Abstract
We demonstrate rapid vibrational imaging based on sum frequency generation (SFG) microscopy with a collinear excitation geometry. Using the tunable picosecond pulses from a high-repetition-rate optical parametric oscillator, vibrationally selective imaging of collagen fibers is achieved with submicrometer lateral resolution. We furthermore show simultaneous SFG and second harmonic generation imaging to emphasize the compatibility of the microscope with other nonlinear optical modalities.
Highlights
VR-sum frequency generation (SFG) has been extensively used to study the orientation and dynamics of chemical compounds at planar interfaces [3,4,5,6], its unique vibrational contrast has not found widespread use in microscopic imaging
We demonstrate a Vibrationally resonant sum frequency generation (VR-SFG) microscope that overcomes many of the existing shortcomings of this imaging technique
The generated nonlinear signal is detected in both the forward and epi directions by photomultiplier tubes (PMT). 632 ± 22 nm bandpass filters were used for the epi PMT for capturing the SFG signal, while the second-harmonic generation (SHG) signal was simultaneously collected in the forward PMT with 400 ± 40 nm bandpass filters
Summary
VR-SFG has been extensively used to study the orientation and dynamics of chemical compounds at planar interfaces [3,4,5,6], its unique vibrational contrast has not found widespread use in microscopic imaging. Mid-IR radiation from low repetition rate (Hz–kHz), high pulse energy (μJ–mJ) laser systems used in VR-SFG microscopes [7] provide an unfavorable balance between sample damage and signal integration time. An objective lens has been used to focus the visible/near-IR beam, while the mid-IR radiation is applied in a wide-field illumination geometry [13].
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