Alexander Egner

Numerical modeling of scattering type scanning near-field optical microscopy

Apertureless scattering-type Scanning Near-field Optical Microscopy (s-SNOM) has been used to study the electromagnetic response of infrared antennas below the diffraction limit. The ability to simultaneously resolve the phase and amplitude of the evanescent field relies on the implementation of several experimentally established background suppression techniques. We model the interaction of the probe with a patch antenna using the Finite Element Method (FEM). Greens theorem is used to predict the far-field, cross-polarized scattering and to construct the homodyne amplified signal. This approach allows study of important experimental phenomena, specifically the effects of the reference strength, demodulation harmonic, and detector location.

Recent progress in the study of surface chemistry on various noble metal surfaces by ultrahigh vacuum tip-enhanced Raman spectroscopy (Conference Presentation)

Tip-Enhanced Raman Spectroscopy (TERS) affords the spatial resolution of traditional Scanning Probe Microscopy (SPM) while collecting the chemical information provided by RAMAN spectroscopy. This system, further aided by the benefits of Ultra-High Vacuum, is uniquely capable of obtaining surface data that would otherwise be unobtainable with less-specialized methods. Large polyatomic molecular adsorbates on various single crystal surface (Ag, Cu and Au) will be explored in this talk. By investigating substrate structures, superstructures, and the adsorption orientations obtained from vibrational modes, we extract novel surface-chemistry data at an unprecedented spatial (<1nm) and chemical resolution.

Nanoplasmonic multiplexing of optical angular momentum from the visible to terahertz range (Conference Presentation)

Similar to the other physical dimensions of light, such as time, space, polarization, wavelength, and intensity, optical angular momentum (AM) is another physically-orthogonal dimension of light. Owing to an unbounded set of orbital angular momentum (OAM) modes carried by helically-phased beams, the availability of using AM-carrying beams as information carrier to generate, transport and detect optical signals has recently been largely explored in both classical and quantum optical communications, suggesting that AM is indeed a promising candidate to dramatically boost the optical multiplexing capacity. However, the extrinsic nature of OAM modes restricts conventional OAM multiplexing to bulky phase sensitive elements, imposing a fundamental limit for realizing on-chip OAM multiplexing. Recently, we demonstrate an entirely-new concept of nanoplasmonic multiplexing of AM of light, which for the first time enables AM multiplexing to be carried out by an integrated device with six orders of magnitude reduced footprint as compared to the conventional OAM detectors. We show that nanoring slit waveguides exhibit a distinctive outcoupling efficiency on tightly-confined plasmonic AM modes coupled from AM-carrying beams. More intriguingly, unlike the linear momentum sensitivity with a typical sharp resonance, the discovered AM mode-sorting sensitivity is nonresonant in nature, leading to an ultra-broadband AM multiplexing ranging from visible to terahertz wavelengths. This nanoplasmonic manipulation of AM of ultra-broadband light offers exciting avenues for future on-chip AM applications in highly-sensitive bio-imaging and bio-sensing, ultrahigh-bandwidth optical communications, ultrahigh-definition displays, and ultrahigh-capacity data storage.

Sharply focused azimuthally polarized beam characterized by photoinduced force microscopy (Conference Presentation)

A sharply focused azimuthally polarized beam (APB) presents a strong longitudinal magnetic field with a vanishing electric field at its beam axis, forming an effective magnetic dominant region at the vicinity. This magnetic dominance is extremely desirable in the proposed high-speed ultra-compact optical magnetic force manipulation and microscopy, where the interaction between matter and the magnetic field of light can be exclusively exploited. However, direct characterization of such beam is challenging due to its subwavelength features. Here we show for the first time a direct characterization on a sharply focused APB in nanoscale using the novel Photoinduced Force Microscopy (PIFM) technique, which simultaneously excites and detects incident beam in near-field. Comparing to the Scanning Near-field Optical Microscopy (SNOM) which has near-field excitation and far-field detection, PIFM boasts a much smaller background noise and a more robust system. Based on the measured force-map, we develop a theoretical model to retrieve the corresponding electric and magnetic field distribution, and correct the distortion caused by the imperfect probe-tip of the PIFM. This research pioneers the exploration in the experimental investigation on the sharply focused structured light, unveiling its potentials in a plethora of optoelectronics, chemical, or biomedical applications.

Front Matter: Volume 9554

This PDF file contains the front matter associated with SPIE Proceedings Volume 9554, including the Title Page, Copyright information, Table of Contents, Invited Panel Discussion, and Conference Committee listing.

Optical nanoscopy to reveal structural and functional properties of liver cells (Presentation Recording)

The advent of optical nanoscopy has provided an opportunity to study fundamental properties of nanoscale biological functions, such as liver sinusoidal endothelial cells (LSEC) and their fenestrations. The fenestrations are nano-pores (50-200 nm) on the LSEC plasma membrane that allow free passage of molecules through cells. The fenestrated LSEC also hase a voracious appetite for waste molecules, viruses and nanoparticles. LSEC daily remove huge amounts of waste, nanoparticles and virus from the blood. Pharmaceuticals also need to pass through these fenestrations to be activated (e.g. cholesterol reducing statins) or detoxified by hepatocytes. And, when we age, our LSEC fenestrations become smaller and fewer. Today, we study these cells and structures using either conventional light microscopy on living cells, or high-resolution (but static) methods such as transmission and scanning electron microscopy on fixed (i.e. dead) tissue. Such methods, while very powerful, yield no real time information about the uptake of virus or nanoparticles, nor any information about fenestration dynamics. Therefore, to study LS-SEC, we are now using optical nanoscopy methods, and developing our own, to map their functions in 4 dimensions. Attaining this goal will shed new light on the cell biology of the liver and how it keeps us alive. This paper describes the challenges of studying LS-SEC with light microscopy, as well as current and potential solutions to this challenge using optical nanoscopy.