Graphene-Based Absorbers Could Enable Ultrafast Lasers in THz Range

A terahertz saturable absorber has been created using printable graphene inks produced by liquid phase exfoliation (LPE) and deposited by transfer coating and ink jet printing. Such an absorber could enable the development of ultrafast lasers in the THz range. These lasers could be useful in applications where short time scale excitation of specific transitions is important, such as time-resolved spectroscopy of gasses and molecules.

Researchers at CNR-Istituto Nanoscienze used LPE of graphite to formulate both a water-based ink and a surfactant-free, low boiling point, ethanol-based ink. They demonstrated THz saturable absorption from films produced by both vacuum filtration and inkjet printing.

Through the combination of open-aperture z-scan experiments, transport analysis of field effect transistors (FETs) embedding these inks, and Fourier transform infrared (FTIR) spectroscopy, researchers showed a transparency modulation almost one order of magnitude larger than that reported to date for THz frequencies. These results could open the way for the integration of graphene with existing sources to realize ultrafast, mode-locked lasers and passive ultrafast components across the THz frequency range.

Researchers at CNR-Istituto Nanoscienze created a terahertz saturable absorber using printable graphene inks with an order of magnitude higher absorption modulation than other devices produced to date. Courtesy of Graphene Flagship.

“We started working on saturable terahertz absorbers to solve the problem of producing a miniaturized mode-locked terahertz laser with thin and flexible integrated components that also had good modulation,” said researcher Miriam Vitiello.

LPE, the technique used by the researchers, is a method of producing graphene that is suited to mass production. The team used LPE to prepare inks that could be easily deposited by transfer coating or ink jet printing.

“It was important to us to use a type of graphene that could be integrated into the laser system with flexibility and control,” Vitiello said. “Ink jet printing along with transfer coating achieved that.”

Using mode-locked lasers to produce ultrafast pulses in the THz range could lead to a range of applications, from medical imaging to high-speed communications.

“These devices could have applications in medical diagnostics when time of flight topography is of importance — you could see a tumor inside a tissue,” said Vitiello.

The research was published in Nature Communications (doi:10.1038/ncomms15763).