Münster 1999 – wissenschaftliches Programm
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CP: Chemische Physik
CP 16: Neue Methoden
CP 16.6: Vortrag
Dienstag, 23. März 1999, 17:30–17:45, Gg
Coherent Anti-Stokes Raman Scattering Microscopy — •Andreas Zumbusch1, Gary R. Holtom2, and X.Sunney Xie2 — 1Inst. Physikalische Chemie, Uni Muenchen, Sophienstr. 11, 80333 Muenchen — 2PNNL, EMSL, P.O. Box 999, Richland, Washington 99352, USA
We report a new nonlinear optical method for high resolution microscopy which is based on Coherent Anti-Stokes Raman Scattering ( CARS ). The method is complementary to confocal and two-photon fluorescence microscopy, which find widespread applications. Unlike these techniques native fluorescence or stain is not required, yet the capability to reconstruct 3D images is preserved.
CARS is a special case of four-wave mixing. Molecular properties are contained in the third-order susceptibility. When the difference in frequency of a pump laser and a signal wave at lower frequency is equal to a molecular vibration, the third-order susceptibility becomes resonant, and the detected signal rises substantially. Thus a vibrational contrast mechanism is established and vibrational spectroscopical selectivity is obtained by tuning the frequency difference of the two exciting lasers.
Two amplified laser beams at 850 nm ( fixed ) and 1.15 microns ( tunable ) with pulse widths of 200 fs are focused onto the sample with a high numerical aperture lens. The sample is moved with a piezo scanning unit, while the signal is collimated by an identical lens, passed through a bandpass filter and detected with a photomultiplier.
Using this technique, a spatial resolution of 300 nm in the xy-plane and 1.2 microns in z-direction at a spectral resolution of 50 wavenumbers are demonstrated. The necessary average power levels of less than 0.1 mW allow us to acquire images of living biological samples.