Can 2 beams of ultraviolet light intersect and be visible where they intersect? Is it possible that if you have 2 ultraviolet lasers, that are invisible to the human eye, and if you aim their beams to intersect at some point, that the place of intersection will show a lower visible wavelength of light, caused by interference of the light freqency?  Can any other form of heat or energy be generated at the intersection?
If so, can someone provide a link to the explanation?  I am curious about this.
EDIT:  I should add that the 2 lasers would have different light frequencies while they are both invisible to the human eye.  So, I am wondering about interference between light freqencies.
 A: What you say is not possible with interference. Interference of light does not produce new colors of light. Light would have to scatter inelastically off of some molecules to produce a down-shifted frequency (Raman scattering or some type of wave-mixing phenomena). The point is, the light should interact with matter to change its frequency.
A: You'd have more luck using two infrared lasers - if you shone two infrared lasers at your eye (or at a camera) with frequencies that are half that of a visible photon, a small percentage of them would undergo two-photon absorption; two photons each with half the energy needed would be absorbed by a sensor element at the same time, causing the sensor to detect the equivalent of a visible-light photon.
The intensities would have to be very high for such an effect to be visible; I haven't done the calculations, but I'm confident the infrared lasers would completely cook your eye before you managed to see anything.
A: If you use the appropriate non-linear media,
and both beams have a high enough intensity
(probably requiring pulsed lasers),
you may be able to have a visible effect
at the point inside the media where the beams intersect.
Such nonlinear optics are pretty difficult to get working in practice, but not theoretically impossible.
My understanding is that pretty much all optically-pumped lasers convert (typically incoherent) high-energy (short wavelength) photons into laser light with somewhat lower-energy (longer wavelength) photons.
A: The basic reason the answer is NO, as everybody says, is because light, an electromagnetic wave, is an emergent phenomenon from innumerable individual photons. Thus your question boils down to :
is there a photon photon interaction? can a photon scatter off a photon?
The answer is : yes, there exists a two photon interaction,  but with such a tiny probability that it is improbable to see a collective effect unless at very high energies .


A Feynman diagram (box diagram) for photon–photon scattering, one photon scatters from the transient vacuum charge fluctuations of the other

Note that there are four electromagnetic vertices here, and the electromagnetic coupling constant that ends up as squared in the calculations is (1/137)^1/2, four times. This is a very small number and ensures the observations: that electromagnetic beams do not interact in vacuum except at very high energies when the crossection rises. 
There are proposals for gamma gamma colliders, not exactly visible electromagnetic radiation as an output, but lots of elementary particles.
