Session J02: Atomic, Molecular, and Optical Physics II

Live

Light-sound coupling mediated by radiation pressure has enabled sophisticated methods to manipulate mechanical oscillators, permitting control over mechanical dissipation, the preparation and interrogation of quantum states, and cooling of mesoscopic systems to their quantum ground state. Historically, these efforts have focused on the control of micromechanical systems. However, recently, with the advent of a new class of nano-photonic waveguide for light and sound, laser light has been used to cool bands of travelling-wave phonons on silicon chips. Here, we demonstrate this physics for first time within an optical fiber. As our system, we utilize a 1m optical fiber comprised of a silica cladding and a 450nm radius CS$_{\mathrm{2}}$ liquid core where it is possible to achieve single mode operation for light, acoustic guidance for sound waves along the fiber core, and very large coupling between these light and sound fields. Using spontaneous backward Brillouin scattering measurements, we reveal the thermal population and effective decay rates of phonons participating in Stokes and anti-Stokes processes. These measurements show that with increasing probe power not only is the thermal population of anti-Stokes (Stokes) phonons depleted (increased) (quantified by the peak height), but the effective decay rates are altered as well (indicating how detailed balance is altered).Within this system, we reduce the temperature of a band of traveling-wave anti-Stokes phonons by 60K from room temperature, revealing that optomechanical cooling is possible in macroscopic linear waveguide systems without an optical cavity or discrete acoustic modes.   

Live

When the wavelength of light is comparable to the scale of a surface's roughness, physical and geometrical optics approximations of reflectance fail. Since even the smoothest surfaces have nanometer-scale roughness, finding alternative methods is important in the extreme ultraviolet. To directly calculate reflectance, one can solve the electric field integral equation (EFIE) over a surface. In this project the Nystr\"{o}m method was used with the EFIE to calculate far-field reflection of monochromatic plane-wave light from a one-dimensional blazed grating. Three imperfections were studied: uncorrelated and correlated random variation in line spacing, and surface roughness. Changes in resolution and resolving power were considered. These were compared to an ideal blazed grating at the Littrow configuration for first-order diffraction. The impact of random variations up to 5{\%} of ideal line spacing and grating amplitude were studied alone and in tandem with other relevant defects. Each test was performed 1000 times to find the net effect of roughness for various random surfaces. Tests were performed for grating widths up to 1mm, line spacings between 1000-5000 lines/mm, and wavelengths from 30-100nm. Results are given and discussed.   

Live

Periodic arrays of metallic nanoparticles are an ideal platform for a wide range of applications, from ultrasensitive sensors to nanolasers, due to their ability to support collective modes known as lattice resonances. These excitations, which occur at wavelengths commensurate with the periodicity of the array, give rise to strong and spectrally narrow optical responses that can be controlled by changing the geometrical properties of the array. Recently, there has been a significant effort dedicated to understanding the optical response of periodic arrays of nanoparticles with complex unit cells that contain more than one particle. These systems exhibit much richer optical responses than those with single-particle unit cells. Inspired by this, here, we provide a comprehensive analysis of the optical response of arrays of nanoparticles with a unit cell built from the periodic removal of particles from a square single-particle array. We find that the introduction of these vacancies can give rise to lattice resonances not present in the pristine system. The results of our work therefore serve to advance the fundamental understanding of the optical response of periodic arrays of metallic nanoparticles and provide an alternative method to control it.   

Live

Plasmonic nanostructures can manipulate light in a well-controlled manner. To fabricate them efficiently a detailed understanding of nonlinear responses from nanostructures with characterized localized surface plasmon resonance (LSPR) is vital. We investigate the nonlinear response from gold nanocrescent antennas which have wavelength and polarization-sensitive LSPRs in the visible and near-infrared wavelength range. Coupling Maxwell’s equations to the nonlinear hydrodynamic model for metal and utilizing a fully vectorial three-dimensional approach we analyze linear transmission, reflection, and nonlinear power spectra. It is shown that the effects of higher-order LSPRs, such as quadrupole and multipole resonances that occur at second harmonic (SH) wavelengths are important in governing the SH generation process. Also, the results indicate that the nanoscale variations of the nanocrescent’s shape plays an important role in the dependency of SH signals from the incident polarization angle.   

Live

Radiation pressure shot noise (RPSN) fundamentally limits optical displacement measurements but is also a resource for generating optomechanical quantum correlations. We have built a device which consists of an ultra-high-Q silicon nitride ``trampoline'' resonator placed inside a high finesse optical cavity, designed to detect RPSN at 1 -- 100 kHz. Observing RPSN in this frequency band is interesting for a variety of ``quantum sensing" applications, as well as searches for fundamental weak signals such as ultralight dark matter. I will discuss the challenges we've faced in attempting to observe RPSN with this system at room temperature, including the large thermal motion of \newline the resonator, degradation of the mechanical Q, and laser noise, along with the device's prospects as a quantum-enhanced accelerometer.   

Numerical studies of cross correlation analysis of excited states.

In pump-probe experiments the pumping laser excites a quantum system to a linear combination of excited states before it is tested by a second probe pulse. Observables such as ionization measured at various relative delays can be used in order to gain information about excited states of these systems. We apply numerical solutions of the time-dependent Schrodinger equation using a basis state method to analyze such scenarios.