1,720,979 research outputs found
Acousto-optofluidics for high-throughput laser processing (Conference Presentation)
No full textThe inherent flexibility of laser direct writing (LDW) systems is compromised by its sequential nature and consequent sacrifice in throughput. Efforts to address this use include simultaneous multi-spot processing or the generation of multi-beam interference patterns. However, these approaches are normally limited to patterning arrayed features or uniformly distributed aperiodic patterns. Even if changing the number of beams or the angles between them enables to control the distribution and periodicity of the patterns, this task typically involves the mechanical displacement of a focusing lens or the displacement of several optical elements. Other beam shaping methods, such as a spatial light modulator, offer unparalleled flexibility, but their limited refresh rate precludes the fast control of patterns. Here, we explore the unique interactions between sound, liquids, and light to split a laser beam at microsecond timescales. By using the acoustic standing waves generated in a resonant cavity filled with a liquid, we are able to split a beam into multiple spots along two orthogonal directions, namely the X and Y axis. Notably, no Doppler shifting occurs between the diffracted beams. Thus, blocking the zeroth diffraction order can be used to generate multi-beam interference patterns, with a geometry that can be user-selected by adjusting the frequency of the acoustic wave. We provide a theoretical foundation of the working principle of our acousto-optic approach, which is in good agreement with experiments, and demonstrate the myriad of possibilities it offers by laser fabrication of patterns in both subtractive as well as additive modalities
Sub-wavelength Laser Nanopatterning using Droplet Lenses
No full textWhen a drop of liquid falls onto a screen, e.g. a cell phone, the pixels lying underneath appear magnified. This lensing effect is a combination of the curvature and refractive index of the liquid droplet. Here, the spontaneous formation of such lenses is exploited to overcome the diffraction limit of a conventional laser direct-writing system. In particular, micro-droplets are first laser-printed at user-defined locations on a surface and they are later used as lenses to focus the same laser beam. Under conditions described herein, nanopatterns can be obtained with a reduction in spot size primarily limited by the refractive index of the liquid. This all-optics approach is demonstrated by writing arbitrary patterns with a feature size around 280 nm, about one fourth of the processing wavelength
Selective fluorescence functionalization of dye-doped polymerized structures fabricated by direct laser writing (DLW) lithography
No full textThe continuous development of the vast arsenal of fabrication techniques is a pivotal factor in the breakthrough of nanotechnology. Although the broad interest is generally focused on the reduction of the dimensions of the fabricated structures, localized functionalization of the nanomaterials emerges as a key factor closely linked to their potential applications. In particular, fabrication of spatially selective fluorescence nanostructures is highly demanded in nanophotonics, as for example in three-dimensional (3D) optical data storage (ODS), where massive storage capacity and fast writing–reading processes are promised. We have developed an innovative method to control the location and intensity of the fluorescence signal in dye-doped photopolymerized structures fabricated with Direct Laser Writing (DLW) lithography. Well-defined fluorescent pixels (area = 0.24 μm2) were written inside a polymer matrix with the help of a femtosecond pulsed laser (multiphoton absorption) via a thermally-induced di-aggregation of a fluorescent dye. Moreover, we have accomplished a fine control of the fluorescence intensity which can increase the storage capacity of ODS systems fabricated with this approach
λ/20 axial control in 2.5D polymerized structures fabricated with DLW lithography
No full textAn astonishing λ/20 height control is accomplished in 2.5D photopolymerized structures by taking advantage of the induced expansion of the resin. Our nanofabrication method is a one-pot approach with two processing steps: (i) regular 2.5D photopolymerization of the resin monomer by using multiphoton direct laser writing (DLW) lithography and (ii) spatially-selective irradiation of the photopolymerized features before development resulting in a nanometer-controlled height increase of the structure. The UV-visible-NIR sub-wavelength axial feature size (~40 nm) of this method allows fabricating devices with applications in multiple technological fields such as nanoelectronics and photonics
Simultaneous multiplane imaging for 3D confocal microscopy using high-speed z-scanning multiplexing
No full textOne of the key frontiers in optical imaging is to maximize the spatial information retrieved from a sample while minimizing acquisition time. Confocal laser scanning microscopy is a powerful imaging modality that allows real-time and high-resolution acquisition of two-dimensional (2D) sections. However, in order to obtain information from threedimensional (3D) volumes it is currently limited by a stepwise process that consists of acquiring multiple 2D sections from different focal planes by slow z-focus translation. Here, we present a novel method that enables the capture of an entire 3D sample in a single step. Our approach is based on an acoustically-driven varifocal lens integrated in a commercial confocal system that enables axial focus scanning at speeds of 140 kHz or above. Such high-speed allows for one or multiple focus sweeps on a pixel by pixel basis. By using a fast acquisition card, we can assign the photons detected at each pixel to their corresponding focal plane allowing simultaneous multiplane imaging. We exemplify this novel 3D confocal microscopy technique by imaging different biological fluorescent samples and comparing them with those obtained using traditional z-scanners. Based on these results, we find that image quality in this novel approach is similar to that obtained with traditional confocal methods, while speed is only limited by signal-to-noise-ratio. As the sensitivity of photodetectors increases and more efficient fluorescent labeling is developed, this novel 3D method can result in significant reduction in acquisition time allowing the study of new fundamental processes in science
Direct Writing of 100% Fill-Factor Geometry-Controllable Microlens Arrays with Laser Catapulting
No full textMicrolenses and microlens arrays (MLAs) are widely used in various applications, such as lab-on-a-chip, CMOS camera, and solar cells [1] . However, current fabrication methods are restricted to low fill-factor arrays, few geometry options, and flat, often rigid only, substrates. Here, we present a novel additive direct-write method, termed laser catapulting or LCP, for the rapid and customized fabrication of high fill-factor MLAs over a large variety of substrates [2] , [3] . A schematic description of LCP is shown in Fig. 1a . We used a single nanosecond laser pulse to delaminate and catapult, at user-selectable positions, either a single or a multitude of microdisks (up to 260 lenses/mm 2 ) from a donor thin film onto receiver substrate. Following thermal reflow, the printed microdisks are converted into planoconvex microlenses with excellent sphericity and high smoothness ( Fig. 1b,c ). We used as donor a positive photoresist, however, other materials can be transferred in a solid state under appropriate conditions that involve the mechanical and geometrical properties of the selected disk [4]
Characterization of nanostructures fabricated with two-beam DLW lithography using STED microscopy
No full textThe development of optical fabrication tools such as direct laser writing (DLW) lithography provides an unprecedented ability to rapidly generate arbitrary structures with control down to the nanoscale. Key to the further advance of these strategies is the development of simple and straightforward methods to monitor or characterize the fabricated structures. Here, we use a two-beam approach based on the reversible saturable optical fluorescence transition (RESOLFT) concept that enables the fabrication as well as the rapid characterization of nanometer-sized DLW lithography structures since both steps can be performed in the same experimental system. Our two-step approach uses two-beam DLW lithography based on the triplet state absorption (TSA) mechanism to polymerize a resist containing isopropyl thioxanthone (ITX) as the photoinitiator and Chromeo 488 carboxylic acid derivative as a fluorescent reporter, and then stimulated emission depletion (STED) microscopy to rapidly characterize the size and morphology of the polymerized structures after the development of the sample. Our results show photopolymerized lines with a linewidth of ~90 nm whose size was properly determined with STED microscopy
Towards nanopatterning by femtosecond laser ablation of pre-stretched elastomers
No full textDiffraction limits the focusing capabilities of an optical system seriously constraining the use of lasers for nanopatterning. In this work, we present a novel and simple approach to reduce the minimum feature size of a laser-direct write system by ablating a pre-stretched material. In particular, by focusing and scanning a femtosecond laser beam on the surface of a uniaxially pre-stretched elastomeric membrane we are able to obtain microstructures according to a desired pattern. After removing the stress applied to the elastomer, the membrane relaxes to its original size and the ablated patterns shrink while preserving their shape. In this way, the minimum feature size that is typically determined by the optical properties of the focusing system can be now controlled by the strain applied to the elastomer during the ablation process. We demonstrate this approach by ablating lines on a stretchable polymeric membrane at different strain conditions. Experimental results are in good agreement with theoretical predictions. The proposed method opens up new interesting possibilities for the rapid prototyping of micro- and nano-structures suitable for a wide range of applications such as soft-lithography, micro-/nano-fluidics and lab-on-chip
Microbeads embedded in AFM cantilevers broaden the atomic force microscopy to high-resolution optical microscopy (Conference Presentation)
No full textThe combination of the AFM technique and the sphere-mediated microscopy (SMM) opens a new opportunity to the Atomic Force Microscopy (AFM). With the help of a tipless AFM cantilever is possible to place and scan a microspheres (MS) close to the surface. From the optical point of view, when a MS is close to a surface act as high NA nanolenses whose optical characteristics define the maximum attainable resolution. By using the stages of a standard AFM, the microsphere can easily scan over the surface. The deflection of the cantilever could still be used to control the distance between microsphere and sample. With an optical detector and a low N.A. objective is so possible to obtain optical high resolution maps synchronized with the topography ones. Despite microspheres do not to break the Abbe diffraction limit or produce super-resolution, they can be used as portable and cheap optical elements that can enhance the effective NA of a system. A systematic optical characterization of the system will be presented in parallel with some preliminary results of forthcoming applications of SMM in nanolithography, micro or nano Raman spectroscopy and Near Filed Optical Microscopy (SNOM)
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