Forward-deployed security personnel and warfighters have to quickly and reliably determine various compounds or residues found in the field to differentiate between inert materials and home-made explosive (HME) compounds. Forensic experts require timely data to find those responsible, and contain the propagation of HME attacks.
Reliable, rapid and timely data is helpful to contain the proliferation of HME attacks.
Raman spectroscopy is a proven technique for chemical identification. However, existing techniques can sometimes produce incorrect readings, and cannot be used to determine “Who made it?”
Forensic experts need data relating to ingredient sources, manufacturing methods (or synthetic pathways), and contaminants, and the formulation technique and storage environment that offers information on where it was created. To obtain this additional information, special sample handling and preparation methods, and large, expensive equipment are essential.
Low-frequency/THz-Raman analysis identifies and differentiates ingredients, (Figure 1) formulations, and synthetic pathways. It also shows changes regarding environment and storage (such as heat and humidity).
These factors can reveal “fingerprints” or “signatures” in the molecular structure, with which forensic specialists can narrow or speed up their hunt for the perpetrator.
THz-Raman® systems extend the range of conventional Raman spectroscopy to the THz/low frequency regime, where differentiation of inter- and intra-molecular structures is clearly visible. Anti-Stokes signals also improve SNR, and add to Raman intensity.
Figure 1. Multiple samples of ETN, representing systematic variations in primary ingredients as well as types of acids, salts, and preparation routes, show distinctive differences.
The key features and advantages of the Coherent systems are as follows:
- Fast, simultaneous capture of structural and chemical data
- Improved reliability and sensitivity due to additional low frequency anti-Stokes signals
- Works with small traces of materials
- No sample preparation required
- Simple, compact, and cost-effective
- Non-contact and non-destructive
- Works at standoff distance
- Miniaturization is possible for portable or field use
Single System Handles THz-Raman and Fingerprint Region Measurements
Figure 2 shows THz-Raman analysis of hexamethylene triperoxide diamine (HMTD) and ammonium nitrate. The distinctive peaks in the low-frequency/THz-Raman region (green background) are higher than the traditional fingerprint range.
This adds signal, enhances sensitivity, and lowers false positives. Peak symmetry about the excitation line enables improved data, auto-calibration, and system reliability.
Figure 2. THz-Raman analysis of HMTD and ammonium nitrate.
With the patented THz-Raman® spectroscopy system from Coherent, the Raman spectroscopy range is expanded into the THz/low frequency regime. Consequently, it is possible to explore energy transitions with the same range of THz spectroscopy without limiting the capability to measure the fingerprint region.
Chemical composition and molecular structure can be analyzed simultaneously for advanced materials characterization.
Coherent offers a complete range of compact and robust THz-Raman® systems. The plug-and-play platforms are user-friendly, and offer superior throughput and speed at an affordable cost. They have a number of optional polarization control, sample interfaces, and a broad excitation wavelength range of 488 - 1064 nm, making them suitable for any applications.
Figure 3. THz-Raman® systems showing benchtop, probe and microscope configurations.
This information has been sourced, reviewed and adapted from materials provided by Coherent.
For more information on this source, please visit Coherent.