Publications by authors named "Rachel Grange"

26 Publications

  • Page 1 of 1

Gallium Phosphide Nanowires in a Free-Standing, Flexible, and Semitransparent Membrane for Large-Scale Infrared-to-Visible Light Conversion.

ACS Nano 2020 Aug 12;14(8):10624-10632. Epub 2020 Aug 12.

Alferov University (formerly St. Petersburg Academic University), Khlopina 8/3, 194021, St. Petersburg, Russia.

Engineering of nonlinear optical response in nanostructures is one of the key topics in nanophotonics, as it allows for broad frequency conversion at the nanoscale. Nevertheless, the application of the developed designs is limited by either high cost of their manufacturing or low conversion efficiencies. This paper reports on the efficient second-harmonic generation in a free-standing GaP nanowire array encapsulated in a polymer membrane. Light coupling with optical resonances and field confinement in the nanowires together with high nonlinearity of GaP material yield a strong second-harmonic signal and efficient near-infrared (800-1200 nm) to visible upconversion. The fabricated nanowire-based membranes demonstrate high flexibility and semitransparency for the incident infrared radiation, allowing utilizing them for infrared imaging, which can be easily integrated into different optical schemes without disturbing the visualized beam.
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http://dx.doi.org/10.1021/acsnano.0c04872DOI Listing
August 2020

How to organize an online conference.

Nat Rev Mater 2020 Mar 18:1-4. Epub 2020 Mar 18.

7The Blackett Laboratory, Department of Physics, Imperial College London, London, UK.

The first online-only meeting in photonics, held on 13 January 2020, was a resounding success, with 1100 researchers participating remotely to discuss the latest advances in photonics. Here, the organizers share their tips and advice on how to organize an online conference.
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http://dx.doi.org/10.1038/s41578-020-0194-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7095294PMC
March 2020

Forward and Backward Switching of Nonlinear Unidirectional Emission from GaAs Nanoantennas.

ACS Nano 2020 Feb 2;14(2):1379-1389. Epub 2020 Jan 2.

Nonlinear Physics Centre, Research School of Physics , The Australian National University , Canberra , ACT 2601 , Australia.

High-index III-V semiconductor nanoantennas have gained great attention for enhanced nonlinear light-matter interactions, in the past few years. However, the complexity of nonlinear emission profiles imposes severe constraints on practical applications, such as in optical communications and integrated optoelectronic devices. These complexities include the lack of unidirectional nonlinear emission and the severe challenges in switching between forward and backward emissions, due to the structure of the susceptibility tensor of the III-V nanoantennas. Here, we propose a solution to both issues via engineering the nonlinear tensor of the nanoantennas. The special nonlinear tensorial properties of zinc-blende material can be used to engineer the nonlinear characteristics via growing the nanoantennas along different crystalline orientations. Based on the nonlinear multipolar effect, we have designed and fabricated (110)-grown GaAs nanoantennas, with engineered tensorial properties, embedded in a transparent low-index material. Our technique provides an approach not only for unidirectional second-harmonic generation (SHG) forward or backward emission but also for switching from one to another. Importantly, switching the SHG emission directionality is obtained only by rotating the polarization of the incident light, without the need for physical variation of the antennas or the environment. This characteristic is an advantage, as compared to other nonlinear nanoantennas, including (100)- and (111)-grown III-V counterparts or silicon and germanium nanoantennas. Indeed, (110)-GaAs nanoantennas allow for engineering the nonlinear nanophotonic systems including nonlinear "Huygens metasurfaces" and offer exciting opportunities for various nonlinear nanophotonics technologies, such as nanoscale light routing and light sources, as well as multifunctional flat optical elements.
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http://dx.doi.org/10.1021/acsnano.9b07117DOI Listing
February 2020

Image-based autofocusing system for nonlinear optical microscopy with broad spectral tuning.

Opt Express 2019 Jul;27(14):19915-19930

We present an image-based autofocusing system applied in nonlinear microscopy and spectroscopy with a wide range of excitation wavelengths. The core of the developed autofocusing system consists of an adapted two-step procedure maximizing an image score with six different image scorings algorithms implemented to cover different types of focusing scenarios in automated regime for broad wavelength region. The developed approach is combined with an automated multi-axis alignment procedure. We demonstrate the key abilities of the autofocusing procedure on different types of structures: single nanoparticles, nanowires and complex 3D nanostructures. Based on these experiments, we determine the optimal autofocusing algorithms for different types of structures and applications.
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http://dx.doi.org/10.1364/OE.27.019915DOI Listing
July 2019

Crystalline heterogeneity in single ferroelectric nanocrystals revealed by polarized nonlinear microscopy.

Sci Rep 2019 02 8;9(1):1670. Epub 2019 Feb 8.

Aix Marseille Univ, CNRS, Centrale Marseille, Institut Fresnel, F-13013, Marseille, France.

Ferroelectric nanocrystals have considerable interest for applications in nanophotonics, optical memories and bio-imaging. Their crystalline nature at the nanoscale remains however poorly known, mostly because structural investigation tools on single nanocrystals are lacking. In this work we apply polarization resolved second harmonic generation (P-SHG) imaging on isolated Barium Titanate (BaTiO) nanocrystals to unravel their crystalline nature, exploiting the sensitivity of polarized SHG to local non-centrosymmetry and nanocrystals surface responses. We evidence crystalline heterogeneities in BaTiO nanocrystals manifested by a centrosymmetric shell around the tetragonal core of the crystals, corroborating hypotheses from previous ensemble structural investigations. This study shows that in contrast to bulk materials, nanocrystals exhibit a complex composition, which is seen to be reproducible among nanocrystals. P-SHG appears furthermore as a powerful methodology that reports structural behaviors in nanoscale dielectrics materials, at the individual nanoparticle scale.
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http://dx.doi.org/10.1038/s41598-018-38229-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6368600PMC
February 2019

Reshaping the Second-Order Polar Response of Hybrid Metal-Dielectric Nanodimers.

Nano Lett 2019 02 10;19(2):877-884. Epub 2019 Jan 10.

Optical Nanomaterial Group, Institute for Quantum Electronics , ETH Zurich , 8093 Zurich , Switzerland.

We combine the field confinement of plasmonics with the flexibility of multiple Mie resonances by bottom-up assembly of hybrid metal-dielectric nanodimers. We investigate the electromagnetic coupling between nanoparticles in heterodimers consisting of gold and barium titanate (BaTiO or BTO) nanoparticles through nonlinear second-harmonic spectroscopy and polarimetry. The overlap of the localized surface plasmon resonant dipole mode of the gold nanoparticle with the dipole and higher-order Mie resonant modes in the BTO nanoparticle lead to the formation of hybridized modes in the visible spectral range. We employ the pick-and-place technique to construct the hybrid nanodimers with controlled diameters by positioning the nanoparticles of different types next to each other under a scanning electron microscope. Through linear scattering spectroscopy, we observe the formation of hybrid modes in the nanodimers. We show that the modes can be directly accessed by measuring the dependence of the second-harmonic generation (SHG) signal on the polarization and wavelength of the pump. We reveal both experimentally and theoretically that the hybridization of plasmonic and Mie-resonant modes leads to a strong reshaping of the SHG polarization dependence in the nanodimers, which depends on the pump wavelength. We compare the SHG signal of each hybrid nanodimer with the SHG signal of single BTO nanoparticles to estimate the enhancement factor due to the resonant mode coupling within the nanodimers. We report up to 2 orders of magnitude for the SHG signal enhancement compared with isolated BTO nanoparticles.
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http://dx.doi.org/10.1021/acs.nanolett.8b04089DOI Listing
February 2019

Tunable 2D binary colloidal alloys for soft nanotemplating.

Nanoscale 2018 Dec 28;10(47):22189-22195. Epub 2018 Nov 28.

Laboratory for Interfaces, Soft matter and Assembly, Department of Materials, ETH Zurich, 8093 Zurich, Switzerland.

The realization of non-close-packed nanoscale patterns with multiple feature sizes and length scales via colloidal self-assembly is a highly challenging task. We demonstrate here the creation of a variety of tunable particle arrays by harnessing the sequential self-assembly and deposition of two differently sized microgel particles at the fluid-fluid interface. The two-step process is essential to achieve a library of 2D binary colloidal alloys, which are kinetically inaccessible by direct co-assembly. These versatile binary patterns can be exploited for a range of end-uses. Here we show that they can for instance be transferred to silicon substrates, where they act as masks for the metal-assisted chemical etching of binary arrays of vertically aligned silicon nanowires (VA-SiNWs) with fine geometrical control. In particular, continuous binary gradients in both NW spacing and height can be achieved. Notably, these binary VA-SiNW platforms exhibit interesting anti-reflective properties in the visible range, in agreement with simulations. The proposed strategy can also be used for the precise placement of metallic nanoparticles in non-close-packed arrays. Sequential depositions of soft particles enable therefore the exploration of complex binary patterns, e.g. for the future development of substrates for biointerfaces, catalysis and controlled wetting.
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http://dx.doi.org/10.1039/c8nr07059hDOI Listing
December 2018

Anapoles in Free-Standing III-V Nanodisks Enhancing Second-Harmonic Generation.

Nano Lett 2018 06 24;18(6):3695-3702. Epub 2018 May 24.

ETH Zurich , Optical Nanomaterial Group, Institute for Quantum Electronics, Department of Physics , Auguste-Piccard Hof 1 , 8093 Zurich , Switzerland.

Nonradiating electromagnetic configurations in nanostructures open new horizons for applications due to two essential features: a lack of energy losses and invisibility to the propagating electromagnetic field. Such radiationless configurations form a basis for new types of nanophotonic devices, in which a strong electromagnetic field confinement can be achieved together with lossless interactions between nearby components. In our work, we present a new design of free-standing disk nanoantennas with nonradiating current distributions for the optical near-infrared range. We show a novel approach to creating nanoantennas by slicing III-V nanowires into standing disks using focused ion-beam milling. We experimentally demonstrate the suppression of the far-field radiation and the associated strong enhancement of the second-harmonic generation from the disk nanoantennas. With a theoretical analysis of the electromagnetic field distribution using multipole expansions in both spherical and Cartesian coordinates, we confirm that the demonstrated nonradiating configurations are anapoles. We expect that the presented procedure of designing and producing disk nanoantennas from nanowires becomes one of the standard approaches to fabricating controlled chains of standing nanodisks with different designs and configurations. These chains can be essential building blocks for new types of lasers and sensors with low power consumption.
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http://dx.doi.org/10.1021/acs.nanolett.8b00830DOI Listing
June 2018

Extreme electro-optic tuning of Bragg mirrors integrated in lithium niobate nanowaveguides.

Opt Lett 2018 Apr;43(7):1515-1518

Bragg reflectors (BRFs) are essential elements in optical telecommunication and sensing applications. Their miniaturization down to the sub-micron scale has been achieved in silicon-on-insulator chips. However, their tunability is limited only to thermal tuning. In order to achieve a faster and more practical tunability operation, here we report on electro-optically tunable BRFs with ∼14  dB signal filtering on a lithium-niobate-on-insulator platform, while keeping sub-micron cross-sections. Due to the lithium niobate electro-optic properties and the chosen electrodes configuration, a Bragg tunability coefficient of 23.37±0.55  pm/V is achieved, which enhances ∼33 times the tunability performance of state-of-the-art BRFs.
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http://dx.doi.org/10.1364/OL.43.001515DOI Listing
April 2018

Enhanced Second-Harmonic Generation from Sequential Capillarity-Assisted Particle Assembly of Hybrid Nanodimers.

Nano Lett 2017 09 9;17(9):5381-5388. Epub 2017 Aug 9.

Optical Nanomaterial Group, Institute for Quantum Electronics, Department of Physics, ETH Zürich , Auguste-Piccard- Hof 1, 8093 Zürich, Switzerland.

We show enhanced second-harmonic generation (SHG) from a hybrid metal-dielectric nanodimer consisting of an inorganic perovskite nanoparticle of barium titanate (BaTiO) coupled to a metallic gold (Au) nanoparticle. BaTiO-Au nanodimers of 100 nm/80 nm sizes are fabricated by sequential capillarity-assisted particle assembly. The BaTiO nanoparticle has a noncentrosymmetric crystalline structure and generates bulk SHG. We use the localized surface plasmon resonance of the gold nanoparticle to enhance the SHG from the BaTiO nanoparticle. We experimentally measure the nonlinear signal from assembled nanodimers and demonstrate an up to 15-fold enhancement compared to a single BaTiO nanoparticle. We further perform numerical simulations of the linear and SHG spectra of the BaTiO-Au nanodimer and show that the gold nanoparticle acts as a nanoantenna at the SHG wavelength.
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http://dx.doi.org/10.1021/acs.nanolett.7b01940DOI Listing
September 2017

Nonlinear mode switching in lithium niobate nanowaveguides to control light directionality.

Opt Express 2017 Feb;25(4):3013-3023

The ability of nanowaveguides to confine and guide light has been applied for developing optical applications such as nanolasers, optical switching and localized imaging. These and others applications can be further complemented by the optical control of the guided modes within the nanowaveguide, which in turn dictates the light emission pattern. It has been shown that the light directionality can be shaped by varying the nanowire cross-sections. Here, we demonstrate that the directionality of the light can be modified using a single nanowaveguide with a nonlinear phenomenon such as second-harmonic generation. In individual lithium niobate nanowaveguides, we use second-harmonic modal phase-matching and we apply it to switch the guided modes within its sub-micron cross-section. In doing so, we can vary the light directionality of the generated light from straight (0° with respect to the propagation direction) to large spread angles (almost 54°). Further, we characterize the directionality of the guided light by means of optical Fourier transformation and show that the directionality of the guided light changes for different wavelengths.
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http://dx.doi.org/10.1364/OE.25.003013DOI Listing
February 2017

Polar Second-Harmonic Imaging to Resolve Pure and Mixed Crystal Phases along GaAs Nanowires.

Nano Lett 2016 10 28;16(10):6290-6297. Epub 2016 Sep 28.

Optical Nanomaterial Group, Institute for Quantum Electronics, Department of Physics, ETH Zurich , Auguste-Piccard Hof 1, 8093 Zurich, Switzerland.

In this work, we report an optical method for characterizing crystal phases along single-semiconductor III-V nanowires based on the measurement of polarization-dependent second-harmonic generation. This powerful imaging method is based on a per-pixel analysis of the second-harmonic-generated signal on the incoming excitation polarization. The dependence of the second-harmonic generation responses on the nonlinear second-order susceptibility tensor allows the distinguishing of areas of pure wurtzite, zinc blende, and mixed and rotational twins crystal structures in individual nanowires. With a far-field nonlinear optical microscope, we recorded the second-harmonic generation in GaAs nanowires and precisely determined their various crystal structures by analyzing the polar response for each pixel of the images. The predicted crystal phases in GaAs nanowire are confirmed with scanning transmission electron and high-resolution transmission electron measurements. The developed method of analyzing the nonlinear polar response of each pixel can be used for an investigation of nanowire crystal structure that is quick, sensitive to structural transitions, nondestructive, and on-the-spot. It can be applied for the crystal phase characterization of nanowires built into optoelectronic devices in which electron microscopy cannot be performed (for example, in lab-on-a-chip devices). Moreover, this method is not limited to GaAs nanowires but can be used for other nonlinear optical nanostructures.
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http://dx.doi.org/10.1021/acs.nanolett.6b02592DOI Listing
October 2016

Fabrication of free-standing lithium niobate nanowaveguides down to 50 nm in width.

Nanotechnology 2016 Feb 18;27(6):065301. Epub 2015 Dec 18.

Institute of Applied Physics, Abbe Center of Photonics, Friedrich-Schiller-Universität Jena, Max-Wien-Platz 1, 07743 Jena, Germany.

Nonlinear optical nanoscale waveguides are a compact and powerful platform for efficient wavelength conversion. The free-standing waveguide geometry opens a range of applications in microscopy for local delivery of light, where in situ wavelength conversion helps to overcome various wavelength-dependent issues, such as biological tissue damage. In this paper, we present an original patterning method for high-precision fabrication of free-standing nanoscale waveguides based on lithium niobate, a material with a strong second-order nonlinearity and a broad transparency window covering the visible and mid-infrared wavelength ranges. The fabrication process combines electron-beam lithography with ion-beam enhanced etching and produces nanowaveguides with lengths from 5 to 50 μm, widths from 50 to 1000 nm and heights from 50 to 500 nm, each with a precision of few nanometers. The fabricated nanowaveguides are tested in an optical characterization experiment showing efficient second-harmonic generation.
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http://dx.doi.org/10.1088/0957-4484/27/6/065301DOI Listing
February 2016

Fabrication of nanoscale lithium niobate waveguides for second-harmonic generation.

Opt Lett 2015 Jun;40(12):2715-8

Nanoscale waveguides are basic building blocks of integrated optical devices. Especially, waveguides made from nonlinear optical materials, such as lithium niobate, allow access to a broad range of applications using second-order nonlinear frequency conversion processes. Based on a lithium niobate on insulator substrate, millimeter-long nanoscale waveguides were fabricated with widths as small as 200 nm. The fabrication was done by means of potassium hydroxide-assisted ion-beam-enhanced etching. The waveguides were optically characterized in the near infrared wavelength range showing phase-matched second-harmonic generation.
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http://dx.doi.org/10.1364/OL.40.002715DOI Listing
June 2015

Second-harmonic generation in lithium niobate nanowires for local fluorescence excitation.

Opt Express 2013 Aug;21(16):19012-21

Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University, Max-Wien Platz 1, 07743 Jena, Germany.

We study the nonlinear optical properties of lithium niobate (LiNbO(3)) nanowires (NWs) fabricated by a top-down ion beam enhanced etching method. First, we demonstrate generation and propagation of the second-harmonic (SH) light in LiNbO(3) NWs of typical rectangular cross-sections of 400 x 600 nm(2) and length from 10 to 50 μm. Then, we show local fluorescent excitation of 4',6-diamidino-2-phenylindole (DAPI) dye with the propagated SH signal in standard concentrations as for biological applications. By measuring the detected average power of the propagated fundamental harmonic (FH) and the SH signal at the output of the NWs, we directly prove the dominating role of the SH signal over possible two-photon excitation processes with the FH in the DAPI dye. We estimate that 63 ± 6 pW of the propagated SH average power is required for detectable dye excitation. Finally, we model the waveguiding of the SH light to determine the smallest NW cross-section (around 40x60 nm(2)) which is potentially able to excite fluorescence with a FH intensity below the cell damage threshold.
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http://dx.doi.org/10.1364/OE.21.019012DOI Listing
August 2013

Second-harmonic generation of single BaTiO3 nanoparticles down to 22 nm diameter.

ACS Nano 2013 Jun 24;7(6):5343-9. Epub 2013 May 24.

Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Max-Wien-Platz 1, 07743 Jena, Germany.

We investigate the second-harmonic generation (SHG) signal from single BaTiO3 nanoparticles of diameters varying from 70 nm down to 22 nm with a far-field optical microscope coupled to an infrared femtosecond laser. An atomic force microscope is first used to localize the individual particles and to accurately determine their sizes. Power and polarization-dependent measurements on the individual nanoparticles reveal a diameter range between 30 and 20 nm, where deviations from bulk nonlinear optical properties occur. For 22 nm diameter particles, the tetragonal crystal structure is not applicable anymore and competing effects due to the surface to volume ratio or crystallographic modifications are taking place. The demonstration of SHG from such small nanoparticles opens up the possibilities of using them as bright coherent biomarkers. Moreover, our work shows that measuring the SHG of individual nanoparticles reveals critical material properties, opening up new possibilities to investigate ferroelectricity at the nanoscale.
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http://dx.doi.org/10.1021/nn401198gDOI Listing
June 2013

Far-field imaging for direct visualization of light interferences in GaAs nanowires.

Nano Lett 2012 Oct 21;12(10):5412-7. Epub 2012 Sep 21.

Institute of Applied Physics, Abbe Center of Photonics, Friedrich Schiller University Jena, Max-Wien-Platz 1, 07743 Jena, Germany.

The optical and electrical characterization of nanostructures is crucial for all applications in nanophotonics. Particularly important is the knowledge of the optical near-field distribution for the design of future photonic devices. A common method to determine optical near-fields is scanning near-field optical microscopy (SNOM) which is slow and might distort the near-field. Here, we present a technique that permits sensing indirectly the infrared near-field in GaAs nanowires via its second-harmonic generated (SHG) signal utilizing a nonscanning far-field microscope. Using an incident light of 820 nm and the very short mean free path (16 nm) of the SHG signal in GaAs, we demonstrate a fast surface sensitive imaging technique without using a SNOM. We observe periodic intensity patterns in untapered and tapered GaAs nanowires that are attributed to the fundamental mode of a guided wave modulating the Mie-scattered incident light. The periodicity of the interferences permits to accurately determine the nanowires' radii by just using optical microscopy, i.e., without requiring electron microscopy.
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http://dx.doi.org/10.1021/nl302896nDOI Listing
October 2012

Imaging with second-harmonic radiation probes in living tissue.

Biomed Opt Express 2011 Sep 2;2(9):2532-9. Epub 2011 Aug 2.

We demonstrate that second-harmonic radiation imaging probes are efficient biomarkers for imaging in living tissue. We show that 100 nm and 300 nm BaTiO(3) nanoparticles used as contrast markers could be detected through 50 μm and 120 μm of mouse tail tissue in vitro or in vivo. Experimental results and Monte-Carlo simulations are in good agreement.
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http://dx.doi.org/10.1364/BOE.2.002532DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3184862PMC
September 2011

Imaging through turbid layers by scanning the phase conjugated second harmonic radiation from a nanoparticle.

Opt Express 2010 Sep;18(20):20723-31

School of Engineering, EPFL, Station 17, 1015 Lausanne, Switzerland.

We demonstrate imaging through a turbid layer by using digital phase conjugation of the second harmonic field radiated from a beacon nanoparticle. We show that the phase-conjugated focus can be displaced from its initial position by illuminating the same region of the turbid layer with an angular offset. An image is obtained by scanning the phase-conjugated focus through the turbid layer in a region around the nanoparticle. We obtain a clear image of the target by measuring the light transmitted through it when scanning the focused beam.
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http://dx.doi.org/10.1364/OE.18.020723DOI Listing
September 2010

Nonlinear optical properties of core-shell nanocavities for enhanced second-harmonic generation.

Phys Rev Lett 2010 May 19;104(20):207402. Epub 2010 May 19.

Optics Laboratory, School of Engineering, Ecole Polytechnique Fédérale de Lausanne, BM 4.107, Station 17, CH-1015 Lausanne, Switzerland.

A nonlinear optical plasmonic core-shell nanocavity is demonstrated as an efficient, subwavelength coherent light source through second-harmonic generation. The nonlinear optical plasmonic nanocavity incorporates a noncentrosymmetric medium, which utilizes the entire mode volume for even-order nonlinear optical processes. In previous plasmonic nanocavities, enhancement of such processes was only possible at the interface but symmetry prohibited in the body. We measured an enhancement of over 500 times in the second-harmonic radiation power. Calculations show that an enhancement of over 3500 times is achievable.
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http://dx.doi.org/10.1103/PhysRevLett.104.207402DOI Listing
May 2010

Second harmonic generation from nanocrystals under linearly and circularly polarized excitations.

Opt Express 2010 May;18(11):11917-32

School of Engineering, EPFL, Station 17, 1015 Lausanne, Switzerland.

We study second harmonic generation (SHG) from non-centrosymmetric nanocrystals under linearly polarized (LP) and circularly polarized (CP) excitations. Theoretical models are developed for SHG from nanocrystals under both plane-wave and focused excitations. We find that the focused excitation reduces the polarization dependency of the SHG signal. We show that the SHG response under CP excitation is generally inferior to the average of LP excitations over all orientations. We verify the theory by measuring the SHG polar responses from BaTiO3 nanocrystals with a scanning confocal microscope. The experimental data agrees well with the theory.
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http://dx.doi.org/10.1364/OE.18.011917DOI Listing
May 2010

Digital phase conjugation of second harmonic radiation emitted by nanoparticles in turbid media.

Opt Express 2010 Jun;18(12):12283-90

School of Engineering, EPFL, Station 17, 1015 Lausanne, Switzerland.

We demonstrate focusing coherent light on a nanoparticle through turbid media based on digital optical phase conjugation of second harmonic generation (SHG) field from the nanoparticle. A SHG active nanoparticle inside a turbid medium was excited at the fundamental frequency and emitted SHG field as a point source. The SHG emission was scattered by the turbid medium, and the scattered field was recorded by off-axis digital holography. A phase-conjugated beam was then generated by using a phase-only spatial light modulator and sent back through the turbid medium, which formed a nearly ideal focus on the nanoparticle.
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http://dx.doi.org/10.1364/OE.18.012283DOI Listing
June 2010

Bioconjugation of barium titanate nanocrystals with immunoglobulin G antibody for second harmonic radiation imaging probes.

Biomaterials 2010 Mar 8;31(8):2272-7. Epub 2009 Dec 8.

School of Engineering, EPFL, Station 17, 1015 Lausanne, Switzerland.

The second harmonic generation (SHG) active nanocrystals have been demonstrated as attractive imaging probes in nonlinear microscopy due to their coherent, non-bleaching and non-blinking signals with a broad flexibility in the choice of excitation wavelength. For the use of these nanocrystals as biomarkers, it is essential to prepare a chemical interface for specific labeling. We developed a specific labeling scheme for barium titanate (BaTiO3) nanocrystals which we use as second harmonic radiation imaging probes. The specificity was achieved by covalently coupling antibodies onto the nanocrystals. We demonstrate highly specific labeling of the nanocrystal conjugates in an antibody microarray and also the membrane proteins of live biological cells in vitro. The development of surface functionalization and bioconjugation of SHG active nanocrystals provides the opportunities of applying them to biological studies.
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http://dx.doi.org/10.1016/j.biomaterials.2009.11.096DOI Listing
March 2010

Three-dimensional harmonic holographic microcopy using nanoparticles as probes for cell imaging.

Opt Express 2009 Feb;17(4):2880-91

School of Engineering, EPFL, Station 17, 1015 Lausanne, Switzerland.

Luminescent markers play a key role in imaging techniques for life science since they provide a contrast mechanism between signal and background. We describe a new type of marker using second harmonic generation (SHG) from noncentrosymmetric BaTiO(3) nanocrystals. These nanoparticles are attractive due to their stable, non-saturating and coherent signal with a femtosecond-scale response time and broad flexibility in the choice of excitation wavelength. We obtained monodispersed BaTiO(3) nanoparticles in colloidal suspensions by coating the particle surface with amine groups. We characterized the SHG efficiency of 90-nm BaTiO(3) particles experimentally and theoretically. Moreover, we use the coherent SHG signal from BaTiO(3) nanoparticles for three-dimensional (3D) imaging without scanning. We built a harmonic holographic (H(2)) microscope which records digital holograms at the second harmonic frequency. For the first time, high-resolution 3D distributions of these SHG markers in mammalian cells are successfully captured and interpreted by the H(2) microscope.
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http://dx.doi.org/10.1364/oe.17.002880DOI Listing
February 2009

Solid-state Er:Yb:glass laser mode-locked by using single-wall carbon nanotube thin film.

Opt Lett 2007 Jan;32(1):38-40

Research Center for Advanced Science and Technology, University of Tokyo, Tokyo, Japan.

We design single-wall carbon nanotube (SWNT) thin-film saturable absorbers (SAs) integrated onto semiconductor distributed Bragg reflectors for mode-locking solid-state Er:Yb:glass lasers. We characterize the low nonsaturable loss, high-damage-threshold SWNT SAs and verify their operation up to a pulse fluence of 2 mJ/cm(2). We demonstrate passive fundamental continuous-wave mode locking with and without group-delay dispersion compensation. Without compensation the laser produces chirped 1.8 ps pulses with a spectral width of 3.8 nm. With compensation, we obtain 261 fs Fourier-transform-limited pulses with a spectral width of 9.6 nm.
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http://dx.doi.org/10.1364/ol.32.000038DOI Listing
January 2007

Pulse energy scaling to 5 microJ from a femtosecond thin disk laser.

Opt Lett 2006 Sep;31(18):2728-30

Department of Physics, Institute of Quantum Electronics, Zurich, Switzerland.

We report an increase in pulse energy to 5.1 microJ obtained directly from a femtosecond diode-pumped Yb:YAG thin disk laser without external amplification. Stable passive mode locking was obtained with a semiconductor saturable absorber mirror (SESAM). The laser delivers 63 W of average output power in a nearly diffraction-limited beam (M2=1.1) at a center wavelength of 1030 nm. The pulse repetition rate is 12.3 MHz, and the pulses have a duration of 800 fs, which results in a peak power of 5.6 MW. The laser was operated in a box flooded with helium because the nonlinearity of air was found to be a limiting factor for the stability of the pulse formation at increasing pulse energies.
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http://dx.doi.org/10.1364/ol.31.002728DOI Listing
September 2006