Aleksander K. Gluszek

Compact CH4 sensor system based on a continuous-wave, low power consumption, room temperature interband cascade laser

A tunable diode laser absorption spectroscopy-based methane sensor, employing a dense-pattern multi-pass gas cell and a 3.3 μm, CW, DFB, room temperature interband cascade laser (ICL), is reported. The optical integration based on an advanced folded optical path design and an efficient ICL control system with appropriate electrical power management resulted in a CH4 sensor with a small footprint (32 × 20 × 17 cm3) and low-power consumption (6 W). Polynomial and least-squares fit algorithms are employed to remove the baseline of the spectral scan and retrieve CH4 concentrations, respectively. An Allan-Werle deviation analysis shows that the measurement precision can reach 1.4 ppb for a 60 s averaging time. Continuous measurements covering a seven-day period were performed to demonstrate the stability and robustness of the reported CH4 sensor system.

Mid-infrared dual-gas sensor for simultaneous detection of methane and ethane using a single continuous-wave interband cascade laser

A continuous-wave (CW) interband cascade laser (ICL) based mid-infrared sensor system was demonstrated for simultaneous detection of atmospheric methane (CH₄) and ethane (C₂H₆). A 3.337 µm CW ICL with an emitting wavenumber range of 2996.0-3001.5 cm^-1 was used to simultaneously target two absorption lines, C₂H₆ at 2996.88 cm^-1 and CH₄ at 2999.06 cm^-1, respectively. The sensor performance was first evaluated for single-gas detection by only targeting the absorption line of one gas species. Allan deviations of 11.2 parts per billion in volume (ppbv) for CH₄ and 1.86 ppbv for C₂H₆ with an averaging time of 3.4 s were achieved for the detection of these two gases. Dual-gas detection was realized by using a long-term scan signal to target both CH₄ and C₂H₆ lines. The Allan deviations increased slightly to 17.4 ppbv for CH₄ and 2.4 ppbv for C₂H₆ with an averaging time of 4.6 s due to laser temperature and power drift caused by long-term wavelength scanning. Measurements for both indoor and outdoor concentration changes of CH₄ and C₂H₆ were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost compared to two separate sensor systems.

Mid-Infrared Trace Gas Sensor Technology Based on Intracavity Quartz-Enhanced Photoacoustic Spectroscopy

The application of compact inexpensive trace gas sensor technology to a mid-infrared nitric oxide (NO) detectoion using intracavity quartz-enhanced photoacoustic spectroscopy (I-QEPAS) is reported. A minimum detection limit of 4.8 ppbv within a 30 ms integration time was demonstrated by using a room-temperature, continuous-wave, distributed-feedback quantum cascade laser (QCL) emitting at 5.263 µm (1900.08 cm−1) and a new compact design of a high-finesse bow-tie optical cavity with an integrated resonant quartz tuning fork (QTF). The optimum configuration of the bow-tie cavity was simulated using custom software. Measurements were performed with a wavelength modulation scheme (WM) using a 2f detection procedure.

Infrared Dual-Gas CH4/C2H6Sensor Using Two Continuous-Wave Interband Cascade Lasers

An infrared dual-gas sensor system for the simultaneous detection and monitoring of methane (CH₄) and ethane (C₂H₆) at parts-per-billion by volume (ppbv) concentration levels was developed using two room temperature, distributed feedback interband cascade lasers, and two miniature multipass cells with an effective absorption length of 54.6 m. Laser direct absorption spectroscopy was used to detect CH₄ utilizing the 3038.5-cm^-1 absorption line, and second-harmonic wavelength modulation spectroscopy method was used to detect C₂H₆ using the 2996.88-cm^-1 absorption line. The 1σ CH₄ detection limit is ~2.7 ppbv with a 1-s averaging time and exhibits a minimum value of ~1.7 ppbv for a 9-s averaging time; the 1σ C₂H₆ detection limit is ~2.6 ppbv with a 3.4-s averaging time and shows an optimum averaging time of 65 s corresponding to a stability of ~0.36 ppbv. Using the dualgas sensor system, 24 h monitoring of the two atmospheric gases was performed in the Greater Houston area, TX, USA.

Terahertz trace gas spectroscopy based on a fully-electronic frequency-comb radiating array in silicon

A silicon integrated circuit is reported for radiating picosecond pulses with tunable repetition rate, covering frequencies from 30 GHz to 1.03 THz. This source is used in a gas spectroscopy setup to measure the absorption lines of ammonia and water in the terahertz region.

CW DFB-QCL- and EC-QCL-based sensor for simultaneous NO and NO2 measurements via frequency modulation multiplexing using multi-pass absorption spectroscopy

Nitrogen oxides (NOx), including nitric oxide (NO) and nitrogen dioxide (NO2) play important roles in determining the photochemistry of the ambient atmosphere, controlling the production of tropospheric ozone, affecting the concentration levels of the hydroxyl radical, and forming acid precipitation. A sensor system capable of simultaneous measurements of NO and NO2 by using a commercial 76 m astigmatic multi-pass gas cell (MPGC) was developed in order to enable fastresponse NOx detection. A continuous wave (CW), distributed-feedback (DFB) quantum cascade laser (QCL) and a CW external-cavity (EC) QCL were employed for targeting a NO absorption doublet at 1900.075 cm-1 and a NO2 absorption line at 1630.33 cm-1, respectively. Both laser beams were combined and transmitted through the MPGC in an identical optical path and subsequently detected by a single mid-infrared detector. A frequency modulation multiplexing scheme was implemented by modulating the DFB-QCL and EC-QCL at different frequencies and demodulating the detector signal with two Labview software based lock-in amplifiers to extract the corresponding second-harmonic (2f) components. Continuous monitoring of NO and NO2 concentration levels was achieved by locking the laser frequencies to the selected absorption lines utilizing a reference cell filled with high concentrations of NO and NO2. The experimental results indicate minor performance degradation associated with frequency modulation multiplexing and no cross talk between the two multiplexed detection channels. The performance of the reported sensor system was evaluated for real time, sensitive and precise detection of NO and NO2 simultaneously.

Fully-monolithic single-active fiber difference frequency generation source for simultaneous multi-species gas sensing

Laser spectroscopy based trace gas detection systems are implemented in various applications: industry, medicine, homeland security, environmental monitoring and several more [1]. More sophisticated applications require simultaneous monitoring of several gas species, that possess strong absorption lines in the mid-IR wavelength region. This usually requires using several independent laser sources that will enable targeting the desired transitions of the analytes — for example relatively expensive quantum cascade lasers [2]. We propose a novel, multi-wavelength, fully-monolithic, fiber-based difference frequency generation mid-IR source, incorporating our patented dual-wavelength double-clad (DC) configuration, which enables amplification of ∼1.55 μm radiation and simultaneous generation of 1.064 μm wavelength [3-5]. Schematic is shown in Fig. 1.

Low energy consumption, compact setup for isotopie analysis of methane at 3007.95 cm −1 and 3008.39 cm −1 using room-temperature CW interband cascade laser (ICL)

Isotopie measurements of methane are very important for environment. The level of gas in the atmosphere has significant impact on its radiative forcing, increase is estimated to 0.48 W/m2 since pre-industrial times [1]. Isotopic ratio of carbon in CH4 provides information about the origin of the gas. The recent development of compact interband cascade lasers (ICLs) permits the targeting of strong fundamental rotational-vibrational transitions absorption lines at room temperature conditions with wide wavelength span. Therefore it is possible to build compact, robust, field deployable gas sensors [3].

Low power consumption quartz-enhanced photoacoustic gas sensor employing a quantum cascade laser in pulsed operation

We report here an analysis of the performance of a quartz-enhanced photoacoustic (QEPAS) system operating in a pulsed mode by employing a quantum cascade laser (QCL). The QEPAS system is based on a quartz tuning fork (QTF) having fundamental resonance frequency of 4.2 kHz and a first overtone resonance of 25.4 KHz. Water vapor was used as a target gas by selecting its absorption line falling at 1296.5 cm-1 with a line strength of 1.69⋅10-22 cm/molecule. The QEPAS signal was investigated, while varying the QCL duty-cycle from continuous wave operation, down to 5%, which corresponds to a laser power consumption of 0.17 mW and a pulse-width of 4 μs.

A compact mid-infrared dual-gas CH4/C2H6 sensor using a single interband cascade laser and custom electronics

A compact mid-infrared (MIR) dual-gas sensor system was demonstrated for simultaneous detection of methane (CH4) and ethane (C2H6) using a single continuous-wave (CW) interband cascade laser (ICL) based on tunable laser absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS). Ultracompact custom electronics were developed, including a laser current driver, a temperature controller and a lock-in amplifier. These custom electronics reduce the size and weight of the sensor system as compared with a previous version based on commercial electronics. A multipass gas cell with an effective optical length of 54.6 m was employed to enhance the absorption signal. A 3337 nm ICL was capable of targeting a C2H6 absorption line at 2996.88 cm-1 and a CH4 line at 2999.06 cm-1. Dual-gas detection was realized by scanning both the CH4 and C2H6 absorption lines. Based on an Allan deviation analysis, the 1 σ minimum detection limit (MDL) was 17.4 ppbv for CH4 and 2.4 ppbv for C2H6 with an integration time of 4.3 s. TDLAS based sensor measurements for both indoor and outdoor mixing ratios of CH4 and C2H6 were conducted. The reported single ICL based dual-gas sensor system has the advantages of reduced size and cost without influencing the midinfrared sensor detection sensitivity, selectivity and reliability.