Wavelength-tunable ultrafast two arm fiber laser system for transient interferometric scattering microscopy on nanoscopic objects

Abstract

Ultrafast time-resolved microscopy of single nano-objects is particularly challenging because of minute sample volumes and correspondingly small signal levels together with the possibility of photobleaching. We present a compact pulsed two arm fiber laser-based system suited for highly sensitive transient interferometric scattering (TiSCAT) microscopy of nanomaterials. A continuously tunable probe arm is used for spectrally resolved detection of the transient sample response in the range between 810 and 960 nm upon pulsed excitation at 780 nm by the pump arm. Coupled to a scanning confocal microscope with high numerical aperture objective, the system provides spectral maps with sub-300 nm spatial and 300 fs temporal resolution. We tested the platform using monolayer MoSe2 and individual (6,4) single-walled carbon nanotubes as model samples. Confocal microscopy images recorded for an exfoliated monolayer MoSe2 reveal spatially varying excited state decay, highlighting the need for local probing. Spectrally resolved TiSCAT measurements on individual (6,4) single-walled carbon nanotubes show that the transient response is dominated by ground-state bleaching with picosecond recovery times. The obtained data illustrate the excellent noise properties and stability of the newly developed laser system, which allow for nearly shot-noise limited TiSCAT detection at the low probe fluences required for avoiding photodegradation of sensitive nanomaterials.