Abstract
We demonstrate a multi-color background-free coherent anti-Stokes Raman scattering (CARS) imaging system, using a robust, all-fiber, low-cost, multi-wavelength time-lens source. The time-lens source generates picosecond pulse trains at three different wavelengths. The first is 1064.3 nm, the second is tunable between 1052 nm and 1055 nm, and the third is tunable between 1040 nm and 1050 nm. When the time-lens source is synchronized with a mode-locked Ti:Sa laser, two of the three wavelengths are used to detect different Raman frequencies for two-color on-resonance imaging, whereas the third wavelength is used to obtain the off-resonance image for nonresonant background subtraction. Mixed poly(methyl methacrylate) (PMMA) and polystyrene (PS) beads are used to demonstrate two-color background-free CARS imaging. The synchronized multi-wavelength time-lens source enables pixel-to-pixel wavelength-switching. We demonstrate simultaneous two-color CARS imaging of CH2 and CH3 stretching vibration modes with real-time background subtraction in ex vivo mouse tissue.
Highlights
Coherent Raman scattering (CRS) microscopy, with contrast from coherent anti-Stokes Raman scattering (CARS) [1,2] or stimulated Raman scattering (SRS) [3], is a valuable imaging technique that overcomes some of the limitations of spontaneous Raman microscopy
We demonstrate the capability of the multi-wavelength time-lens source by performing simultaneous two-color CARS imaging of CH2 and CH3 stretching vibration modes with real-time nonresonant background subtraction
The channels are combined by a wavelength division multiplexer (WDM)
Summary
Coherent Raman scattering (CRS) microscopy, with contrast from coherent anti-Stokes Raman scattering (CARS) [1,2] or stimulated Raman scattering (SRS) [3], is a valuable imaging technique that overcomes some of the limitations of spontaneous Raman microscopy. Multiple methods have been used to suppress or eliminate nonresonant background in order to retrieve pure Raman responses, including polarization-sensitive detection [15], time-resolved detection [16], frequency modulation [17,18], and nonlinear interferometric vibrational imaging [19] These techniques are limited by either resonant signal attenuation or complicated implementation. The capability of synchronization with any mode-locked laser is the most appealing advantage of the time-lens source, apart from other benefits such as robust all-fiber configuration, picosecond pulse width, and high peak power. We demonstrate the capability of the multi-wavelength time-lens source by performing simultaneous two-color CARS imaging of CH2 and CH3 stretching vibration modes with real-time nonresonant background subtraction
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