Coherent Phonon‐Induced Gigahertz Optical Birefringence and Its Manipulation in SrTiO₃

Abstract

Birefringence, which modulates the polarization of electromagnetic wave, has been commercially developed and widely used in modern photonics. Fostered by high-frequency signal processing and communications, feasible birefringence technologies operating in gigahertz (GHz) range are highly desired. Here, a coherent phonon-induced GHz optical birefringence and its manipulation in SrTiO 3 (STO) crystals are demonsrated. With ultrafast laser pumping, the coherent acoustic phonons with low damping are created in the transducer/STO structures. A series of transducer layers are examined and the optimized one with relatively high photon-phonon conversion efficiency, i.e., semiconducting LaRhO 3 film, is obtained. The most intriguing finding here is that, by virtue of high sensitivity to strain perturbation of STO, GHz optical birefringence can be induced by the coherent acoustic phonons and the birefringent amplitudes possess crystal orientation dependence. Optical manipulation of both coherent phonons and its induced GHz birefringence by double pump technique are also realized. These findings reveal an alternative mechanism of ultrafast optical birefringence control, and offer prospects for applications in high-frequency acoustic-optics devices.

Large Polarization Near 50 μC/cm2 in a Single Unit Cell Layer SrTiO3

“…23 In particular, ferroelectricity in SrTiO 3 can be induced by applying terahertz electric fields and photoexcitation of lattice vibrations, 27,28 which will trigger novel manipulations of polar states inside SrTiO 3 via external fields and in-depth explorations of related applications. 29 Strain engineering has demonstrated its efficacy in stabilizing the ferroelectricity and increasing the ferroelectric transition temperature (T c ) in the SrTiO 3 heterostructure. 30 Likewise, interface engineering has emerged as a potent tool for triggering polar states in nonpolar materials and unlocking exotic interface physics and functions.…”

“…Defects and doping are highly effective in developing high-performance piezoelectrics and electrostatic energy storage devices. − In addition, they also play a crucial role in stabilizing the vulnerable ferroelectric order inside SrTiO 3 . − For example, upon introduction of M/O-deficient (M for metal) nanoregions, significant room-temperature ferroelectric polarization and high thermal stability have been achieved in SrTiO 3 films . In particular, ferroelectricity in SrTiO 3 can be induced by applying terahertz electric fields and photoexcitation of lattice vibrations, , which will trigger novel manipulations of polar states inside SrTiO 3 via external fields and in-depth explorations of related applications …”