Coherent’s patented THz-Raman® Spectroscopy Systems combine chemical detection and structural analysis in one instrument. These systems are saving time and money; improving forensic and scientific analysis; and delivering faster, more reliable results across a wide variety of applications.
Key challenges for the pharmaceutical industry include polymorph identification, raw material quality control, and detection of counterfeit drugs. THz-Raman® reveals “structural fingerprints” that can rapidly differentiate polymorphs, isomers, conformers, co-crystals, and other structural variations of substances and compounds. Combining both structural and chemical measurements saves time, lowers costs, and improves measurement reliability.
Measurement and control of reactions, crystallization rates and/or amorphous states is increasingly important across the chemical, pharmaceutical and electronics industries. Clear, unambiguous determination of material structure (such as polymorphs), crystallinity, and phase is essential to chemical process development, formulation and material system characterization. Most measurement modalities require special sample preparation for offline, destructive analysis and can’t provide real-time feedback.
Explosives Detection and Source Attribution
THz-Raman® goes beyond chemical detection to reveal a “structural fingerprint” that can be attributed to specific ingredients, methods of manufacture, and storage/handling of many popular home-made explosive (HME) materials. This provides the warfighter and forensic expert with the means to gather information about both “what” they have found and “who” is responsible.
Graphene and carbon nanotubes are just two of the many nanomaterials that exhibit strong low-frequency signals. For Graphene, THz-Raman® analysis can determine the number of monolayers, and for carbon nanotubes, the diameter of the structure. Differences in structural characteristics and defects in crystals can also be detected.
Gas Sensing and Petrochemicals
THz-Raman® reveals the rotational modes of gases, with much higher signal strength than traditional chemical fingerprint spectra (from vibrational modes). This allows for very sensitive detection of some gases and analysis of mixtures.
Mineralogy and Gemology
The highly crystalline nature of most minerals and gems typically generate strong, differentiable THz-Raman signals, improving spectral libraries for forensic analysis and research.
Raman spectroscopy has rapidly gained acceptance as an invaluable tool for detecting, quantifying, and analyzing the chemical composition of materials across a broad range of industries, enabling faster, easier, less expensive, more compact, and even portable spectral analysis for an ever-broadening list of applications. However many material characterization tasks require the analysis of the molecular structure of a substance as well as deciphering its chemical constituents and concentrations. Molecular structure is important because molecules can exist in different or “polymorphic” forms that can significantly impact their chemical, optical, electromechanical, and/or biological properties. Additionally, molecular structure can be indicative of formulation/synthesis methods, storage and environmental exposures (heat, moisture), and contaminants.
Today, structural chemistry is principally the domain of x-ray diffraction (XRD), Fourier transform infrared (FTIR), and terahertz (THz) absorption spectroscopy. Unfortunately, these techniques can be destructive, expensive, and/or require large sample sizes and preparation, and in some cases are further limited by physical form of the sample (gas, liquid, or solid) or experimental conditions (such as the presence of moisture or air). Coherent’s patented VHG-based THz-Raman® systems extend Raman into the terahertz/low frequency/low wavenumber regime, delivering both chemical identification and structural analysis in a simplified, one-measurement solution.
As with all Raman systems, THz-Raman® spectroscopy is inherently nondestructive, non-invasive, works with trace amounts of any substance in nearly any lab or field environment, and requires no sample preparation. However, THz-Raman systems cover both anti-Stokes and Stokes shifts from <-3000cm-1 to > 3000cm-1 (depending on spectrometer range), while only blocking the Rayleigh excitation frequency to within about +/- 5 cm-1 . This allows probing of low-energy vibrations in terahertz frequencies (also known as low frequency, or low wavenumber regions), which correlate to molecular structure.
The various spectral regions are shown schematically:
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