Shaped pulse calibrating

We use common sense to find the correct power level We know we want lower power, and for Bruker that means a larger number. So we add this to 3 dB to get a power setting of 58.4 dB. As this power level corresponds to the maximum power of the Gaussian shaped pulse, we can set this power level for our shaped pulse and get a 180° rotation. This would be the starting point for the pulse calibration. 

Having determined the necessary pulse duration, the transmitter power must be calibrated so that the pulse delivers the appropriate tip angle. As already alluded to, this can be avoided on instruments with linearised amplifier outputs, provided accurate hard-pulse calibrations are known. The calibration of soft pulses differs from that for hard pulses where one uses a fixed-pulse amplitude but varies its duration. For practical convenience, amplitude calibration is usually based on previously recorded calibrations for a soft rectangular pulse (as described below), from which an estimate of the required power change is calculated. Table 10.3 also summarises the necessary changes in transmitter attenuation for various envelopes of equivalent duration, with the more elaborate pulse shapes invariably requiring increased rf peak amplitudes (decreased attenuation of transmitter output). 

The properties of some widely used selective pulses are described, together with methods for calibration. The emphasis is on an overview of what may be expected from a given pulse shape in terms of selectivity, duration, quality of profile, sensitivity to relaxation, and range of applicability. 

Figure 6.12 Experimental two-color setup featuring an IR beamline, to generate intense shaped IR pump pulses, and a VIS probe beamline, to provide time-delayed probe pulses of a different color. Both beams are focused collinearly into a supersonic beam to interact with isolated K atoms and molecules. Photoelectrons released during the interaction are measured by an energy-calibrated TOE spectrometer. The following abbreviations are used SLM, spatial light modulator DL, delay line ND, continuous neutral density filter L, lens S, stretcher T, telescope DM, dichroic mirror MCP, multichannel plate detector.

Figure 14.15—Pulsed hollow cathode lamp background correction, a) Shape of the emission line from a hollow cathode lamp under normal operating conditions, b) the 4000 Smith-Hieftje model from Thermo Jarrell Ash uses the principle of pulsed-source correction. The mercury source and the retractable mirrors are used for calibration of the monochromator. (Reproduced by permission of Thermo Jarrell Ash.)...

Abstract Measurement of the effective acquisition time of a spectrum by the pulser method is described. The measurement results were verified up to count rates of 12000 s1 at various settings of the pulse processing electronics and spectral shapes. Systematic effects of up to 2% were observed. The clocks in the spectrometers were calibrated by counting pulses generated by the DCF 77... 

This section is primarily intended for those who need to set-up experiments or those who have new hardware to install for which new calibrations are required. As with any analytical instrumentation, correct calibrations are required for optimal and reproducible instrument performance. All the experiments encountered in this book are critically dependent on the application of rf and gradient pulses of precise amplitude, shape and duration and the calibrations described below are therefore fundamental to the correct execution of these sequences. Periodic checking of these calibrations, along with the performance tests described in the following section, also provides an indication of the overall health of the spectrometer. 

The excitation profile of soft pulses is defined by the duration of the pulse, these two factors sharing an inverse proportionality. More precisely, pulse shapes have associated with them a dimensionless bandwidth factor which is the product of the pulse duration. At, and its effective excitation bandwidth, Af, for a correctly calibrated pulse. This is fixed for any given pulse envelope, and... 

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