Research | Zimin Lab

Watching Charges Multiply and Disappear

Fri, 04 Sep 2026 00:00:00 +0000

Our work Plasmascopy of Ultrafast Hot Charge Carriers is published in Physical Review Letters.

When light excites solids, electrons can acquire enough energy to trigger a cascade of interactions with other electrons and with the material around them, a process important for carrier multiplication and technologies such as photodetectors. This effect is however short-lived, as the carriers might get trapped within the medium and become immobile.

In this work, we have developed a new fieldoscopic approach and applied it to unravel these ultrafast dynamics in one of the most common optoelectronic materials - germanium.

Rather than measuring only how much light a photoexcited material absorbs or reflects, the technique records the electric field of an ultrashort light pulse after it passes through the material. A direct access to the electric field provides us access to the plasma frequency that is proportional to the concentration of photoexcited charges.

The experiment exposes a competition between rapid carrier multiplication and the subsequent loss of mobile charges. During the first few tens of femtoseconds, the plasma frequency rises, indicating increase of mobile charge carriers. At later times, the plasma frequency decreases suggesting carrier trapping, in which mobile charges become localized.

The new method helps to understand how energy and charge flow through materials immediately after excitation, and in future studies could unravel other ultrafast many-body phenomena in various solids on some of the shortest timescales.

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Bridging Fields and Photons

Mon, 09 Feb 2026 00:00:00 +0000

Our work Fieldoscopy at the Quantum Limit is published in Light: Science & Applications.

We have developed a new approach for measuring the electric field of light at extraordinarily low intensities, reaching the single-photon regime and beyond. The advance opens a route to directly investigating the quantum properties of light with sub-cycle, attosecond-scale precision.

Light is both a wave and a quantum object made up of photons. While the intensity of light can be measured even at extremely low photon numbers, resolving its rapidly oscillating electric field is considerably more challenging. Existing techniques for measuring optical electric fields typically require relatively intense light pulses, placing the quantum regime largely beyond their reach.

The new work overcomes this limitation, extending electric-field measurements to light levels where individual photons and quantum fluctuations become important. Crucially, the technique retains temporal resolution shorter than a single oscillation cycle of the light wave. At optical frequencies, this corresponds to attosecond timescales—billionths of a billionth of a second.

Accessing this regime creates a powerful connection between two traditionally distinct areas of research: quantum optics, which investigates the quantum nature of light, and attosecond science, which resolves some of the fastest processes in nature. Rather than characterizing quantum light only through photon statistics or time-averaged measurements, the approach provides access to its electric-field properties on sub-cycle timescales.

This capability could enable new ways to investigate quantum states of light, ultrafast light–matter interactions, and quantum fluctuations, bringing researchers closer to observing and controlling quantum optical phenomena on their natural, attosecond timescale.

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How Optical Response Emerges in Solids

Sun, 01 Sep 2024 00:00:00 +0000

Our work Dynamic optical response of solids following 1-fs-scale photoinjection is published in Nature.

When an intense pulse of light strikes a solid, it can excite electrons from their normal states and create mobile charge carriers. This process can dramatically change how the material interacts with light. But how quickly do these new optical properties emerge?

In this study, published in Nature, we directly observed how the optical properties of silicon and fused silica evolve during the first few femtoseconds after electrons are excited by an ultrashort laser pulse. One femtosecond is one millionth of a billionth of a second.

We used an intense laser pulse to inject charge carriers within approximately one femtosecond. Instead of relying on conventional pump–probe techniques, they employed field-resolved optical measurements, allowing them to follow changes to the actual oscillating electric field of a probing light pulse. This provides access to dynamics occurring within a single cycle of light.

Remarkably, the experiments showed that the familiar optical response associated with the newly created electron–hole plasma—the Drude–Lorentz response—develops within only a few femtoseconds. This is substantially faster than the characteristic plasma timescale that might have been expected to govern the emergence of the collective electronic response.

The result shows that a solid can acquire new electronic and optical properties almost immediately after ultrafast excitation. Understanding these earliest moments of light–matter interaction is important for attosecond and petahertz optoelectronics, where researchers aim to manipulate electronic signals using the electric field of light itself. Ultimately, such insights could help establish how quickly future light-controlled electronic devices can operate.

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