  Spectral and temporal coincidence and single-particle photon wave packets are
described and their widths and durations are found. The degree of entanglement
is characterized by the experimentally measurable parameter R defined as the
ratio of the coincidence and single-particle spectral widths. In the frequency
representation, this parameter is found as a function of the pump-pulse
duration. This function is shown to have a minimum and even in the minimum, at
rather natural conditions, the parameter R is found to be very high (R=73>>1).
The Schmidt number K is found for both short and long pump pulses and
interpolated for arbitrary pulse durations. All functional dependences of R and
K are found to be identical and numerical difference between them is shown to
be not exceeding 20%. Two-time temporal wave function of a biphoton state is
investigated in details, and a rather significant difference between the cases
of short and long pump pulses is found to occur. In the case of long pulses,
the temporal parameter R is defined as the ratio of durations of the
single-particle and coincidence signals, and the defined in such a way
parameter R is shown to be very close to the Schmidt number K.
