Abstract
Femtosecond spectroscopy is an important tool used for tracking rapid photoinduced processes in a variety of materials. To spatially map the processes in a sample would substantially expand the method's capabilities. This is, however, difficult to achieve, due to the necessity of using low-noise detection and maintaining feasible data acquisition time. Here, we demonstrate realization of an imaging pump-probe setup, featuring sub-100 fs temporal resolution, by using a straightforward modification of a standard pump-probe technique, which uses a randomly structured probe beam. The structured beam, made by a diffuser, enabled us to computationally reconstruct the maps of transient absorption dynamics based on the concept of compressed sensing. We demonstrate the setup's functionality in two proof-of-principle experiments, where we achieve spatial resolution of 20 μm. The presented concept provides a feasible route to imaging, by using the pump-probe technique and ultrafast spectroscopy in general.
Highlights
Ultrafast spectroscopy provides us with essential information about processes in many systems of interest, including semiconductor nanostructures, conjugated polymers, or lightharvesting biological complexes [1,2,3,4,5]
Implementation of imaging in ultrafast spectroscopy is a complex issue. We will illustrate this on the pump-probe (P-P) technique – an archetypal technique of ultrafast spectroscopy used to measure the kinetics of transient absorption (TA) or reflectance on the fs timescale [7]
In the structured sample, in addition to the previous effects, we observe a rapid onset and decay in the TA signal due to surface traps induced on the surface of the quantum dots (QDs) and a range of lifetimes in a variety of Rhodamine 6G agglomerates [30,31]
Summary
Ultrafast spectroscopy provides us with essential information about processes in many systems of interest, including semiconductor nanostructures, conjugated polymers, or lightharvesting biological complexes [1,2,3,4,5]. The ability to carry out imaging of measured dynamics elevates the potential of the technique even higher [6]. By employing it one can, for instance, map and identify the “leaking” points of a solar cell, where the carriers rapidly recombine. Implementation of imaging in ultrafast spectroscopy is a complex issue. We will illustrate this on the pump-probe (P-P) technique – an archetypal technique of ultrafast spectroscopy used to measure the kinetics of transient absorption (TA) or reflectance on the fs timescale [7]. Detection in a P-P setup is carried out by a photodiode array, a cooled line CCD coupled to a spectrograph, or a photodiode measuring the total probe intensity
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