E-field measurement of pulses in the time domain
For pulse measurement in time domain, the choice of the right measurement system is not straightforward as no infinite bandwidth system exists.
Any measurement system always presents both low and high frequency cutoffs. Depending on the pulse shape, the requirements for the measurement system will differ. However, whatever the pulse shape, it can be shown that any pulse measurement system needs to cover at least 2.5 decades of frequency in order not to induce too much distortion nor attenuation of the pulse to be measured. For simulating the response of any Kapteos measurement system, we have considered four shapes of pulse with unitary peak amplitude as shown below.
Kapteos measurement systems for time-domain pulse measurements are based on:
an E-field probe,
an optoelectronic converter to use the probe,
a Digital Sampling Oscilloscope (DSO) to digitize the signal delivered by the E-field measurement system composed of the E-field probe and the optoelectronic converter.
We make also the assumption that the used DSO presents a wider bandwidth than the E-field measurement system itself.
Kapteos most sensitive E-field probes EL5 and ET5 can almost be considered as infinite bandwidth sensors as they cover more than 9 decades from 10 Hz up to more than 10 GHz. However the optoelectronic converters that are required to use the probes do not cover such huge bandwidth. Nevertheless, with only three optoelectronic converters and the same E-field probe, pulse measurements can be carried out for pulse Full Width Half Maximum (FHWM) ranging from 235 ps up to 1.5 ms, i.e. on 6.8 decades!
Simulation of E-field measurement system response for classical pulse shapes
Considering any of Kapteos E-field probe with our new generation of optoelectronic converter eoSense™ LF for which the bandwidth has been increased by almost 1 decade, pulse measurements can now be carried out for pulse FWHM ranging from 30 ns up to 1.5 ms.
Kapteos optoelectronic converters adapted for pulse measurements
In Kapteos optoelectronic converters line, four models are fulfilling requirements for reliable pulse measurements:
eoSense™ LF for 30 ns to 1.5 ms pulse FWHM,
eoSense™ MF for 1.5 ns to 750 ns pulse FWHM,
eoSense™ HF for 470 ps to 1.5 ns pulse FWHM,
eoSense™ SHF-0.01-6.4 for 235 ps to 1.5 ns pulse FWHM,
The figure below summarizes these data and allow a straightforward selection of the right optoelectronic converter for a given pulse FWHM.
However, for very specific pulse shape and/or for FWHM values close to operating limitations appearing in the figure above, never hesitate to contact Kapteos with your requirements taking your specific pulse shape and FWHM into account in order to get a free simulation of the measurement with a given optoelectronic converter (OEC). This will permit to get a precise idea of the measurement result you will obtain with the E-field measurement system that we will recommend to your need.
To get a more complete review on this subject please refer to our application note on Time-Domain Pulse Measurement.