Ultrafast laser-pulse transmission and imaging through biological tissues

Area of Science:

• Biomedical Optics
• Biophysics
• Laser Physics

Background:

• Ultrafast laser pulse propagation through biological tissues is crucial for various imaging and therapeutic applications.
• Understanding light scattering and absorption in tissues is key to overcoming imaging depth limitations.

Purpose of the Study:

• To investigate the transmission characteristics of 100-fs ultrafast laser pulses through biological tissues of varying thicknesses.
• To explore the potential for imaging embedded objects within thick biological tissues using time-resolved detection.

Main Methods:

• Femtosecond and picosecond time-resolved detection techniques were employed to measure transmitted laser pulses.
• Analysis focused on pulse broadening and the characteristics of early-arriving photons.

Main Results:

• Transmitted pulse broadening increased with tissue thickness.
• A distinct ballistic pulse was absent in thinner tissues due to continuous dielectric variations and scattering.
• Early-arriving photons formed a broadened portion of the transmitted pulse.

Conclusions:

• Despite the absence of a clear ballistic pulse, early-arriving photons can be utilized for imaging.
• Submillimeter resolution imaging of opaque objects within 6.5 mm of biological tissue is achievable by selecting these early photons.