The goal of this project is to build a new, robust, and compact source for Coherent anti-Stokes Raman Spectroscopy (CARS) microscopy based on fiber lasers. CARS is a potentially powerful technique for microscopy because the molecular identity of cellular components (e.g. lipids, proteins, or DNA) can be imaged without the need for fluorescence labeling. Optical sectioning is intrinsic to the CARS process because of the nonlinear dependence on pulse intensity. In addition, near-infrared wavelengths can be used for increased tissue penetration. Therefore, CARS microscopy has the potential to be an important biomedical and clinical tool. However, the laser sources required are typically bulkly, expensive and hard to handle, and as a result CARS microscopy has so far found limited application. We propose to develop a technique based on fiber lasers: Fiber Laser EXcitation CARS ("FLEX- CARS"), which uses a single fiber laser as the source of pump and "Stokes" pulses. A nonlinear optical fiber (photonic crystal fiber) will be used to shift the wavelength of the Stokes pulses. As a result, pump, probe, and Stokes are automatically synchronized in time. We will develop FLEX- CARS based on a fiber laser at 1030 nm. The frequency resolution of FLEX-CARS will be significantly improved by a novel pulse "chirping" method that utilizes the full pulse power of pump and Stokes pulses. The wavelength of the Stokes beam can be tuned or switched rapidly on the microsecond time scale, allowing new methods to probe multiple vibrational frequencies. Signal quality will be enhanced by rejection of nonresonant background components through the implementation of polarization and time-delay methods to select the vibrationally resonant signal. The unique capability for fast wavelength switching in the proposed system also makes frequency modulated (FM) CARS straightforward, which helps further rejection of non-resonant background. FLEX-CARS will be applied first to standard samples and then to brain tissue to demonstrate the potential of the method as a robust system for CARS microsocpy.

Public Health Relevance

Upon completion of the project, we expect to have built and demonstrated a new, robust, flexible and relatively inexpensive source for CARS microscopy. A CARS system based on a single fiber laser will enable greatly simplified CARS systems and make state-of-the-art techniques of CARS microscopy accessible not only to top research institutions, but also in clinical and biomedical research settings.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Exploratory/Developmental Grants (R21)
Project #
8R21GM103478-02
Application #
8298124
Study Section
Special Emphasis Panel (ZRR1-BT-7 (01))
Program Officer
Friedman, Fred K
Project Start
2011-08-01
Project End
2014-07-31
Budget Start
2012-08-01
Budget End
2013-07-31
Support Year
2
Fiscal Year
2012
Total Cost
$175,482
Indirect Cost
$50,482
Name
University of Kansas Lawrence
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
076248616
City
Lawrence
State
KS
Country
United States
Zip Code
66045
Su, Jue; Xie, Ruxin; Johnson, Carey K et al. (2013) Single fiber laser based wavelength tunable excitation for CRS spectroscopy. J Opt Soc Am B 30:1671-1682