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Wavelength-tunable femtosecond light sources are essential in various research fields and technologies, including medical diagnostics, biophotonics, and metrology. Although fiber lasers have emerged as leaders in the development of such sources, achieving wide spectral tunability for femtosecond pulses remains a significant challenge. To address this challenge, dispersive wave generation offers a powerful solution. In this study, we exploit the concept of quasi-phase matching to enable multi-order dispersive wave formation with unprecedented spectral tunability and femtosecond durations. Here, liquid-core fibers (LCFs) with periodically controlled dispersion of a higher-order mode along the fiber are applied, achieved by axial modulation of the liquid core diameter, relying on the strong dependence of dispersion on the core diameter. Nonlinear optical experiments and simulations, as well as phase-mismatching considerations based on an effective dispersion, confirm the conversion process and reveal unique emission features This resonance-empowered approach provides a versatile photonic platform with unique dispersion control capabilities for efficient, coherent femtosecond multi-frequency conversion.
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