UC Santa Barbara

For centuries, the understanding of waves has gone hand in hand with the development of interferometry, the study of interference. Interference occurs when multiple waves are combined which can result in enhancement or destruction of wave intensity. The patterns produced by interference can contain information about the wave which is otherwise difficult to measure.

In the solid state, many properties are explained by considering the wavefunctions of electrons in periodic crystals, called Bloch wavefunctions. However, interferometry experiments in driven condensed matter systems are difficult due to the large amount of interactions in real materials that cause dephasing on sub-picosecond timescales.

This work develops polarimetry of high-order sidebands as a promising method that measures the interference of electron-hole pairs in materials. These sidebands are created through high-order sideband generation (HSG) where a weak near-infrared laser (NIR) and a strong terahertz (THz) laser are coincident on a semiconductor. The NIR excites electron-hole pairs that are accelerated by the THz. When the electrons and holes collide, they annihilate and release light at a higher energy, called a sideband. Multiple types of electron-hole pair can contribute to the sideband, resulting in an interference that is caused by the accumulation of phases during acceleration and imprinted on the polarization of the sideband.

In gallium arsenide we have extracted information about Bloch waves from sideband polarimetry. By studying the dependence of polarization on crystal angle, we measure Hamiltonian parameters and reconstruct the Bloch waves that take part in HSG.

Here we also study the effect of dephasing on HSG, especially with regards to temperature dependence. We report polarimetry experiments that are robust to increases of temperature up to 200 K, and from this data we are able to extract the dephasing coefficients associated with phonon interactions for different Bloch waves.

Current experiments have focused on understanding the role of the dynamical phase in sideband polarimetry, but we discuss how strain can introduce geometric phases in gallium arsenide and how this could be probed in future experiments.

Sideband polarimetry has been developed as a Bloch wave interferometer in gallium arsenide, but this method could be applied to many semiconductors to access a wide range of wavefunction phases in materials.