Laser Induced Forward Transfer (LIFT) is a digital, non-contact printing technology of solid metals as well as viscous inks and pastes. It is highly promising for various printed electronics applications, also when high-resolution is required given its versatility in printable materials, controlled droplet volume down to <100 fL and accurate positioning down to <~5μm. Moreover, since typically no post-processing is required, deposition on a wide range of sensitive substrates is made possible. We will demonstrate high speed and high-resolution LIFT printing of electrical circuitry relying on fast material supply in the form of metal coated foil and fast, random access, laser beam steering. Examples of printed porous material structures will be shown as a demonstration to the capacity to design and fabricate materials with specific thermal, electrical and mechanical properties.
The surfaces of laser-induced forward transfer (LIFT) printed metal structures show typical roughness characteristic of the metal droplet size (3 to 10 μm). Submicron voids are often observed in the bulk of such printed metal structures with consequences on the mechanical strength, chemical resistivity, and electrical conductivity. We present the results of our efforts to reduce surface roughness and bulk voids by controlled laser melting. We have used temporally shaped pulses from a fiber laser tunable in the range from 1 to 600 ns in order to improve the quality of LIFT printed copper and aluminum structures. For the best case shown, roughness was improved from RRMS=0.8 μm to RRMS=0.2 μm and the relative percentage of the voids was reduced from 7.3% to 0.9%.
To date, a full-scale solar sail has never flown in space. Furthermore, solar sail technology development represents a field that only recently has enjoyed significant support. The goal of this work is to contribute to the development of a low-mass ODS for solar sails that would include research and development in the areas of photogrammetry and thermography. The focus of this work was on the development of the thermography system. A measurement protocol was designed for obtaining accurate temperature measurements using thermal imaging when heat was applied to the membrane surface. Two main limitations were considered during the experimental process. The first is that conventional infrared detector arrays must be kept cool. To minimize the effect that an imager's operating temperature would have on the ODS, a miniature, un-cooled microbolometer was used to acquire temperature measurements from the membrane surface. A second limitation is that a detector array cannot distinguish between emitted and reflected photons, thus presenting a significant problem if one cannot predict the reflected component or if the reflected component is significantly greater than the emitted. To address this limitation, spectral properties of the membrane, including reflectance and transmission, were analyzed using a Hemispherical Directional Reflectometer (HDR) to predict the effects that optical properties would have on sail membrane temperatures. A thermal modeling strategy was also developed. The results of this investigation are presented.
Multi-Photon Laser Scanning Microscopy (MPLSM) requires efficient two-photon absorbing fluorescent (TPF) probes. In particular, probes exhibiting bio-functionality are very attractive for MPLSM studies of biological samples. We have synthesized and studied a new class of TPF probes capable of caging metal ions, such as Ca+2 and Na+, which play an important role in neuronal mechanisms. The TPF probes are based on a tetraketo derivative with a symmetric Donor-Acceptor-Donor (D-A-D) structure. The donor is an azacrown moiety, which also serves as a metal ion-caging unit. We studied the linear and the non-linear spectroscopic properties of these TPF probes as a function of conjugation length and the size of the crown ring. We find that this new class of TPF probes possesses very large two-photon excitation cross-section coefficients (~1000GM) at near IR wavelengths as well as affinity to metal ions. In the presence of changing sodium ion concentration the dye spectra reveals four distinguishable forms and the TPF efficiency changes strongly. We therefore conclude that the dye can perform as a sensitive metal ion TPF probe.
An important ingredient in improving Multi Photon Laser Scanning Microscopy, MPLSM, is the development of efficient two-photon fluorescent (TPF) probes. We previously reported on a new class of TPF probes, specifically designed in order to maximize their efficiency in potential MPLSM applications. The fluorophores are based on a tetraketo derivative (TK) with a symmetric structure Donor-Acceptor-Donor (D-A-D). Those fluorophores have the following properties: a) Very large two-photon absorption coefficients (δ ~ 1000GM); b) Two-photon excitation (TPE) peak wavelength strongly shifted to the red (λ ~ 1µm); c) High fluorescence quantum efficiency; d) Large Stokes shifts of the fluorescence bands. We extended our work to a new fluorophore from this class that is more suitable for biological settings. This new fluorophore has a structure of crown-TK-crown that incorporates the ability to trap metal ions such as calcium. The TPE wavelength dependence of the TK-crown derivative is very similar to its analogous linear derivative with enhancement in the value of the cross-section, due to the stronger donor moieties. The TPE cross-section for the TK-crown derivative was about δ = 950 GM at λmax = 980 nm.
Langmuir-Blodgett films have been prepared from amphiphilc molecules containing an indandione-based nonlinear chromophore. Study of the pressure-area (π-A) isotherm enabled us to find optimal conditions for monolayer transfer to a glass substrate. The multilayer films thus formed exhibited strong optical second harmonic generation with a bulk nonlinear co-efficient equal to the ideal value predicted by the product of the chromophore density and its known molecular hyperpolarizability.
One limitation of using electric field induced second harmonic (EFISH) to determine the molecular first hyperpolarizability (beta) of nonlinear optical molecules lies in the fact that part of the second harmonic signal comes from the second hyperpolarizability (gamma) produced by mixing two optical fields with the DC field. In analyzing EFISH results, the second hyperpolarizability contribution of the studied molecules is generally neglected. We present a modified time resolved EFISH technique that allows us, in a single experiment, to determine separately the beta and the gamma contributions. We study para-nitro aniline dissolved in Glycerol, a highly viscous solvent, and apply the DC field via a high voltage pulse with a fast rise time of approximately 40 nsec. As a result, the orientation of the molecules under the applied electric field is slow relative to the build-up of the field, enabling us to directly measure only the DC induced second harmonic (gamma contribution), at the beginning of the HV pulse. The pure beta contribution is determined from the difference between this signal and the conventional EFISH signal at the plateau of the HV pulse. Our result confirm that the gamma contribution is indeed less than 10% of the total.
Probing photon density in diffusive media is very important in order to model and understand their propagation. It is possible to detect photons outside the medium, but their non-invasive detection inside it is still an unsolved problem. An elegant, semi-invasive approach to perform this task is to scan a small absorbing sphere inside the turbid medium and measure the light outside the sample when the sphere is present and when it is not. However this method requires the medium to be liquid and such a procedure cannot be performed in the case of biological tissues. Ultrasound tagging of light has been introduced initially for transillumination imaging in turbid media, and then extended to the case of reflection imaging. Here we present results showing that it is possible to map the photon density inside solid turbid media by locally tagging photons using an ultrasonic field. We experimentally retrieve the well-known banana-shaped photons distribution when the source and the detectors are in a back-scattering configuration, using a gel-based homogeneous phantom. We also present experiments where hemoglobin has been introduced inside the gel. By fitting the experimental results with the theoretical formula, we are able to quantitatively retrieve the amount of hemoglobin introduced inside the gel, not only from data obtained by scanning the ultrasound waist inside the phantom, the in put and output fibers staying fixed.
AsSeTe/AsSe chalcogenide glasses are photosensitive materials with large refractive index. These properties make these glasses suitable for the fabrication of photonic crystals, waveguide components and MOEMS. We present in this article fabrication of 3D photonic crystals, composed from AsSeTe and air, with sub-micron feature size. The method of fabrication is relatively simple and cheap using only vapor deposition and optical holographic lithography. The interferometric alignment allows to eliminate requirement for a mask aligner.
An important ingredient in improving Multi Photon Laser Scanning Microscopy, MPLSM, is the development of efficient exogenous two-photon fluorescent (TPF) probes. Here we report on a new class of two-photon fluorophores, specifically designed in order to maximize their efficiency in potential MPLSM applications. The fluorophores possess a symmetric Donor-Acceptor-Donor (D-n-A-n-D) structure with varying conjugation length and have strong donors and acceptors. We have studied the two-photon excitation (TPE) properties of these fluorophores and found the following properties: (1) Very large two-photon absorption coefficients (6 > 1000 GM); (2) Peak TP excitation wavelength which are strongly shifted to the red ((lambda) 1 micrometer); (3) Large fluorescence quantum efficiency; (4) Large Stokes shifts of the fluorescence bands. These properties make them particularly suitable for imaging thicker samples, relying on the large improvement in TPE cross-sections and the reduced attenuation at both the excitation and emission wavelengths. We also describe TPE fluorescence anisotropy experiments revealing the tensorial shape of the fluorophores.
We have studied the two-photon absorption (TPA) and fluorescence properties of a series of phenylpolyenes with N-carbazolyl as donor end-groups in symmetric positions. The symmetric substitution of carbazole end-groups enhances the photostability of the molecules and maintains high TP coefficients. High fluorescence quantum efficiencies have been measured. The results suggest that TP chromophores with carbazole donors are promising materials for applications in two-photon imagin and sensitization. The study covers a broad excitation spectrum from 580nm to 820nm using a picosecond optical parametric source. We take advantage of the correlation between idler and signal waves emerging from the parametric generator and calibrate our results against Rhodamine B for which reliable data is available in the long wave range.
The second order nonlinearity of conjugated organic molecules involving, 1,3 indandione derivatives as an acceptor moiety has been studied. Varying the donor from dialkylamino to the chemically similar substituent, N- carbazolyl resulted in a drastic reduction of electric field induced second harmonic (beta) values. For some molecules, even a small negative value of (beta) was received. Quantum chemical calculations indicate that the decrease occurs as a result of two overlapping transitions, which contribute to (beta) with opposite signs. The charge transfer band gives a positive (beta) zzz along the molecular long axis, while a transition essentially within the carbazole moiety provides a negative (betazzz contribution to (betaEFISH. Thus, these molecules must be described with a 2D model as opposed to the 'classical' model of 1D nonlinear optical chromophores. The prediction of the 2D model was verified experimentally by using a combination of two methods, EFISH and Hyper-Rayleigh Scattering, which probe different combination of the (beta) tensor elements.
Optical gain media filled with strong scatterers present a laser-like emission when optically pumped.Different regimes can be evidenced where amplified spontaneous emission together with multiple scattering play the main role. A mapping technique where both the concentrations of dye molecules and scatterers are independently varied allows to differentiate between those regimes. A simple model based on photon diffusion is presented and threshold for lasing emission is derived, and is compared with the experiment. Qualitative agreement is found, showing that the threshold critically depends on the samples macroscopic size.
We report on a new unique photochromic material which is based on a reversible formation - cleavage of a C-C bond. The bicyclic bindon derivative, 2 undergoes a photochemical and/or thermally induced ring opening to form the isomer 3. The form 3 presents a conjugated donor-acceptor system and exhibits a considerable second-order optical nonlinearity as found by the field induced SHG measurements. The photochromic conversion is also observed in the crystalline form indicated visually by a crystal red-to-green color change. We have studied the reversible ring opening - closure process in liquid and polymeric solutions. Optical and thermal switching and the NLO efficiency of these guest- host polymer are reported.
An important potential application of organic materials for nonlinear optics lies in the field of optical switching and power limiting. One advantage of using polymeric suspensions is that one can chemically control the position of the absorption peaks thereby changing nonlinear properties associated with absorption. In this work we report on the nonlinear transmission characteristics of Poly(isothianaphtene) suspended in various solvents. The polymers were synthesized from Dichloro-o-xylene and polymerized with the use of several oxidizing agents. Submicronic particles were obtained by crushing and straining the polymers. We investigated the nonlinear transmission threshold its dependence on the oxidizing agents and the solvents and the mechanisms leading to the nonlinearity. Measurements were carried out at 1064 nm. In some cases nonlinear transmission thresholds were found to be comparable to that of carbon black suspensions. The absorption per particle was found to be important in determining the nonlinearity threshold. The mechanism responsible for the nonlinearity was identified as thermal in nature and is characterized by scattering, plasma formation, self action of the medium and increased absorption due to particle break up. This mechanism is close to that found in carbon-black suspensions but with some important differences that will be discussed.