Self-Initiated Microwave Plasma Formation and Interaction Within a 2D Photonic Crystal

The ability for a 2D photonic crystal with a point defect to cause self-initiated gas breakdown within the defect is demonstrated experimentally. The point defect forms a highQ resonant cavity which, when an electromagnetic wave is incident, enhances the electric field within the cavity facilitating gas breakdown and the formation of a stable freespace microwave plasma within the cavity. We demonstrate that self-initiated plasma formation is possible in lowpressure argon (10 Torr) using as low as 1.4 W of microwave power when applied at the resonant frequency of the cavity (8.614 GHz). Plasma formation within the defect cavity decreases the transmission of energy through the photonic crystal by approximately two orders of magnitude. Plasma formation time is shown to be a function of gas pressure and input power, with transient times measured to be as fast at 100 ns at low pressure (5 Torr) and relatively high input powers (9 W). Using power transmission through the photonic crystal as a diagnostic tool, electron densities of the microwave plasma are shown to be 10
¹⁶
– 10
¹⁷
m
⁻³
for argon pressures between 10 and 50 Torr. Experimental results suggest that a self-initiated plasma within a photonic crystal has an application as a simple power limiter. Simulations also suggest device scaling to a 45 GHz resonance is possible with even greater enhancement of the electric field.