Sensitivity enhancement of laser absorption spectroscopy by magnetic rotation effect

Litfin, G.; Pollock, Clifford R.; Curl, R. F.; Tittel, Frank K.

doi:10.1063/1.439117

Cited by 148 publications

(72 citation statements)

References 11 publications

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“…For low magnetic fields the signal increases linearly with the field strength. As the field is increased, the slope decreases and the peak value of the FAMOS signal reaches a maximum for an optimum magnetic field of 156 Gauss (rms), after which it starts to decrease due to over modulation, in agreement with earlier predictions [1][2].…”

Section: Resultssupporting

confidence: 75%

“…Theoretical descriptions of the FAMOS signal from Q-transitions in NO have previously been given in the literature [1][2][3][4]. It was recently shown by Westberg et al [6] …”

Section: Theorymentioning

confidence: 99%

“…Primarily due to the rapid development of quantum cascade lasers during recent years, the FAMOS technique has lately been repeatedly used for detection of NO addressing the strong fundamental rotational-vibrational transitions, where one particular transition, 3/2 (3 / 2) Q , at 5.33 µm, has been identified as the most sensitive [1][2][3][4]. Using an external cavity quantum cascade laser (QCL), a high performance, transportable FAMOS spectrometer, capable of detecting 4.7 ppb of NO with a 1 second response time, has recently been realized by Lewicki et al.…”

Section: Introductionmentioning

confidence: 99%

“…Faraday Modulation Spectroscopy (FAMOS) is a spectroscopic detection technique for detection of paramagnetic molecules in general, and nitric oxide (NO) in particular [1][2][3][4][5]. The technique utilizes the fact that, in the presence of a magnetic field, a transition in a paramagnetic molecule can rotate the polarization plane of linearly polarized light.…”

Section: Introductionmentioning

confidence: 99%

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Faraday rotation spectrometer with sub-second response time for detection of nitric oxide using a cw DFB quantum cascade laser at 5.33 μm

et al. 2010

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Lewicki et al. [4]. However, since that system is based upon an external cavity laser it requires stable running conditions to obtain the optimum detectability, which restricts its use in industrial applications. In addition, it utilizes a laser source with a moderate output power (3 mW) that is modulated through a mechanical actuator.Here, we present a Faraday modulation spectrometer for sensitive detection of NO that is based upon a distributed feedback (DFB) QCL with an output power of 60 mW and a Peltier cooled mercury-cadmium-telluride (MCT) detector. A DFB laser provides more output power than an external cavity laser, which increases the sensitivity of the spectrometer. It is also more 3 compact and it is solely scanned through the injection current of the laser, which makes it less susceptible to drifts (as no mechanical parts are involved in scanning the laser wavelength).Furthermore, application of a rapid magnetic field modulation (in the kHz regime) and a fast wavelength scan allow for further enhancement of the signal-to-noise ratio and at the same time yields a sub-second response time of the spectrometer. In addition, the concentration of NO is extracted via curve fitting, which is an advantage when high accuracy assessments are to be made since it reduces the risk for contributions from structured or drifting background signals.All these features make the presented spectrometer suitable for industrial and field applications.An Allan variance analysis demonstrates that the system has an excellent stability, i.e. a white noise behavior, for up to several hours of operation, with a detection limit of 4.5 ppb for a response time of 1 s. Theory ExperimentThe experimental set-up is shown in Figure 1. A room temperature cw QCL DFB laser emitting /W. The photocurrent from the reference detector was amplified by a DC-coupled transimpedance amplifier and sent to a DAQ board (NI-USB 6251). The direct absorption signal from the reference cell was used for accurate determination of the laser frequency in the signal processing. 6The main part of the beam was transmitted through a CaF 2 wedge and passed two wire grid polarizers stacked in series to clean up and define the plane of polarization from the laser.After the polarizers, the laser beam passed through a 25 cm long absorption cell with an outer diameter of 12 mm. The cell tube was made of borofloat glass whereas the optical windows were made of 2 mm thick CaF 2 plane parallel discs (with a diameter of 12 mm). The cell was connected via a pressure controller to a gas mixing device (HOVAGAS). The cell was inserted in a 15 cm long solenoid with an inner diameter of 12.5 mm. The solenoid, which consisted of 765 turns of 1 mm thick copper wire with 0.3 mm thick isolation, coupled in series with a capacitor stack, was driven by a power audio amplifier. The resonant circuit was tuned to obtain a maximum magnetic field at a frequency of 7.4 kHz. We found this choice of modulation frequency to be a good compromise between the performance of the instrument ...

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Section: Resultssupporting

confidence: 75%

“…Theoretical descriptions of the FAMOS signal from Q-transitions in NO have previously been given in the literature [1][2][3][4]. It was recently shown by Westberg et al [6] …”

Section: Theorymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Faraday rotation spectrometer with sub-second response time for detection of nitric oxide using a cw DFB quantum cascade laser at 5.33 μm

et al. 2010

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“…From this point of view, Faraday rotational spectroscopy (FRS) seems to be the most favourable among the spectroscopic techniques, because it is not sensitive to diamagnetic molecules such as H 2 O or CO 2 . The technique, first described in the 1980s [20], appears to be a powerful and versatile method for quantitative and selective detection of paramagnetic molecules, such NO, O 2 or OH − . For NO sensing with FRS, the 5.3 µm region is commonly used [15,21,22].…”

Section: Faraday Rotation Spectroscopymentioning

confidence: 99%

Spectroscopic monitoring of NO traces in plants and human breath: applications and perspectives

et al. 2012

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Optical methods based on quantum cascade lasers (QCLs) are becoming popular in many life science applications. We report on two trace gas detection schemes based on continuous wave QCLs for on-line detection of nitric oxide (NO) at the sub-part-per-billion level by volume (ppbv, 1 : 10 −9 ), using wavelength modulation spectroscopy (WMS) and Faraday rotation spectroscopy (FRS) at 1894 cm −1 and 1875.73 cm −1 , respectively. Several technical incremental steps are discussed to further improve the sensitivity of these methods. Examples are included to demonstrate the merits of WMS-based sensor: direct monitoring of NO concentrations in exhaled breath, and from plants under pathogen attack. A simple hand-held breath sampling device that allows single breath collection at various exhalation flows (15, 50, 100 and 300 mL/s, respectively) is developed for off-line measurements and validated in combination with the WMS-based sensor. Additionally, the capability of plants to remove environmental NO is presented.

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Photonic Sensing of Reactive Atmospheric Species

Chen

et al. 2017

Encyclopedia of Analytical Chemistry

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Chemically reactive short‐lived atmospheric species play a crucial role in tropospheric processes that affect regional air quality and global climate change. Contrary to long‐lived species (such as greenhouse gases), fast, interference‐free, accurate, and precise in situ monitoring of such strongly reactive species represents a real challenge owing to their very high reactivity resulting in short lifetimes (∼1–100 s) and ultralow concentrations (∼pptv). In this article, we give an overview of the recent progress in the development of absorption spectroscopy‐based photonic instruments involving modern photonic light sources (quantum cascade laser, distributed feedback diode laser, and light‐emitting diode) combined with high‐sensitivity spectroscopic measurement techniques such as incoherent broadband cavity‐enhanced absorption spectroscopy, Faraday rotation spectroscopy, wavelength‐modulation‐enhanced off‐axis integrated cavity output spectroscopy, tuning fork‐ or microphone‐based photoacoustic spectroscopy, and open‐path multipass absorption spectroscopy. Illustrative examples of monitoring some key atmospheric reactive species (such as HONO, OH, NO 3 , N 2 O 5 , and NO 2 ) will be presented for applications in intensive field campaigns, instrumented atmospheric simulation chamber, or laboratory investigation.

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Sensitivity enhancement of laser absorption spectroscopy by magnetic rotation effect

Cited by 148 publications

References 11 publications

Faraday rotation spectrometer with sub-second response time for detection of nitric oxide using a cw DFB quantum cascade laser at 5.33 μm

Faraday rotation spectrometer with sub-second response time for detection of nitric oxide using a cw DFB quantum cascade laser at 5.33 μm

Spectroscopic monitoring of NO traces in plants and human breath: applications and perspectives

Photonic Sensing of Reactive Atmospheric Species

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