“…As opposed to the continuous, large bandwidth spectrum needed to be acquired by FT- spectrometers, emerging laser technologies offer higher intensities, shorter acquisition times and computer-controlled spectral accuracy. In particular, bright quantum cascade lasers (QCL) have facilitated the development of new-generation rapid imaging, − and promised a better trade-off between analyte localization, scanning speed, and spectral SNR. − QCL-based instruments also allow tuning to specific vibrational bands of interest for fast (time-resolved) sensing − and discrete frequency IR (DFIR) imaging, − while their intrinsically narrow spectral linewidth also provides a unique advantage for applications requiring high spectral resolution. − However, QCL outputs are relatively noisy , – with external cavity (EC), pulsed, and widely tunable configurations being most notably so–yet, they are also the most appropriate design choice for broad-bandwidth mid-IR spectral measurements. − In general, QCL-based spectroscopy is limited by optical power instability that offsets advantages associated with high-intensity throughput. ,, This noise directly affects absorbance measurements and longer acquisitions become necessary to converge on a precise estimate, usually involving hundreds to thousands of pulses. , Alternatively, lock-in demodulation at the pulsing frequency can also be used to estimate average intensity but causes an increase in integration time per spectral band and/or longer spatial dwell time per pixel. Data collected with longer integration times may also suffer from system drift and water vapor variations whereas larger pixel dwell times become the bottleneck for high-resolution, wide-coverage imaging.…”