The ability of a naturally hyperbolic van der Waals material α-MoO3 to sustain hyperbolic phonon-polaritons allows extreme localization of the mid-infrared electromagnetic field on a subwavelength scale. We propose periodic nanohole arrays in exfoliated α-MoO3 nanoflakes to tune the wavelength of phonon-polariton resonances. We report on the optical properties of α-MoO3 nanohole arrays and their dependence on their geometry. Results have been confirmed using the finite-difference time-domain simulations and near-field mapping of phonon-polaritonic modes. We observe an unusual behavior of the transmission spectra in the fundamental absorption band, where the phononic absorption can be almost entirely alleviated.
We discuss our recent results in nanophotonic properties of engineered naturally hyperbolic van der Waals materials. We thermomechanically control thin MoO3 flakes to tune their crystallographic and phonon-polaritonic properties. We show induction of an irreversible strain of up to -2.4% and tuning of the phonon-polaritonic dispersion relationship by more than 10%. By patterning a nanohole array in the exfoliated flakes, resonant phonon-polaritonic excitations result in more than an order of magnitude in mid-infrared field enhancement, resulting in a strong experimentally verified near-field response and enhancement of nonlinear optical properties.
Near field scanning optical microscopy (NSOM) has evolved into a rich field of study with many different variants over the past 25 years. In this talk we review recent results from an entirely new modality of microscopy where optical imaging is performed by measuring the dipole-dipole interaction force (or the trapping force) between an optically driven sample and its mirror image in the tip. Photo induced force microscopy is capable of measuring both the linear and non-linear optical response of a sample on the nanoscale. We shall review recent data both in the visible and in the mid infrared range of the spectrum.
We propose to engineer the excitation light in photo-induced force microscopy that enables the nanoscale detection of longitudinal and transverse (with respect to the propagation direction) components of chirality of samples. We employ an achiral tip in the vicinity of a chiral specimen, and illuminate the tip-sample interactive system with appropriate engineered structured light to explore both components. Particularly, we discuss using circularly polarized light to detect the transverse chirality, and the superposition of specifically-engineered radially and azimuthally polarized beams to detect longitudinal chirality. We obtain all the mentioned results through a rigorous theoretical analysis with several numerical examples. The proposed technique may have a high impact especially in biomedicine and pharmaceutics.
We propose a novel high resolution microscopy technique for enantio-specific detection of chiral samples based on force measurement down to sub-100 nm where spectroscopic techniques for chirality detection encounter major challenges due to the very weak interaction of light with chiral nanoparticles. Specifically, we delve into the differential photo-induced optical force exerted on an achiral plasmonic probe in the vicinity of a chiral sample, when left and right circularly polarized beams separately excite the sample-probe interactive system. We analytically prove that the differential force is entangled with the enantiomer type of the sample enabling enantio-specific detection of chiral inclusions. Moreover, we demonstrate that the aforementioned differential force is linearly dependent on both the chiral response of the sample and the electric response of the tip and is inversely related to the quartic power of probe-sample distance. We support our theoretical achievements by several numerical examples, highlighting the potential application of the derived analytic properties. Lastly, we demonstrate the sensitivity of our method to enantio-specify nanoscale chiral samples. By establishing this high resolution measurement technique for biomedical applications, we essentially advance the characterization of chiral samples for controlling constructive reaction between drugs and receptors.
KEYWORDS: Nanostructures, Atomic force microscopy, Magnetism, Silicon, Microscopy, Near field optics, Nanoprobes, Structured light, Polarization, Near field
Optical magnetism has long been the elusive, missing component in light-matter interaction. Interesting applications may emerge if optical magnetism is effectively harnessed and exploited. Of particular interest is the possible manipulation of the optical magnetic force, in the form of photo-induced magnetic force microscopy. We propose an optical system for inducing magnetic forces in an axis-aligned Si disk under azimuthally polarized beam illumination. The designed Si disk can support a magnetic resonance in the visible range under azimuthal polarization by interacting with the longitudinal magnetic field at the overlapping axis. Such structure can serve as the unique magnetic probe to “feel” the magnetic force of light. In our current step, we use photo-induced force microscopy to characterize the near-field electric field distribution of this system. Measurements show a stronger electric field enhancement near the edge of the Si disk which indicates a longitudinal magnetic field enhancement at the overlapping axis. This measurement is in accordance with theoretical modeling, confirming the observed magnetic enhancement. This indirect measurement on the magnetic response of the Si disk defines an important step towards our final goal of achieving direct mapping of the local magnetic field with photo-induced magnetic force microscopy. Also, our methodology can be extended to the characterization of arbitrary nanostructures, including metamaterials and metasurfaces, under structured light illumination.
Due to the weak magnetic responsibility of natural existing materials at optical frequency, optical magnetism remains a “dark state” of light which is largely unexplored. However, optical magnetism is also very desirable because of the many splendid possibilities it may lead to, including ultra-compact opto-magnetic storage devices, high speed magnetic imaging, magnetic tweezers etc. Here we design a Si nano-disk structure as the magnetic nanoprobe which supports magnetic resonance in visible range with the incident azimuthally polarized beam (APB). APB features a donut shape beam profile, with a strong longitudinal magnetic field and a vanishing electric field at the beam axis. Therefore, on the magnetic resonance while the probe is aligned to the APB axis, a longitudinal magnetic dipole is excited in the probe, and interacts with the incident APB inducing an exclusive magnetic force. Making such magnetic nanoprobe under APB illumination serves as an important first step to realize the proposed photoinduced magnetic force microscopy (PIMFM), which selectively exploits the interaction between matter and the magnetic field of light to characterize the optical magnetism in nanoscale. Such investigation of the optical magnetism in samples is dearly needed in many mechanical, chemical, and life-science applications.
KEYWORDS: Magnetism, Microscopy, Near field scanning optical microscopy, Super resolution, Polarized microscopy, Near field optics, Optical microscopy, Optical scanning systems, Distortion, Medical research
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.
Highly sensitive and stable detection of minute ac and pseudo-dc (i.e. , very low frequency) vibrations is performed by means of a differential fiber optic Michelson interferometer. Any residual instabilities are eliminated by means of an ac feedback control loop. The stabilization technique is not affected by the variations in the reflectivity of the sample and by launch inefficiencies into the fiber. This approach also provides a simple, quantitative method for calibrating sample vibrations. Results are presented on the operation of the system in stabilizing its output as well as on the detection of the vibration of a silicon sample.
KEYWORDS: Photomasks, Atomic force microscopy, Phase shifts, Quartz, Chemical species, Optical lithography, Integrated circuits, Metrology, Inspection, Process control
In recent years, optical phase shifting masks (PSM) have become of interest for the enhancement of submicron lithographic techniques. Various schemes of PSMs have been published in the literature demonstrating improvement in performance of optical lithography techniques for 0.5 micrometers features and below. Some of these schemes require features on the PSMs that are micron or submicron in size. Monitoring the depth as well as the lateral dimensions of these small features is important in order to meet the dimensional tolerances. In this paper we report the application of an atomic force microscope (AFM) to obtain both quantitative as well as qualitative information about the etched features in a PSM.
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