Third harmonic generation imaging for fast, label-free pathology of human brain tumors

In brain tumor surgery, recognition of tumor boundaries is key. However, intraoperative assessment of tumor boundaries by the neurosurgeon is difficult. Therefore, there is an urgent need for tools that provide the neurosurgeon with pathological information during the operation. We show that third harmonic generation (THG) microscopy provides label-free, real-time images of histopathological quality; increased cellularity, nuclear pleomorphism, and rarefaction of neuropil in fresh, unstained human brain tissue could be clearly recognized. We further demonstrate THG images taken with a GRIN objective, as a step toward in situ THG microendoscopy of tumor boundaries. THG imaging is thus a promising tool for optical biopsies.

Magnetic field dependence of the circular dichroism in EuTe

The absorption magnetic circular dichroism in EuTe was investigated as a function of the magnetic field at T = 2 K. In order to describe the optical spectra theoretically, we developed a model that takes into account the magnetic order of the lattice as a function of the magnetic field. The model allows us to calculate the absorption spectrum as a continuous function of the magnetic field intensity. The theory accounts for the strongly dichroic absorption seen at high fields, and for its continuous evolution towards the B = 0 spectrum, which is described by a much weaker and much broader absorption line. The drastic changes observed in the experimental spectra as a function of magnetic field are fully explained by the dependence of the Eu(2+) spin arrangement on the external magnetic field.