Nonlinear optical microscopy with an obscuration-free, freeform reflective objective.

Area of Science:

• Optics and Photonics
• Microscopy
• Biomedical Imaging

Background:

• Refractive microscope objectives in nonlinear optical (NLO) imaging suffer from chromatic aberrations and temporal dispersion, limiting performance.
• Existing reflective objectives, while achromatic, have central obscurations that reduce throughput and introduce diffraction artifacts.
• Current limitations restrict NLO imaging, particularly for short- to mid-wave infrared excitation.

Purpose of the Study:

• To develop an improved reflective microscope objective for NLO imaging.
• To overcome the limitations of central obscuration in conventional reflective designs.
• To provide an achromatic and dispersion-free alternative for NLO microscopy.

Main Methods:

• Designed a reflective microscope objective using freeform mirrors in a non-coaxial geometry.
• Eliminated central obscuration present in traditional reflective objectives.
• Integrated the freeform objective into a standard laser-scanning microscope for NLO imaging.

Main Results:

• Achieved an obscuration-free design with a 0.65 numerical aperture (NA).
• Demonstrated near diffraction-limited imaging performance with improved transmission and wider fields-of-view.
• Successfully performed NLO microscopy across a broad range of excitation wavelengths, outperforming standard reflective designs.

Conclusions:

• The developed freeform reflective microscope objective is a superior alternative to refractive lenses for NLO imaging.
• This obscuration-free design enhances imaging quality, signal brightness, and transmission range.
• Enables advanced NLO microscopy applications, particularly in the short- to mid-wave infrared spectrum.