Arbitrary waveform generators

Stored waveform inverse Fourier transform (SWIFT) pulses [17] have been applied as a means of broadband ejection of matrix ions generated by Cs+ desorption [18]. These pulses are generated by taking the inverse Fourier transform of the desired frequency domain spectrum and applying the stored time domain waveform to the endcap electrodes via an arbitrary waveform generator. The magnitude of the SWIFT pulse determines the degree of excitation for ions of specific secular frequencies. 

To perform broadband FTMW spectroscopy we require a microwave source that can produce phase-locked linear frequency sweeps over an 11 GHz frequency range in times ranging from 100 ns to 1 ps (sweep rates of 10 ° - lO" MHz/s). The short sweep durations are required so that the sample is polarized on a time scale faster than the pure dephasing of the rotational free indnction decay (FID). Traditional microwave synthesized sweepers are typically limited to sweep rates of about 10 MHz/s. We have developed a microwave source based on a 4 Gs/s arbitrary waveform generator that can produce the required excitation pulses. A schematic of the microwave source is shown in Figure 1. 

Figure 1. Experimental setup of the pulse shaper AOM, Ge acousto-optic modulator AWG, arbitrary waveform generator CM, cylindrical mirror grating, 200-g/mm ruled grating. Pulses are dispersed by the grating, focused at a CM, shaped at the AOM, collimated at a CM, and recombined at a grating.

The use of Cu(ii) or other transition metal centres as one of spectroscopically orthogonal labels for DEER measurements is complicated by the width of the corresponding ERR spectrum. A broad spectrum typically results in a strong selection of orientations and low modulation depth (if these species are pumped). While orientation selection can be useful, it clearly complicates the determination of inter-spin distance distributions. These problems might be resolved by employing pulses with very broad excitation bands, available for the pulse EPR setups based on arbitrary waveform generators. Recently such experiments were reported for Cu(ii)-nitroxide and Co(ii)-nitroxide spin pairs. °° It is worth mentioning recent work on DEER-based distance determination between nitroxide radicals and low-spin Fe(iii). ° ... 

Fig. 5.6 Quasi-arbitrary voltage waveform generated inside LabVIEW and used for the AWG hardware of the system top) digital signal used to turn the discharge switch on bottom) [5] 2012 IEEE...

Wigout works by generating sequences of sample segments that, taken together, compose a waveform. It can generate complex combinations of waveforms of arbitrary length, limited only by the amount of memory on the computer (see Chapter 5 for more details about the sequential waveform composition technique). 

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