Time-Resolved THz Spectroscopy
Time–resolved THz spectroscopy (TRTS) is an optical pump/THz probe technique which is used to study systems in which a visible excitation initiates a change in far-infrared absorption properties on a sub-picosecond timescale.
The base of our TRTS setup is a regeneratively amplified Ti:sapphire laser which outputs 100-fs, 800-nm pulses at a repetition rate of 1 kHz. The output is split into two beams: one for the pump beam and one for THz generation and detection. THz radiation is generated via optical rectification in a ZnTe(110) crystal and detected via free-space electo-optic sampling in an additional ZnTe(110) crystal. The THz beam is focused onto the sample at the same spatial and temporal position as the pump beam. A schematic of our setup is presented in Figure 1.
Two different types of experiments are possible with TRTS. In one type, the change in the peak THz time-domain transmission is monitored as a function of the time delay between the pump and probe beams. Because the pump beam is chopped, the measured signal is the change in THz transmission observed upon photoexcitation (see figure 2). These “pump scans” provide information about the timescale associated with the onset of photoconductivity and the lifetime of that conductivity.
With the other technique, the full THz waveform is collected at a fixed pump delay time. From the THz waveform, the photo-excited absorption coefficient, refractive index, and thus conductivity can be calculated.
Related Publications
Baxter, J. B., C. Richter, and C. A. Schmuttenmaer , Ultrafast Carrier Dynamics in Nanostructures for Solar Fuels , Annu Rev Phys Chem , 2014 , 65 , 423-447
Ding, W., C. F. A. Negre, J. L. Palma, A. C. Durrell, L. J. Allen, K. J. Young, R. L. Milot, C. A. Schmuttenmaer, G. W. Brudvig, R. H. Crabtree, et al. , Linker Rectifiers for Covalent Attachment of Transition-Metal Catalysts to Metal-Oxide Surfaces , Chem Phys Chem , 2014 , 15 , 1138–1147
Negre, C. F. A., R. L. Milot, L. A. Martini, W. Ding, R. H. Crabtree, C. A. Schmuttenmaer, and V. S. Batista , Efficiency of Interfacial Electron Transfer from Zn-Porphyrin Dyes into TiO2 Correlated to the Linker Single Molecule Conductance , J Phys Chem C , 2013 , 117 , 24462-24470
Milot, R. L., G. F. Moore, R. H. Crabtree, G. W. Brudvig, and C. A. Schmuttenmaer , Electron Injection Dynamics from Photoexcited Porphyrin Dyes into SnO2 and TiO2 Nanoparticles , J Phys Chem C , 2013 , 117 , 42 , 21662 - 21670
Martini, L. A., G. F. Moore, R. L. Milot, L. Z. Cai, S. W. Sheehan, C. A. Schmuttenmaer, G. W. Brudvig, and R. H. Crabtree , Modular Assembly of High-Potential Zinc Porphyrin Photosensitizers Attached to TiO2 with a Series of Anchoring Groups , J Phys Chem C , 2013
Richter, C., and C. A. Schmuttenmaer , Exciton-like trap states limit electron mobility in TiO2 nanotubes , Nat. Nanotechnol. , 2010 , 5 , 769-772
Beard, M. C., G. M. Turner, and C. A. Schmuttenmaer , Terahertz spectroscopy , J. Phys. Chem. B , 2002 , 106 , 7146-7159
Turner, G. M., M. C. Beard, and C. A. Schmuttenmaer , Carrier localization and cooling in dye-sensitized nanocrystalline titanium dioxide , J. Phys. Chem. B , 2002 , 106 , 11716-11719
Beard, M. C., G. M. Turner, and C. A. Schmuttenmaer , Transient photoconductivity in GaAs as measured by time-resolved terahertz spectroscopy , Phys. Rev. B , 2000 , 62 , 15764-15777