Synchronous multiple modulation

However, for the same data collection time, interferometry is more sensitive to multiplicative noise (i.e., noise proportional to the signal) than continuous-scan interferometry [591]. To eliminate the multiplicative and 1// noise, phase modulation (at 400 Hz) of IR radiation in conjunction with LIA demodulation is used [591]. Since the LIA and some IR detectors need the IR signal to be modulated at a single carrier frequency, a mechanical chopper, phase modulation (when at each position the fixed mirror is dithered at a fixed frequency), or modulation of absorption of the sample is used to produce a carrier frequency. In this case, the TR measurement is referred to as a synchronous multiple-modulation experiment. Multiple modulation is unnecessary if the so-called dc coupled detector which does not require a varying signal is used. 

Our analysis of multiple, field-driven qubits that are coupled to partly correlated or independent baths or undergo locally varying random dephasing allows one to come up with an optimal choice between global and local control, based on the observation that the maximal suppression of decoherence is not necessarily the best one. Instead, we demand an optimal phase relation between different but synchronous local modulations of each particle. The merits of local versus global modulations have been shown to be essentially twofold ... 

Some of the most useful polarization-dependent NSOM methods, however, involve modulation of the polarization from the probe (see Figure 3.20),224 coupled with synchronous detection of the near-field signals. Such methods allow for multiple imaging modalities so that topography, absorption dichroism, and/or birefringence information can all be readily obtained. 

In the homonuclear case, the synchronous and matched irradiation at two frequencies and Vj can be implemented by placing the transmitter midway between the selected frequency ranges Rj and Rj and by modulating a band-selective multiple-pulse sequence with cos r(i, — Vj)/2]. This method can be regarded as an extension of the doubly selective HOHAHA experiment (Konrat et al., 1991), where a weak square pulse, rather than a multiple-pulse sequence, is amplitude-modulated. Implementations based on the principle of interleaved DANTE sequences (Morris and Freeman, 1978 Patt, 1992 Kupce and Freeman, 1992c) are also feasible. 

Other modulation techniques are oscillation (tilting) of an interference filter [3] and modulation of the electron beam scan pattern in a vidicon or image-disk-sector photomultiplier spectrophotometer [34]. This was the first nonmechanical wavelength modulation. Wavelength modulation induces a synchronous modulation of the amplitude. If these intensities are expanded, for instance, in the form of a Taylor series in Aq, and the powers of the sine functions are expressed as sine and cosine functions of the corresponding multiple angles, then the derivatives can be obtained from the Fourier coefficients (see Sec. 2.1.3.3) of these series. The second derivative is obtained from the second harmonic of the induced intensity. 

It is very useful to synchronize the Amplitude Modulation effect with the tempo and beat of a project. Amplitude Modulation is a faster-period effect that may occur on the beat or often multiple times each beat. See the previous discussion on calculating rates in the General FX Controls section of this chapter for information about how to calculate and synchronize this effect with a project. 

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