Collaborative Research: Two-photon absorption engineering in laser diodes for ultrafast pulse generation

Semiconductor lasers are one of the most impactful photonic technologies on the market, with applications ranging from communications to medicine. However, the amount of power that can be obtained from short pulses of light remains low, despite decades of research. The problem is due to physical constraints, which the project will address through an interdisciplinary effort combing emerging materials synthesis with advanced optical physics to create short pulses with power well beyond the current state of the art.

This will enable significant advances in both scientific understanding and practical performance, and will yield sources ideal for applications ranging from laser radar for autonomous vehicle navigation to advanced microscopy. The project will further benefit society by integrating research results with education through courses, and into an online course that was launched as part of the University of Colorado Boulder's Master of Science in Electrical Engineering (an online Master's degree).

Additional dissemination and engagement will occur through avenues ranging from undergraduate research opportunities, a diversity, equity, and inclusion seminar series, ECEE Connects at the University of Colorado Boulder, as well as science events at the Texas School for the Deaf.

Nonlinearities like two-photon absorption limit semiconductor lasers in both the high power CW and ultrashort pulse arenas, constraining the available peak powers, pulse widths, and pulse energies. For pulsed sources, dispersion compensation provides some improvement; however, less-compact alternatives, such as fiber and solid-state lasers currently offer vastly superior performance.

This project will combine recent advances in crystal growth and optical laser pulse shaping techniques to solve these issues and dramatically advance the performance of semiconductor ultrafast sources. Specifically. high-bandgap semiconductor cladding layers can now be epitaxially integrated with longer-wavelength gain media to reduce two-photon absorption by orders of magnitude.

When coupled with a new pulse shaping mechanism and pulse stacking, it is anticipated that this approach will enable kW peak powers and femtosecond pulses on a chip-scale semiconductor platform. The impact of the project will be further enhanced through a number of engagements and outreach activities and undergraduate research opportunities.

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.