Tuning donut profile for spatial resolution in stimulated emission depletion microscopy

Area of Science:

• Optical Microscopy
• Super-resolution Imaging
• Biophysics

Background:

• Stimulated emission depletion (STED) microscopy relies on a donut-shaped depletion beam for high resolution.
• The precise profile of this donut beam significantly impacts the achievable resolution.

Purpose of the Study:

• To investigate the transformation of the donut-shaped depletion beam focused by a high numerical aperture (NA) microscope objective.
• To model the STED point spread function (PSF) based on the donut beam profile.
• To identify critical parameters for optimizing STED microscope performance.

Main Methods:

• Experimental investigation of donut beam transformation under high NA objective.
• Mathematical modeling of STED PSF as a function of donut beam and excitation profiles.
• Analysis of dye properties and depletion beam polarization effects.

Main Results:

• The dark kernel's intensity profile can be approximated by a parabolic function.
• Effective NA and residual central intensity are critical for STED imaging resolution.
• Depletion beam polarization influences the residual intensity at the donut's center.
• A CW STED microscope achieved 70 nm resolution.

Conclusions:

• Effective NA and polarization are crucial parameters for STED resolution and imaging quality.
• Properly managing the depletion beam profile is essential for maximizing STED microscope performance.
• This research provides guidance for constructing and developing advanced STED microscopes.