A Ytterbium-doped fiber laser in a unidirectional ring cavity containing a polarizer placed between two in-line polarization controllers is presented. Depending on the equivalent saturableabsorber the laser operates in continuous, Q-switched, Q-switched mode-locked or CW modelocked regimes. The passive method exposed here allowed us to choose the operating regime of the fiber laser by rotating the two polarization controllers and adjusting the pump power. As there is no active element inside the cavity, this laser potentially has more advantages than conventional pulsed fibre laser systems. Furthermore, the operation processes are analyzed theoretically.

The steady state and time resolved fluorescence spectrum of ethanol-water solution has been studied. The three different emission bands located at 290 nm, 305 nm and 330 nm,respectively, and the three corresponding excitation lights with the absorption peaks of 265 nm,280 nm and 236 nm have been measured respectively by the fluorescent spectra and the excitation spectra. The decay process of fluorescence intensity was detected and the curve was fitted by an exponential function. The lifetime parameters of different fluorescent photons were obtained by the numerical analysis procedure of deconvolutions. The characteristic of the steady state spectra and the three different lifetimes confirm the fact that there are three clusters in ethanol-water solution.

In the intensity inhomogeneity correction of magnetic resonance imaging, since entropy minimization method did not consider space information, a better correction method based on joint information minimization was proposed, which integrated image intensity features with additional spatial image features. The space features referred to intensity derivatives. The joint entropy between image intensities and corresponding derivatives in a corrupted image is greater than that in an uncorrupted one,and it is calculated by using the joint probability distribution of image intensities and corresponding derivatives. The results on simulated brain images and clinical brain MR images show that joint information minimization method between intensities and their second derivatives is good. It can largely decrease the overlap between white matter and gray matter.