  Time resolved electron density measurements in pulsed RF discharges are shown
using a hairpin resonance probe using low cost electronics, on par with normal
Langmuir probe boxcar mode operation. Time resolution of less than one
microsecond has been demonstrated. A signal generator produces the applied
microwave frequency; the reflected waveform is passed through a directional
coupler and filtered to remove the RF component. The signal is heterodyned with
a frequency mixer and read by an oscilloscope. At certain points during the
pulse, the plasma density is such that the applied frequency is the same as the
resonance frequency of the probe/plasma system, creating a dip in the reflected
signal. The applied microwave frequency is shifted in small increments in a
frequency boxcar routine to determine the density as a function of time. The
system uses a grounded probe to produce low cost, high fidelity, and highly
reproducible electron density measurements that can work in harsh chemical
environments. Measurements are made in an inductively coupled system, driven by
a single frequency pulsing generator driven at 13.56 MHz and are compared to
results from literature.
