We present the results on two-photon total-internal-reflection fluorescence correlation spectroscopy. The combination of
liquid crystal spatial light modulator, providing radial polarization, with ultrafast laser (picosecond Nd:GdVO4 laser)
allowed us to take the advantage of nonlinear optical contrast mechanisms to suppress the side-lobe energy specific for
radial polarization and reduce the effective excited volume twice compared to one-photon evanescent wave excitation in
fluorescence correlation spectroscopy.
The application of stochastic cooling to trapped atoms is theoretically studied. We develop a quantum-field approach and investigate the fundamental limits of stochastic cooling, being determined by quantum-noise effects such as atom-number fluctuations and measurement back action. Moreover, using a spatially resolved operation, acting only on a fraction of the atomic cloud, is shown to lead to additional noise effects.