We show that an external coupled cavity containing a nonlinear quantum-well reflector can continuously selfstart a dispersion-compensated Ti:sapphire laser, which produces stable time-transform-limited pulses as short as 70 fs in a TEM(00) mode. In this mode of operation, the quantum wells do not control the mode-locking process, as in previous research on the resonant passive mode-locked laser. By separating the mode-locking and starting processes, we show that the presence of higher-order spatial modes is not required to start or sustain mode locking.

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Using Photon-Density-Waves (PWD), (multiple) objects embedded in a highly scattering medium with optical properties similar to tissue are detected. The measurements were performed with near-infra-red laser light at 675 nm which was either kept continuous-wave (CW) or amplitude modulated (AM) at 219 MHz or 650MHz. We find that the spatial resolution of the projection image shows only slight improvements as the frequency is increased. This improvement comes at the expense of signal strength in the modulated part of the light. That is, the PWD shows a much stronger attenuation as compared to the CW light intensity. The implications of the lower signal-tonoise ratio at high modulation frequencies is that the modulated light projections are less suitable for further data processing. For a given data acquisition system, this fact cancels the advantages of the higher raw resolution of PWD as compared to CW light. Therefore, we find no clear advantage of PWD over CW light for obtaining sharper tomographic images of the diffuse media, regardless of the inverse scattering method used.