What is it about?
Inside every electronic device, charges move — and until now, watching them do so has meant either inferring their motion from external currents, or perturbing the device to observe it. Here we introduce Carrier Dynamics by Pockels Imaging (CDPI), a method that images the electric field inside a working device directly, non-invasively, and in both space and time. Because any excess charge reshapes the local field, CDPI lets us watch photogenerated electron clouds drift from one electrode to the other. We apply it to CdTe radiation detectors, resolving micrometre-scale features on nanosecond timescales, and show that the internal field dynamics and the current flowing in the external circuit are two views of the same process.
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Why is it important?
Charge transport has always been studied from the outside in: we measure the current at the terminals and infer what the carriers must have been doing inside. Our findings show that the internal picture can now be obtained directly. CDPI uses the Pockels effect — a fast, non-absorbed optical probe — to image the local electric field as the carriers move, without perturbing them, and correlates this with the external current measured independently. In CdTe detectors we resolve electron clouds in real space and real time, revealing how their shape, speed and spread evolve, how they respond to trapping and detrapping, and how the internal field reshapes in response to the cloud itself. The technique extends beyond CdTe to any material with an appreciable electro-optic response, including perovskites, organics and 2D materials, opening a new route to designing devices where charge collection is critical.
Perspectives
What I find most rewarding about this work is that it answers a question that had previously been answered only by inference. We know how to measure current at the terminals of a device — that is routine. What we could not do, until now, was watch the charges themselves as they moved, without disturbing them. CDPI gives us that view: it links space and time — the cloud's position and shape at each instant — and it links the internal field to the external current, showing that the two are not separate quantities but two descriptions of the same event. The method works because the physics is simple at heart: any excess carrier reshapes the local electric field, and a material with a Pockels response will tell us about that reshaping if we look at it with light. Because the probe beam is not absorbed, the measurement is non-invasive; because the effect is rooted in the medium's polarizability, it is fast. What surprised us along the way were the details the method revealed: clouds that expand and then contract, tails that appear at high optical power and indicate trapping, and the clear correspondence between those tails in space and the long decays seen in the current. I hope this work encourages others to use CDPI, or techniques like it, to look inside their own devices.
Dr Lorenzo Dominici
CNR NANOTEC, Institute of Nanotechnology
Read the Original
This page is a summary of: Direct visualization of charge dynamics by Pockels imaging in optoelectronics, Matter & Light, October 2026, Elsevier,
DOI: 10.1016/j.matlit.2026.100141.
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