研究目的
To find the macroscopic conditions that optimize the harmonic yield in a specific spectral domain around 40 eV through a multi-dimensional parameter scan in high-order harmonic generation.
研究成果
The multi-dimensional parameter scan identified optimal parameter combinations for high harmonic yield around 40 eV, with the highest yield achieved for specific laser energies, pressures, and cell positions. The results provide practical guidelines for designing high-flux HHG beamlines, and the methods can be scaled using established principles. The study confirms the importance of phase-matching and off-axis radiation in efficient harmonic generation.
研究不足
The study is based on numerical simulations and may not fully capture all experimental complexities. Practical limitations include the availability of long lab space and mechanical stability for implementing scaled-up configurations. The model assumes constant gas pressure and does not account for multiple ionization processes in this specific study.
1：Experimental Design and Method Selection:
A 3D non-adiabatic model for pulse propagation and high-order harmonic generation (HHG) was used, based on solving the unidirectional propagation equation from Maxwell equations in cylindrical coordinates with paraxial approximation. The model includes calculations of the effective refractive index, single-atom dipole response using the Lewenstein integral, and time-dependent phase-matching.
2：Sample Selection and Data Sources:
Simulations were performed with argon gas as the medium, with parameters chosen to model a loose focusing configuration.
3：List of Experimental Equipment and Materials:
Not applicable as this is a numerical simulation study; no physical equipment is used.
4：Experimental Procedures and Operational Workflow:
A multi-dimensional parameter scan was conducted by varying laser pulse energy (3 mJ,
5：6 mJ), gas pressure (1, 38, 41, 31, 20 mbar), cell entrance position relative to focus (-50, -25, -10, 0, 10, 25, 50 cm), and cell length (4, 8, 12, 16, 20 cm). Fixed parameters included pulse duration (10 fs), central wavelength (800 nm), focal length (21 m), beam waist radius (30 mm), and gas type (argon). Data Analysis Methods:
Harmonic yield was calculated as a power spectrum by radially integrating the Fourier transform of the harmonic field. Phase-matching mechanisms were analyzed using time-dependent and static models.
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