Detector Noise equivalent power

NEP = Detector noise equivalent power, 1 Hz Band (watts), Act = Spectral resolution (cm-1),... 

There are important figures of merit (5) that describe the performance of a photodetector. These are responsivity, noise, noise equivalent power, detectivity, and response time (2,6). However, there are several related parameters of measurement, eg, temperature of operation, bias power, spectral response, background photon flux, noise spectra, impedance, and linearity. Operational concerns include detector-element size, uniformity of response, array density, reflabiUty, cooling time, radiation tolerance, vibration and shock resistance, shelf life, availabiUty of arrays, and cost. 

Detectivity. Detector sensitivity (1,2) is expressed in terms of the minimum detectable signal power or noise equivalent power (NEP) given in units of watts or W. The reciprocal function when normalized for detector area, M, and noise bandwidth, is defined as detectivity, D, in units of /W. Thus,... 

The main parameter which characterizes a calorimeter is the resolution, whereas in astronomical bolometers the qualifying parameter is the NEP (noise equivalent power, see later). Also the size is very different bolometers are usually very smaller. Their more sophisticated technology allows the realization of large arrays of detectors. In operation, bolometers usually handle a chopped signal (tens of Hertz) of much smaller energy than calorimeters. 

The fundamental performance parameter of any detector is its noise equivalent power (NEP). This is simply the input irradiance power necessary to achieve a detector output just equal to the noise. This NEP is dependent on a number of detector and signal variables such as modulation frequency and wavelength (the input signal is defined as sine wave modulated monochromatic light), and detector area, bandwidth and temperature. 

There are a variety of FPA detectors available that are sensitive in the NIR spectral region. The optimal choice of detectors depends on several factors desired wavelength range, whether the application will be laboratory based or part of a process environment, the sensitivity needed to adequately differentiate sample spectra and price. The figure of merit most often used to describe detector performance is specific detectivity or D, which is the inverse of noise equivalent power (NEP), normalized for detector area and unit bandwidth. NEP is defined as the radiant power that produces a signal-to-dark-current noise ratio of unity. 

It is evidently insufficient to consider only the response of a detector when analysing its usefulness for a particular application. It is generally necessary to analyse both intrinsic and extrinsic noise signals and compare them with the response. The result of this comparison can be expressed in many different ways. One of the most useful is the noise-equivalent power nep which is the power of an rms signal input (in watts) required to give a response equal to the total rms noise voltage AVN. Then ... 

The noise level can be expressed in terms of the power incident on the detector necessary to give a signal equivalent to the noise. If the noise voltage is A EN then the noise equivalent power (NEP) is defined by... 

Typical detectivity values as a function of wavelength for PbS photoconductive and various photovoltaic detectors. is a figure of merit defined as A /NEP, where A is the detector area and NEP is the noise-equivalent power, the rms radiant power in watts of a sinusoidally modulated input incident on the detector that gives rise to an rms signal equal to the rms dark noise in a 1-Hz bandwidth. Data from Hughes Aircraft Company. 

The responsivity (E) or specific detectivity (D ) and the noise equivalent power NEP (Wn), are often used to measure the sensitivity of a detector. The responsivity depends on the wavelength of the radiation and the temperature of the detector. The NEP, also called minimum detectable power, is the quotient of detector noise (N) divided by voltage responsivity (E). The D is the reciprocal of NEP, thus W = NIE and D = 1/Wn- A more sensitive detector has a smaller NEP and larger D, which results in less noise and a faster response time. 

The noise equivalent power (NEP) of an infrared detector is a measure of the noise generated by the detector and is given by ... 

Figure 3. Broadband spectrum of a conventional 2000 Globar IR source (short dashed line), and the spectrum of the NSLS synchrotron source (solid line) limited by an experimental throughput of 4.4><1 O 4 mm2sr. This is the etendue for a 1 pm by 1 pm sample measured with an infrared microscope. The measured, background limited Noise Equivalent Power (NEP) of a Mercury Cadmium Telluride (MCT) (long dashed line) detector is shown. This detector is operated at liquid nitrogen temperatures.

An InSb bolometer working at the temperature of boiling helium ( 4.2 K) will have an intrinsic response time of about 1 fcs, a sensitivity of the order 10VmW and a noise equivalent power below 10pWHz 5. The working bandwidth of the detector spans from DC to the IR region, and response is effectively fiat over the MMW spectrum. The QMC Instruments Ltd. InSb... 

The noise equivalent power (NEP) and specific detectivity (D ) are figures of merit that express the sensitivity of infrared detectors. The NEP is the root-mean-square (rms) power in a sinusoidally modulated radiation signal incident on the detector that gives a response equal to the rms dark noise in a 1-Hz... 

FT-instruments show — under the conditions of Raman spectroscopy — a multiplex r/isadvantage , since the statistical noise of the exciting radiation scattered onto the detector is transformed to noise at all frequencies in the Raman spectrum. The Raman conversion efficiency in the NIR spectral range, and differences in NEP (Noise Equivalent Power) at the corresponding detectors, can be compensated as follows. 

At the Detector Noise Moduie, the Noise Equivalent Power (NEP) associated to the detectors and the 1 // noise are calculated. In parallel, with the physical properties of the system defined, the Background Power Module calculates the background power noise due to the instmment and the Cosmic Microwave Background (CMB), Cosmic Infrared Background (CIB) and Zodiacal Light. 

These calculations allow us to have an idea of the background power level at the detectors. However, to include these contributions to the simulator the Noise Equivalent Power (NEP) is calculated following Lamarre s derivations (Lamarre... 

The Detector Noise Module calculates the Noise Equivalent Power (NEP) and the 1 // noise of the selected detection system. This module is flexible and different types of detectors will require the computation of different parameters. The detector selected for further development is the Lumped Element Kinetic inductance Detector (Doyle et al. 2008), LeKID, as it presents the most promising solution high sensitivity spectro-spatial interferometry. For the current version of the simulator, a single pixel and single mode detector is assumed for simplicity and computational reasons. 

This signal should be larger than the noise equivalent power NEP (this is the input power of the detector which gives the same detector output as the noise). 

A figure of merit which has been largely superseded by D for infrared detectors, but still finds application in optical detectors, is the noise equivalent power, or NEP, frequently symbolized as P - The NEP is the rms incident radiant power... 

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