Corey Orlik

Structural probing of multiferroic bismuth ferrite via second-harmonic generation

This week we feature senior Physics student, Corey Orlik who spent the summer studying the properties and applications of Bismuth Ferrite with his team. The goal of their experiment was to identify different properties of the Bismuth Ferrite compound, a substance that Orlik describes as both “ferroelectric and antiferromagnetic at room temperature, making it useful in more applications and when it is grown epitaxially (on another perovskite structure crystal).”

Orlik was able to get the Bismuth Ferrite deposited onto a substrate and use the lattice disparity between the two crystals to change its point group symmetry (orientation around a fixed point). This process allowed him to enhance the original electric polarization making it even more pronounced. “We did a direct measurement of p-polarization-in to p-polarization-out to approximate the nonlinear optical tensor coefficients. We got large values (>40 pm/V) meaning that our sample could be used in Terahertz generation, which has applications in biomolecular identification and explosive detection.”

Orlik and his team then worked to determine the point group symmetry of his sample. In order to do this, they performed an optical process that combines two photons of the same frequency into a single photon with twice the frequency, a second-harmonic generation (SHG). The intensity of the SHG is defined by an optical susceptibility tensor which changes depending on point group symmetry of the input. Using this method, Orlik was able to measure his sample of Bismuth Ferrite and map out the intensity of the SHG on a polar plot. Corey explains that, “When we first detected the SHG signal after aligning the setup[, it] was a very exciting moment. It meant that the project is feasible and we can take data and find some way to interpret it, even if at the time we weren't entirely sure how”. Once he had this data, Orlik and his team then worked to cross reference their experimentally measured plot with theoretical tensor forms. There was a clear match and the team was able to ascertain that the altered Bismuth Ferrite sample has monoclinic point group symmetry.

I thought [The Summer Scholars Program] was an excellent way to get funding for research over the summer, as well as a fantastic networking opportunity with other departments and in general a good way to learn about the different kinds of research or projects other undergraduates do everyday in their respective fields.