Narrow band tunable terahertz lasers may change material research and technology

A group of researchers from the Max Planck Institute for Material Structure and Dynamics in Germany explored the effect of manipulating the properties of quantum materials far from equilibrium through customized laser drivers. They found a more effective method to create previously observed metastable superconducting states in fullerene based materials using lasers.

By tuning the light source to 10 THz, a lower frequency than before, the team reconstructed a long-lived superconducting state in fullerene based materials while reducing the pulse intensity by 100 times. Although researchers attempted to directly observe this photo induced state at room temperature for 100 picoseconds, they predicted its lifespan to be at least 0.5 nanoseconds.

For many years, we have been interested in the nonlinear response of materials, especially how molecular or phonon modes in solids are driven to large amplitudes, "said Andrea Cavalleri, founding director of the Max Planck Institute for Material Structure and Dynamics, a professor of physics at the University of Hamburg and the University of Niujin. Many new phenomena have occurred in this state, one of which is the amplification of electronic properties such as superconductivity.

The research results of this group will help reveal more details about the potential microscopic mechanisms of photo induced superconductivity. The determination of resonance frequency will enable theorists to understand which excitation is important, as there is no widely accepted theoretical explanation for this effect in K3C60, "said Edward Rowe, a doctoral student who collaborated with Cavalleri.

A light source with a higher repetition rate at a frequency of 10 THz may help maintain metastability for a longer period of time. If we can transmit each new pulse before the sample returns to a non superconducting equilibrium state, it is possible to maintain the superconducting state continuously, "Rowe said.

Amplification of superconductivity
The work of this group is based on the excitation of lattice vibrations, which are then coupled to the electronic degrees of freedom of the system through electron phonon coupling.

Although microphysics is far from clear, the coherent modulation of these modes seems to be able to 'cool' the fluctuations within superconducting electrons, reduce decoherence, and stabilize superconductivity at temperatures that cannot be achieved in non driving or equilibrium systems, "Cavalleri said.

A new type of physical phenomenon is waiting for research and development - it is related to the function of materials controlled by light. The bottleneck at this stage is the availability and complexity of mid infrared and terahertz light sources, most of which are broadband single cycle light sources, "Cavalleri explained. Narrowband tunable lasers and amplifiers that can cover the spectral region of 1 to 20 THz will have a revolutionary impact on material research and technology.

The results of this group were obtained after ten years of research, and their progress was the systematic characterization of material response pump frequency. But increasing efficiency by 100 times is a remarkable and unexpected result, and it is very beneficial, "Cavalleri said.

Along the way, we encountered some challenges. Cavalleri added, "The design of optical parametric amplifiers, their operation under stable conditions, and the preparation of K3C60 samples are all very challenging.

Future high-speed equipment?
Although it is still too early to know exactly what types of applications the team's work will achieve, "if these materials can be designed to the same standards as superconducting platforms used for magnetic manipulation and sensing or electrical transmission, and if terahertz lasers are more widely used outside complex laboratory environments, we can envision applications in high-speed equipment," Cavalieri said.

What is the next step for the team? We are currently developing a platform to study the magnetic and electrical responses of these materials and are interested in exploring the effects of laser driven quantum tunneling, "Cavalleri said.

Source: Laser Network