Rydberg Atoms Enable High-Speed IR Imaging

Barbara Grant

Researchers at the FOM Institute for Atomic and Molecular Physics have developed an infrared imager that performs faster and with greater wavelength selectivity than most conventional long-wavelength cameras. Using the properties of gas-phase atoms in a Rydberg state, the innovation allows detection of low-energy IR photons at specific wavelengths while screening out unwanted broadband radiation.

Electrons are bound to atoms at very low energies in the Rydberg state, explained Bart Noordam, femtophysics department head at the institute, who designed the camera with Marcel Drabbels, a fellow at the Free University of Amsterdam.

To create a thin film of Rydberg atoms, the researchers illuminated a cloud of potassium or cesium vapor with UV laser radiation from a Lambda Physik pulsed dye laser and applied an electric field across the excitation region. They directed a Spectra-Physics Nd:YAG laser at 1.064 µm through a mask and onto the film to photoionize the atoms. A set of microchannel plates with a phosphor screen passed the resulting visible photons into a Dalsa charge-coupled device camera, which captured an image for display on a computer.

"By using a subnanosecond UV pulse, the film can be activated within a nanosecond," Noordam said. Researchers can also control exposure time by applying a pulsed voltage to the microchannel plates. They select IR wavelengths by controlling the electric field strength across the atomic vapor to produce specific Rydberg states.

Noordam added that the camera's wavelength response can be tuned between 1 and 100 µm, with spectral bandpasses of less than 1 percent of the selected wavelength. This capability allows researchers "to zoom in on the emission wavelength of an object while missing most of the background thermal radiation," he said.

Although the camera requires no cooling, and system response can be as fast as 1 ns, it collects only one out of 100 million photons. Noordam said he expects to increase this factor by three orders of magnitude by creating more dense Rydberg clouds.

Experiments using Felix, a free-electron laser in Nieuwegein, The Netherlands, have demonstrated the camera's ability to operate at 55 µm, Noordam added. The researchers have patented the technology and are working with industry to develop commercial applications, he said.