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Updated: Jul 18, 2026

Direct Imaging of Laser-driven Ultrafast Molecular Rotation
Published on: February 4, 2017
Spatiotemporal evolution in femtosecond second-harmonic generation with back-conversion
Abstract:
We systematically investigate second-harmonic generation (SHG) in a lithium triborate (LBO) crystal by a femtosecond laser system (1030 nm, 195 fs, 30 W) with particular emphasis on back-conversion phenomena. For a selected 5 mm thick crystal, an optimal conversion efficiency of 54% is achieved at 18 W input power with beam quality factor M2 of 1.275 (horizontal) and 1.173 (vertical). Beyond the saturation threshold where back-conversion initiates, spectral broadening, temporal compression and beam quality deterioration emerge, accompanied by decreasing conversion efficiency. Increasing the beam diameter or reducing the crystal length effectively mitigates back-conversion phenomena. These findings establish valuable guidelines for optimizing the performance of femtosecond visible laser sources.
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