We demonstrate a direct laser writing setup combining 405 nm multi-photon lithography with 4Pi excitation enabled by a spherical reflector (SR) refocussing the transmitted excitation. The SR provides a simplified implementation of the 4Pi geometry, avoiding the need for an additional objective and its interferometrically stabilised excitation beam path, while also recycling the beam power. The reflected beam position is measured by imaging the reflected beam and is controlled by a feedback loop to 10nm in all three dimensions. Using this instrument, the fabrication of sinusoidally modulated nanowires and helicoids with sub-100nm near-isotropic cross-section is demonstrated.
We present a wide-field imaging technique recently developed by us to measure quantitatively the optical extinction cross section σext of individual nanoparticles. The technique is simple, high speed, and enables the simultaneous acquisition of hundreds of nanoparticles in the wide-field image for statistical analysis, with a sensitivity corresponding to the detection of a single gold nanoparticle down to 2nm diameter. Notably, the method is applicable to any nanoparticle (dielectric, semiconducting, metallic), and can be easily and cost-effectively implemented on a conventional wide-field microscope. Of specific significance for accurate quantification, we show that σext depends on the numerical aperture of the microscope illumination due to the oblique incidence, even for spherical particles in an isotropic environment. This "long shadow" effect needs to be taken into account when comparing σext to theoretical values calculated under plane wave illumination at normal incidence. Owing to the accurate experimental quantification of σext, one can then use it to determine the nanoparticle size, as demonstrated here on gold nanoparticles of 30nm nominal diameter. This technique thus has the potential to become a simple and cost-effective new tool for accurate size characterization of single small nanoparticles, complementing time consuming and expensive methods such as electron microscopy.
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.