Here we report our recent achievements towards a compact, portable, handheld device for contactless real-time detection and identification of explosives and hazardous substances via reflectance spectroscopy in the 7.5 μm – 10 μm spectral region. The mid-IR spectroscopic measurement principle relies on selective illumination of the target using broadly tunable external cavity quantum cascade lasers (EC-QCLs). A resonant micro-opto-electro-mechanical systems (MOEMS) grating enables fast wavelength tuning in the external cavity, allowing the full spectral scan to be completed in <1 ms. The diffusely backscattered light’s intensity dependence on illumination wavelength provides spectroscopic information to identify threat compounds via our spectral database, containing a large number of materials relevant in a security context. We present a handheld portable, albeit tethered, device capable of real-time identification of hazardous substances at a range of 1 m. We will outline future improvements to increase the system’s usability, such as integrated computing power, automated focusing to that allow use over a range of detection distances and spatial scanning for background subtraction.
We report on mid-IR spectroscopic measurements performed with rapidly tunable external cavity quantum cascade lasers (EC-QCLs). Fast wavelength tuning in the external cavity is realized by a microoptoelectromechanical systems (MOEMS) grating oscillating at a resonance frequency of about 1 kHz with a deflection amplitude of up to 10 deg. The entire spectral range of the broadband QCL can therefore be covered in just 500 μs, paving the way for real-time spectroscopy in the mid-IR region. In addition to its use in spectroscopic measurements conducted in backscattering and transmission geometry, the MOEMS-based laser source is characterized regarding pulse intensity noise, wavelength reproducibility, and spectral resolution.