a low frequency noise level of 6 × 10 −15 A (3-db high-frequency roll-off = 3 Hz) at the output of the detector was reached at room temperature. This noise can be ascribed completely to the preamplifier. Cooling the photodiodes has no effect on the noise level and can be omitted. A perfectly linear response over at least three orders of magnitude above the noise level and a spectral resolution equivalent to that attained with photomultiplier and exit slit were established. Comparison of the signal-to-noise (S/N) ratio of the photodiodes with that of various types of photomultiplier showed that photomultipliers were superior by a factor of 100–500 in the S/N ratio at low light levels in the wavelength region between 2500 and 5500 Å. Prospects for further research on photodiode devices for dual-channel intensity measurements (simultaneous measurement of line-plus-background and background) are discussed.

Total active area silicon photodiode array

A novel approach is described for fabricating high resolution silicon photodiode arrays whereby virtually none of the irradiated array area is lost for interelement isolation or lead contacting requirements. Element isolation is achieved by biasing a p-v-n diode so that the depletion layer reaches a pattern of grooves etched into the side opposite the radiation. Experiments illustrating the concept feasibility on a two element array are presented as well as preliminary results on a 7×7 array having elements on centers separated by 0.013 cm.

A Charge Storage Target for Electron Image Sensing

A charge storage target consisting of a dense array of silicon photodiodes has been described as the image-sensing element in a vidicon type of camera tube for the Picturephone® station set. The target stores a spatially distributed charge pattern corresponding to an optical image in the form of a partial discharge of the reverse-bias voltage of the diodes. The discharge results from leakage current associated with hole-electron pairs created in the silicon substrate by incident photons during the raster interval. Recharging of the diodes to the full reverse-bias voltage along a prescribed raster by the scanning, low energy, electron beam creates the desired video signal. This paper describes creation of the hole-electron pairs in the silicon substrate by impinging high energy electrons. Since these electrons, incident from the side opposite the diode array, create a multiplicity of pairs, charge gain results. As in photon sensing, the discreteness of the array allows preservation of detail in the spatial distribution of impinging electrons. Measurements of charge gain as a function of electron energy and target resolution are presented. Applications in scan conversion, low light level TV, X-ray image intensification, and electron microscopy are indicated.