Imaging properties of microsphere-assisted microscopy under transmitted illumination

Area of Science:

• Optical microscopy
• Super-resolution imaging
• Nanophotonics

Background:

• Microsphere-assisted microscopy (MAM) is a label-free super-resolution technique.
• Current research predominantly uses reflected illumination (RI).
• The impact of transmitted illumination (TI) on MAM imaging properties requires further investigation.

Purpose of the Study:

• To systematically investigate the effects of microsphere properties and immersion environments on MAM imaging under transmitted illumination (TI).
• To compare imaging properties under TI with those under reflected illumination (RI).
• To elucidate the underlying mechanisms governing MAM performance.

Main Methods:

• Investigated microsphere size, refractive index, and immersion environment (air, partial, full immersion in SU-8).
• Imaged a 300-nm-period grating sample using MAM under transmitted illumination (TI).
• Analyzed imaging properties including resolution, magnification, and contrast.

Main Results:

• Under TI, smaller microsphere size yielded higher resolution.
• Higher microsphere refractive index resulted in greater magnification.
• Optimal contrast and resolution were achieved with lower refractive index SiO2 microspheres in partial immersion and higher refractive index BaTiO3 microspheres in full immersion.
• Magnification is influenced by relative refractive index; contrast is affected by interfacial reflection and relative refractive index.
• Photonic nanojet (PNJ) characteristics (narrow FWHM, proximity to surface) are crucial for improved resolution.

Conclusions:

• Microsphere properties and immersion conditions significantly impact MAM performance under transmitted illumination.
• The findings reveal similarities in imaging properties between TI and RI modes.
• Understanding these parameters, including PNJ effects, can advance MAM applications in super-resolution microscopy.