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We demonstrate instrumentation and methods to enable fluorescence-detected photothermal infrared (F-PTIR) microscopy, then demonstrate the utility of F-PTIR to characterize the composition within phase-separated domains of model amorphous solid dispersions (ASDs) induced by water sorption. In F-PTIR, temperature-dependent changes in fluorescence quantum efficiency are shown to sensitively report on highly localized absorption of mid-infrared radiation. The spatial resolution with which infrared spectroscopy can be performed is dictated by fluorescence microscopy, rather than the infrared wavelength. Following proof of concept F-PTIR demonstration on model systems of polyethylene glycol (PEG) and silica gel, F-PTIR enabled the characterization of chemical composition within inhomogeneous ritonavir / polyvinylpyrrolidone-vinyl acetate (PVPVA) amorphous dispersions. Phase separation is implicated in the observation of critical behaviors in ASD dissolution kinetics, with the results of F-PTIR supporting the formation of phase-separated drug-rich domains upon water absorption in spin-cast films., 5 pages, 4 figures

Building on our previous development of a compact, portable, and low SWaP gas analyzer (11” x 6.7” x 5.1”, 7.8 lbs) based on photoacoustic spectroscopy and using broadband quantum cascade laser arrays, we demonstrate here compositional analysis of airborne aerosols using this instrument. With an integration time of 330-ms per laser, and ~70 seconds for a spectrum covering 950-1500 cm-1, our instrument showed a detection sensitivity at the mg/m3 level for solid and liquid-loaded solid aerosols. Additionally, Malathion-loaded aerosols can be discriminated from pure Syloid aerosols based on their absorption features. The preliminary results show a potential path for developments of a portable real-time aerosol composition analyzer.

Mid-infrared spectral “fingerprints” of many hazardous and harmful gaseous substances are characterized by broad absorption bands, resulting from the merging of several absorption lines corresponding to ro-vibrational transitions. Broadband absorption spectroscopy is fundamental to detect and discriminate these substances. Here we report on a quartz-enhanced photoacoustic spectroscopy sensor for broadband absorbers detection, employing a monolithic array of 32, individually addressable, distributed-feedback quantum cascade lasers as the excitation source. This light source combines a fast tuning speed with a large tuning range, from 1190 cm−1 to 1340 cm−1 together with a high stability. The QEPAS sensor was tested for nitrous oxide (N2O) and methane (CH4) detection, exhibiting absorption features in the laser source emission spectral range. The two broad P- and R- absorption branches of N2O have been accurately reconstructed, as well as several absorption features of CH4, for gas concentrations ranging from 200 to 1000 part-per-million in nitrogen.

We report a portable broadband photoacoustic spectroscopic system for trace gas detection using distributed feedback quantum cascade laser arrays. By sequentially firing 128 lasers, our system acquires a photoacoustic spectrum covering 565 c m − 1 ( 935 − 1500 c m − 1 ) with a normalized-noise-equivalent-absorption coefficient of 2.5 × 10 − 9 c m − 1 W H z − 1 / 2 . The firing sequence that determines when and which laser to activate is programmable, which enables frequency-multiplexing excitation. For demonstration, 12 lasers are modulated simultaneously at distinct frequencies, and a photoacoustic spectrum is acquired within 13 ms. The compactness ( 28 c m × 17 c m × 13 c m , 3.5 kg) and low power consumption enable convenient installation for on-site monitoring.

We present a portable broadband photoacoustic spectroscopic system for trace gas or aerosol detection using distributed feedback quantum cascade laser arrays. By sequentially firing 128 lasers, our system acquires a photoacoustic spectrum covering 565 cm-1 (935-1500 cm-1) with a normalized-noise-equivalent-absorption coefficient of 2.5×10-9 cm−1WHz−1/2. In addition to sequential firing mode, the laser source can be operated in multiplexing mode. The firing sequence that determines when and which laser to be activated is programmable, which enables frequency-multiplexing excitation. For demonstration, we modulate 12 lasers at 12 distinct frequencies and a photoacoustic spectrum is acquired within 13 ms.

Graphical abstract, Highlights • Quartz-enhanced photoacoustic-based broadband detection is demonstrated. • Methane detection sensitivity of 200 ppb in 10 s integration time is achieved. • Multi-gas detection of mixtures of methane and nitrous oxide is demonstrated. • Analytes concentration is retrieved despite absorption spectra significant overlap., Here we report on the broadband detection of nitrous oxide (N2O) and methane (CH4) mixtures in dry nitrogen by using a quartz-enhanced photoacoustic (QEPAS) sensor exploiting an array of 32 distributed-feedback quantum cascade lasers, within a spectral emission range of 1190−1340 cm−1 as the excitation source. Methane detection down to a minimum detection limit of 200 ppb at 10 s lock-in integration time was achieved. The sensor demonstrated a linear response in the range of 200−1000 ppm. Three different mixtures of N2O and CH4 in nitrogen at atmospheric pressure have been analyzed. The capability of the developed QEPAS sensor to selectively determine the N2O and CH4 concentrations was demonstrated, in spite of significant overlap in their respective absorption spectra in the investigated spectral range.

We report on a quartz-enhanced photoacoustic (QEPAS) sensor employing a monolithic distributed-feedback quantum cascade laser array operating in a pulsed mode as a light source. The array consists of 32 quantum cascade lasers emitting in a spectral range from 1190 cm-1 to 1340 cm-1, which covers two absorption branches of nitrous oxide (N2O) and several absorption features of (CH4). The versatility of the QEPAS technique combined with the rapid wavelength tuning provided by the ultra-compact, low-power consuming laser source allowed the detection of N2O and CH4 with detection sensitivities below a part-per-million at atmospheric pressure.

Using rapidly-tunable quantum cascade laser arrays, we demonstrate acquisition of absorption spectra over 50cm-1 with < 0.1cm−1 resolution and a minimum detectable absorbance of 1 × 10−4 over the full spectrum in < 0.5s.

This article presents new spectroscopic results in standoff chemical detection that are enabled by monolithic arrays of Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs), with each array element at a slightly different wavelength than its neighbor. The standoff analysis of analyte/substrate pairs requires a laser source with characteristics offered uniquely by a QCL Array. This is particularly true for time-evolving liquid chemical warfare agent (CWA) analysis. In addition to describing the QCL array source developed for long wave infrared coverage, a description of an integrated prototype standoff detection system is provided. Experimental standoff detection results using the man-portable system for droplet examination from 1.3 meters are presented using the CWAs VX and T-mustard as test cases. Finally, we consider three significant challenges to working with droplets and liquid films in standoff spectroscopy: substrate uptake of the analyte, time-dependent droplet spread of the analyte, and variable substrate contributions to retrieved signals.

We present a gas sensing system based on quartz-enhanced photoacoustic spectroscopy (QEPAS) employing a monolithic distributed-feedback quantum cascade laser (QCL) array operated in a pulsed mode as a light source. The array consists of 32 quantum cascade lasers emitting in a spectral range from 1190 cm−1 to 1340 cm−1. The optoacoustic detection module was composed of a custom quartz tuning fork with a prong spacing of 1 mm, coupled with two micro-resonator tubes to enhance the signal-to-noise ratio. The QEPAS sensor was validated by detecting the absorption of the P- and R-branches of nitrous oxide. The measurements were performed by switching the array QCLs in sequence while tuning their operating temperature to retrieve the fine structure of the two N2O branches. A sensor calibration was performed, demonstrating a linear responsivity for N2O:N2 concentrations from 1000 down to 200 parts-per-million. With a 10 s lock-in integration time, a detection sensitivity of less than 60 parts-per-billion was achieved permitting the monitoring of nitrous oxide at global atmospheric levels.

This article presents new spectroscopic results in standoff chemical detection that are enabled by monolithic arrays of Distributed Feedback (DFB) Quantum Cascade Lasers (QCLs), with each array element at a slightly different wavelength than its neighbor. The standoff analysis of analyte/substrate pairs requires a laser source with characteristics offered uniquely by a QCL Array. This is particularly true for time-evolving liquid chemical warfare agent (CWA) analysis. In addition to describing the QCL array source developed for long wave infrared coverage, a description of an integrated prototype standoff detection system is provided. Experimental standoff detection results using the man-portable system for droplet examination from 1.3 meters are presented using the CWAs VX and T-mustard as test cases. Finally, we consider three significant challenges to working with droplets and liquid films in standoff spectroscopy: substrate uptake of the analyte, time-dependent droplet spread of the analyte, and variable substrate contributions to retrieved signals.

Predictable tuning behavior and stable laser operation are both crucial for laser spectroscopy measurements. We report a sampled grating quantum cascade laser (QCL) with high spectral tuning stability over the entire tuning range. We have determined the minimum loss margin required to suppress undesired lasing modes in order to ensure predictable tuning behavior. We have quantified power fluctuations and drift of our devices by measuring the Allan deviation. To demonstrate the feasibility of sampled grating QCLs for high-precision molecular spectroscopy, we have built a simple transmission spectroscopy setup. Our results prove that sampled grating QCLs are suitable light sources for highly sensitive spectroscopy measurements.

This presentation presents the spectroscopic concepts and results enabled by arrays of Distributed Feedback (DFB) QCLs, with each element at a slightly different wavelength than its neighbor. In optical systems, such as standoff detectors and in situ gas analyzers, this increases analyte sensitivity and selectivity by broadening spectral source coverage and by allowing for extremely fast all-electronic wavelength tuning with no moving parts. The QCL array is also an increasingly essential solution to the power scaling of QCLs. This talk will present the QCL array concept and our packaging systems before moving to discuss molecular spectroscopy results for a) multigas sensing, b) standoff explosives detection, and c) power scaling for directed energy.

Eos Photonics manufactures DFB QCL arrays, with each element unique wavelength. In spectroscopy systems, such as standoff detectors and gas analyzers, this enables broad coverage and fast, all-electronic wavelength tuning with no moving parts.

We demonstrate a double-waveguide quantum cascade laser (QCL) consisting of two full broadband QCLs vertically integrated into a single monolithic device. Up to 1.1W peak power at room temperature is obtained for this record thick QCL. Coupling between the two laser waveguides is minimized to reduce gain competition. Simultaneous lasing on Fabry-Perot modes separated by as much as 360 cm−1 is obtained. This design opens the route to high-power ultra-broadband mid-infrared sources.

A multiwavelength array of distributed feedback (DFB) quantum cascade lasers (QCLs) that spans λ = 8.28 to 9.62 μm is wavelength beam combined (WBC) using both single-grating and dual-grating designs. WBC with a single grating results in a pointing error of 3-times the beam divergence for a single laser and arises from the nonlinear dispersion of the grating. By adding a second grating to compensate for the nonlinear dispersion, the pointing error is reduced to only 13% of the beam divergence for a single laser. A transceiver based on the dual-grating-WBC QCL was used to measure the transmittance of a polymer sheet placed between itself and a retroreflector over a round-trip distance of 70 meters.