- Starts: 3:00 pm on Thursday, December 12, 2024
- Ends: 5:00 pm on Thursday, December 12, 2024
ECE PhD Prospectus Defense: Purva Bhumkar
Title: Novel Light Sources via Cascaded Multimodal Nonlinearities
Presenter: Purva Bhumkar
Advisor: Professor Siddharth Ramachandran
Chair: Professor Anna Swan
Committee: Professor Siddharth Ramachandran, Professor Anna Swan, Professor Tianyu Wang
Google Scholar Profile: https://scholar.google.com/citations?user=m686C4AAAAAJ&hl=en&oi=ao
Abstract: Visible lasers at on-demand power levels and wavelengths are advantageous for applications such as underwater communications, remote sensing (LiDAR), nonlinear microscopy and spectroscopy. Since laser gain dopants in the visible spectral range are either inefficient or not readily available, a common approach exploits nonlinear optics. Four-wave mixing (FWM) in an optical fiber enables energy exchange from two pump photons to generate “Stokes” and “anti-Stokes” waves while conserving momentum. Because FWM also satisfies energy conservation, the anti-Stokes output from a single FWM process pumped at ~1030-1080 nm (the most common and high-power lasers available) is limited to a wavelength no shorter than 7xx nm. This is because the corresponding Stokes photon, by energy conservation, would need to remain below the 2400-nm transparency limit of Silica optical fibers. Hence, conventional approaches exploiting single-mode fibers are unsuitable for applications that require high-power visible pulses, and the field remains reliant on bulky, alignment-sensitive, free-space optical parametric oscillators.
In this thesis, we explore the feasibility of accessing visible wavelengths through intermodal FWM cascades. The first FWM process converts light from a conventional, high-power ~1064-nm-laser to an intermediary near infrared wavelength (between 700 and 900 nm), which then becomes the pump for a second process and facilitates high-power visible emission in a single fiber. Such a process would not be feasible in single-mode fibers, nor in conventional multimode fibers, where mode mixing inhibits FWM efficiency. An ideal platform would be multimode ring-core fibers that have shown to support many stably guided Orbital Angular Momentum (OAM) modes, with large effective areas and long interaction lengths, enabling >100 kW peak power handling capabilities. The rich OAM modal basis provides thousands of phase-matched possibilities with increased selectivity to target specific wavelengths without relying on material dispersion.
We experimentally demonstrate emission at 659 nm from a single fiber through a self-organized, cascaded FWM process that is non-degenerately pumped. We also show emission at 680 nm using a two-fiber system and a cascaded process that is degenerately pumped. Both these processes use an intermediary pump at 814 nm (8-13 kW peak power pulses) that is generated with high peak-power conversion efficiency (40%) when the first process is pumped at 1064 nm (32 kW peak power pulses) and seeded at 1538 nm. We propose further investigation and optimization of different phase-matching possibilities to target blue photons. More generally, we aim to investigate cascaded FWM in OAM fibers for realizing single-pass, alignment-free, power-scalable visible laser sources capable of kW-level peak power operation with excellent spatial beam coherence.
- Location:
- PHO 339