Tunneling Probability: Solving for Incident Angle $\theta$

[keniwas]

Homework Statement

A particle of mass m is incident on a planar barrier which we represent by a potential $$V(z)=\lambda\delta(x)$$. If the energy of the particle is E, and the incident velocity makes an angle $$\theta$$ with the z axis, what is the probability that the particle will penetrate the barrier?

The Attempt at a Solution

I can solve the problem for the case of normal incidence, as this is just the case of a delta potential barrier. However I have no idea how to include the incidence angle in the problem. This is where I am stuck, how/where does the angle $$\theta$$ come into the setup of the problem?

 

[keniwas]

Anyone have any ideas on this? I just need some advice on how to setup the problem... I am lost on it =/