This Conference Presentation, "Adhesion properties of polymeric microstructures fabricated by two-photon polymerization," was recorded at Photonics West 2020 held in San Francisco, California, United States.
We developed a module for dual-output, dual-wavelength lasers that facilitates multiphoton imaging and spectroscopy experiments and enables hyperspectral imaging with spectral resolution up to 5 cm−1. High spectral resolution is achieved by employing spectral focusing. Specifically, two sets of grating pairs are used to control the chirps in each laser beam. In contrast with the approach that uses fixed-length glass rods, grating pairs allow matching the spectral resolution and the linewidths of the Raman lines of interest. To demonstrate the performance of the module, we report the results of spectral focusing CARS and SRS microscopy experiments for various test samples and Raman shifts. The developed module can be used for a variety of multimodal imaging and spectroscopy applications, such as single- and multi-color two-photon fluorescence, second harmonic generation, third harmonic generation, pump-probe, transient absorption, and others.
Liposomes play a relevant role in the biomedical field of drug delivery. The ability of these lipid vesicles to encapsulate and transport a variety of bioactive molecules has fostered their use in several therapeutic applications, from cancer treatments to the administration of drugs with antiviral activities. Size and uniformity are key parameters to take into consideration when preparing liposomes; these factors greatly influence their effectiveness in both in vitro and in vivo experiments. A popular technique employed to achieve the optimal liposome dimension (around 100 nm in diameter) and uniform size distribution is repetitive extrusion through a polycarbonate filter. We investigated two femtosecond laser direct writing techniques for the fabrication of three-dimensional filters within a microfluidics chip for liposomes extrusion. The miniaturization of the extrusion process in a microfluidic system is the first step toward a complete solution for lab-on-a-chip preparation of liposomes from vesicles self-assembly to optical characterization.
In recent years two-photon microscopy with fixed-wavelength has raised increasing interest in life-sciences: Two-photon (2P) absorption spectra of common dyes are broader than single-photon ones. Therefore, excitation of several dyes simultaneously with a single IR laser wavelength is feasible and could be seen as an advantage in 2P microscopy. We used pulsed fixed-wavelength infrared lasers with center wavelength at 1040 nm, for two-photon microscopy in a variety of biologically relevant samples, among these a mouse brain sample, a mouse artery (within the animal, acute preparation), and a preparation of mouse bladder. The 1040 nm laser proved to be efficient not only in exciting fluorescence from yellow fluorescent protein (YFP) and red fluorescent dyes, but also for second harmonic generation (SHG) signals from muscle tissue and collagen. With this work we demonstrate that economical, small-footprint fixedwavelength lasers can present an interesting alternative to tunable lasers that are commonly used in multiphoton microscopy.
Two-photon polymerization (TPP) is a promising micro/nanofabrication technique, which is capable of fabricating 3D micro/nanostructures beyond the diffraction limit of light. However, the study of TPP process with a focus on the dependence of degree of conversion on TPP parameters using a non-destructive and efficient method is still lacking. We studied the quantitative relationships between the TPP parameters and the cross-linking of an acrylic-based IP-L 780 photoresist via systematic Raman characterization. The differences in the Raman spectra between the non-polymerized and the polymerized IP-L 780 photoresists were observed by probing the excitation of carbon-carbon double bond (C=C) vibrations. We obtained the relationship between the degree of conversion in TPP and the Raman spectra of the IP-L 780 resin, in which the intensity of the characteristic Raman peak of IP-L 780 at 1635 cm-1 decreases with the increase of the TPP laser dose. A mathematic model of the degree of conversion with respective to the TPP parameters, including laser average power and writing speed, has been established. The method provides a simple and effective way to characterize and optimize the TPP micro/nanofabrication processes. The established model for the degree of conversion as the function of TPP parameters will contribute to the advanced 3D TPP micro/nanofabrication by providing a guidance to optimize the laser doses, voxel sizes, and the mechanical strength of the polymers.
In this work we describe a device that extends capabilities of multiphoton microscopes based on dual wavelength output femtosecond laser sources. CARS with 17cm-1 spectral resolution is experimentally demonstrated. Our approach is based on spectral focusing CARS. For pulse shaping of the pump and Stokes beams we utilize transmission gratings based stretcher. It allows the dispersion of the stretcher to be continuously adjusted in wide range. The best spectral resolution is achieved when the chirp rates in both pump and Stokes beam are matched. The device is automated. Any change in the beam path lengths due to the stretcher adjustment or wavelength tuning is compensated by the delay line. We incorporated into the device a computer controlled beam pointing stabilization system that compensates the beam pointing deviation due to dispersion in the system. High level of automation and computer control makes the operation of the device easy. We present CARS images of several samples that demonstrate high spectral resolution, high contrast and chemical selectivity.
We describe a stand alone CARS module allowing upgrade of a two-photon microscope with CARS modality. The
Stokes beam is generated in a commercially available photonic crystal fiber (PCF) using fraction of the power of
femtosecond excitation laser. The output of the fiber is optimized for broadband CARS at Stokes shifts in 2900cm-1
region. The spectral resolution in CARS signal is 50 cm-1. It is achieved by introducing a bandpass filter in the pump
beam. The timing between the pump and Stokes pulses is preset inside the module and can be varied. We demonstrate
utility of the device on examples of second harmonic, two-photon fluorescence and CARS images of several biological
and non-biological samples. We also present results of studies where we used CARS modality to monitor in real time the
process of fabrication of microstructures by two-photon polymerization.
Two-photon polymerization (TPP) is an enabling technology that allows fast prototyping of parts with sub-100 nm
resolution. Due to its ability to fabricate microstructures with arbitrary three-dimensional geometries, TPP has been
employed in diverse fields such as photonics, microelectronics, microelectromechanical systems, and microfluidics.
However, no information is available to date that microscopically correlates the experimental conditions used in TPP
with the properties of the ultimate microstructure. We present a study where the distribution of polymer cross-linking in
three-dimensional microstructures fabricated by TPP is visualized by means of nonlinear microscopy. In particular,
coherent anti-Stokes Raman scattering (CARS) microscopy is employed to image polymer microstructures with
chemical specificity. The characterization of the microstructures based on the acquired images permits rational
optimization of the TPP process.
We present a comparative study of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) imaging in turbid media at 800- and 1300-nm excitation. The depth-dependent decay of TPEF and SHG signals in turbid tissue phantoms is used to estimate the impact of light scattering on excitation intensity at each wavelength. A 50 to 80% increase in scattering length is observed using 1300-nm excitation, while peak TPEF emission intensity is obtained 10 to 20 µm beneath the surface for both sources. The increased penetration depth at 1300 nm is confirmed by TPEF and SHG microscopy of tissue phantoms composed of gelatin/microspheres and 3-D organotypic collagen-fibroblast cultures, respectively. Our results establish the feasibility of 1.3-µm excitation in nonlinear optical microscopy.
A variety of novel ZnO nanostructures such as nanowires, nanowalls, hierarchical nanostructures with 6-, 4-, and 2-fold symmetries, nanobridges, nanonails have been successfully grown by a vapor transport and condensation technique. Doping both In and Sn into ZnO hierarchical nanostructures can be created. The 2-fold eutectic ZnO structures can also be created without any doping in the source. It was found that the hierarchical nanostructures can be divided into two
categories: homoepitaxial and heteroepitaxial where heteroepitaxy creates the multifold nanostructures. The novel ZnO nanowalls and aligned nanowires on a-plane of sapphire substrate have also been synthesized and the photoluminescence is studied. The ZnO nanowires also demonstrated very good field emission properties, comparable to carbon nanotubes. These nanostructures may find applications in a variety of fields such as field emission, photovoltaics, transparent EMI shielding, supercapacitors, fuel cells, high strength and multifunctional nanocomposites, etc. that require not only high
surface area but also structural integrity.
We demonstrate that three-dimensional multiphonon microfabrication using photopolymerization can be accomplished using a small fraction of the output of a mode- locked Ti:sapphire laser by employing an appropriate commercially-available photoinitiator. Using this photoinitiator we have been able to develop resins with a broad range of physical and chemical characteristics for use in microfabrication. The combination of optical and chemical nonlinearity in the photopolymerization reaction allows us to make structures readily with submicron features. The use of a variable beam expander allows us to create features with a broad range of sizes using a single objective while avoiding out-of-focus polymerization.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.