Adapting to a new laser
Sonia’s winning poster presents the development of a gallium arsenide (GaAs)-based photoconductive terahertz (THz) light source, which she plans to use in the THz microscopy setup she is currently working on. Her goal is ultimately to apply the technique to semiconductor imaging and metrology.
“To generate these THz pulses, we use femtosecond lasers,” says Sonia. “Traditionally, Ti:sapphire lasers operating at wavelengths around 800 nm have been widely used for this purpose, and that’s what we used to have in our lab. However, when I started here, we got a new Yb-based femtosecond laser operating at 1030 nm. These lasers are becoming more attractive because of their high average power, compact design, and ease of operation. So, we wanted to have a THz source that could work directly at 1030 nm with our laser.”
Surprisingly strong pulses
What makes her design special is that it requires no microfabrication, making it simpler to fabricate than conventional photoconductive antennas, which are devices used to generate and detect THz light.
Interestingly, her emitter generates quite strong THz pulses, even though the photon energy at 1030 nm is below the bandgap of GaAs. This is possible through two-photon absorption, which generates charge carriers in GaAs that move under an applied electric field, producing THz pulses.
Terahertz time-domain spectroscopy
Sonia developed this new THz source with the goal of using it for a metrology technique called terahertz time-domain spectroscopy (THz-TDS). Unlike conventional intensity-based spectroscopy, this technique measures the electric field of THz pulses over time, providing both amplitude and phase information. This allows for the direct determination of a material’s complex refractive index, providing detailed information about its properties.
Learn more
You can find more information about Sonia’s research, as well as that of her colleagues, on the Light-Matter Interaction research group page.
