Table 3.

Comparison of the path length needed, the detection threshold of HCN concentration and the figure of merit between different THz gas sensors.

	Path length	Threshold	FOM
Photonic crystal cavity11	5 mm	2 ppm	0.1
Photonic crystal fiber10	100 mm	2 ppm	0.005
Resonant cavity8	480 mm	0.003 ppm	0.694
This work	0.15 mm	10 ppm	0.667