Spatial frequency modulated imaging in coherent anti-Stokes Raman microscopy

Area of Science:

• Nonlinear optical microscopy
• Coherent anti-Stokes Raman Scattering (CARS)
• Second-harmonic generation (SHG) imaging

Background:

• Single-point-scanning CARS microscopy suffers from suboptimal signal-to-noise ratio (SNR) with sparse samples or ambient light.
• Conventional methods struggle to achieve high-quality imaging in demanding optical environments.

Purpose of the Study:

• To introduce and validate a novel imaging technique, spatial frequency modulated imaging (SPIFI), for CARS and SHG microscopy.
• To improve SNR performance in challenging imaging scenarios for nonlinear microscopy.

Main Methods:

• Replacing point illumination with a periodically structured focus line in CARS.
• Acquiring transmitted CARS intensity using a single detector.
• Numerically processing CARS signals recorded with varying structured line periods.
• Experimental demonstration of SPIFI in CARS (SPIFI-CARS) and SHG (SPIFI-SHG).

Main Results:

• SPIFI-CARS and SPIFI-SHG were experimentally demonstrated to be feasible.
• The proposed SPIFI technique shows improved SNR compared to single-point-scanning methods in specific situations.
• Successful acquisition of object information along an illuminated line through numerical processing.

Conclusions:

• SPIFI offers a viable alternative to conventional point-scanning microscopy for enhanced SNR.
• This technique is particularly beneficial for imaging sparse samples or in the presence of ambient light.
• SPIFI-CARS and SPIFI-SHG represent significant advancements in nonlinear optical imaging capabilities.