## 2 Materials and Methods  
Figure 1a shows the experimental setup used in this work, with detailed views of the light collection scheme shown in Figure 1b. Figure 1c presents an example of the waveform applied to the high voltage (HV) electrode without plasma ignition. The plasma jet device presented in Figure 1a consists mainly of a DBD type reactor, composed by a metal pin electrode placed inside a closed-end quartz tube, which in turn is placed inside a dielectric chamber. The working gas is fed into the chamber and flushed to the ambient air through a 1-meter long and flexible plastic tube connected to the reactor output. The plastic tube material is nylon-6, with outer and inner diameters equal to 4.0 mm and 2.0 mm, respectively. A conducting wire with 0.25 mm in diameter is put inside the plastic tube (see the floating electrode in Figure 1a). This floating electrode penetrates a few millimeters inside the reactor in a way that it does not touch the quartz tube. The other wire tip ends 2 mm before the plastic tube exit. When the primary discharge inside the DBD reactor is on it polarizes the floating electrode and a small plasma jet is ignited at the end of the plastic tube. This remote plasma jet was directed towards a copper plate, placed at a distance **d** from the plasma outlet, which is connected to an electric circuit whose impedance follows an international standard (IEC 60601-1). It is a simplified electrical circuit model aimed to mimic the electrical properties of the human body [29]. To obtain controllable gas admixtures of He and O\({}_{2}\) as a working gas, both gases have their flow rates  
controlled by mass flow controllers and are introduced into a gas mixer prior to entering the DBD reactor. The power source employed to produce the plasma was a commercial AC generator (Minipuls4 GBS Elektronik GmbH, Germany). We choose to apply the specific HV waveform shown in Figure 1c instead of a pure sinusoidal signal because the former produces lower ohmic heating on the experimental setup components shown in Figure 1a. That HV waveform presents a sinusoidal HV \"burst\" with an oscillation frequency (\(f_{osc}\)) of 29 kHz followed by a voltage off period, which repeats at a repetition period (\(T\)) of 1.7 ms.  
To obtain the mean discharge power (\(P_{dis}\)), simultaneous measurements of the voltage applied on the powered electrode and the voltage across a serial capacitor (C = 10 nF) were carried out. The calculation of \(P_{dis}\) values takes into account all voltage oscillations in each burst that produce a charge variation in C. To measure the applied voltage a 1000:1 voltage probe (Tektronix model P6015A) was used. The signals waveforms were recorded using a 200 MHz oscilloscope (Tektronix model 2024B). Then, the \(P_{dis}\) value is calculated  
Figure 1: (a) Schematic of the experimental setup. (b) Details of the arrangement for the optical fibers. (c) Example of a typical HV waveform applied to the pin electrode without producing plasma. by summing the area of the \(q-V\) Lissajous figures formed between the voltage (\(V(t)\)) and charge (\(q(t)\)) signals, divided by the burst period \(T\) that is [30; 31; 32]:  
\[P_{dis}=\frac{1}{T}\oint q(V)dV \tag{1}\]  
By applying the [PERSON]'s theorem to (1), \(P_{dis}\) can be calculated using:  
\[P_{dis}=\frac{1}{2T}\int_{t_{1}}^{t_{2}}\bigl{[}V(t)q^{\prime}(t)-V^{\prime}( t)q(t)\bigr{]}dt \tag{2}\]  
where \(\{V^{\prime}(t),q^{\prime}(t)\}=d\{V(t),q(t)\}/dt\). Equation (2) has the advantage that it can be used to calculate the area of the Lissajous figure without the need to plot the \(q-V\) curve. We also measured the waveform for the current that passes through the system using a current monitor from PearsonTM (model 4100). Then in each case the recorded signal was used to perform the calculation of effective discharge current (\(i_{RMS}\)).