We report on our studies of atoms contained in a magneto-optical trap using the nonlinear spectroscopy methods. Absorption and four-wave mixing signals are recorded for the probe frequency near the cooling transition frequency and the two methods are compared. The differences in the signal structure and their sensitivity on external conditions are discussed. It is revealed that central feature of these spectra consists of several contributions of different origin.
We report details of the apparatus and the experimental procedure leading to production of the Bose-Einstein condensate of ^{87}Rb atoms. Basic hydrodynamic properties of the condensate, like quadrupole oscillations and free fall expansion, are investigated. They provide also characteristics of the magnetic trap crucial for interpretation of future experiments.