Repository logo

Theses and Dissertations

Permanent URI for this collection

https://hdl.handle.net/10217/100500

Browse

Browsing Theses and Dissertations by Subject "atomic resonance"

Now showing 1 - 1 of 1
  • Thumbnail Image
    ItemOpen Access
    Near-resonant and resonant light in ultracold gases
    (Colorado State University. Libraries, 2020) Gilbert, Jonathan, author; Roberts, Jacob, advisor; Yost, Dylan, committee member; Bradley, Mark, committee member; Marconi, Mario, committee member
    This dissertation describes experiments and calculations involving light manipulation of atoms and light propagation in ultracold gases. There are three major sections to this dissertation. Each section presents a research topic connected to the main subject of near-resonant and resonant light in ultracold gases. First, this dissertation details the theoretical description and experimental implementation of a novel cooling technique for ultracold atoms trapped in a confining potential. Manipulating the internal states of atoms by applying near-resonant laser pulses at specified times leads to high energy atoms being preferentially selected and then slowed to achieve cooling. We call the technique "spatially truncated optical pumping (STOP) cooling." Advantages of the technique include its straightforward adaptability into experiments already using a magneto-optical trap; its applicability to any species that can be laser cooled and trapped in a confining potential; it does not depend on highly specific transitions for cooling; it does not depend on number loss for cooling. We present experimental results from applying the technique to an ultracold gas of 87Rb. We also present theoretical predictions of expected cooling rates, along with possible improvements to our apparatus that could lead to further cooling. Next, this dissertation details numerical calculations of near-resonant light propagation through a highly absorptive elongated ultracold gas. The confined gas modeled by these calculations are representative of gases commonly found in ultracold atom experiments. The spatial density distribution and spatial extent of these gases leads to a substantial gradient in the index of refraction. In addition, these gases can have a smaller spatial extent than that of the cross section of a laser beam that illuminates them. We present calculations that show the index variation in these systems can lead to frequency-dependent focusing or defocusing of incident near-resonant light. In some cases, focusing results in light intensities inside of the gas that are over an order of magnitude higher than the incident value. Additionally, we show that refraction and diffraction of the light results in non-intuitive patterns forming in the directions perpendicular to the light propagation. Lastly, this dissertation details the theoretical treatment and experimental measurements of the time-dependent absorption and phase response of an ultracold gas that is suddenly illuminated by near-resonant light. These studies focus on dynamics occurring over timescales on the order of an atomic excited state lifetime. Because the atoms cannot respond instantaneously to the applied light, both the absorption response and phase response require time to develop, with the phase response being slower than the absorption response. Related polarization effects such as Faraday rotation are due to phase shifts imparted by the gas, and therefore these effects also require time to develop. We detail our experimental measurements of the time-dependent development of Faraday rotation in an ultracold gas of 85Rb and compare the results to predictions using a theoretical approach based on solving optical Bloch equations. We identify how parameters such as the applied magnetic field strength and optical thickness of the gas influence the response timescales of the gas.