# Multi-frequency Raman amplifiers

## TL;DR

This paper explores multi-frequency Raman amplifiers that use separated pump frequencies, demonstrating their efficiency, higher seed intensities, shorter spikes, and reduced noise compared to traditional single-frequency amplifiers through fluid models and PIC simulations.

## Contribution

It introduces and analyzes multi-frequency Raman amplification, showing its advantages over single-frequency methods in efficiency, noise reduction, and pulse characteristics.

## Key findings

- Similar efficiency to single-frequency amplifiers
- Higher seed intensities with shorter spikes
- Reduced noise backscattering

## Abstract

In its usual implementation, the Raman amplifier features only one pump carrier frequency. However, pulses with well-separated frequencies can also be Raman amplified while compressed in time. Amplification with frequency-separated pumps is shown to hold even in the highly nonlinear, pump-depletion regime, as derived through a fluid model, and demonstrated via particle-in-cell (PIC) simulations. The resulting efficiency is similar to single-frequency amplifiers, but, due to the beat-wave waveform of both the pump lasers and the amplified seed pulses, these amplifiers feature higher seed intensities with a shorter spike duration. Advantageously, these amplifiers also suffer less noise backscattering, because the total fluence is split between the different spectral components.