Graded transmission in a bent orifice

We calculate the transmission of a bent orifice. The bending angle φ is assumed to be small [(Formula presented) and also (Formula presented) where ω is the incoming particle energy, and (Formula presented) is the threshold one, L is the orifice width]. We find graded transmission: There is a critical angle (Formula presented) For (Formula presented) and for (Formula presented) the transmission is dropped abruptly to (Formula presented) We suggest an explanation for this phenomenon.