Far-Field Subdiffraction Imaging of Semiconductors Using Nonlinear Transient Absorption Differential Microscopy

Label-free absorption spectroscopies are frontline techniques to reveal the spectral fingerprint, composition and environment of materials and are applicable to a wide range of samples. In an effort to improve the spatial resolution of far-field absorption microscopy, which is limited by the diffraction of light, an imaging technique based on transient absorption saturation has recently been developed. Here we report a far-field transient absorption microscopy that does not require the sample to exhibit saturable absorption to break the diffraction barrier. By alternating the wavefront of the pump beams and exploiting a nonlinearity in the transient absorption intrinsic to semiconductors, we demonstrate imaging, beyond the diffraction limit, in CdSe nanobelts. This differential technique is applied for label-free super-resolution absorption microspectroscopy.