Luis Grave de Peralta

Imaging nanoscale features with plasmon-coupled leakage radiation far-field superlenses

Optical images from nano-scale features were obtained by collection of leakage radiation coupled to surface plasmon polaritons excited by near-field fluorescence. Plasmonic crystals with spatial periods as small as 190 nm and non-periodic features separated by 80 nm, corresponding to ~λ/7, were clearly visible in the real plane images using this far-field technique. We show that the leaked light from the investigated samples carries detailed information to the far-field which is not present in the images obtained with conventional optical microscopy.

Far-field optical superlenses without metal

The spatial resolution in traditional optical microscopy is limited by diffraction. This prevents imaging of features with dimensions smaller than half of the wavelength (λ) of the illumination source. Superlenses have been recently proposed and demonstrated to overcome this issue. However, its implementation often involves complex sample fabrication and lossy metal layers. Alternatively, a superlens without metals can be realized using surface waves as the illumination source at the interface between two dielectrics, at the total internal reflection condition, where one of the dielectrics is doped with a fluorescent material. Non-scanning far-field images with resolution of ∼λ/5 and without the need of any post-processing or image reconstruction can be achieved with this approach.

Hemispherical digital optical condensers with no lenses, mirrors, or moving parts

We present a simple method for obtaining direct non-scanning images in the far-field with subwavelength resolution. Our approach relies on the use of a digital optical condenser comprised of an array of light emitting diodes uniformly distributed inside of a hollow hemisphere. We demonstrate experimental observation of minimum feature sizes of the order of λ/6 with the proposed technique. Although our experiments were performed at visible frequencies, we anticipate that the proposed approach to subwavelength resolution can be extended to the ultraviolet and infrared spectral regions.

Fundaments of optical far-field subwavelength resolution based on illumination with surface waves

We present a general discussion about the fundamental physical principles involved in a novel class of optical superlenses that permit to realize in the far-field direct non-scanning images with subwavelength resolution. Described superlenses are based in the illumination of the object under observation with surface waves excited by fluorescence, the enhanced transmission of fluorescence via coupling with surface waves, and the occurrence of far-field coherence-related fluorescence diffraction phenomena. A Fourier optics description of the image formation based on illumination with surface waves is presented, and several recent experimental realizations of this technique are discussed. Our theoretical approach explains why images with subwavelength resolution can be formed directly in the microscope camera, without involving scanning or numerical post-processing. While resolution of the order of λ/7 has been demonstrated using the described approach, we anticipate that deeper optical subwavelength resolution should be expected.

Ultra-thin condensers for optical subwavelength resolution microscopy

We present optical subwavelength resolution images of periodic patterned nanostructures using ultra-thin condensers (UTCs) illuminated by evanescent waves. We demonstrate bright and dark field microscopy using UTCs based on two types of surface wave illumination: surface plasmon polaritons and evanescent waves related to total internal reflection. We provide a discussion about the potential of UTCs for deep subwavelength resolution microscopy, and we discuss the similarities and differences between proposed UTCs, traditional bulky optical condensers, and several demonstrated superlenses.

Study of interference between surface plasmon polaritons by leakage radiation microscopy

Interference between two perpendicular surface plasmon polariton (SPP) beams was studied using a leakage radiation microscope, which allows for the observation of SPP propagation without disturbing the two-dimensional interference pattern formed at the region where the beams cross each other. Interference fringes were observed at the image plane of the microscope. Experimental results were discussed using both classical and quantum descriptions of light. Features observed in the Fourier-plane image directly demonstrate that, in correspondence with the widespread quantum description of light, photons do not propagate following the classical lines of electromagnetic energy flow.

Fourier Plane Imaging Microscopy for Detection of Plasmonic Crystals with Periods beyond the Optical Diffraction Limit

Using a simple optical microscope, composed of a plasmonic ultrathin condenser, an objective lens, and a camera, we show that the captured Fourier plane images can provide more information than the real plane images that would be obtained from the corresponding compound microscope. Using this simple Fourier plane imaging approach, we demonstrate that reconstructed non-scanning images of plasmonic crystals with lateral resolution beyond the optical diffraction limit can be obtained.

Two-dimensional Bessel-like surface plasmon-polariton beams

We present experimental evidence of non-diffracting two-dimensional Bessel-like surface plasmon-polariton (SPP) beams using the simultaneous excitation of two grating couplers forming an angle. The Bessel-like SPP beam properties were verified experimentally using the plasmon-coupled leakage radiation microscopy technique. The good agreement between simulations and measured intensity beam profiles confirms the effectiveness of the grating-coupler approach. Our results revealed that the spreading and propagation length characteristics of the Bessel-like SPP beams are primarily influenced by the angle between the grating couplers.

Super-resolution imaging of photonic crystals using the dual-space microscopy technique.

We present an experimental implementation of the recently proposed dual-space microscopy (DSM), an optical microscopy technique based on simultaneous observation of an object in the position and momentum spaces, using computer-controlled hemispherical digital condensers. We demonstrate that DSM is capable of resolving structures below the Rayleigh resolution limit.

Versatile optical microscopy using a reconfigurable hemispherical digital condenser

We present a computer-controlled hemispherical digital condenser and demonstrate that a single device can be used to implement a variety of both well established and novel optical microscopy techniques. We verified the condenser capabilities by imaging fabricated periodic patterned structures and biological samples.