Two-photon fluorescence scanning near-field microscopy based on a focused evanescent field under total internal...

Area of Science:

• Optics and Photonics
• Microscopy Techniques
• Nanotechnology

Background:

• Two-photon fluorescence microscopy offers enhanced resolution and reduced photobleaching.
• Near-field microscopy techniques provide sub-wavelength imaging capabilities.
• Existing two-photon near-field probes often suffer from sample heating and complex distance control.

Purpose of the Study:

• To introduce a novel two-photon fluorescence near-field microscopy method.
• To demonstrate a technique that overcomes limitations of current near-field probes.
• To achieve high-resolution imaging with reduced experimental complexity.

Main Methods:

• Utilizing a ring beam under total internal reflection to generate a focused evanescent field.
• Employing a high-numerical-aperture objective to confine the evanescent field.
• Characterizing the system using two-photon-excited images of nanocrystals.

Main Results:

• The focused evanescent field was confined to a small volume, enabling efficient two-photon excitation.
• Images revealed a distinct two-lobed focal spot due to enhanced longitudinal polarization.
• Theoretical predictions confirmed the observed focal field distribution.
• The method demonstrated no sample heating and eliminated the need for probe-to-sample distance control.

Conclusions:

• The presented two-photon fluorescence near-field microscopy technique is effective for nanoscale imaging.
• This approach offers advantages over existing methods, including no heating and simpler operation.
• The unique focal field characteristics enable precise excitation and imaging at the nanoscale.