A frequency-domain non-contact photoacoustic microscope based on an adaptive interferometer

Area of Science:

• Biomedical Optics
• Microscopy Techniques
• Acoustic Imaging

Background:

• Photoacoustic microscopy (PAM) offers label-free imaging capabilities.
• Non-contact detection methods are crucial for sensitive biological specimens.
• Frequency-domain approaches can enhance signal detection in PAM.

Purpose of the Study:

• To develop and present a novel frequency-domain, non-contact photoacoustic microscopy (PAM) system.
• To demonstrate the capability of the system for imaging biological samples.
• To analyze the characteristics of photoacoustic wave detection at different depths.

Main Methods:

• Utilized amplitude-modulated (0.1-1 MHz) 638-nm laser for excitation.
• Employed a 2-wave mixing interferometer with a 532-nm probe for non-contact detection.
• Used a lock-in amplifier for sensitive photoacoustic signal acquisition.
• Acquired images of tissue phantoms, red blood cells, and retinal vasculature.

Main Results:

• Demonstrated 2D projection imaging of the sample volume via single-frequency pump modulation.
• Observed distinct signal modulations (phase and intensity) for superficial targets.
• Identified predominantly phase modulation for deeper targets beyond the ballistic photon regime.
• Successfully imaged microvasculature and cellular structures.

Conclusions:

• The developed frequency-domain, non-contact PAM system provides effective label-free imaging.
• The method distinguishes between superficial and deeper targets based on detected probe beam modulations.
• This technique shows promise for in-situ, non-invasive imaging of biological tissues.