Tunable nanowire nonlinear optical probe Page: 2 of 19
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One crucial challenge for subwavelength optics has been the development of a
tunable source of coherent laser radiation for use in the physical, information, and
biological sciences that is stable at room temperature and physiological conditions.
Current advanced near-field imaging techniques using fiber-optic scattering probes'
2 have already achieved spatial resolution down to the 20-nm range. Recently
reported far-field approaches for optical microscopy, including stimulated emission
depletion (STED)3, structured illumination4, and photoactivated localization
microscopy (PALM)5, have also enabled impressive, theoretically-unlimited spatial
resolution of fluorescent biomolecular complexes. Previous work with laser
tweezers6-8 has suggested the promise of using optical traps to create novel spatial
probes and sensors. Inorganic nanowires have diameters substantially below the
wavelength of visible light and have unique electronic and optical properties9'10 that
make them prime candidates for subwavelength laser and imaging technology.
Here we report the development of an electrode-free, continuously-tunable coherent
visible light source compatible with physiological environments, from individual
potassium niobate (KNbO3) nanowires. These wires exhibit efficient second
harmonic generation (SHG), and act as frequency converters, allowing the local
synthesis of a wide range of colors via sum and difference frequency generation
(SFG, DFG). We use this tunable nanometric light source to implement a novel
form of subwavelength microscopy, in which an infrared (IR) laser is used to
optically trap and scan a nanowire over a sample, suggesting a wide range of
potential applications in physics, chemistry, materials science, and biology.
Nanometer-scale photonics is emerging as a key ingredient for novel sensing and imaging
applications, as well as for advanced information technology, cryptography, and signal
processing circuits. A key requirement for a versatile and useful nonlinear circuit
element for integrated optical networks is the ability to frequency-double light via SHG, a
second-order nonlinear optical phenomenon. In this process, two photons with the
fundamental angular frequency w are converted through a nonlinear crystal polarization
into a single photon w2 at twice the fundamental frequency (c0_ = 2(0i). We have recently
demonstrated and characterized harmonic generation", waveguiding, and optically
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Nakayama, Yuri; Pauzauskie, Peter J.; Radenovic, Aleksandra; Onorato, Robert M.; Saykally, Richard J.; Liphardt, Jan et al. Tunable nanowire nonlinear optical probe, article, February 18, 2008; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc897928/m1/2/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.