Near two-photon resonance femtosecond pulse propagation in a CdS quantum dot waveguide

The authors performed pulse propagation experiments in cadmium sulfide (CdS) QD doped glass waveguides using a femtosecond laser system tuned near a two-photon resonance while being well below the lowest one-photon transitions. The samples were single-mode waveguides of CdS-doped borosilicate sol-gel glass, and were prepared with a CdS concentration of 6.2 wt%. The waveguides were fabricated by potassium-sodium ion exchange through 3-mm openings in an aluminum mask. The radius of the dots was determined as R = (1.5 ± 0.45) nm, the mean radius being half a Bohr radius, and the linear absorption spectrum showed the lowest one-photon transition as a shoulder appearing at 460 nm.