Showing papers on "Responsivity published in 1968"

FERROELECTRIC Sr1−xBaxNb2O6 AS A FAST AND SENSITIVE DETECTOR OF INFRARED RADIATION

Abstract: It has been found that ferroelectric Sr1−xBaxNb2O6 has a very large pyroelectric coefficient at room temperature for 0.25 < x < 0.5. This suggested that the material may be useful as a detector of infrared radiation. A detector, constructed with a value of x=0.33 was successfully used at 300°K to detect single pulses of 10.6‐μ radiation from a Q‐switched CO2 laser with a rise time of less than 30 nsec. Detectors with a low frequency responsivity of better than 104 V/W and a minimum detectable power of 4 × 10−9 W‐cm−1‐cps−1/2 are easily constructed. Methods of improving on these results are discussed.

FAR‐INFRARED PHOTOCONDUCTIVITY IN HIGH‐PURITY EPITAXIAL GaAs

Abstract: Extrinsic far‐infrared photoconductivity has been observed at 4.2°K in high‐purity n‐type epitaxial layers of GaAs grown on Cr‐doped semi‐insulating GaAs substrates. Measurements of the responsivity and noise in the detection system at 300 Hz in a 1‐Hz bandwidth yield an NEP of 1.2 × 10−11 W at 195 μ, 1.4 × 10−12 W at 337 μ and 6 × 10−11 W at 902 μ. The time constant of the detector has been determined to be shorter than 1 μsec using a Ge avalanche modulator to chop the incident radiation. A time constant of about 5 nsec has been measured using impact impurity ionization in the GaAs.

Source-detector spectral matching factors.

Abstract: Procedures are described for simplifying the computation of detector responsivity (output per unit input) from known detector calibration data. These procedures involve the computation, tabulation, and use of certain dimensionless spectral matching factor ratios. These ratios effectively express the relative degree of overlap occurring between the spectral response distribution of the detector and the spectral distribution of the incident flux to be detected. All three basic systems of units for expressing detector responsivity (A/W, A/lm, and electrons/photon) are considered.

Copper-doped germanium detectors

Abstract: Background limited operation of copper-doped germanium detectors has been obtained for a background as low as 10-11watts (5 × 103photons/second) in the 8-12 µ region. The temperature dependence of the observed responsivity for detectors, each containing the same copper concentration but having different donor concentration does not agree with any of the usual theories involving the free hole velocity, mobility, or capture cross section.

InSb Photoconductive Detectors in the Far Infrared

Abstract: Far infrared detectors using n-type InSb element with lower carrier concentrations are studied to obtain optimum bias current and spectral responsivities as a function of magnetic field. The maximum responsivity of the best detector at 4.2?K is 2600 ?V/?W at 190 ?m with half width of 40 ?m in the magnetic field of 7.32 kOe. The wavelength gibing peak response varies with magnetic field in accordance with cyclotron resonance. Element with low carrier concentration shows desirable characteristics as a narrow band detector. Optimum bias current of the detector is determinable from current-voltage characteristic of the element. Time constant of less than 0.4 ?s in rise time and 1.0 ?s in decay time is obtained by measuring a cyanide laser pulse. The detector has response even at 2 mm-wavelength and is superior in response and time constant of a Si point contact rectifier.

A fast, room temperature, millimeter and submillimeter electric-tunnel effect detector

Abstract: It is well known that current can flow between two metal electrodes, separated by a thin oxide or insulator layer of the order of 50A thick, by means of the electric-tunnel effect. Estimates have been made that it requires 10-16sec for an electron to tunnel from one electrode to the other. Calculations by Simmons and others have shown that for low voltages dissimilar electrode junctions are to a first approximation ohmic. We show in this paper that to a second approximation an asymmetry square law dependence appears for an ideal trapezoidal barrier, Which can lead to detection. The I-V curves and responsivity (volts/watt) of the detector are calculated for typical parameters.

Procedures for determining the spectral responsivity of an infrared radiometer.

Abstract: With the increasing number of commercial radiometers employing rather varied and sophisticated optical designs, the determination of the spectral responsivity of these radiometers has accordingly become more involved. A joint National Bureau of Standards-U. S. Army (Missile Electronics Warfare Technical Area, White Sands Missile Range, New Mexico) calibration of an ir radiometer was conducted at the White Sands Missile Range facility. The radiometer chosen for the measurements employed an uncooled PbS detector with a 10-cm Cassegrainian optical system. The selection of this particular type of instrument permitted two methods of measurement (each employing different standards and techniques) to be investigated. In order to simulate infinitely distant point sources, a 30-cm off-axis collimator was used in both methods of calibration. The methods of calibration and the uncertainties associated with each method are described and the application of the responsivity values to field measurements is discussed. The agreement of the spectral responsivity values as determined by each method is within the estimated uncertainty computed for each procedure.