  We study photoionization of cold rubidium atoms in a strong infrared laser
field using a magneto-optical trap (MOT) recoil ion momentum spectrometer.
Three types of cold rubidium target are provided, operating in two-dimension
(2D) MOT, 2D molasses, and 3D MOT with densities in the orders of $10^7$
atoms/cm$^3$, $10^8$ atoms/cm$^3$, and $10^9$ atoms/cm$^3$, respectively. The
density profile and the temperature of 3D MOT are characterized using the
absorption imaging and photoionization. The momentum distributions of Rb$^+$
created by absorption of two- or three-photon illuminate a dipole-like
double-peak structure, in good agreement with the results in the strong field
approximation. The yielding momentum resolution of $0.12 \pm 0.03$ a.u. is
achieved in comparison with theoretical calculations, exhibiting the great
prospects for the study of electron correlations in alkali metal atoms through
interaction with strong laser pulses.
