Specific detectivity

Specific detectivity, or D*, for a photodetector is a figure of merit used to characterize performance, equal to the reciprocal of noise-equivalent power (NEP), normalized per square root of the sensor's area and frequency bandwidth (reciprocal of twice the integration time). Specific detectivity, or D*, for a photodetector is a figure of merit used to characterize performance, equal to the reciprocal of noise-equivalent power (NEP), normalized per square root of the sensor's area and frequency bandwidth (reciprocal of twice the integration time). Specific detectivity is given by D ∗ = A Δ f N E P {displaystyle D^{*}={frac {sqrt {ADelta f}}{NEP}}} , where A {displaystyle A} is the area of the photosensitive region of the detector, Δ f {displaystyle Delta f} is the bandwidth, and NEP the noise equivalent power in units . It is commonly expressed in Jones units ( c m ⋅ H z / W {displaystyle cmcdot {sqrt {Hz}}/W} ) in honor of Robert Clark Jones who originally defined it. Given that noise-equivalent power can be expressed as a function of the responsivity R {displaystyle {mathfrak {R}}} (in units of A / W {displaystyle A/W} or V / W {displaystyle V/W} ) and the noise spectral density S n {displaystyle S_{n}} (in units of A / H z 1 / 2 {displaystyle A/Hz^{1/2}} or V / H z 1 / 2 {displaystyle V/Hz^{1/2}} ) as N E P = S n R {displaystyle NEP={frac {S_{n}}{mathfrak {R}}}} , it is common to see the specific detectivity expressed as D ∗ = R ⋅ A S n {displaystyle D^{*}={frac {{mathfrak {R}}cdot {sqrt {A}}}{S_{n}}}} .