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Lasers, Optical spectroscopy, microscopy, and imaging

FWM and CARS imaging

We are constructing a four-wave mixing (FWM) spectrometer and a CARS imaging system. We will study various cells and marine bacteria using FWM spectroscopy and CARS imaging.

SFG microscopy and imaging

We have constructed an SFG microscope using IR focus lens, as well as SFG imaging equipment using a CCD detector. This will make possible the study of how polymers and proteins segregate into different domains at interfaces. Spatially resolved imaging will be a valuable extension of our previous surface studies.

Double Resonance SFG (DRSFG)

One of our SFG systems has been upgraded with double-resonance capability. In DR-SFG, the frequency of the UV-visible input beam is tuned to match electronic transitions of the molecule, just as the IR input beam is tuned to match vibrational transitions. This dramatically increases the sensitivity of SFG for the study of low concentrations and weak signals; double resonance also makes it possible to selectively study specific chemical groups (such as from a particular amino acid).

Holography

A dual-wavelength digital holography system has been constructed to study various cells and interactions between cells and nanoparticles.

Spectroscopy

1. Polarization Mapping

One great strength of SFG is the use of multiple polarized beams, which provides increased measurements for more reliable orientation determination. We have developed a polarization mapping method that uses multiple polarizations (including intermediate measurements) to reliably fit complicated SFG spectra, such as those obtained from proteins.

2. Chiral SFG

In certain cases, strong chiral SFG signals can be detected. These provide additional measurements that are useful for detailed structural studies, as was demonstrated for interfacial β-sheet peptides.