Minimum detectable power

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. 

There is no unique set of characteristics which can be used to describe the ideal infrared detector. The ideal detector has nearly as many definitions as there are applications. For hot box detection on railroad-caraxles, reliability and simple maintenance are measures of perfection. For satellite operations compactness, light weight, low power and high sensitivity may be the important yardsticks. In the discussion which follows, an ideal detector is defined as one whose minimum detectible power is determined by the statistical fluctuation in... 

Equation (2.65) implies that if the signal-to-noise power ratio is unity, then the minimum detectable power is just the energy of a photon multiplied by twice the measurement bandwidth and divided by the quantum efficiency. For any real... 

This result can be expressed in terms of a minimum detectable power. Since the energy per photon is hc/A, the minimum detectable power required in order that there be at least a 99% probability of detecting a photon in an observation time Tq is... 

Figure 2.20 illustrates the minimum detectable power from a 500 K black body as a function of wavelength, illustrating the composite of the signal fluctuation and background fluctuation limits. The same values of the param-... 

After briefly reviewing conventional optical and infrared heterodyne detection, we examine the behavior of a multiphoton absorption heterodyne receiver. Expressions are obtained for the detector response, signal-to-noise ratio, and minimum detectable power for a number of cases of interest. Receiver performance is found to depend on the higher-order correlation functions of the radiation field and on the local oscillator irradiance. This technique may be useful in regions of the spectrum where high quantum efficiency detectors are not available since performance similar to that of the conventional unity quantum efficiency heterodyne receiver can theoretically be achieved. Practical problems which may make this difficult are discussed. A physical interpretation of the process in terms of the absorption of monochromatic and nonmonochromatic photons is given. The double-quantum case is treated in particular detail the results of a preliminary experiment are presented and... 

We recall from (7.4) that rj2 is itself proportional to the irradiance of the LO, and we must have 4 /2 <1- The result is therefore similar to that for the singlequantum heterodyne detector given in (7.1) in that case, however, rj is independent of the LO. The two-quantum minimum detectable power (MDP) [7.4,5] therefore becomes... 

An alternate approach involves the use of spatially uniform detectors. Blevin and Brown (26) developed a gold-film bolometer with a broadband response that was uniform to within 2% over an area of 9 x 4 mm for a 0.25-mm beam spot. The detector used a NaCl window and had a minimum detectable power of 4 nW for a bandwidth of 1 Hz. Hanssen and Snail (49) measured the spatial uniformity of a windowless, 14 x 14-mm gold-black coated pyroelectric (LiTaOj) detector at 10.6 /im. For a 0.25-mm beam spot, the response was uniform to within +1.7% over 13 mm, excluding one narrow scratched region where a 10-15% deviation was observed. The minimum detectable power was 1 /iW (standard uncertainty) for a bandwidth of 1 Hz (50). 

Equation (16) holds only if again wTr 1. the detector impedance is much smaller than that of the load, and wr, I, where t, C /I is the electrical time constant of the whole RC circuit, c is the dielectric constant and F is the irradiated detector area. To obtain a maximum signal noise/ratio with the satiK conditions as given above, a u.se(ul figure of merit is the reciprocal of the minimum detectable power (IPJ [163] ... 

Cooper, J. (1962). Minimum detectable power of a pyroelectric thermal receiver. Review of Scientific Instruments, 33,92-5. 

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