Wavelength conversion of quadrupled Nd:YAG laser radiation to the vacuum ultraviolet by anti-Stokes stimulated Raman scattering

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Abstract
Up‐converted beams of a conventional quadrupled Nd:YAG laser by anti‐Stokes Raman scattering in hydrogen are characterized as a vacuum ultraviolet light source. The beams diverge with the increase of the hydrogen pressure and also with the increase of the order of anti‐Stokes scattering. Although the profiles of anti‐Stokes beams vary from a Gaussian‐like shape to a typical ring shape, the maximum energy conversion is always obtained with a near‐Gaussian beam profile. The output energy ranges from 5.9 mJ for the first‐order anti‐Stokes wave (240 nm) to 8 μJ for the ninth‐order anti‐Stokes wave (133 nm). The energy of the sixth‐order anti‐Stokes wave (160 nm) fluctuates ±45% of the average output energy. The beam characteristics are described well by a model on the basis of phase matching between four waves related to each Raman process.