Two-photon excitation provides a means of activating chemical or physical processes with high spatial resolution in three dimensions and has made possible the development of three-dimensional fluorescence imaging, optical data storage, and lithographic microfabrication. These applications take advantage of the fact that the two-photon absorption probability depends quadratically on intensity, so under tight-focusing conditions, the absorption is confined at the focus to a volume of order λ3 (where λ is the laser wavelength). Any subsequent process, such as fluorescence or a photoinduced chemical reaction, is also localized in this small volume. Although three-dimensional data storage and microfabrication have been illustrated using two-photon-initiated polymerization of resins incorporating conventional ultraviolet-absorbing initiators, such photopolymer systems exhibit low photosensitivity as the initiators have small two-photon absorption cross-sections (δ). Consequently, this approach requires high laser power, and its widespread use remains impractical. Here we report on a class of π;-conjugated compounds that exhibit large δ (as high as 1, 250 × 10−50 cm4 s per photon) and enhanced two-photon sensitivity relative to ultraviolet initiators. Two-photon excitable resins based on these new initiators have been developed and used to demonstrate a scheme for three-dimensional data storage which permits fluorescent and refractive read-out, and the fabrication of three-dimensional micro-optical and micromechanical structures, including photonic-bandgap-type structures.

Two-photon polymerization initiators for three-dimensional optical data storage and microfabrication

We first provide an overview of 3-D shape measurement us- ing various optical methods. Then we focus on structured light tech- niques where various optical configurations, image acquisition tech- niques, data postprocessing and analysis methods and advantages and limitations are presented. Several industrial application examples are presented. Important areas requiring further R&D are discussed. Finally, a comprehensive bibliography on 3-D shape measurement is included, although it is not intended to be exhaustive. © 2000 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(00)00101-X)

Overview of three-dimensional shape measurement using optical methods

Fluorescence is widely used in optical devices, microscopy imaging, biology, medical research and diagnosis. Improving fluorescence sensitivity, all the way to the limit of single-molecular detection needed in many applications, remains a great challenge. The technique of surface enhanced fluorescence (SEF) is based upon the design of surfaces in the vicinity of the emitter. SEF yields an overall improvement in the fluorescence detection efficiency through modification and control of the local electromagnetic environment of the emitter. Near-field coupling between the emitter and surface modes plays a crucial role in SEF. In particular, plasmonic surfaces with localized and propagating surface plasmons are efficient SEF substrates. Recent progress in tailoring surfaces at the nanometre scale extends greatly the realm of SEF applications. This review focuses on the recent advances in the different mechanisms involved in SEF, in each case highlighting the most relevant applications.

http://turroserver.chem.columbia.edu/surfaceplasmons/pdf/53_jpd_41_1_2008_sefsrev.pdf

Surface enhanced fluorescence

This work presents the fabrication of biologically inspired artificial compound eyes The artificial ommatidium, like that of an insect's compound eyes, consists of a refractive polymer microlens, a light-guiding polymer cone, and a self-aligned waveguide to collect light with a small angular acceptance The ommatidia are omnidirectionally arranged along a hemispherical polymer dome such that they provide a wide field of view similar to that of a natural compound eye The spherical configuration of the microlenses is accomplished by reconfigurable microtemplating, that is, polymer replication using the deformed elastomer membrane with microlens patterns The formation of polymer waveguides self-aligned with microlenses is also realized by a self-writing process in a photosensitive polymer resin The angular acceptance is directly measured by three-dimensional optical sectioning with a confocal microscope, and the detailed optical characteristics are studied in comparison with a natural compound eye

http://science.sciencemag.org/content/sci/312/5773/557.full.pdf

Biologically inspired artificial compound eyes.

Modal decomposition of light has been known for a long time, applied mostly to pattern recognition. With the commercialization of liquid-crystal devices, digital holography as an enabling tool has become accessible to all, and with it all-digital tools for the decomposition of light have finally come of age. We review recent advances in unravelling the properties of light, from the modal structure of laser beams to decoding the information stored in orbital angular momentum (OAM)-carrying fields. We show application of these tools to fiber lasers, solid-state lasers, and structured light created in the laboratory by holographic laser beam shaping. We show by experimental implementation how digital holograms may be used to infer the intensity, phase, wavefront, Poynting vector, polarization, and OAM density of some unknown optical field. In particular, we outline how virtually all the previous ISO-standard beam diagnostic techniques may be readily replaced with all-digital equivalents, thus paving the way for unravelling of light in real time. Such tools are highly relevant to the in situ analysis of laser systems, to mode division multiplexing as an emerging tool in optical communication, and for quantum information processing with entangled photons.

Creation and detection of optical modes with spatial light modulators

In this paper we show that it is possible to make a heterodyne interferometer with a single photorefractive BGO crystal using the technique of moving gratings The main problems of obtaining good fidelity of the phase conjugate wavefront with such a method are discussed theoretically within the framework of the well-known scalar approximation to the photorefractive four-wave mixing process (no absorption, no pump depletion) Experimental phase measurements for obtaining the phase distribution of the signal wave are also presented

Heterodyne Interferometer with Photorefractive BGO Crystals

Spatial coherence on micrometer scale measured by a nanohole array

2.1. Aufgabe war es, insbesondere fur tiefenlimitierte Messzwecke, eine dreidimensionale Objektauswertung mit geringem Aufwand, mit sehr hoher Messgeschwindigkeit und ohne Einbuse an Messgenauigkeit zu ermoglichen. Dabei sollen bei hohen Messgenauigkeiten (relative Messgenauigkeit besser als 1.0*10 -4 ) extrem hohe 3D Aufnahmeraten von mehr als 500 Hz erzielbar sein. 2.2. Erfindungsgemas wird zumindest ein optisches Muster, vorzugsweise eines Lichtbilds (3) von einem Projektor (4), zur standortunterschiedlichen Detektion und dreidimensionalen Auswertung auf die zu vermessende Oberflache (2) eines Objekt (1) abgebildet und dort in Lage und/oder Form, beispielsweise durch einen motorisch (6) bewegten Umlenkspiegel (5) beliebig verandert. Wahrend der Veranderung des zumindest einen optischen Musters werden wenigstens zwei standortunterschiedliche zueinander synchronisierte Bildsequenzen des tiefenlimitierten Objektes aufgenommen, wobei die Korrespondenzzuordnung dieser Bildsequenzen zwecks kurzer Mess-Sequenzen in einem an die Tiefenlimitierung des Objektes angepassten, eingeschrankten Suchfeld festgelegt wird. 2.3. Das Verfahren wird zur schnellen und hochauflosenden tiefenlimitierten optischen Objektvermessung, wie der Qualitatskontrolle, eingesetzt.

Verfahren zur 3d-messung von tiefenlimitierten objekten

Two new copolymers based on methylmethacrylate (MMA) with methacrylamide (MAA) and methacrylic acid (MA) containing distributed phenanthrenequinone (PQ) molecules are fabricated for the purpose of optical recording by generating holographic diffractive structures under argon laser illumination. Chemical conditions for the formation of holograms are discussed and confirmed by the spectral characteristics of the material. Thermal and adhesive properties were improved with the aim of expanding the range of polymer application and generating of diffractive elements with long term stability and high optical quality.

New thermostable copolymers for holographic storage based on methylmethacrylate with methacrylamide or methacrylic acid

Aufgabe war es, Objekte mit geringem Aufwand, schnellstmoglich und hochgenau dreidimensional zu vermessen. Erfindungsgemas wird zumindest ein statistisches optisches Muster, vorzugsweise eines Lichtbilds (3) von einem Projektor (4), zur standortunterschiedlichen Detektion und dreidimensionalen Auswertung auf die zu vermessende Oberflache (2) eines Objekt (1) abgebildet und dort in Lage und/oder Form, beispielsweise durch einen motorisch (6) bewegten Umlenkspiegel (5) beliebig verandert. Das Verfahren wird zur schnellen und hochauflosenden optische Oberflachenvermessung, wie der Qualitatskontrolle, eingesetzt.

Richard Kowarschik

Papers

Heterodyne Interferometer with Photorefractive BGO Crystals

Spatial coherence on micrometer scale measured by a nanohole array

Verfahren zur 3d-messung von tiefenlimitierten objekten

New thermostable copolymers for holographic storage based on methylmethacrylate with methacrylamide or methacrylic acid

Verfahren zur 3d-messung von objekten