Revolutionizing Material Research: A New Method for Generating Elliptically Polarized Light

Wednesday - April 3 2024, 09:52 UTC - 1 year ago

A new study by JILA introduces a simple method for generating elliptically polarized light, which is essential for advanced material research. This method could pave the way for improved electronic devices and has implications for the study of chiral and magnetic materials, leading to potential advancements in fields such as computing and data storage.

In a new study published in Scientific Reports, JILA Fellow and University of Colorado Boulder physics professor Andreas Becker and his team theorized a new method to produce extreme ultraviolet (EUV) and x-ray light with elliptical polarization, a special shape in which the direction of light waves’ oscillation is changing. This method could provide experimentalists with a simple technique to generate such light, which is beneficial for physicists to further understand the interactions between electrons in materials on the quantum level, paving the way for designing better electronic devices such as circuit boards, solar panels, and more.

Many physicists use a process called High-harmonic Generation (HHG) as a source to generate ultrashort EUV and x-ray laser light and use this light to study the ultrafast dynamics of charged particles in different materials. By shooting high-powered laser pulses into a gas of atoms, the researchers can force the atoms to absorb the photons from the laser pulses. This causes the electrons in the atoms to jump to a higher energy level, then fall back to the ground level and emit energy as the atoms radiate in integral multiples of the laser frequency. JILA graduate student and first author Bejan Ghomashi explained that “these [energies] will be the harmonics. So, if an 800-nanometer light is absorbed, it’s also emitted, along with 400 nanometers, 200 nanometers, etc.” .

This process can be conveniently performed within a tabletop laser setup, as pioneered in the laboratories of JILA Fellows Margaret Murnane and Henry Kapteyn. It gives scientists a relatively cost-effective option to learn more about ultrafast electron dynamics.

“More people have access to an idea and can explore it,” Becker added.

Light polarization is a way to describe the direction in which light waves are oscillating. More specifically, polarization describes in which direction the oscillation of the electric field of the light in a laser beam varies over time. For example, the light’s electric field may wiggle along a line, making it linearly polarized. In other cases, the direction of the wiggling electric field may rotate, making the light circularly polarized. Creating light in which the electric field varies along an elliptical shape is a middle-ground between pure linearly and circularly polarized light.

Historically, it has however been challenging to produce elliptically polarized HHG light, but in this new study, Becker and his team explored how to use two linearly cross-polarized lasers at differing frequencies and directions to produce this desired shape. Unlike other, more complex, methods proposed to generate elliptically polarized HHG, an experimental set-up with two cross-polarized laser pulses interacting with an atomic gas is relatively simple.

Sources of elliptically polarized X-ray and EUV light can be useful in helping to study chiral and magnetic materials. Chirality is a term used to describe the difference between two molecules that are mirror images of each other, like a left and a right hand, while magnetism refers to the behavior of a material in the presence of a magnetic field. Understanding the interactions of light with these types of materials is crucial for developing next-generation technologies in fields such as computing and data storage.

The latest study builds on Becker's previous work, published last year, which also introduced a new twist to HHG that could produce linearly polarized high harmonics. In this new study, the researchers added a second drive laser pulse to the mix, perpendicular to the first, to create even more extreme optical fields, and hence, control of the polarization dynamics. According to co-author and former JILA postdoctoral researcher Nathan Shafer, “Adding the second laser allows us to suppress a large class of energy pathways that lead to unwanted elliptical polarization.” .

The team's theoretical studies predict that their method can produce light with a soaring degree of elliptical polarization of up to 95%, which is sufficient for the types of experiments and applications proposed in the study. However, Ghomashi cautions that their technique is not yet perfect, and there's room to improve the process.