Fiber-based tunable repetition rate source for deep tissue two-photon fluorescence microscopy.

Area of Science:

• Biomedical Optics
• Neuroimaging
• Laser Physics

Background:

• Deep tissue multiphoton imaging demands high peak laser power for signal enhancement and low average power to mitigate thermal damage.
• Conventional methods often adjust average power, which can compromise imaging quality or safety.
• Optimizing laser parameters is crucial for effective in vivo studies.

Purpose of the Study:

• To investigate the impact of laser repetition rate tuning on deep tissue multiphoton imaging performance.
• To identify the optimal repetition rate range for deep two-photon imaging in the mouse brain.
• To develop and evaluate a novel fiber-based laser source with tunable repetition rate for enhanced imaging.

Main Methods:

• Utilized a fiber-based laser source with an arbitrarily tunable repetition rate between 1 and 10 MHz.
• Performed comparative in vivo imaging of mouse brain vasculature using the developed fiber source and a standard mode-locked Ti:Sapphire (Ti:S) laser.
• Quantified imaging performance by measuring signal strength and required average power at different repetition rates.

Main Results:

• The ideal repetition rate for deep two-photon imaging in the mouse brain was determined to be between 1 and 10 MHz.
• The fiber-based laser source demonstrated effective tunability within the identified optimal range.
• At 2.5 MHz, the fiber source achieved equivalent signal intensity to a Ti:S laser at 80 MHz, but with 5.1 times less average power.

Conclusions:

• Laser repetition rate tuning is a superior strategy to average power adjustment for optimizing deep tissue multiphoton imaging.
• The developed fiber laser source offers a practical and efficient solution for deep brain imaging applications.
• This approach enhances signal quality and reduces thermal load, paving the way for improved in vivo neuroscience research.