CAREER: Continuous-wave Terahertz laser employing HTS Josephson junctions

Proposal Number: 2045957 Principal Investigator: Timothy M Benseman Title: CAREER: Continuous-wave Terahertz laser employing HTS Josephson junctions Institution: CUNY Queens College Nontechnical Abstract

Powerful and lightweight lasers that operate at frequencies between 0.3 trillion Hertz and 1.5 trillion Hertz will offer a leap forward for numerous applications, such as secure and ultrafast wireless data networking, detection of concealed drugs and explosives, and early-warning identification of tooth decay and skin cancer. They will far surpass the capabilities of lasers and laser-like electromagnetic radiation sources currently available in this frequency range, which either have low power output, or are too large, heavy, and power-consuming to be used in field-portable applications.

This project establishes a new type of laser technology uniquely based on high-temperature superconductors that will be ideal for the above applications in this ‘terahertz gap’ frequency range. To date, milliwatt-level power from this type of laser has only been theoretically predicted, at the level of fundamental physics. This project tests the ideas empirically and engineers the technology to make it available for deployment.

The cryocooling requirements of this technology take advantage of micro-cryocoolers that are already used for infrared cameras and night vision goggles. To complement the superconductivity research project, a program of scientific outreach activities is performed. These are based on superconductive levitation experiments to inspire high schoolers and community college students, particularly from underrepresented demographics, into STEM fields.

A graduate-level course module focuses on lithographic fabrication techniques for microelectronics and prepares students for careers in device microfabrication research. Technical Abstract

At present, the sources of coherent radiation available between approximately 0.3 trillion Hertz and 1.5 trillion Hertz all have serious engineering drawbacks that limit their usefulness. Existing technologies that work at these frequencies either generate very low levels of output power, or are very heavy, bulky, and power-consuming. User-friendly lasers operating in this ‘terahertz gap’ range would revolutionize a number of fields, including high-bandwidth data transmission, scientific and medical imaging, and security and defense technologies.

Stacked ‘intrinsic’ superconductor-insulator-superconductor (Josephson) junctions in the extremely anisotropic high-temperature superconducting compound Bi2Sr2CaCu2O8 are one of the most promising candidates for filling the ‘terahertz gap’. These intrinsic Josephson junctions can be used to engineer the only compact terahertz laser source that currently offers tunability, high power, and continuous-wave operation.

This project engineers terahertz laser sources based on Bi2Sr2CaCu2O8 Josephson junctions to achieve at least an order-of-magnitude enhancement in the terahertz power output of these devices to 1 milliwatt or more, while also at least doubling their operating frequency range to at least 1.0 terahertz. These enhancements in terahertz power and emission frequency are targeted even at operation temperatures of 77 Kelvin or more, in order to minimize cryocooling requirements.

Terahertz sources are microfabricated by patterning stacks on Bi2Sr2CaCu2O8 crystals using optical lithography and argon-ion milling. The feasibility of doing this at volume for commercial-scale terahertz laser applications will be tested. Finally, a further research aim of this project is to measure the behavior of a novel type of Josephson plasmon in Bi2Sr2CaCu2O8.

Experimentally understanding this plasmon would make it possible to engineer an entire new class of highly efficient electronic devices for terahertz signal detection and mixing.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.