  We propose a method to characterize the ultra-narrow momentum distribution of
atomic gases by employing a standing-wave light-pulse sequences beam-splitter.
The mechanism of beam splitting is analyzed in detail, and the influence of a
finite-width momentum distribution on the population of each diffraction order
is given. The temperature of ultracold atomic gases can be calibrated by
measuring the ratio of population in different diffraction orders after double
standing-wave light-pulses. We obtain analytical expressions for two typical
cases, and demonstrate phase space evolution in the whole process by using the
Wigner function. This method is valid for both classical atomic gas and
Bose-Einstein condensates, and it is suited for temperature measurement on the
space ultra-cold atomic physics platform, in which the ultra-narrow momentum
distribution of atomic gas is on the order of 100pK or even lower.
