In the past, the formation of microscale patterns in the far field by light has been diffractively limited in resolution to roughly half the wavelength of the radiation used. Here, we demonstrate lines with an average width of 36 nanometers (nm), about one-tenth the illuminating wavelength lambda1 = 325 nm, made by applying a film of thermally stable photochromic molecules above the photoresist. Simultaneous irradiation of a second wavelength, lambda2 = 633 nm, renders the film opaque to the writing beam except at nodal sites, which let through a spatially constrained segment of incident lambda1 light, allowing subdiffractional patterning. The same experiment also demonstrates a patterning of periodic lines whose widths are about one-tenth their period, which is far smaller than what has been thought to be lithographically possible.

Perovskite quantum dots (PQDs) attract significant interest in recent years because of their unique optical properties, such as tunable wavelength, narrow emission, and high photoluminescence quantum efficiency (PLQY). Recent studies report new types of formamidinium (FA) PbBr PQDs, PQDs with organic-inorganic mixed cations, divalent cation doped colloidal CsPb M Br PQDs (M = Sn , Cd , Zn , Mn ) featuring partial cation exchange, and heterovalent cation doped into PQDs (Bi ). These PQD analogs open new possibilities for optoelectronic devices. For commercial applications in lighting and backlight displays, stability of PQDs requires further improvement to prevent their degradation by temperature, oxygen, moisture, and light. Oxygen and moisture-facilitated ion migration may easily etch unstable PQDs. Easy ion migration may result in crystal growth, which lowers PLQY of PQDs. Surface coating and treatment are important procedures for overcoming such factors. In this study, new types of PQDs and a strategy of improving their stabilities are introduced. Finally, this paper discusses future applications of PQDs in light-emitting diodes.

In this Letter, we report the confinement of a uniform beam of light (lambda(1) = 400 nm) at the nodes of a standing wave (lambda(2) = 532 nm) via absorbance modulation. In the present implementation of absorbance modulation, a thin polymer film containing a photochromic azobenzene side chain is exposed to a standing wave at lambda(2) and a uniform beam at lambda(1), resulting in alternate regions of high and low absorbance. Light at lambda(1) is localized around the low-absorbance regions. Using photoresist exposures, we mapped out the localized light intensity distribution, which agrees well with our theoretical model. Since the width of this distribution is primarily determined by the ratio of the intensities at the two wavelengths, this technique opens up the possibility of localizing light fields below the diffraction limit using far-field optics.

We report the imaging of sub-diffraction limited features using an optical probe generated by focusing a round spot at one wavelength, lambda(1) = 405 nm, and a ring-shaped spot at a second wavelength, lambda(2) = 532 nm, onto a thin photochromic layer that coats the nanostructures. Illumination at lambda(2) turns the photochromic layer opaque to lambda(1) everywhere except at the centre of the ring, where the illumination at lambda(1) penetrates and probes the underlying nanostructure. We confirm that this optically confined probe increases image contrast and is able to resolve features smaller than the far-field diffraction limit. Furthermore, by using an array of dual-wavelength diffractive microlenses, we demonstrate the feasibility of parallelizing this approach. Compared to previous approaches, our technique is not limited to fluorescence imaging.

We exploit a technique, based on nonlinear optimization, to design diffractive lenses that focus optical nulls without any phase singularities. To ensure ease of fabrication, these lenses are composed of concentric circular zones. Furthermore, we show that this technique is readily extended to multiple wavelengths and can be used to improve tolerance to fabrication errors.