Lab 1 Time resolved spectroscopy

Optical-pump terahertz-probe (OPTP) spectroscopy, that is, time-resolved terahertz (THz) spectroscopy, has become a powerful all-optical, noncontact tool for investigating local charge transport and ultrafast charge carrier generation with subpicosecond resolution. It is a technique that is analogous to photoinduced absorption spectroscopy but is performed in the far-IR part of the electromagnetic spectrum with a nonperturbing low energy (<10 meV) photon probe. Because typical carrier scattering times are between 10 fs and 1 ps with corresponding scattering rates in the frequency range 1-100 THz, the THz probe is directly sensitive to charge carriers. The schematic of the set-up is as shown below.

Lab 2 Transient photoabsorption and time resolved photoluminescence

Transient Absorption Spectroscopy is an example of a pump-probe technique; it uses two light pulses, the pump and the probe in order to examine the change in absorption or transmission of the probe pulse owing to the preceding pump pulse. It allows the observation of processes induced by absorption of light after 5 ns up to seconds over a wide spectral range which ranges between the UV and the NIR.

An important application is the investigation of the dynamical behaviour of photoinduced species in photovoltaic devices and their relative components by probing their associated spectral signatures. The set-up presents an exceptional sensitivity in order to be able to resolve excitation dynamics in a regime which is comparable to the steady state condition of AM 1.5 (1 sun).

Time-resolved Photoluminescence investigates emission processes in a time window from 1ns to milliseconds with a resolution of about 2 ps. Use of the  streak camera technology allows photon-counting detection sensitivity as well as simultaneous multi-channel time / wavelength measurements.
The technique has a wide range of applications, such as the probing of emissive species involved in light conversion processes in hybrid solar-cells or the influence of quantum size effects on photoinduced dynamics in colloidal quantum dots/multipods.

Lab 3  Modulation spectroscopy and confocal spectroscopy laboratories

In the Modulation Spectroscopy Lab we can perform  Continuous Wave Photoinduced Absorption, Electroabsorption, and Charge Modulation Spectroscopy.  Continuous Wave Photoinduced Absorption allows to study photoexcited states on the millisecond timescale, typically triplet and charged states. The importance of these molecular species is well known both in light emitting devices and in photodetectors, where the triplet emission and the charge recombination dynamics play a key-role. Electroabsorption is useful in studying the fine-structure of the optical absorption, identifying the formation of non-optically allowed states, and estimating important physical parameters such as polarizability and dipole moment which characterize the charge-transfer states. Charge Modulation Spectroscopy allows to directly probe charge carriers in conducting and semiconducting films.

A confocal microscope is a powerful instrument for optical imaging and characterization of nano/micro structured samples. It operates by revealing the light transmitted or reflected by the illuminated focal area of the sample, or as a fluorescence microscope, gathering light re-emitted by the fluorophore, following excitation. In our lab a home-made confocal microscope has been realized, implemented and coupled to the modulation spectroscopy techniques presented above. This innovative instrument, beyond the standard acquisition of photoluminescence maps, allows to study microstructured materials and devices from both the imaging and the spectroscopic point of view, relating conformational geometries to optical properties and molecular excited states characteristics.