Experimental confirmation of Bethe's diffraction theory

Utilizing high power CW THz Coupled Cavity BWO (CCBWO), over 10
⁸
of Signal to Noise Ratio (SNR) is obtained. Extreme subwavelength apertures are perforated on ultrathin aluminum films by micro-photo-etching and It is proved that the transmittance normalized to hole size is proportional to 4th power of the ratio between hole size to incident wavelength for a<;<;λ as Bethe's expectation.