# Laser frequency upconversion in plasmas with finite ionization rates

## TL;DR

This paper explores how laser frequency can be upconverted in plasmas with finite ionization rates, revealing the roles of wave partitioning, static currents, and ionization timing in the process.

## Contribution

It provides a theoretical framework describing laser frequency upconversion in plasmas considering finite ionization rates, aligning with experimental observations.

## Key findings

- Maximum output waves occur with rapid ionization
- Static magnetic fields depend on ionization timing
- Wave amplitudes are influenced by ionization rates and pulse duration

## Abstract

Laser frequency can be upconverted in a plasma undergoing ionization. For finite ionization rates, the laser pulse energy is partitioned into a pair of counter-propagating waves and static transverse currents. The wave amplitudes are determined by the ionization rates and the input pulse duration. The strongest output waves can be obtained when the plasma is fully ionized in a time that is shorter than the pulse duration. The static transverse current can induce a static magnetic field with instant ionization, but it dissipates as heat if the ionization time is longer than a few laser periods. This picture comports with experimental data, providing a description of both laser frequency upconverters as well as other laser-plasma interaction with evolving plasma densities.