# Nonlinear Optics Group

The Nonlinear Optics group is lead by Prof. Martti Kauranen.

We study fundamental issues regarding the nonlinear optical response of materials. This work is made possible by our unique measurement techniques and theoretical models, which allow the nonlinear responses to be precisely characterized.

We are particularly interested in the separation of surface and bulk effects to the nonlinear response and their multipole contributions. Nanostructured materials are another important topic. We use both plasmonic metal nanoparticles and purely dielectric materials, with the goal of designing nonlinear metamaterials with enhanced nonlinear properties.

### Contents

- Research topics
- Publications
- People (link opens on different page)

*Multipole effects*

*Multipole effects*

*Multipolar symmetry rules*

Second-order nonlinear optical processes are forbidden in centrosymmetric materials when only electric-dipole interactions between light and matter are taken into account. The broken symmetry at interfaces justifies such processes as probes of surfaces and thin films. When magnetic and quadrupole interactions are taken into account, second-order effects can occur even in centrosymmetric bulk materials.

*Theoretical challenges*

The magnetic dipoles and electric quadrupoles are usually treated as effective electric dipoles. This approach, however, fails in properly describing all aspects of the multipoles. Our goal is to develop new theoretical approaches that treat all multipoles explicitly and to verify their predictions experimentally.

*Relation to structure of materials*

The multipole interactions depend on material properties. Magnetic interactions are important in chiral materials, whereas quadrupole interactions are enhanced by field and material gradients, e.g., at surfaces or in nanostructures. Metamaterials are artificial materials whose electric and magnetic properties follow from their structural features. For nanoparticles, one needs to distinguish between atomic-scale multipole interactions and effective multipoles arising from field retardation across the particles.

*Multipolar materials*

The magnetic and quadrupole responses can potentially overcome the traditional noncentrosymmetry requirement of second-order materials. One goal of our work is to identify materials with large multipolar responses, which could lead to new concepts for nonlinear components.

*Surface and bulk effects*

*Surface and bulk effects*

*Surface and bulk symmetries*

The second-order nonlinear response of centrosymmetric bulk materials is forbidden when only electric-dipole interactions between light and matter are considered, however, becomes allowed when magnetic-dipole and electric-quadrupole interactions are taken into account. The broken symmetry at interfaces gives rise to a dipolar surface response.

*Separable and inseparable contributions*

Separation of the surface and bulk effects has been a long-standing problem in nonlinear optics, because it involves several complicated issues. For example, the bulk contribution has two parts: a part separable from the surface response and a part that behaves as an effective surface contribution. The effective surface response, on the other hand, has three parts: the true electric-dipole contribution, the surface-like bulk contribution, and the quadrupole contribution from surface gradients.

*Separation of surface and bulk responses*

We have shown that the surface and bulk responses can be separated in an unambiguous and quantitative way by a new technique, where second-harmonic generation is performed with two non-collinear beams at the fundamental frequency. Presently, the separation is limited to the distinction between the separable bulk contribution and the effective surface contribution. Our future goal is to distinguish the various parts to the surface response.

*Nanostructured materials*

*Nanostructured materials*

*Local-field enhancement*

The electromagnetic field of light can be significantly modified by properly designed nanostructures with structural features smaller than wavelength. In particular, the local field can contain very strong nanoscale features. Such “hot spots” are associated with the electromagnetic resonances of the structure and can greatly enhance optical interactions. Such properties can therefore enable photonic components and devices with significantly improved performance.

*Plasmonic metal structures*

The electromagnetic resonances of metal nanoparticles are plasmonic, i.e., they arise from collective oscillations of conduction electrons. The resonances depend on the size and shape of the particles as well their dielectric environment, and can be further modified by the mutual arrangement of several particles. The plasmon resonances and the details of the local electromagnetic fields can play a subtle role in nonlinear optics, not yet well understood. We are building the basic understanding of such issues with the goal of designing metamaterials with tailored nonlinear properties.

*Dielectric resonant structures*

It is not so well known that purely dielectric structures can also lead to strong local fields. In particular, resonance waveguide gratings act simultaneously as a waveguide and a grating that couples light into and out of a waveguide mode. On resonance the local fields in the structure are significantly enhanced, but without the losses associated with metals. We are using such structures to enhance nonlinear interactions.

*Nonlinear microscopy*

*Nonlinear microscopy*

*Coherent nonlinear microscopy*

Optical microscopy is being revolutionized by nonlinear optical approaches. Nonlinear processes scale with high power of the laser intensity, therefore producing a signal only from the focus and giving rise to 3D imaging. Coherent processes, such as second-harmonic and sum-frequency generation or coherent anti-Stokes Raman scattering can provide a signal without molecular probes, thus being sensitive to inherent properties of the sample.

*Tensorial nonlinear response*

The nonlinear responses are described by the respective nonlinear susceptibility tensors. The tensorial character is directly related to the structural properties of the sample, such as molecular orientation or chirality. The tensors determine the polarization dependent nonlinear responses. However, this possibility has been underexploited in microscopy, mainly because of difficulties in controlling the vectorial focal field.

*Polarization-based nonlinear microscopy*

We use spatial light modulators to define high-order polarization modes (e.g., radial or azimuthal polarization) at the entrance pupil of the focusing objective. The goal is to achieve full control of the field vector in the focal volume in order to increase the image contrast and to characterize the structural properties of samples in unprecedented ways. The techniques will be applied to nanostructures, molecular films, and biological samples.

*Organic materials*

*Organic materials*

*Optical response*

Strong optical response and easy modifiability through synthetic chemistry make organic molecules a viable choice for many applications in optics. By embedding strongly photoreactive organic molecules into a polymer matrix solid materials with remarkable optical properties can be produced.

*Liquid crystal nonlinear optics*

Liquid crystals allow nonlinear optical effects to be observed at very low optical powers. Nematic liquid crystals give rise to spatial solitons, i.e., waveguides induced by optical beams themselves. We aim to tailor the properties of liquid crystals for improved performance of such waveguides for novel functionalities, including second-order nonlinear effects, random lasing and fixing the light-induced structures.

*Photoisomerization*

Certain organic molecules change their isomer when they absorb a photon. The properties of the isomers are often very different, allowing the optical response of the material to be modified through irradiation. In addition, repeated isomerization cycles can lead to molecular reorientation and relatively stable changes in the material properties.

*Photoinduced effects*

Birefringence, dichroism and destruction of inversion symmetry are only a few examples of properties that can be induced into certain organic materials by properly chosen optical fields. Our goal is to use supramolecular interactions to enhance such effects and thus to develop improved materials for optical applications.

*Molecular ordering*

The second-order nonlinear optical response depends sensitively on the structural properties of materials. Our goal is to develop nonlinear techniques for the characterization of molecular ordering at surfaces and in thin films. The techniques rely on detailed polarization measurements and will be extended to nonlinear microscopy.

### Publications (Articles in refereed journals)

The complete list of publications (including conference papers) can be found in TUTCRIS database.

**2017**

- K. Koskinen, R. Czaplicki, A. Slablab, T. Ning, A. Hermans, B. Kuyken, V. Mittal, G. S. Murugan, T. Niemi, R. G. Baets, and M. Kauranen, "
*Enhancement of bulk second-harmonic generation from silicon nitride films by material composition,"*Optics Letters**42**, 5030-5033 (2017). - F. A. Sala, N. F. Smyth, U. A. Laudyn, M. A. Karpierz, A. A. Minzoni, and G. Assanto
*"Bending reorientational solitons with modulated alignment,"*J. Opt. Soc. Am. B**34**, 2459-2466 (2017). - C. P. Jisha and A. Alberucci,
*"*Paraxial light beams in structured anisotropic media*,"*J. Opt. Soc. Am. A.**34**, 2019-2024 (2017). - K. B. Bhavitha, A. K.Nair, S. Perumbilavil, S. Joseph, M.S. Kala, A. Sahad, R. Aravinda Narayanan, N. Hameed, S. Thomas, O. S. Oluwafemi, and N. Kalarikkal,
*"Investigating solvent effects on aggregation behaviour, linear and nonlinear optical properties of silver nanoclusters,"*Opt. Mater.**73**, 695-705 (2017). - U. A. Laudyn, M. Kwasny, F. A. Sala, M. A. Karpierz, N. F. Smyth, and G. Assanto
*"Curved optical solitons subject to transverse acceleration in reorientational soft matter,"*Sci. Rep.**7**, 12385 (2017). - U. A. Laudyn, M. Kwasny, M. A. Karpierz, and G. Assanto
*"Three-color vector nematicon,"*Photon. Lett. Poland**9**, 36-38 (2017). - A. Alberucci, U. A. Laudyn, A. Piccardi, M. Kwasny, B. Klus, M. A. Karpierz, and G. Assanto
*"Nonlinear continuous-wave optical propagation in nematic liquid crystals: Interplay between reorientational and thermal effects,"*Phys. Rev. E**96**, 012703 (2017). - L. Turquet, J.-P. Kakko, L. Karvonen, H. Jiang, E. Kauppinen, H. Lipsanen, M. Kauranen, and G. Bautista
*"Probing the longitudinal electric field of Bessel beams using second-harmonic generation from nano-objects,"*J. Opt.**19**, 084011 (2017). - N. Karimi, M. Virkki, A. Alberucci, O. Buchnev, M. Kauranen, A. Priimagi, and G. Assanto,
*"Molding Optical Waveguides with Nematicons,"*Advanced in Optical Materials**5**, 1700199 (2017). - G. Bautista, J.-P. Kakko, V. Dhaka, X. Zang, L. Karvonen, H. Jiang, E. Kauppinen, H. Lipsanen, and M. Kauranen
*"Nonlinear microscopy using cylindrical vector beams: Applications to three-dimensional imaging of nanostructures,"*Opt. Express**25**, 12463-12468 (2017). - L. Turquet, J.-P. Kakko, H. Jiang, T. J. Isotalo, T. Huhtio, T. Niemi, E. Kauppinen, H. Lipsanen, M. Kauranen, and G. Bautista
*"Nonlinear imaging of nanostructures using beams with binary phase modulation,"*Opt. Express**25**, 10441-40448 (2017). - L. Devasy, C.P. Jisha, A. Alberucci and V. C. Kuriakose,
*"Nonlinear waves in repulsive media supported by spatially localized parity-time-symmetric potentials,"*Phys. Lett. A**381**, 1955-1961 (2017). - A. D. Boardman, A. Alberucci, G. Assanto, V. Grimalsky, B. Kibler, J. McNiff, I. Nefedov, Y. Rapoport, and C. Valagiannopoulos,
*"Waves in hyperbolic and double negative metamaterials including rogues and solitons,"*Nanotechnology**28**, 444001 (2017). - A. Hermans, C. Kieninger, K. Koskinen, A. Wickberg, E. Solano, J. Dendooven, M. Kauranen, S. Clemmen, M. Wegener, C. Koos, and R. Baets,
*"On the determination of χ*Sci. Rep.^{(2)}in thin films: a comparison of one-beam second-harmonic generation measurement methodologies,"**7**, 44581 (2017). - K. Koskinen, A. Slablab, S. Divya, R. Czaplicki, S. Chervinskii, M. Kailasnath, P. Radhakrishnan, and M. Kauranen
*"Bulk second-harmonic generation from thermally-evaporated indium selenide thin films,"*Opt. Lett.**42**, 1076-1079 (2017). - S. Perumbilavil, A. Piccardi, O. Buchnev, M. Kauranen, G. Strangi, and G. Assanto
*"All-optical guided-wave random laser in nematic liquid crystals,"*Opt. Express**25**, 4672-4679 (2017). - J. Noga, A. Sobolewska, S. Bartkiewicz, M. Virkki, and A. Priimagi
*"Periodic Surface Structures Induced by a Single Laser Beam Irradiation,"*Macromol. Mater. Eng.**302**, 1600329 (2017). - Y. Izdebskaya, V. Shvedov, G. Assanto, and W. Krolikowski
*"Magnetic routing of light-induced waveguides,"*Nat. Commun.**8**, 14452 (2017). - C. P. Jisha, A. Alberucci, L. Marrucci, and G. Assanto
*"Interplay between diffraction and the Pancharatnam-Berry phase in inhomogeneously twisted anisotropic media,"*Phys. Rev. A**95**, 023823 (2017). - C. P. Jisha and A. Alberucci,
*"Spin-orbit interactions in optically active materials,"*Opt. Lett.**42**, 419-422 (2017). - L. Turquet, J.-P. Kakko, X. Zang, L. Naskali, L. Karvonen, H. Jiang, T. Huhtio, E. Kauppinen, H. Lipsanen, M. Kauranen, and G. Bautista,
*"Tailorable second-harmonic generation from an individual nanowire using spatially phase-shaped beams,"*Laser & Photon. Rev.**11**, 1600175 (2017). - A. Piccardi, A. Alberucci, N. Kravets, O. Buchnev, and G. Assanto,
*"Bistable Beam Propagation in Liquid Crystals,"*IEEE J. Quantum Electron.**53**, 5400111 (2017).

**2016**

- N. F. Smyth, A. Picardi, A. Alberucci, and G. Assanto,
*"Highly nonlocal optical response: Benefit or drawback?,"*J. Nonlinear Optic. Phys. Mat.**25**, 1650043 (2016). - A. Slablab, T. J. Isotalo, J. Mäkitalo, L. Turquet, P.-E. Coulon, T. Niemi, C. Ulysse, M. Kociak, D. Mailly, G. Rizza, and M. Kauranen,
*"Fabrication of Ion-Shaped Anisotropic Nanoparticles and their Orientational Imaging by Second-Harmonic Generation Microscopy,"*Sci. Rep.**6**, 37469 (2016). - A. Alberucci, C. P. Jisha, L. Marrucci, and G. Assanto,
*"Electromagnetic confinement via spin-orbit interaction in anisotropic dielectrics,"*ACS Photon.**3**, 2249-2254 (2016). - A. Alberucci, C. P. Jisha, and G. Assanto,
*"Breather solitons in highly nonlocal media,"*J. Opt.**18**, 125501 (2016). - J. Du, J. Harra, M. Virkki, J. M. Mäkelä, Y. Leng, M. Kauranen, and T. Kobayashi,
*"Surface-Enhanced Impulsive Coherent Vibrational Spectroscopy,"*Sci. Rep.**6**, 36471 (2016). - S. Perumbilavil, A. Piccardi, O. Buchnev, M. Kauranen, G. Strangi, and G. Assanto,
*"Soliton-assisted random lasing in optically-pumped liquid crystals,"*Appl. Phys. Lett.**109**, 161105 (2016). - A. Alberucci, C. P. Jisha, A. D. Boardman, and G. Assanto,
*"Anomalous diffraction in hyperbolic materials,"*Phys. Rev. A**94**, 033830 (2016). - S. Slussarenko, A. Alberucci, C. P. Jisha, B. Piccirillo, E. Santamato, G. Assanto, and L. Marrucci,
*"Guiding light via geometric phases,"*Nat. Photon.**10**, 571-575 (2016). - G. Bautista and M. Kauranen,
*"Vector-Field Nonlinear Microscopy of Nanostructures,"*ACS Photon.**3**, 1351-1370 (2016). - E. H. M. Sakho, O. S. Oluwafemi, S. Perumbilavil, R. Philip, M. S. Kala, S. Thomas, and N. Kalarikkal,
*"Rapid and facile synthesis of graphene oxide quantum dots with good linear and nonlinear optical properties,"*J. Mater. Sci. Mater. El.**27**, 10926 (2016). - N. Karimi, P. Kunwar, J. Hassinen, R. H. A. Ras, and J. Toivonen,
*"Micropatterning of silver nanoclusters embedded in polyvinyl alcohol films,"*Opt. Lett.**41**, 3627-3630 (2016). - R. Czaplicki, A. Kiviniemi, J. Laukkanen, J. Lehtolahti, M. Kuittinen, and M. Kauranen,
*"Surface lattice resonances in second-harmonic generation from metasurfaces,"*Opt. Lett.**41**, 2684-2687 (2016). - A. Piccardi, S. Residori, and G. Assanto,
*"Nonlocal soliton scattering in random potentials,"*J. Opt.**18**, 07LT01 (2016). - P. Kunwar, J. Toivonen, M. Kauranen, and G. Bautista,
*"Third-harmonic generation imaging of three-dimensional microstructures fabricated by photopolymerization,"*Opt. Express**24**, 9353-9358 (2016). - A. Piccardi, N. Kravets, A. Alberucci, O. Buchnev, and G. Assanto,
*"Voltage driven beam bistability in a reorientational uniaxial dielectric,"*APL Photon.**1**, 011302, (2016). - N. Karimi, A. Alberucci, O. Buchnev, M. Virkki, M. Kauranen, and G. Assanto,
*"Phase- front curvature effects on nematicon generation,"*J. Opt. Soc. Am. B**33**, 903-909 (2016). - N. Karimi, A. Alberucci, M. Virkki, A. Priimagi, M. Kauranen, and G. Assanto,
*"Quenching nematicon fluctuations via photo-stabilization,"*Photon. Lett. Poland**8**, 2-4 (2016). - P. Kunwar, J. Hassinen, G. Bautista, R. H. A. Ras, and J. Toivonen,
*"Sub-micron scale patterning of fluorescent silver nanoclusters using low-power laser,"*Sci. Rep.**6**, 23998 (2016). - U. A. Laudyn, P. S. Jung, M. A. Karpierz, and G. Assanto,
*"Quasi two-dimensional astigmatic solitons in soft chiral metastructures,"*Sci. Rep.**6**, 22923 (2016). - Y. Izdebskaya, W. Krolikowski, N. F. Smyth, and G. Assanto,
*"Vortex stabilization by means of spatial solitons in nonlocal media,"*J. Opt.**18**, 054006 (2016). - P. Kunwar, L. Turquet, J. Hassinen, R. H. A. Ras, J. Toivonen, and G. Bautista,
*"Holographic patterning of fluorescent microstructures comprising silver nanoclusters,"*Opt. Mater. Express**6**, 946-951 (2016). - K. Koskinen, R. Czaplicki, T. Kaplas, and M. Kauranen,
*"Recognition of multipolar second-order nonlinearities in thin-film samples,"*Opt. Express**24**, 4972-4978 (2016). - M. Virkki, O. Tuominen, M. Kauranen, A. Priimagi,
*"Photoinduced nonlinear optical response in azobenzene-functionalized molecular glass,"*Opt. Express**24**, 4964-4971 (2016). - G. Assanto and N. F. Smyth,
*"Light Induced Waveguides in Nematic Liquid Crystals,"*IEEE J. Select. Top. Quant. Electron.**22**, 4400306 (2016).

**2015**

- T. Ning, C. Tan, T. Niemi, M. Kauranen, and G. Genty,
*"Enhancement of second- harmonic generation from silicon nitride with gold gratings,"*Opt. Express**23**, 30695-30700 (2015). - U. A. Laudyn, M. Kwasny, A. Piccardi, M. A. Karpierz, R. Dabrowski, O. Chojnowska, A. Alberucci, and G. Assanto,
*"Nonlinear competition in nematicon propagation,"*Opt. Lett.**40**, 5235-5238 (2015). - S. Clemmen, A. Hermans, E. Solano, J. Dendooven, K. Koskinen, M. Kauranen, E. Brainis, C. Detavernier, and R. Baets,
*"Atomic layer deposited second-order nonlinear optical metamaterial for back-end integration with CMOS-compatible nanophotonic circuitry,"*Opt. Lett.**40**, 5371-5374 (2015). - N. Kravets, A. Piccardi, A. Alberucci, O. Buchnev, and G. Assanto,
*"Observation of Beam Self-Induced Transition from Positive to Negative Optical Refraction in Nematic Liquid Crystals,"*Mol. Cryst. Liq. Cryst.**619**, 28-34 (2015). - A. Alberucci, C. P. Jisha, and G. Assanto, "
*Nonlinear negative refraction in reorientational soft matter,"*Phys. Rev. A**92**, 033835 (2015). - A. Alberucci, A. Piccardi, N. Kravets, O. Buchnev, and G. Assanto,
*"Soliton enhancement of spontaneous symmetry breaking,"*Optica**2**, 783-789 (2015). - Y. Izdebskaya, G. Assanto, and W. Krolikowski,
*"Observation of stable-vector vortex solitons,"*Opt. Lett.**40**, 4182-4185 (2015). - L. Devassy, C. P. Jisha, A. Alberucci, and V. C. Kuriakose,
*"Parity-time-symmetric solitons in trapped Bose-Einstein condensates and the influence of varying complex potentials: A variational approach,"*Phys. Rev. E**92**, 022914 (2015). - M. Virkki, O. Tuominen, A. Forni, M. Saccone, M. Pierangelo, G. Resnati, M. Kauranen, and A. Priimagi,
*"Halogen Bonding Enhances Nonlinear Optical Response in Poled Supramolecular Polymers,"*J. Mater. Chem. C**3**, 3003-3006 (2015). - G. Bautista, J. Mäkitalo, Y. Chen, V. Dhaka, M. Grasso, L. Karvonen, H. Jiang, M. J. Huttunen, T. Huhtio, H. Lipsanen, and M. Kauranen, "
*Second-Harmonic Generation Imaging of Semiconductor Nanowires with Focused Vector Beams,"*Nano Lett.**15**, 1564-1569 (2015). - A. Alberucci, C. P. Jisha, N. F. Smyth, and G. Assanto, "
*Spatial optical solitons in highly nonlocal media,"*Phys. Rev. A**91**, 013841 (2015). - R. Czaplicki, J. Mäkitalo, R. Siikanen, H. Husu, J. Lehtolahti, M. Kuittinen, and Kauranen,
*"Second-Harmonic Generation from Metal Nanoparticles: Resonance Enhancement versus Particle Geometry,"*Nano Lett.**15**, 530-534 (2015). - M. J. Huttunen, M. Partanen, G. Bautista, S.-W. Chu, and M. Kauranen,
*"Nonlinear optical activity effects in complex anisotropic three-dimensional media,"*Opt. Mater. Express**5**, 11-21 (2015).

**2014**

- L. W. Sciberras, A. A. Minzoni, N. F. Smyth, and G. Assanto,
*"Steering of optical solitary waves by coplanar low power beams in reorientational media,"*J. Nonliner Opt. Phys. Mater.**23**, 1450045 (2014). - A. Alberucci, G. Assanto, J. M. L. MacNeil, and N. F. Smyth,
*"Nematic liquid crystals: An excellent playground for nonlocal nonlinear light localization in soft matter,"*J. Nonliner Opt. Phys. Mater.**23**, 1450045 (2014). - F. A. Sala, M. A. Karpierz, and G. Assanto,
*"Spatial routing with light-induced waveguides in uniaxial nematic liquid crystals,"*J. Nonliner Opt. Phys. Mater.**23**, 1450045 (2014). - A. Alberucci, N. Kravets, A. Piccardi, O. Buchnev, M. Kaczmarek, and G. Assanto,
*"Nematicons in planar cells subject to the optical Fréedericksz threshold,"*Opt. Express**22**, 30663-30668 (2014). - J. Mäkitalo, S. Suuriniemi, and M. Kauranen,
*"Enforcing symmetries in boundary element formulation of plasmonic and second-harmonic scattering problems,"*J. Opt. Soc. Am. A**31**, 2821-2832 (2014). - G. Bautista, S. G. Pfisterer, M. J. Huttunen, S. Ranjan, K. Kanerva, E. Ikonen, and M. Kauranen,
*"Polarized THG Microscopy Identifies Compositionally Different Lipid Droplets in Mammalian Cells,"*Biophys. J.**107**, 2230-2236 (2014). - P. Kunwar, J. Hassinen, G. Bautista, R. H. A. Ras, and J. Toivonen,
*"Direct Laser Writing of Photostable Fluorescent Silver Nanoclusters in Polymer Films,"*ACS Nano**8**, 11165-11171 (2014). - L. Naskali, M. J. Huttunen, M. Virkki, G. Bautista, A. Dér, and M. Kauranen,
*"Microscopic Determination of Second-Order Nonlinear Optical Susceptibility Tensors,"*J. Phys. Chem. C**118**, 26409-26414 (2014). - M. Zdanowicz, J. Harra, J. M. Mäkelä, E. Heinonen, T. Ning, M. Kauranen, and G. Genty,
*"Second-harmonic response of multilayer nanocomposites of silver-decorated nanoparticles and silica,"*Sci. Rep.**4**, 5745 (2014). - M. J. Huttunen, K. Lindfors, D. Andriano, J. Mäkitalo, G. Bautista, M. Lippitz, and M. Kauranen,
*"Three-dimensional winged nanocone optical antennas,"*Opt. Lett.**39**, 3686-36892 (2014). - J. Mäkitalo, M. Kauranen, and S. Suuriniemi,
*"Modes and resonances of plasmonic scatterers,"*Phys. Rev. B**89**, 165429 (2014). - G.-Y. Zhuo, H. Lee, K.-J. Hsu, M. J. Huttunen, M. Kauranen, Y.-Y. Lin, and S.-W. Chu,
*"Three-dimensional structural imaging of starch granules by second-harmonic generation circular dichroism,"*J. Microsc.**253**, 183-190 (2014).

**2013**

- M. Zdanowicz, J. Harra, J. M. Mäkelä, E. Heinonen, T. Ning, M. Kauranen, and G. Genty,
*"Ordered multilayer silica-metal nanocomposites for second-order nonlinear optics,"*Appl. Phys. Lett.**103**, 251907 (2013). - M. Kauranen,
*"Freeing Nonlinear Optics from Phase Matching,"*Science**342**, 1182-1183 (2013). - G. Bautista, M. J. Huttunen, J. M. Kontio, J. Simonen, and M. Kauranen,
*"Third- and second-harmonic generation microscopy of individual metal nanocones using cylindrical vector beams,"*Opt. Express**21**, 21918-21923 (2013). - M. J. Huttunen, O. Herranen, A. Johansson, H. Jiang, P. R. Mudimela, P. Myllyperkiö, G. Bautista, A. G. Nasibulin, E. I. Kauppinen, M. Ahlskog, M. Kauranen, and M. Pettersson,
*"Measurement of optical second-harmonic generation from an individual single-walled carbon nanotube,"*New J. Phys.**15**, 083043 (2013). - H. Lee, M. J. Huttunen, K. J. Hsu, M. Partanen, G. Y. Zhuo, M. Kauranen, and S. W. Chu,
*"Chiral imaging of collagen by second-harmonic generation circular dichroism,"*Biomed. Opt. Express**4**, 909-916 (2013). - R. Czaplicki, H. Husu, R. Siikanen, J. Mäkitalo, J. Laukkanen, J. Lehtolahti, M. Kuittinen, and M. Kauranen,
*"Enhancement of Second-Harmonic Generation from Metal Nanoparticles by Passive Elements,"*Phys. Rev. Lett.**110**, 093902 (2013). - T. Y. Ning, O. Hyvärinen, H. Pietarinen, T. Kaplas, M. Kauranen, and G. Genty,
*"Third-harmonic UV generation in silicon nitride nanostructures,"*Opt. Express**21**, 2012-2017 (2013).

**2012**

- R. Czaplicki, M. Zdanowicz, K. Kosikinen, H. Husu, J. Laukkanen, M. Kuittinen, and M. Kauranen,
*"Linear and nonlinear properties of high-quality L-shaped gold nanoparticles,"*Nonl. Opt. Quant. Opt.**45**, 71-83 (2012). - H. Husu, K. Koskinen, J. Laukkanen, M. Kuittinen, and M. Kauranen,
*"Sample Quality and Second-Harmonic Generation from Gold Nanoparticles,"*Nonl. Opt. Quant. Opt.**43**, 355- 361 (2012). - A. Priimagi, K. Ogawa, M. Virkki, J. Mamiya, M. Kauranen, and A. Shishido,
*"High- Contrast Photoswitching of Nonlinear Optical Response in Crosslinked Ferroelectric Liquid-Crystalline Polymers,"*Adv. Mater.**24**, 6410-6415 (2012). - M. J. Huttunen, J. Makitalo, G. Bautista, and M. Kauranen,
*"Multipolar second- harmonic emission with focused Gaussian beams,"*New J. Phys.**14**, 113005 (2012). - M. Kauranen and A. V. Zayats,
*"Nonlinear plasmonics,"*Nat. Photon.**6**, 737-748 (2012). - T. Y. Ning, H. Pietarinen, O. Hyvarinen, R. Kumar, T. Kaplas, M. Kauranen, and G. Genty,
*"Efficient second-harmonic generation in silicon nitride resonant waveguide gratings,"*Opt. Lett.**37**, 4269-4271 (2012). - J. Harra, J. Makitalo, R. Siikanen, M. Virkki, G. Genty, T. Kobayashi, M. Kauranen, and J. M. Makela,
*"Size-controlled aerosol synthesis of silver nanoparticles for plasmonic materials,"*J. Nanopart. Res.**14**, 870 (2012). - G. Bautista, M. J. Huttunen, J. Makitalo, J. M. Kontio, J. Simonen, and M. Kauranen,
*"Second-Harmonic Generation Imaging of Metal Nano-Objects with Cylindrical Vector Beams,"*Nano Lett.**12**, 3207-3212 (2012). - T. Ning, H. Pietarinen, O. Hyvarinen, J. Simonen, G. Genty, and M. Kauranen,
*"Strong second-harmonic generation in silicon nitride films,"*Appl. Phys. Lett.**100**, 161902 (2012). - H. Husu, R. Siikanen, J. Makitalo, J. Lehtolahti, J. Laukkanen, M. Kuittinen, and M. Kauranen,
*"Metamaterials with tailored nonlinear optical response,"*Nano Lett.**12**, 673-677 (2012).

**2011**

- R. Czaplicki, M. Zdanowicz, K. Koskinen, J. Laukkanen, M. Kuittinen, and M. Kauranen,
*"Dipole limit in second-harmonic generation from arrays of gold nanoparticles,"*Opt. Express**19**, 26866-26871 (2011). - M. J. Huttunen, J. Makitalo, and M. Kauranen,
*"Polarization-controllable winged nanocone tip antenna,"*J. Nonlinear Opt. Phys. Mater.**20**, 415-425 (2011). - J. Makitalo, S. Suuriniemi, and M. Kauranen,
*"Boundary element method for surface nonlinear optics of nanoparticles,"*Opt. Express**19**, 23386-23399 (2011). - M. Virkki, M. Kauranen, and A. Priimagi,
*"Different chromophore concentration dependence of photoinduced birefringence and second-order susceptibility in all-optical poling,"*Appl. Phys. Lett.**99**, 183309 (2011). - H. Husu, J. Makitalo, R. Siikanen, G. Genty, H. Pietarinen, J. Lehtolahti, J. Laukkanen, M. Kuittinen, and M. Kauranen,
*"Spectral control in anisotropic resonance-domain metamaterials,"*Opt. Lett.**36**, 2375-2377 (2011). - M. J. Huttunen, G. Bautista, M. Decker, S. Linden, M. Wegener, and M. Kauranen,
*"Nonlinear chiral imaging of subwavelength-sized twisted-cross gold nanodimers,"*Opt. Mater. Express**1**, 46-56 (2011). - M. Zdanowicz, S. Kujala, H. Husu, and M. Kauranen,
*"Effective medium multipolar tensor analysis of second-harmonic generation from metal nanoparticles,"*New J. Phys.**13**, 23025 (2011).

**2010**

- S. Rao, M. J. Huttunen, J. M. Kontio, J. Makitalo, M. R. Viljanen, J. Simonen, M. Kauranen, and D. Petrov,
*"Tip-enhanced Raman scattering from bridged nanocones,"*Opt. Express**18**, 23790-23795 (2010). - H. Husu, J. Makitalo, J. Laukkanen, M. Kuittinen, and M. Kauranen,
*"Particle plasmon resonances in L-shaped gold nanoparticles,"*Opt. Express**18**, 16601-16606 (2010). - M. J. Huttunen, M. Virkki, M. Erkintalo, E. Vuorimaa, A. Efimov, H. Lemmetyinen, and M. Kauranen,
*"Absolute Probe of Surface Chirality Based on Focused Circularly Polarized Light,"*J. Phys. Chem. Lett.**1**, 1826-1829 (2010). - A. Saari, G. Genty, M. Siltanen, P. Karvinen, P. Vahimaa, M. Kuittinen, and M. Kauranen,
*"Giant enhancement of second-harmonic generation in multiple diffraction orders from sub-wavelength resonant waveguide grating,"*Opt. Express**18**, 12298-12303 2010). - F. X. Wang, F. J. Rodriguez, W. M. Albers, and M. Kauranen,
*"Enhancement of bulk-type multipolar second-harmonic generation arising from surface morphology of metals,"*New J. Phys.**12**, 63009 (2010). - A. Priimagi, A. Shevchenko, M. Kaivola, F. J. Rodriguez, M. Kauranen, and P. Rochon,
*"High and stable photoinduced anisotropy in guest-host polymer mediated by chromophore aggregation,"*Opt. Lett.**35**, 1813-1815 (2010). - A. Priimagi, M. Kaivola, M. Virkki, F. J. Rodriguez, and M. Kauranen,
*"Suppression of chromophore aggregation in amorphous polymeric materials: Towards more efficient photoresponsive behavior,"*J. Nonlinear Opt. Phys. Mater.**19**, 57-73 (2010).

**2009**

- F. X. Wang, F. J. Rodriguez, W. M. Albers, R. Ahorinta, J. E. Sipe, and M. Kauranen,
*"Surface and bulk contributions to the second-order nonlinear optical response of a gold film,"*Phys. Rev. B**80**, 233402 (2009). - J. M. Kontio, H. Husu, J. Simonen, M. J. Huttunen, J. Tommila, M. Pessa, and M. Kauranen,
*"Nanoimprint fabrication of gold nanocones with similar to 10 nm tips for enhanced optical interactions,"*Opt. Lett.**34**, 1979-1981 (2009). - S. N. Volkov, K. Dolgaleva, R. W. Boyd, K. Jefimovs, J. Turunen, Y. Svirko, B. K. Canfield, and M. Kauranen,
*"Optical activity in diffraction from a planar array of achiral nanoparticles,"*Phys. Rev. A**79**, 43819 (2009). - M. J. Huttunen, M. Erkintalo, and M. Kauranen,
*"Absolute nonlinear optical probes of surface chirality,"*J. Opt. A: Pure Appl. Opt.**11**, 34006 (2009).

**2008**

- H. Husu, B. K. Canfield, J. Laukkanen, B. Bai, M. Kuittinen, J. Turunen, and M. Kauranen,
*"Chiral coupling in gold nanodimers,"*Appl. Phys. Lett.**93**, 183115 (2008). - A. Priimagi, J. Vapaavuori, F. J. Rodriguez, C. F. J. Faul, M. T. Heino, O. Ikkala, M. Kauranen, and M. Kaivola,
*"Hydrogen-Bonded Polymer-Azobenzene Complexes: Enhanced Photoinduced Birefringence with High Temporal Stability through Interplay of Intermolecular Interactions,"*Chem. Mater.**20**, 6358-6363 (2008). - K. Miettinen, E. Vuorimaa, S. Cattaneo, A. Efimov, H. Lemmetyinen, and M. Kauranen,
*"Effect of the deposition type on the structure of terthiophene-vinylbenzoate Langmuir-Blodgett films,"*Thin Solid Films**516**, 7764-7769 (2008). - S. Kujala, B. K. Canfield, M. Kauranen, Y. Svirko, and J. Turunen,
*"Multipolar analysis of second-harmonic radiation from gold nanoparticles,"*Opt. Express**16**, 17196-17208 (2008). - F. J. Rodriguez, F. X. Wang, and M. Kauranen,
*"Calibration of the second-order nonlinear optical susceptibility of surface and bulk of glass,"*Opt. Express**16**, 8704-8710 (2008). - M. Siltanen, E. Vuorimaa, H. Lemmetyinen, P. Ihalainen, J. Peltonen, and M. Kauranen,
*"Nonlinear optical and structural properties of Langmuir-Blodgett films of thiohelicenebisquinones,"*J. Phys. Chem. B**112**, 1940-1945 (2008). - B. K. Canfield, H. Husu, J. Kontio, J. Viheriala, T. Rytkonen, T. Niemi, E. Chandler, A. Hrin, J. A. Squier, and M. Kauranen,
*"Inhomogeneities in the nonlinear tensorial responses of arrays of gold nanodots,"*New J. Phys.**10**, 13001 (2008).

**2007**

- B. K. Canfield, S. Kujala, H. Husu, M. Kauranen, B. Bai, J. Laukkanen, M. Kuittinen, Y. Svirko, and J. Turunen,
*"Local-field and multipolar effects in the second-harmonic response of arrays of metal nanoparticles,"*J. Nonlinear Opt. Phys. Mater.**16**, 317-328 (2007). - M. Siltanen, S. Leivo, P. Voima, M. Kauranen, P. Karvinen, P. Vahimaa, and M. Kuittinen,
*"Strong enhancement of second-harmonic generation in all-dielectric resonant waveguide grating,"*Appl. Phys. Lett.**91**, 111109 (2007). - F. X. Wang, M. Siltanen, and M. Kauranen,
*"Uniqueness of determination of second-order nonlinear optical expansion coefficients of thin films,"*Phys. Rev. B**76**, 85428 (2007). - F. J. Rodriguez, F. X. Wang, B. K. Canfield, S. Cattaneo, and M. Kauranen,
*"Multipolar tensor analysis of second-order nonlinear optical response of surface and bulk of glass,"*Opt. Express**15**, 8695-8701 (2007). - B. K. Canfield, H. Husu, J. Laukkanen, B. F. Bai, M. Kuittinen, J. Turunen, and M Kauranen,
*"Local field asymmetry drives second-harmonic generation in noncentrosymmetric nanodimers,"*Nano Lett.**7**, 1251-1255 (2007). - S. Kujala, B. K. Canfield, M. Kauranen, Y. Svirko, amd J. Turunen,
*"Multipole interference in the second-harmonic optical radiation from gold nanoparticles,"*Phys. Rev. Lett.**98**, 167403 (2007). - B. K. Canfield, K. Laiho, and M. Kauranen,
*"Polarized second-harmonic generation with broadband femtosecond pulses,"*J. Opt. Soc. Am. B**24**, 1113-1121 (2007). - A. Priimagi, M. Kaivola, F. J. Rodriguez, and M. Kauranen,
*"Enhanced photoinduced birefringence in polymer-dye complexes: Hydrogen bonding makes a difference,"*Appl. Phys. Lett.**90**, 121103 (2007).

**2006**

- A. Priimagi, S. Cattaneo, and M. Kauranen,
*"Real-time monitoring of all-optical poling by two-beam second-harmonic generation,"*Opt. Lett.**31**, 2178-2180 (2006). - B. K. Canfield, S. Kujala, K. Jefimovs, Y. Svirko, J. Turunen, and M. Kauranen,
*"Amacroscopic formalism to describe the second-order nonlinear optical response of nanostructures,"*J. Opt. A: Pure Appl. Opt.**8**, S278-S284 (2006). - M. Siltanen and M. Kauranen,
*"A technique to assess the reliability of the second-order susceptibility determination of thin films,"*Opt. Commun.**261**, 359-367 (2006). - B. K. Canfield, S. Kujala, K. Laiho, K. Jefimovs, T. Vallius, J. Turunen, and M. Kauranen,
*"Linear and nonlinear optical properties of gold nanoparticles with broken symmetry,"*J. Nonlinear Opt. Phys. Mater.**15**, 43-53 (2006). - S. Cattaneo, K. Miettinen, E. Vuorimaa, H. Lemmetyinen, and M. Kauranen,
*"Linear optics in the second-order characterization of thin films,"*Chem. Phys. Lett.**419**, 492-495 (2006). - B. K. Canfield, S. Kujala, K. Laiho, K. Jefimovs, J. Turunen, amd M. Kauranen,
*"Chirality arising from small defects in gold nanoparticle arrays,"*Opt. Express**14**, 950-955 (2006).