We have recently acquired a new-generation, state-of-the art, Raman spectrometer with imaging capability and multi-wavelength excitation. A Raman imaging system will provide molecular maps (similar to the element map provided by an electron microprobe). It will collect a Raman image cube from a sample, then generate a map of minerals, molecular species (H2O/OH), and chemical bonds (e.g., C-H, N-H, C-O, C-C, etc). The spatial distributions and spatial correlations of various species will reveal evidences of past physic-chemical-biologic processes, as well as the genetic relationships among the different species. A Raman system with multiple excitation laser wavelengths is capable of studying a wide variety of materials. A different excitation wavelength will affect the Raman cross sections of materials, sometimes enhancing Raman signals by inducing a Raman resonance effect. More importantly, different excitation wavelengths can help overcome the interference of fluorescence generated by some targets.
Raman imaging system – Renishaw InVia
- Five laser wavelengths for Raman excitation from UV to NIR: 325 nm, 442 nm, 532 nm 633 nm, and 785 nm
- A Raman spectrometer with high spectral resolution (~ 1 cm-1) and wide spectral range (50- 4000 cm-1) for all five excitation wavelengths
- A microscope with high accuracy moving stage and a wide range of microscopic objectives, 5x, 10x, 20xLWD, 50x, 50xLWD, and 100xLWD
- A microscope with cross-polarization for transmitted light and reflected light for visualization and B/W mosaic imaging
- Three ways to take Raman spectra and five ways to take Raman images
- Highest special resolution of 200-300 nm in X-Y direction and 500 nm in Z direction
- Solid samples. Rock chips (less than 1 kg, less than 5 cm height), soils or powders, single gains, films, etc, and no sample preparations are needed. Double-side flat cut surfaces would be preferred for taking Raman images.
- Thin or thick sections. Super-glue is better than epoxy for thin section; the cover slide and carbon coating (if there is any) should be removed.
- Liquid samples. Prepare in glass bottle, glass capillary, liquid cell, or petri dish.
The funds for purchasing this top-level Raman imaging system are from NASA Mars Fundamental Research program, specifically the Planetary Major Equipment program, and from Washington University in St. Louis, specifically the School of Arts & Sciences, Department of Earth and Planetary Sciences, and McDonnell Center for Space Sciences.