Below detection, limit splitting

The quantities of element or compound indicated the peaks in Figure 181 refer to the amount of material entering the plasma (i.e. amount injected corrected for the split ratio). The detection limits, defined as the mass flow rate of lead entering the plasma required to produce a signal to noise ratio of two is given below ... 

The required sampling frequency dictates that the second dimension separation should be as fast as possible while providing adequate resolution and the first dimension separation should be slowed down to accommodate the sampling frequency and second dimension separation time. The total separation time is the product of the second dimension separation time and the total number of fractions injected into the second dimension. Thus, the separation time of the second dimension separation is a major factor in determining the total separation time of comprehensive two-dimensional separations. When more than one separation dimension is utilized in a sequential coupled column mode, a larger dilution of the original injection concentration occurs with loss of sample detectability [88]. The column dilution factors and split ratios used to compute limits of detection are multiplicative per dimension. In critical cases information may be lost when a fraction transferred from the first dimension falls below the detection threshold after separation in the second dimension. 

A typical layout of a squeezing experiment based on a Mach-Zehnder interferometer (Sect. 4.2.3) is shown in Fig. 14.64. The output of a well-stabilized laser is split into two beams, a pump beam bi and a reference beam b2. The pump beam with the frequency co] generates by nonlinear interaction with a medium (e.g., four-wave mixing or parametric interaction) new waves at frequencies o l /. After superposition with the reference beam, which acts as a local oscillator, the resulting beat spectrum is detected by the photodetectors D1 and D2 as a function of the phase difference A0, which can be controlled by a wedge in one of the interferometer arms. The difference between the two detector output signals is monitored as a function of the phase difference A0. Contrary to the situation in Fig. 14.62, the spectral noise power density p(/, 0) (= Pnep per frequency interval d/ = 1 s ) shows a periodic variation with 0. This is due to the nonlinear interaction of one of the beams with the nonlinear medium, which preserves phase relations. At certain values of 0 the noise power density Pn(/, 0) drops below the photon noise limit... 

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