  We consider regimes of Spontaneous Parametric Down-Conversion both
noncollinear and nondegenerate in frequencies. Parameters characterizing
degrees of noncollinearity and of nondgeneracy are defined, and they are shown
to be not independent of each other. At a given degree of nondegeneracy the
emitted photons are shown to propagate along two different cones opening angles
of which are determined by the degree of nondegeneracy. Based on this, the
degree of nondegeneracy can be controlled by means of the angular selection of
photons, e.g., with the help of appropriately installed slits. For such
selected photons their wave functions are found depending on two frequency or
on two temporal variables. Interference effects arising in such states are
tested by analyzes of the Hong-Ou-Mandel type scheme with the varying delay
time in one of two channels and with photons from two channels sent to the
beamsplitter. The temporal pictures arising after the beamsplitter are found to
demonstrate extremely strong interference exhibiting itself in formation of
finite-size temporal combs filled with quantum beats. Parameters of combs
depend on the degree of nondegeneracy, and the physical reasons of this
dependence are clarified.
