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Tuesday, May 31, 2011

Shaped Pulses

Shaped rf pulses are used frequently in modern NMR experiments for selective excitation and more efficient inversion. The figure below shows some of the pulse shapes in the Bruker shape library measured with an oscilloscope on an AVANCE III console. Each 50.3 MHz rf pulse was 1 msec in duration and was measured at the output of the signal generation unit.

3 comments:

Raghav said...

One can also see the shaped pulse profile in the spectometer by using the shaped pulse in the CPD program. On the Bruker spectrometers, set the channel F1 and F2 for 1H nuclei. Use the pulse program zgig. Set cpd program to eretic. (if not create a cpd program (edcpd) with the following lines

1 p62:sp15:0 pl=pl25
jump to 1

) set all the hard pulse power to 120dB and shaped pulse power (sp15 in this CPD program) to a very low value (Say 70dB), set aq=p62 length of the shaped pulse (say 1ms). with ds=0 and ns=1. Acquisition with zg will show you the fid which is the shape pulse profile.
Caution: Use of higher power for the decoupler (pl25 in this case) may damage your reciever.

Peter said...

Dear Glenn,

thanks for you wonderful blog which saved a lot of my time searching for answers. I wanted to reproduce your "shaped pulse oscilloscope" experiment, but unfortunately failed. I connected an 20 MHz oscilloscope to the RF-Out of an SGU and started with a simple "zg" pulse program. Although I could detect a kind of signal, the shape had nothing to do with an rectangular pulse and changing the pulse length / power level didn't even change anything. Are there any tricks for detecting a pulse?

Thanks In advance!

Glenn Facey said...

Peter,
Thank you for your message. When I collected this data, I used an Agilent 1 GHz digital oscilloscope. It took a bit of effort to get the triggering correct but otherwise I do not recall any problems. I collected the signals directly from the SGU's of a Bruker console before going to the amplifiers.
Glenn