Overcoming experimental obstacles in two-dimensional spectroscopy of a single molecule

TL;DR

This paper presents experimental strategies to enhance two-dimensional spectroscopy of single molecules by overcoming photon detection limitations, enabling detailed ultrafast energy transfer studies at the single-molecule level.

Contribution

The authors introduce key experimental techniques that significantly improve photon detection in single-molecule two-dimensional spectroscopy, advancing the method's sensitivity and applicability.

Findings

Successful implementation of broadband acousto-optic modulation

Enhanced photon-counting lock-in detection accuracy

Ability to post-select detection events based on specific criteria

Abstract

Two-dimensional electronic spectroscopy provides information on coupling and energy transfer between excited states on ultrafast timescales. Only recently, incoherent fluorescence detection has made it possible to combine this method with single-molecule optical spectroscopy to reach the ultimate limit of sensitivity. The main obstacle has been the low number of photons detected due to limited photostability. Here we discuss the key experimental choices that allowed us to overcome these obstacles: broadband acousto-optic modulation, accurate phase-locked loops, photon-counting lock-in detection, delay stage linearization, and detector dead-time compensation. We demonstrate how the acquired photon stream data can be used to post-select detection events according to specific criteria.