Multipass Gas Cell Spectral Broadening Without Laser Ionization

The patent divides the spectral broadening process into multiple passes through the multipass cell, with each pass contributing partially to the overall spectral broadening. This segmentation allows the use of moderate pulse energies in each pass while achieving cumulative spectral broadening效果, avoiding ionization that would occur with a single high-energy pass.

The patent applies preliminary spectral broadening in multiple passes before the laser pulse reaches its maximum energy level. By progressively broadening the spectrum across multiple reflections and focus zones, the system achieves the desired spectral width without concentrating all energy in a single high-intensity interaction that would cause ionization.

The patent compensates for the reduced interaction length in a compact multipass cell by increasing the number of passes the laser pulse makes through the cell. The multipass configuration allows the light to traverse the same physical space multiple times, effectively increasing the cumulative interaction length and maintaining spectral broadening efficiency despite the compact overall cell length.

The patent ensures continuous spectral broadening action by configuring the multipass cell to reflect and recirculate the laser pulse multiple times through the focusing elements and filling gas. This continuous circulation maintains the useful nonlinear interaction throughout the compact cell volume, preventing loss of broadening efficiency that would occur with a single-pass configuration.

The patent applies partial focusing in each pass through the multipass cell, where the focus diameter is reduced enough to achieve significant spectral broadening through nonlinear effects, but not reduced to the point of causing ionization. The cumulative effect of multiple partial interactions achieves the desired spectral broadening without the harmful ionization that would result from excessive focusing in a single pass.

The patent uses periodic refocusing of the laser pulse as it circulates through the multipass cell, creating multiple periodic focus zones. Each focus zone provides a controlled intensity peak that contributes to spectral broadening, while the periodic nature of the action allows the system to accumulate broadening效果 over time without sustaining continuously high intensities that would cause ionization.