Limits...
A scanning cavity microscope.

Mader M, Reichel J, Hänsch TW, Hunger D - Nat Commun (2015)

Bottom Line: Imaging the optical properties of individual nanosystems beyond fluorescence can provide a wealth of information.However, the minute signals for absorption and dispersion are challenging to observe, and only specialized techniques requiring sophisticated noise rejection are available.We demonstrate quantitative imaging of the extinction cross-section of gold nanoparticles with a sensitivity less than 1 nm(2); we show a method to improve the spatial resolution potentially below the diffraction limit by using higher order cavity modes, and we present measurements of the birefringence and extinction contrast of gold nanorods.

View Article: PubMed Central - PubMed

Affiliation: 1] Ludwig-Maximilians-Universität München, Fakultät für Physik, Schellingstraße 4, 80799 München, Germany [2] Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany.

ABSTRACT
Imaging the optical properties of individual nanosystems beyond fluorescence can provide a wealth of information. However, the minute signals for absorption and dispersion are challenging to observe, and only specialized techniques requiring sophisticated noise rejection are available. Here we use signal enhancement in a high-finesse scanning optical microcavity to demonstrate ultra-sensitive imaging. Harnessing multiple interactions of probe light with a sample within an optical resonator, we achieve a 1,700-fold signal enhancement compared with diffraction-limited microscopy. We demonstrate quantitative imaging of the extinction cross-section of gold nanoparticles with a sensitivity less than 1 nm(2); we show a method to improve the spatial resolution potentially below the diffraction limit by using higher order cavity modes, and we present measurements of the birefringence and extinction contrast of gold nanorods. The demonstrated simultaneous enhancement of absorptive and dispersive signals promises intriguing potential for optical studies of nanomaterials, molecules and biological nanosystems.

No MeSH data available.


Resolution enhancement by higher transverse modes.(a) Extinction measurement of a single particle using the fundamental mode (i) and the first five higher transverse-mode families (ii)–(vi), combined to yield an enhanced-resolution mode (vii). Scale bars, 5 μm (b) Averaged section (5 rows) through the fundamental mode (red dots) and enhanced-resolution mode (blue dots) together with a fit (solid lines). (c) Achievable spatial resolution improvement, showing the ratio of the reduced (ws) and initial (w0) mode waist as a function of the maximal mode order included. (d) Extinction map of 40 nm Au NPs. (e) Enhanced-resolution map of the same area using the higher mode orders up to m+n=3. Scale bars, 10 μm
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f3: Resolution enhancement by higher transverse modes.(a) Extinction measurement of a single particle using the fundamental mode (i) and the first five higher transverse-mode families (ii)–(vi), combined to yield an enhanced-resolution mode (vii). Scale bars, 5 μm (b) Averaged section (5 rows) through the fundamental mode (red dots) and enhanced-resolution mode (blue dots) together with a fit (solid lines). (c) Achievable spatial resolution improvement, showing the ratio of the reduced (ws) and initial (w0) mode waist as a function of the maximal mode order included. (d) Extinction map of 40 nm Au NPs. (e) Enhanced-resolution map of the same area using the higher mode orders up to m+n=3. Scale bars, 10 μm

Mentions: We evaluate the localization of Ψ by inferring the position ws where Ψ=1/e2 for different numbers of HG modes contributing. At this stage, we remain in the paraxial approximation, and discuss deviations below. We find that the resolution improves according to , where mmax is the largest mode order included, see Fig. 3c. This is in accordance with the expected scaling that results from the increase of the number of transverse field nodes ∝ m and the increase of the mode radii . In consequence, for an optical system where the numerical aperture (NA) is not fully used, resolution can be increased at least down to the diffraction limit. This is the case for optical microcavities, which can have an NA approaching unity for small mirror separation, but where the waist of the fundamental mode remains larger than the diffraction limit because the mirror radius of curvature is large compared to the mirror separation.


A scanning cavity microscope.

Mader M, Reichel J, Hänsch TW, Hunger D - Nat Commun (2015)

Resolution enhancement by higher transverse modes.(a) Extinction measurement of a single particle using the fundamental mode (i) and the first five higher transverse-mode families (ii)–(vi), combined to yield an enhanced-resolution mode (vii). Scale bars, 5 μm (b) Averaged section (5 rows) through the fundamental mode (red dots) and enhanced-resolution mode (blue dots) together with a fit (solid lines). (c) Achievable spatial resolution improvement, showing the ratio of the reduced (ws) and initial (w0) mode waist as a function of the maximal mode order included. (d) Extinction map of 40 nm Au NPs. (e) Enhanced-resolution map of the same area using the higher mode orders up to m+n=3. Scale bars, 10 μm
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4491170&req=5

f3: Resolution enhancement by higher transverse modes.(a) Extinction measurement of a single particle using the fundamental mode (i) and the first five higher transverse-mode families (ii)–(vi), combined to yield an enhanced-resolution mode (vii). Scale bars, 5 μm (b) Averaged section (5 rows) through the fundamental mode (red dots) and enhanced-resolution mode (blue dots) together with a fit (solid lines). (c) Achievable spatial resolution improvement, showing the ratio of the reduced (ws) and initial (w0) mode waist as a function of the maximal mode order included. (d) Extinction map of 40 nm Au NPs. (e) Enhanced-resolution map of the same area using the higher mode orders up to m+n=3. Scale bars, 10 μm
Mentions: We evaluate the localization of Ψ by inferring the position ws where Ψ=1/e2 for different numbers of HG modes contributing. At this stage, we remain in the paraxial approximation, and discuss deviations below. We find that the resolution improves according to , where mmax is the largest mode order included, see Fig. 3c. This is in accordance with the expected scaling that results from the increase of the number of transverse field nodes ∝ m and the increase of the mode radii . In consequence, for an optical system where the numerical aperture (NA) is not fully used, resolution can be increased at least down to the diffraction limit. This is the case for optical microcavities, which can have an NA approaching unity for small mirror separation, but where the waist of the fundamental mode remains larger than the diffraction limit because the mirror radius of curvature is large compared to the mirror separation.

Bottom Line: Imaging the optical properties of individual nanosystems beyond fluorescence can provide a wealth of information.However, the minute signals for absorption and dispersion are challenging to observe, and only specialized techniques requiring sophisticated noise rejection are available.We demonstrate quantitative imaging of the extinction cross-section of gold nanoparticles with a sensitivity less than 1 nm(2); we show a method to improve the spatial resolution potentially below the diffraction limit by using higher order cavity modes, and we present measurements of the birefringence and extinction contrast of gold nanorods.

View Article: PubMed Central - PubMed

Affiliation: 1] Ludwig-Maximilians-Universität München, Fakultät für Physik, Schellingstraße 4, 80799 München, Germany [2] Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Straße 1, 85748 Garching, Germany.

ABSTRACT
Imaging the optical properties of individual nanosystems beyond fluorescence can provide a wealth of information. However, the minute signals for absorption and dispersion are challenging to observe, and only specialized techniques requiring sophisticated noise rejection are available. Here we use signal enhancement in a high-finesse scanning optical microcavity to demonstrate ultra-sensitive imaging. Harnessing multiple interactions of probe light with a sample within an optical resonator, we achieve a 1,700-fold signal enhancement compared with diffraction-limited microscopy. We demonstrate quantitative imaging of the extinction cross-section of gold nanoparticles with a sensitivity less than 1 nm(2); we show a method to improve the spatial resolution potentially below the diffraction limit by using higher order cavity modes, and we present measurements of the birefringence and extinction contrast of gold nanorods. The demonstrated simultaneous enhancement of absorptive and dispersive signals promises intriguing potential for optical studies of nanomaterials, molecules and biological nanosystems.

No MeSH data available.