Summary
UCLA researchers have developed a versatile photonic RF waveform generator based on a silicon-nitride (Si₃N₄) chip that achieves a wide tuning range of repetition rate and generates high-quality, tunable ultrafast pulses. This system uses a fiber-amplified seed followed by a noncollinear optical parametric amplifier (NOPA) to produce signal and idler pulses in the near-infrared (NIR) region with good spectral coverage and high efficiency.
Background
Ultrafast pulses in the visible and near-IR are crucial for applications in spectroscopy, microscopy, quantum materials, imaging, and many fields needing time-resolved measurements. Standard optical parametric amplifier (OPA) systems often rely on white-light continuum (WLC) seeds generated via filamentation, which suffer from spectral energy density limitations, spatial coherence issues, and high noise. These limitations hamper efficiency, stability, and performance in downstream applications. There is a need for seed sources that are more spectral-dense, stable, and efficient in generating ultrafast pulses with tunable repetition rates.
Innovation
The team uses a fiber amplifier chain operating in the gain-managed nonlinear (GMN) regime to produce a broadband seed with much higher spectral energy density than typical white-light continuum sources. This seed is coupled into a noncollinear OPA driven by the second harmonic of a high-repetition-rate ytterbium (Yb) laser. By adjusting parameters like pump-seed delay, phase-matching angles, and optical design, they simulate generation of signal and idler pulses tunable across ~1026-1144 nm (signal) and ~937-1035 nm (idler). The approach achieves ≈16% conversion efficiency in a single OPA stage, with high beam quality, full coherence, and relatively short pulse durations.
Advantages
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Higher spectral energy density than white-light continuum, improving seeding efficiency and reducing noise.
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Good tunability of signal and idler wavelength across NIR bands.
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Simulations suggest robust spatiotemporal beam quality and full coherence.
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High conversion efficiency (~16%) in a single amplification stage with microjoule-scale pump pulses.
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Compatible with high repetition rate (> MHz) Yb-laser systems, beneficial for high average power or fast acquisition applications.
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Useful for applications demanding ultrafast pulses with good stability, spectral bandwidth, and tunability.
Potential Applications
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Ultrafast spectroscopy (e.g., time-resolved dynamics in materials, biological imaging)
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Multiphoton microscopy or nonlinear optical imaging using visible and NIR pulses
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Pump–probe experiments in physics and chemistry
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Optical sources for quantum materials or solid-state physics requiring tunable ultrafast pulses
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Any system needing high repetition rates with tunable pulse wavelengths and high beam quality
Publication
Lu, Brittany; Wernsing, Keith; Carbajo, Sergio; et al. Si₃N₄-Chip-based versatile photonic RF waveforms generator with a wide tuning range of repetition rate. arXiv:2305.03228 (2023). DOI / arXiv ID: 10.48550/arXiv.2305.03228