High-sensitivity Femtosecond Transient Absorption Setup for Chiral Perovskites
Federico Pitzalis a, Angelica Simbula a, Riccardo Pau a b, Stefano Lai a, Selene Matta a, Luyan Wu a, Clarissa Coccia c, Daniela Marongiu a, Francesco Quochi a, Lorenzo Malavasi c, Michele Saba a, Andrea Mura a, Giovanni Bongiovanni a
a Dipartimento di Fisica, Università di Cagliari - Cittadella Universitaria di Monserrato 09042 (CA) Italy
b Zernike Institute for Advanced Materials, University of Groningen, Nijenborgh 4,09747 AG Groningen, The Netherlands
c Department of Chemistry and INSTM, University of Pavia,Via Taramelli 16, Pavia, 27100, Italy
Materials for Sustainable Development Conference (MATSUS)
Proceedings of MATSUS23 & Sustainable Technology Forum València (STECH23) (MATSUS23)
#PhotoPero23 - Photophysics of halide perovskites and related materials – from bulk to nano
València, Spain, 2023 March 6th - 10th
Organizers: Sascha Feldmann, Maksym Kovalenko and Jovana Milic
Poster, Federico Pitzalis, 337
Publication date: 22nd December 2022

Quantum technologies require precise control and manipulation of individual quantum systems, in particular the spin degrees of freedom. Specific goals of spintronics are the interconversion of photon ad electron spin, namely generation of spin current in materials, as well as circularly polarized emission or absorption of light.

Advances in materials for spintronics require scientific tools to manipulate spin on ultrafast time scales. Among them, transient absorption or differential transmission with femtosecond laser pulses is one of the tools of choice. In principle, is possible to use such pump and probe setup with circular polarized pulsed laser to access the spin degrees of freedom of optical excitations. By repeating the measurement with co-circularly and counter-circularly polarized pump and probe, and comparing the two measurements with each other, a time evolution of the spin evolution could be obtained. Such a technique requires however an extended period of time, because there are four possible combinations for the relative polarization of pump and probe, and fluctuations in the laser power, pointing or duration, as well as modifications in the sample may introduce spurious signals and degrade the signal-to-noise ratio.

We introduce here a high sensitivity circular polarization differential transient measurement. An optical switch alternatively rotates the polarization of pump pulses at KHz rate and access the differential absorption shot by shot. The setup was tested for artifacts and its superior sensitivity was demonstrated.

The set-up has been applied to the study of (R/S Br-MBA)2PbI4, two chiral enantiomers of a metal halide perovskite (MBA = methylbenzylammonium) known in literature for selectively absorbing circularly polarized light. Our setup has also been employed to measure the spin lifetime of optical excitations.

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