Measurement of the three-dimensional microscope point spread function using a Shack-Hartmann wavefront sensor.

Area of Science:

• Optical microscopy
• Wavefront sensing
• Image formation

Background:

• Accurate characterization of the three-dimensional point spread function (PSF) is crucial for quantitative microscopy.
• Existing methods for experimental PSF measurement often rely on sub-resolution objects and have limitations in axial range and detector sensitivity.

Purpose of the Study:

• To present a novel technique for the experimental determination of the microscope's three-dimensional PSF.
• To overcome limitations of existing PSF measurement methods, enabling improved imaging performance.

Main Methods:

• Utilizing a Shack-Hartmann wavefront sensor to measure the wavefront in the microscope's exit pupil.
• Reconstructing the wavefront by analyzing lateral displacements of focused spots from a lenslet array.
• Employing Fourier transform to derive the 3D PSF from the measured wavefront.

Main Results:

• The technique successfully measures the wavefront and derives the 3D microscope PSF without requiring sub-resolution objects.
• Enabled imaging of larger, brighter fluorescent objects, reducing detector sensitivity needs.
• Achieved a three-fold increase in the axial range for PSF measurement and provided a continuous PSF description independent of pixel size.

Conclusions:

• The Shack-Hartmann wavefront sensing technique offers a robust and versatile method for experimental 3D PSF determination in microscopy.
• This approach enhances imaging capabilities by expanding the measurable axial range and accommodating larger specimens.