Efficient isolation of multiphoton processes and detection of collective states in dilute samples

TL;DR

This paper introduces a sensitive technique for isolating multiphoton processes and detecting collective states in dilute samples using femtosecond pump-probe spectroscopy, enabling new insights into quantum coherences and resonances.

Contribution

A novel method combining lock-in amplification with femtosecond pump-probe setup for selective detection of multiphoton coherences in dilute samples.

Findings

Isolation of one- and two-photon transitions in rubidium-doped helium droplets

Observation of collective resonances up to fourth order in potassium vapor

Enhanced capabilities for multidimensional spectroscopy in dilute gases

Abstract

A novel technique to sensitively and selectively isolate multiple-quantum coherences in a femtosecond pump-probe setup is presented. Detecting incoherent observables and imparting lock-in amplification, even weak signals of highly dilute samples can be acquired. Applying this method, efficient isolation of one- and two-photon transitions in a rubidium-doped helium droplet beam experiment is demonstrated and collective resonances up to fourth order are observed in a potassium vapor for the first time. Our approach provides new perspectives for coherent experiments in the deep UV and novel multidimensional spectroscopy schemes, in particular when selective detection of particles in dilute gas-phase targets is possible.