Focusing beams of polarization order number +1 onto a quantum well heterostructure

A tunable laser is used as a light source to study a quantum well heterostructure. Beams of polarization order number +1 (radially and azimuthally polarized) are generated using a liquid crystal. When a radially polarized beam is focussed with a high numerical aperture, a strong longitudinal electric field component in the vicinity of the focus is observed . In contrast, the azimuthally polarized field generates a purely transverse electric field at the focus which has a null intensity on the optical axis. The absorption in the quantum well by the heavy and light holes is polarization dependent and occurs at distinct wavelengths. The quantum well is 80 nm from the sample surface and a focussing propagating beam gets refracted at the air-sample interface. This has the effect of reducing the amount of longitudinal component at the focus. We use a solid immersion lens to overcome the problem arising due to the refractive index mismatch.