Stanford scientists earn Department of Energy research awards

Peter Graham

The Department of Energy has awarded two Stanford scientists funding through the agency’s Early Career Research Program. The program is designed to fund principal investigators who are within 10 years of having received a PhD, with a goal to fund novel experiments and research.

PETER GRAHAM, an assistant professor of physics, works on designing ways to search for a new type of particle called the dark photon. There are four fundamental forces in the world, and as all forces are mediated by a particle, the discovery of the dark photon would reveal a fifth force. The dark photon could also possibly be dark matter, adding to its allure as a research topic.

Both of the experiments Graham’s group is developing rely on the fact that the dark photon is in many ways similar to the photon, and so he may be able to measure its unknown force using techniques similar to measuring electricity and magnetism. The first type of experiment is analogous to using an antenna to send out a radio wave and then detecting it with another antenna. It is shielded to prevent normal photons from getting through, which prevents it from registering the known forces of electricity and magnetism. But the dark photon can pass through this shielding, and in doing so, makes its associated force detectable. In place of antennae, the group will actually use resonant microwave cavities – specialized chambers that confine electromagnetic waves for study – to generate the radio waves that could contain previously undetected dark photons.

The second experiment in the works is designed to look for the dark photon and determine if it is indeed dark matter. In this case, the receiver will be built inside a shielded box, and will be a resonant circuit, which acts similarly to a radio receiver in that it can tune into specific frequencies. Because the shielding blocks out all normal electromagnetic fields, if the receiver sees a signal, that will be a detection of dark photon dark matter.

Graham was awarded $750,000, distributed over five years.



Shambhu Ghimire
Shambhu Ghimire

SHAMBHU GHIMIRE, an associate staff scientist at the Stanford PULSE Institute at SLAC, uses intense infrared laser pulses to create extremely fast electron oscillations in crystals. These oscillations take place in attoseconds ­– billionths of a billionth of a second – and result in bright and similarly brief pulses of ultraviolet light. Although attosecond light pulses have been already generated in a gas, Ghimire’s research aims to investigate novel science and technology opportunities that are only possible with solid crystals.

Essentially playing pinball with electrons, Ghimire wields femtosecond pulses from an infrared laser to smack electrons loose from atoms in a zinc oxide crystal and send them accelerating between other atoms in the crystal’s lattice like a pinball between bumpers. When these electrons swing back and forth, they release energetic ultraviolet photons. In addition, due to the interplay between the regular pulses of the laser and the regular structure of the crystal lattice, these ultraviolet photons come in pulses that can last mere attoseconds. During the process the crystal remains unharmed by the laser.

This research promises to give insight into the fundamental processes at work when high-intensity lasers and matter interact. It also could allow scientists to control and customize attosecond pulses in ways they could not with pulses generated from gases. An ability to initiate and control electron dynamics in semiconducting crystals could lead to future technology and advanced metrology.

Ghimire’s award came at the National Lab level, which is a $2.5 million award, distributed over five years.