Researchers introduce a method called Carrier Dynamics by Pockels Imaging (CDPI) that can directly image how charge carriers move inside an operating semiconductor device. The technique is non‑invasive and quantitative. It works by measuring tiny changes in the local electric field inside the device and turning those changes into real‑space pictures of photogenerated electron clouds and their motion over time.

In the experiment the authors use a pump–probe arrangement with two laser pulses. A short pump pulse creates a thin sheet of electron–hole pairs just under a semi‑transparent contact. A delayed probe pulse then passes through the device between crossed polarizers and is imaged on a camera. By taking a series of images at different delays, CDPI produces snapshots T(x,y,t) that show how the electric field—and the associated carrier cloud—changes on micrometre spatial scales and nanosecond time scales. The demonstration reported here used cadmium telluride (CdTe) radiation detectors and focused on electron motion when the cathode was illuminated.

CDPI exploits the Pockels effect, an electro‑optic effect in which the refractive index of some crystals changes linearly with an applied electric field. That field‑dependent index shifts the polarization and transmission of the probe beam, so the recorded images map variations of the internal electric field. From the measured field maps the authors extract key quantities: the spatial derivative of the field gives the local excess carrier density, and the time derivative gives the displacement current. Adding the conduction current (from carriers) and the displacement current produces the total current that can be compared to the externally measured circuit current. The paper reports that the method can detect very small field perturbations, on the order of a few volts per centimetre.