Stimulation of surface ionization waves by pulsed laser irradiation

TL;DR

This work investigates how pulsed laser irradiation can stimulate surface ionization waves (SIW) propagating along a semiconducting barrier (SeBD) in atmospheric-pressure air. By synchronizing a $532$ nm, $2$ ns laser pulse with a nano-second discharge, the authors demonstrate that SIW stimulation occurs only when the laser is delivered within about $3~\mu s$ before plasma initiation, and that the SIW front travels farther with higher optical emission, increasing discharge energy by up to ~7%. The authors attribute the effect to ambipolar diffusion of photoexcited carriers away from the Si–SiO$_2$ interface, ruling out surface-charge desorption and distinguishing the interaction from photodetector–transistor-like devices. These findings reveal a diffusion-driven mechanism linking surface photoexcitation to SIW propagation, with potential implications for optoelectronic plasma devices operating in open air.

Abstract

The inclusion of semiconducting material within a composite barrier enables the perfectly uniform propagation of surface ionization waves (SIW) in air at atmospheric pressure regardless of the polarity of the applied electric field, unlike surface discharges generated using purely dielectric barriers. We exploit the photonic properties of silicon to stimulate the SIW using external irradiation by a 2-ns pulsed laser at 532 nm, with a fluence of 1.3 mJ/cm$^2$ per pulse at the surface. No effect is observed when irradiation occurs more than 3 $μ$s before plasma generation. This timescale is attributed to the ambipolar diffusion of photoexcited carriers away from the Si-SiO$_2$ interface. When this delay shortens to less than 3 $μ$s, the SIW propagates farther and with more intense optical emission. Furthermore, the energy of the discharge increases by up to 7%. The sensitivity to the laser-plasma delay demonstrates that the observed stimulation of the SIW cannot be due to the desorption of surface charge by irradiation.

Figures (5)

• Figure 1: Schematic diagram of the experimental setup for discharge generation, fast imaging, and laser irradiation. The oscilloscope is represented by its input channels labeled "Ch1" and "Ch2".
• Figure 2: Applied voltage (top) and total current (middle) waveforms of the SeBD, without (blue) and with (orange) 2-ns pulsed laser irradiation starting at $t = -35$ ns, covering the region on the wafer surface indicated in Figure \ref{['fig:plasma images']}. Also shown is the corresponding charge-voltage Lissajous plot (bottom). Points indicate the different start times of camera gating.
• Figure 3: Single-shot images of the SeBD at different times without (top) and with (bottom) laser irradiation starting at $t = -35$ ns. The region of irradiation is indicated (circle) in the bottom image for $t_0$.
• Figure 4: Radial profiles of optical emission intensity integrated over the angular range $\Delta\theta$ from $\theta = -119$° to $\theta = -145$°, without and with laser irradiation starting at $t = -35$ ns. The 3-ns exposure time begins at $t_6=$ 28 ns. Baseline subtraction was applied to permit fitting of the SIW front.
• Figure 5: Radial position (top) and integrated optical emission intensity over the angular range $\Delta\theta$ (middle) of the SIW front, as well as total energy of the SeBD (bottom) as a function of the time delay $\tau_d=-t$ of the pulsed laser. Also shown are measurements taken before the SeBD experiences irradiation and immediately after switching off the laser.