Stand-off spatial offset Raman spectroscopy for the detection of concealed content in distant objects.

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Laser Technology

Background:

• Remote analysis of materials is crucial for various applications, including security and quality control.
• Traditional Raman spectroscopy can be limited by surface interference and container opacity.

Purpose of the Study:

• To develop and validate a remote Raman spectroscopy method for analyzing the contents of concealed objects.
• To overcome challenges posed by opaque containers and fluorescent surfaces in remote Raman analysis.

Main Methods:

• Utilized a pulsed frequency-doubled Nd:YAG laser (10 Hz, 4.4 ns pulse) for Raman scattering generation at 12 m.
• Employed a 6-inch telescope for scattered light collection, coupled with an Acton SP-2750 spectrograph and gated intensified charge-coupled device (ICCD) detector.
• Implemented a spatial offset technique between the laser excitation point and the telescope's focal point on the sample.

Main Results:

• Achieved high-quality Raman spectra from solid (NaClO(3)) and liquid (isopropyl alcohol) samples within 10 seconds.
• Successfully analyzed contents through 1.5 mm thick opaque low-density polyethylene (LDPE) plastic bottles.
• Demonstrated effective analysis of isopropyl alcohol in a highly fluorescent plastic container using the spatial offset method.

Conclusions:

• The developed spatial offset technique significantly enhances the ability to perform remote Raman spectroscopy on concealed materials.
• This method is effective for analyzing substances within opaque and/or fluorescent containers, broadening the applicability of remote Raman analysis.
• The technique offers rapid and clear spectral acquisition, promising for real-time material identification in challenging environments.