Tabletop extreme ultraviolet (XUV) sources based on high-order harmonic generation (HHG) play a crucial role in ultrafast and attosecond science. In this work, a compact HHG system employing a differentially finite gas cell is developed, and XUV harmonic generation with a limited interaction length is systematically investigated.

The system is driven by an 800 nm titanium-sapphire femtosecond laser, and efficient macroscopic phase matching is achieved through coordinated optimization of gas species, gas pressure, and driving laser power. Using krypton and xenon as target gases, stable XUV radiation covering photon energies of 20–40 eV is obtained. The harmonic yield clearly depends on gas pressure and laser intensity. In low-ionization-potential gases, increased ionization enhances plasma dispersion and aggravates phase mismatch, thereby limiting further growth of the harmonic intensity.

Numerical simulations based on a macroscopic propagation model, which incorporates neutral-gas dispersion, plasma dispersion, Gouy phase shift, and dipole phase, reveal the formation of a localized phase-matching region near the pinhole. This localized condition facilitates the coherent buildup of harmonic emission and reduces reabsorption. The simulated spectra agree well with experimental results, validating the model. The proposed scheme provides a simple and robust approach for generating stable, reproducible tabletop XUV sources, with potential applications in ultrafast spectroscopy.