Measured 2D space resolved absolute density of atomic oxygen between the electrodes (x-direction) and the quartz walls (y-direction). The powered electrode is located at x = 0, while the grounded electrode is at x = 1 mm. The quartz walls are located at y = 0 mm and y = 1 mm. (a)-(c) Atomic oxygen density measured for different numbers of consecutive driving harmonics, N, in the presence of “peaks” waveforms. (d) Atomic oxygen density for N = 4 and a “valleys” waveform. Note the different ranges of the color scales. The base frequency is f0 = 13.56 MHz and the peak-to-peak value of the driving voltage waveform is kept constant at 500 V. The concentration of the O2 admixture is 0.5 %. The step resolution in x and y directions is set to 1 mm.