Polymer identification via undetected photons using a low footprint nonlinear interferometer

Area of Science:

• Spectroscopy
• Environmental Science
• Materials Science

Background:

• Plastic pollution, including microplastics, is a pervasive global environmental challenge.
• Current monitoring methods like Raman and FTIR spectroscopy lack the portability and speed required for widespread contamination assessment.
• Mid-infrared (MIR) spectroscopy is crucial for material identification but typically requires bulky equipment.

Purpose of the Study:

• To develop a compact, portable, and rapid spectroscopy system for plastic identification.
• To demonstrate the capability of nonlinear interferometer (NLI) technology for retrieving MIR absorption spectra using near-infrared (NIR) photon detection.
• To enable real-time environmental monitoring of plastic contamination.

Main Methods:

• A micro-integrated, thermally-stabilized nonlinear interferometer (NLI) with a Michelson-like geometry was designed and fabricated.
• The NLI operates by detecting NIR signal photons to retrieve MIR absorption spectra, bypassing the need for MIR detectors.
• Performance was benchmarked at room temperature, measuring common polymers like polypropylene, polyethylene, and polystyrene.

Main Results:

• The NLI system achieved a signal-to-noise ratio of 34 at a measurement rate of 100 Hz.
• A spectral resolution of 6 cm^-1 was demonstrated.
• Characteristic vibrational absorption spectra of common polymers were accurately and rapidly retrieved without using MIR technology.

Conclusions:

• The developed compact NLI module is a viable technology for rapid, portable plastic identification.
• This system offers a promising platform for robust, real-time environmental monitoring of plastic pollution.
• The NLI technology has potential applications beyond environmental monitoring, including other MIR spectroscopy applications.