Photon shot noise

Fig. 13. Expected signal and noise levels for RE-TM alloys and Pt/Co multilayers (schematic). The total noise entering the SNR is the sum of the system noise, disk noise, and write noise. The system noise is electronic noise and photon shot noise and is comparable for disks with the same reflectivity.

Remember that the aim is to detect amplitude in the range 10 to 10 , so values given in Eq. (37) are the low limits of what is required. From this last equation we can draw some conclusions. We have only three parameters to play with to lower the photon shot noise arm length, laser power and integration time. 

The signal to noise ratio is limited in any physical intensity measurement, however, by the statistical fluctuations in the photon flux (photon shot noise). This limit can be reached with Fourier transform infrared spectrometers. 

The phase-dependent directionality of photocurrents produced by such a detector entails advantageous properties of the photocurrents cross correlations in nonoverlapping time intervals or spatial regions (considered in Section 4.2.2). These directional time-dependent correlations are measured with one detector only. They involve solely terms dependent on LO phases, in contrast to similar correlations measured by conventional photocounters, which inevitably contain terms depending on photon fluxes such as the LO excess noise. Owing to these properties, the mean autocorrelation function of the SL quadrature is shown in the schemes considered here to be measurable without terms related to the LO noise. LO shot noise, which affects the degree of accuracy to which this autocorrelation is measured (i.e., its variance) is easily obtainable from zero time delay correlations because the LO excess noise is suppressed. The combined measurements of cross correlations and zero time delay correlations yield complete information on the SL in these schemes. 

The intrinsically low intensity of Raman scattering strongly influences both the sensitivity and penetration depth of SORS and its variants. Dominant noise components (photon shot noise or thermal/dark count [1]) can be minimised relative to signal by increasing absolute signal levels. In many Raman systems, collection optics, laser power and other relevant parameters are usually maximised for optimum performance of the system current detectors (CCD devices), for example, have detection efficiencies approaching 100%. Typically, acquisition time provides the only straightforward means available... 

In condensed-phase CARS, the effects of the nonresonant susceptibility x(3)nr are most profound when a sample with weak Raman modes is embedded in a nonlinear medium. The nonresonant background of the latter can be easily comparable to or larger than the resonant contribution from the sample of interest. This is a situation commonly encountered in biological applications of CARS microscopy. Depending on the experimental situation, the CARS detection sensitivity to weak resonances can then be restricted either by the nonresonant background or by the photon shot-noise [62]. To maximize either the relative or the absolute CARS intensity, nonresonant background suppression schemes [44, 60, 61, 63, 64] and optical heterodyne detection (OHD) techniques [65-67] have been developed during recent years. 

Photon shot-noise or preamplifier shot-noise limitations, or source-flicker-noise limitations but utilizing source compensation" techniques... 

Figure 6 Signal-to-noise of a measurement provided as a function of the absorption of a chromophore. When excess electronic noise in the measurement system becomes comparable to the photon shot-noise, better data can be obtained by adjusting the absorption to lower values. (Drawn from data in Krausz )...

Spatially offset Raman spectroscopy (SORS) Conventional Raman Spectroscopy is limited to the near-surface of diffusely scattering objects and to the first few hundred micrometers depth of surface material. Spatially Offset Raman Spectroscopy (SORS) is a variant of Raman Spectroscopy that allows highly accurate chemical analysis of objects beneath obscuring surfaces. This is done by making at least two Raman measurements one at the surface and one at an offset position of t3q>ically a few millimeters away. To do this without using an offset measurement would be severely restricted by photon shot noise generated... 

The first term in the variances is the shot noise (SN) of fight. This can be measured in absence of the interaction where k 0. The quantum nature of the shot noise level is confirmed by checking the linear scaling with photon number of the pulse, see Eq. (4). The second term arises from the projection noise (PN) of atoms. Hence, we may calibrate i f to be the ratio i f = PN/ SN of atomic projection noise to shot noise of fight. Theoretically i f has the linear scaling i f a. /,. Sx T with the macroscopic spin size Jx which must... 

Photon shot noise from the spectrum being measured quickly becomes the predominant source of noise when effective readout noise is lowered through averaging non-... 

Neglecting photon shot noise and dark counts, the lowest theoretical absorbance (A) measurable on a 16-bit camera can be calculated using the Beer-Lambert law ... 

In practice, photon shot noise and variability in dark counts represent less than 1 gray scale unit on a 12-bit scale if 100 pixels are averaged (square-root-of-A -law). Experimentally, we observe noise at the level of approximately 10 A at 0.0 A and 10" A at 1.0 A. 

By neglecting photon shot noise (soon to be considered), I(t) dt has the meaning of the number of absorbed photons in the time interval (0, T) [i.e., since dif /dt) dt is the total work and each photon carries energy... 

Photon Noise. Sometimes called source noise or photon shot noise, this noise is the result of random fluctuations in the number of photons transmitted to the detector. In infrared spectroscopy, this noise does not dominate, but in the visible/UV spectral region where photon counting is possible with high quantum-efficiency detectors, photon noise must be considered. 

The signals detected separately by a Fourier transform instrument and by a dispersion instrument remain the same as stated earlier. Now, however, for photon shot noise the noise level is proportional to the square root of the signal level.35-37 For the dispersion instrument, the signal-to-noise ratio in the spectral element d[Pg.436]

As indicated by this equation, the multiplex gain at the frequency a- offered by Fourier transform spectroscopy in the presence of photon shot noise is a function of the spectral brightness at that frequency and of the overall structure in the total spectrum. This is completely different from the situation presented earlier where detector noise was assumed to dominate. 

Quantmn noise Any noise attributable to the discrete nature of electromagnetic radiation. Examples include shot noise, photon noise, and recombination noise. 

Detection noise is signal independent and therefore additional detectors will increase the total noise of a measurement. This is not the case for the Poisson distributed noise of the emission light (photon shot noise), a significant factor for weak fluorescence signals. It is not significantly affected by the number of... 

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