An investigation was made of the influence of the geometric excitation conditions on the energy dependences of the stimulated scattering of focused laser pulses of ~ 10 −8 sec duration when the sharpness and depth of focusing were varied. The experimental results obtained in this study were interpreted theoretically on the basis of a quantum analysis of stimulated Raman scattering in a two-level system. The experimental relationships could be explained only if an allowance was made for the changes in the populations of the levels participating in the Raman transition. It was possible to select the experimental conditions so that reconstruction of the wavefront of the pump radiation was observed under stimulated scattering conditions in a wide energy range.
We theoretically investigate a scheme in which stimulated Raman scattering (SRS) can be suppressed by coherently controlling the coupling between molecular states. In conventional SRS, two laser beams at different frequencies interact resonantly with molecular vibration to induce a gain and a loss for the two beams, respectively. In our scheme, a third beam is introduced to couple the vibrational state to another coupling state. As a result, SRS is suppressed in a way analogous to electromagnetically induced transparency. We calculated the SRS signal analytically by the density matrix approach, and investigated the feasibility of this scheme for real molecular imaging. In SRS microscopy, a donut-shaped coupling laser can be used to suppress the SRS signal from the rim part of the focal spot, leading to super-resolution. Based on our numerical studies, the lateral resolution starts to be enhanced when the coupling laser intensity exceeds
0.1TW/cm2 at picosecond pulse duration.