Ultrafast nonlinear subwavelength solid immersion spectroscopy at T=8 K

Pump–probe measurements with a subwavelength spatial resolution of 355 nm and a temporal resolution of 130 fs have been performed in a multiple quantum well sample at T=8 K. A solid immersion lens was used to increase the spatial resolution to 0.41⋅λ and the effective numerical aperture to 1.23, demonstrating that the limit of conventional microscopy has been surpassed. The lateral carrier transport was investigated on subpicosecond timescales.