In this work, we present our most recent results on the fabrication of 3D high-resolution woodpile photonic crystals containing an organic-inorganic silicon-zirconium (Si-Zr) composite and cadmium sulfide (CdS) quantum dots (QDs). The structures are fabricated by combining 3D Direct Laser Writing by two-photon absorption and in-situ synthesis of CdS nanoparticles inside the 3D photonic matrix. The CdS-Zr-Si composite material exhibits a high nonlinear refractive index value measured by means of Z-scan method. 3D woodpile photonic structures with varying inlayer periodicity from 600nm to 500nm show clear photonic stop bands in the wavelength region between 1000nm to 450nm.
Plasmonic biosensors form the core label-free technology for studies of biomolecular interactions, but they still need a drastic improvement of sensitivity and novel nano-architectural implementations to match modern trends of nanobiotechnology. Here, we consider the generation of resonances in light reflected from 3D woodpile plasmonic crystal metamaterials fabricated by Direct Laser Writing by Multi-Photon Polymerization, followed by silver electroless plating. We show that the generation of these resonances is accompanied by the appearance of singularities of phase of reflected light and examine the response of phase characteristics to refractive index variations inside the metamaterial matrix. The recorded phase sensitivity (3*104 deg. of phase shift per RIU change) outperforms most plasmonic counterparts and is attributed to particular conditions of plasmon excitation in 3D plasmonic crystal geometry. Combined with a large surface for biomolecular immobilizations offered by the 3D woodpile matrix, the proposed sensor architecture promises a new important landmark in the advancement of plasmonic biosensing technology.
Plasmonic metamaterials for biosensing were designed as artificial materials, composed of gold/silver nanostructured blocks forming a nanolattice, which can provide improved sensing response in optical transduction compared to classical materials and additional sensing functionalities. 2D plasmonic nanoperiodic structures, including nanohole and nanodot arrays are prominent examples of such metamaterials, which can offer a series of novel functionalities, including size selectivity, spectral tuneability, drastical field enhancement etc., although spectral sensitivity of these structures is limited by spatial periodicity related to diffraction nature of plasmon coupling. Here, we consider metamaterials based on 3D plasmonic crystals and show the possibility of a delocalized plasmon mode, which can provide a drastic gain in spectral sensitivity (> 2600 nm/RIU compared to 200-400 nm/RIU for 2D structures). Combined with larger surface for bioimmobilization provided by the 3D matrix, the proposed metamaterial structure promises the advancement of plasmonic biosensing technology.
Three different designs of Fabry-Perot optical sensing microresonators fabricated by direct laser writing on the endface
of a standard telecom fiber using a zirconium-silicon, organic-inorganic hybrid photosensitive material, are
demonstrated. These endface optical fiber sensing probes are used for the detection of common organic alcohols and
chlorinated solvents vapors. The devices operate in the spectral region lying between 1440 nm and 1660 nm, while the
spectra recorded in reflection mode correlate to refractive index or absorption changes due to different vapors trapped
inside the microcavities. A sensitivity of 1503nm/RIU, for a concentration of 4ppm ethanol vapors was succeeded. The
microresonator sensing probe is explained in terms of standard physisorption and molecule packing mechanisms of
organic vapors onto porous surfaces.
Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of ‘interference’ superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with high-precision direct laser writing. Using axicons with apex angle 1400 and rounded tip area as small as ~10 μm diameter, we demonstrate 2-4 μm diameter focused laser ‘needle’ beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ~11 μm that could be achieved if focused by an ‘ideal’ lens of unity numerical aperture. The same technique using a 1600 axicon allowed us to demonstrate few-μm-wide laser ‘needle’ beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.
The focusing of multimode laser diode beams is probably the most significant problem that hinders the expansion of the high-power semiconductor lasers in many spatially-demanding applications. Generally, the ‘quality’ of laser beams is characterized by so-called ‘beam propagation parameter’ M2, which is defined as the ratio of the divergence of the laser beam to that of a diffraction-limited counterpart. Therefore, M2 determines the ratio of the beam focal-spot size to that of the ‘ideal’ Gaussian beam focused by the same optical system. Typically, M2 takes the value of 20-50 for high-power broad-stripe laser diodes thus making the focal-spot 1-2 orders of magnitude larger than the diffraction limit. The idea of ‘superfocusing’ for high-M2 beams relies on a technique developed for the generation of Bessel beams from laser diodes using a cone-shaped lens (axicon). With traditional focusing of multimode radiation, different curvatures of the wavefronts of the various constituent modes lead to a shift of their focal points along the optical axis that in turn implies larger focal-spot sizes with correspondingly increased values of M2. In contrast, the generation of a Bessel-type beam with an axicon relies on ‘self-interference’ of each mode thus eliminating the underlying reason for an increase in the focal-spot size. For an experimental demonstration of the proposed technique, we used a fiber-coupled laser diode with M2 below 20 and an emission wavelength in ~1μm range. Utilization of the axicons with apex angle of 140deg, made by direct laser writing on a fiber tip, enabled the demonstration of an order of magnitude decrease of the focal-spot size compared to that achievable using an ‘ideal’ lens of unity numerical aperture.
A novel organic-inorganic hybrid material is presented containing a quenching moiety for improving the resolution of
Direct femtosecond Laser Writing by multi-photon polymerization. By exploiting the diffusion of the quencher molecule
for confining radical diffusion in the scanned area, sub-100nm resolution is achieved. 3D woodpile structures with rod
spacing of 400nm are successfully fabricated. We optically characterize these woodpiles structures and we show that
they exhibit well-ordered diffraction patterns and stopgaps down to near-infrared wavelengths.
We present our investigations into the design and fabrication of a complex shape, readily assembled micro check-valve
using the two-photon polymerization technique and a hybrid material. A computational fluid dynamics study has been
carried out in order to evaluate the flow performance of the valve under blood pressures exhibited in healthy human
veins. The fabricated micro-valves exhibit good dimensional accuracy when compared to the CAD-created valve design
and the capability of an internal moving component to perform its intended function.
In this work, we prepare and optically characterize novel, titanium-containing hybrid materials that can be
structured three-dimensionally using two-photon polymerization. We investigate the effect on the structurability
of the increase of titanium isopropoxide and methacrylic acid content in this photosensitive composite. We
show that while it is possible to make transparent thin films with titanium isopropoxide molar content as high as
90%, three-dimensional structures can be made only when the titanium isopropoxide molar content is less than
50%. We measure the refractive index of different titanium isopropoxide: methacrylic acid concentrations in the
composite. We show a linear increase of the composite refractive index with titanium isopropoxide
concentration, while the increase of the methacrylic acid content does not it.
Materials processing by ultrafast lasers offers several attractive possibilities for micro/nano fabrication applications.
Several exciting prospects arise in the context of surface and bulk laser induced modifications. These form the basis for
diverse applications, including the development and functionalization of laser engineered surfaces, the laser transfer of
biomolecules and the functionalization of 3D structures constructed by multiphoton stereolithography. In particular, two
examples will be discussed in the following, namely a new approach for the development of superhydrophobic, self
cleaning surfaces and the fabrication of functionalized scaffolds, for tissue engineering applications.
We demonstrate two- and three-dimensional patterning of biological molecules. For the two-dimensional patterning we
employ Laser-Induced Forward Transfer of materials in solution. For the three-dimensional patterning we employ
femtosecond-laser induced three-photon polymerization, a technique which enables the construction of arbitrary 2D and
3D structures of submicron resolution. Biotin is subsequently attached to the 3D structures via UV-activated crosslinking.
The integrity of the photolytically immobilized biotin is confirmed by detecting the binding of fluorescently
labeled avidin via fluorescence microscopy.
In this paper, we present research carried out in our laboratory in the field of applications of high power lasers in cleaning surfaces. More specifically, overviews of three different applications are presented; the use of lasers in the cleaning of marble antiquities, in the restoration and cleaning of painted artworks nad in the repair of the paint of ship hulls.
We report the synthesis and evaluation of new highly polar molecules whose combined non- linear and linear optical properties are of interest for frequency doubling. The generic scheme for the syntheses rests on enamine substitutions of tetracyano-p-quinodimethane (TCNQ). In the case detailed, a novel reaction product is reported from the unexpected reaction of triethylamine and TCNQ. In polar solvents such as DMF, the molecule has a charge separated ground state and a measured bipole moment of 45 D. Also in polar solvents, the value for the resonant (beta) coefficient is measured to be -190 X 10-30 esu. Coupled with acceptable transparency at 460 nm ((epsilon) equals 86 M-1 cm-1) this molecule points to a new approach in the design of such materials.