The detection and measurement of gas concentrations using the characteristic optical absorption of the gas species is important for both understanding and monitoring a variety of phenomena from industrial processes to environmental change. This study reviews the field, covering several individual gas detection techniques including non-dispersive infrared, spectrophotometry, tunable diode laser spectroscopy and photoacoustic spectroscopy. We present the basis for each technique, recent developments in methods and performance limitations. The technology available to support this field, in terms of key components such as light sources and gas cells, has advanced rapidly in recent years and we discuss these new developments. Finally, we present a performance comparison of different techniques, taking data reported over the preceding decade, and draw conclusions from this benchmarking.

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Optical gas sensing: a review

测定：FVC需要测试者尽力呼出肺内气体，这一过程约需20s，老年人或有严重肺疾病患者的体力常不堪耐受。常规的FVC测定值也会因气道阻塞者或健康高龄人的呼气时间而受影响。作者使用6s内用力呼气量(FEV6.0)代替FVC作为肺功能指标，探讨其对诊断气道阻塞和呼吸受限的优越性。

用FEV6．0代替FVC诊断气道阻塞和肺功能受限[英]／Swanney MP…∥Am J Respir Crit Care Med．

We review the current status of interband cascade lasers (ICLs) emitting in the midwave infrared (IR). The ICL may be considered the hybrid of a conventional diode laser that generates photons via electron–hole recombination, and an intersubband-based quantum cascade laser (QCL) that stacks multiple stages for enhanced current efficiency. Following a brief historical overview, we discuss theoretical aspects of the active region and core designs, growth by molecular beam epitaxy, and the processing of broad-area, narrow-ridge, and distributed feedback (DFB) devices. We then review the experimental performance of pulsed broad area ICLs, as well as the continuous-wave (cw) characteristics of narrow ridges having good beam quality and DFBs producing output in a single spectral mode. Because the threshold drive powers are far lower than those of QCLs throughout the λ = 3–6 µm spectral band, ICLs are increasingly viewed as the laser of choice for mid-IR laser spectroscopy applications that do not require high output power but need to be hand-portable and/or battery operated. Demonstrated ICL performance characteristics to date include threshold current densities as low as 106 A cm−2 at room temperature (RT), cw threshold drive powers as low as 29 mW at RT, maximum cw operating temperatures as high as 118 °C, maximum cw output powers exceeding 400 mW at RT, maximum cw wallplug efficiencies as high as 18% at RT, maximum cw single-mode output powers as high as 55 mW at RT, and single-mode output at λ = 5.2 µm with a cw drive power of only 138 mW at RT.

https://iopscience.iop.org/article/10.1088/0022-3727/48/12/123001/pdf

Interband cascade lasers

Silicon crystallized in the usual cubic (diamond) lattice structure has dominated the electronics industry for more than half a century. However, cubic silicon (Si), germanium (Ge) and SiGe alloys are all indirect-bandgap semiconductors that cannot emit light efficiently. The goal1 of achieving efficient light emission from group-IV materials in silicon technology has been elusive for decades2–6. Here we demonstrate efficient light emission from direct-bandgap hexagonal Ge and SiGe alloys. We measure a sub-nanosecond, temperature-insensitive radiative recombination lifetime and observe an emission yield similar to that of direct-bandgap group-III–V semiconductors. Moreover, we demonstrate that, by controlling the composition of the hexagonal SiGe alloy, the emission wavelength can be continuously tuned over a broad range, while preserving the direct bandgap. Our experimental findings are in excellent quantitative agreement with ab initio theory. Hexagonal SiGe embodies an ideal material system in which to combine electronic and optoelectronic functionalities on a single chip, opening the way towards integrated device concepts and information-processing technologies. A hexagonal (rather than cubic) alloy of silicon and germanium that has a direct (rather than indirect) bandgap emits light efficiently across a range of wavelengths, enabling electronic and optoelectronic functionalities to be combined on a single chip.

Direct-bandgap emission from hexagonal Ge and SiGe alloys

Research to realize long-wavelength, GaInNAs quantum well lasers has been intense in the past three years. The results have been very promising considering the relative immaturity and challenges of this new materials system. This paper reviews both the materials challenges and progress in growth of the metastable GaInNAs alloys required to reach the 1.3–1.55 μm communication wavelengths and the challenges and progress in device design for both vertical-cavity surface-emitting lasers and higher power edge-emitting lasers.

https://iopscience.iop.org/article/10.1088/0268-1242/17/8/317/pdf

GaInNAs long-wavelength lasers: progress and challenges

GaInAsN/GaAs double quantum well (DQW) lasers have been grown by solid source molecular beam epitaxy (MBE). Room-temperature pulsed operation is demonstrated for a ridge waveguide laser diode at a wavelength of 1517 nm. This is the first report of room-temperature laser emission in the 1.5 /spl mu/m range based on GaAs.

GaInAsN/GaAs laser diodes operating at 1.52 [micro sign]m

InxGa1−xAs1−yNy/GaAs single quantum wells emitting at room temperature in the wavelength range λ=(1.3–1.55) μm have been studied by photoluminescence (PL). By increasing temperature, we find that samples containing nitrogen have a luminescence thermal stability and a room temperature emission efficiency higher than that of the corresponding N-free heterostructures. The temperature dependence of the PL line shape shows a progressive carrier detrapping from localized to extended states as T is increased. Finally, the extent of the thermal shift of the free exciton energy for different y indicates that the electron band edge has a localized character which increases with nitrogen content.

Effect of temperature on the optical properties of (InGa)(AsN)/GaAs single quantum wells

Real-time multiplex PCR for simultaneous detection of Campylobacter jejuni, Salmonella, Shigella and Yersinia species in fecal samples

Effect of hydrogen on the electronic properties of In x Ga 1-x As 1- y N y /GaAs quantum wells

The development of a continuous wave (CW), thermoelectrically cooled (TEC), distributed feedback (DFB) laser diode based spectroscopic trace-gas sensor for ultra-sensitive and selective ethane (C2H6) concentration measurements is reported. The sensor platform used tunable diode laser absorption spectroscopy (TDLAS) based on a 2f wavelength modulation (WM) detection technique. TDLAS was performed with a 100 m optical path length astigmatic Herriott cell. For an interference free C2H6 absorption line located at 2976.8 cm−1 a 1σ minimum detection limit of 240 pptv (part per trillion by volume) with a 1 second lock-in amplifier time constant was achieved. In addition, reliable and long-term sensor performance was obtained when operating the sensor in an absorption line locked mode.

M. Fischer

Papers

GaInAsN/GaAs laser diodes operating at 1.52 [micro sign]m

Effect of temperature on the optical properties of (InGa)(AsN)/GaAs single quantum wells

Real-time multiplex PCR for simultaneous detection of Campylobacter jejuni, Salmonella, Shigella and Yersinia species in fecal samples

Effect of hydrogen on the electronic properties of In x Ga 1-x As 1- y N y /GaAs quantum wells

Continuous wave, distributed feedback diode laser based sensor for trace-gas detection of ethane