External cavity quantum cascade laser for quartz tuning fork photoacoustic spectroscopy of broad absorption features (original) (raw)
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Remote mid-infrared photoacoustic spectroscopy with a quantum cascade laser
Optics letters, 2015
We demonstrate non-contact remote photoacoustic spectroscopy in the mid-infrared region. A room-temperature-operated pulsed external-cavity quantum cascade laser is used to excite photoacoustic waves within a semitransparent sample. The ultrasonic waves are detected remotely on the opposite side of the sample using a fiber-optic Mach-Zehnder interferometer, thereby avoiding problems associated with acoustic attenuation in air. We present the theoretical background of the proposed technique and demonstrate measurements on a thin polystyrene film. The obtained absorption spectrum in the region of 1030-1230 cm<sup>-1</sup> is compared to a spectrum obtained by attenuated total reflection, showing reasonable agreement.
Photoacoustic spectroscopy using quantum-cascade lasers
Optics Letters, 1999
Photoacoustic spectra of ammonia and water vapor were recorded by use of a continuous-wave quantum-cascade distributed-feedback (QC-DFB) laser at 8.5 mm with a 16-mW power output. The gases were f lowed through a cell that was resonant at 1.6 kHz, and the QC-DFB source was temperature tuned over 35 nm for generation of spectra or was temperature stabilized on an absorption feature peak to permit real-time concentration measurements. A detection limit of 100 parts in 10 9 by volume ammonia at standard temperature and pressure was obtained for a 1-Hz bandwidth in a measurement time of 10 min.
Applied Physics B, 2013
An ultra-sensitive photo-acoustic spectrometer using a 10.4 lm broadly tunable mid-IR external cavity quantum cascade laser (EC-QCL) coupled with optical feedback to an optical power buildup cavity with high reflectivity mirrors was developed and tested. A laser optical power buildup factor of 181 was achieved, which corresponds to an intra-cavity power of 9.6 W at a wavelength of 10.4 lm. With a photo-acoustic resonance cell placed inside the cavity this resulted in the noise-equivalent absorption coefficient of 1.9 9 10 -10 cm -1 Hz -1/2 , and a normalized noise-equivalent absorption of 1.1 9 10 -11 cm -1 W Hz -1/2 . A novel photo-acoustic signal normalization technique makes the photo-acoustic spectrometer's response immune to changes and drifts in the EC-QCL excitation power, EC-QCL to cavity coupling efficiency and cavity mirrors aging and contamination. An automatic lock of the EC-QCL to the cavity and optical feedback phase optimization permitted long wavelength scans within the entire EC-QCL spectral tuning range.
Quantum cascade laser linewidth investigations for high resolution photoacoustic spectroscopy
Applied Optics, 2009
High detection selectivity is extremely important for gas analyzers in order to correctly identify the measured compound. Therefore, laser-based systems require a high optical resolution, which primarily depends on the spectral linewidth of the radiation source. This study examines the effective linewidth (chirp) of a pulsed distributed feedback (DFB) quantum cascade laser (QCL) in a photoacoustic (PA) gas detection system. The influence of the QCL operating parameters pulse duration and pulse current as well as the impact of the modulation technique are investigated. Effective QCL linewidths for pulse gate modulation, pulse frequency modulation, and chopper modulation are compared. The investigations are performed by measuring the PA spectra of nitrogen monoxide absorption lines. The results prove the strong influence of pulse duration and pulse current. They also demonstrate that the modulation technique has a considerable influence and, consequently, affects the detection selectivity of the PA analyzer. The aim of this research is to determine optimum operational parameters for high resolution PA spectroscopy.
Central European Journal of Physics, 2009
The main characteristics that a sensor must possess for trace gas detection and pollution monitoring are high sensitivity, high selectivity and the capability to perform in situ measurements. The photacoustic Helmholtz sensor developed in Reims, used in conjunction with powerful Quantum Cascade Lasers (QCLs), fulfils all these requirements. The best cell response is # 1200 V W−1 cm and the corresponding ultimate sensitivity is j 3.3 × 10−10 W cm−11 Hz−11/2. This efficient sensor is used with mid-infrared QCLs from Alpes Lasers to reach the strong fundamental absorption bands of some atmospheric gases. A first cryogenic QCL emitting at 7.9 μm demonstrates the detection of methane in air with a detection limit of 3 ppb. A detection limit of 20 ppb of NO in air is demonstrated using another cryogenic QCL emitting in the 5.4 μm region. Real in-situ measurements can be achieved only with room-temperature QCLs. A room-temperature QCL emitting in the 7.9 μm region demonstrates the simultan...
Applied Physics B, 2005
Lasers and Optics Applied Physics B a.a. kosterev u y.a. bakhirkin ABSTRACT A trace gas sensor based on quartz-enhanced photoacoustic spectroscopy with a quantum cascade laser operating at 4.55 µm as an excitation source was developed. The sensor performance was evaluated for the detection of N 2 O and CO. A noise-equivalent (1σ) sensitivity of 4 ppbv N 2 O with 3 s response time to (1 − 1/e) of the steady-state level was demonstrated. The influence of the relevant energy transfer processes on the detection limits was analyzed. Approaches to improve the current sensor performance are also discussed. PACS 42.62.Fi; 43.35.Sx
Optics express, 2016
We present a single mode multi-section quantum cascade laser source composed of three different sections: master oscillator, gain and phase section. Non-uniform pumping of the QCL's gain reveals that the various laser sections are strongly coupled. Simulations of the electronic and optical properties of the laser (based on the density matrix and scattering matrix formalisms, respectively) were performed and a good agreement with measurements is obtained. In particular, a pure modulation of the laser output power can be achieved. This capability of the device is applied in tunable-laser spectroscopy of N<sub>2</sub>O where background-free quartz enhanced photo acoustic spectral scans with nearly perfect Voigt line shapes for the selected absorption line are obtained.
Applied Spectroscopy, 2017
Broadband mid-infrared molecular spectroscopy is essential for detection and identification of many chemicals and materials. In this report, we present stand-off mid-infrared spectra of 1,3,5-trinitro-1,3,5-triazine or cyclotrimethylene trinitramine (RDX) residues on a stainless-steel surface measured by a broadband external cavity quantum cascade laser (QCL) system. The pulsed QCL is continuously scanned over 800 cm−1 in the molecular fingerprint region and the amplitude of the reflection signal is measured by either a boxcar-averager-based scheme or a lock-in-amplifier-based scheme with 1 MHz and 100 kHz quartz crystal oscillators. The main background noise is due to the laser source instability and is around 0.1% of normalized intensity. The direct absorption spectra have linewidth resolution around 0.1 cm−1 and peak height sensitivity around 10−2 due to baseline interference fringes. Stand-off detection of 5–50 µg/cm2 of RDX trace adsorbed on a stainless steel surface at the dis...
Photoacoustic spectroscopy with quantum cascade distributed-feedback lasers
Optics Letters, 2001
We present photoacoustic (PA) spectroscopy measurements of carbon dioxide, methanol, and ammonia. The light source for the excitation was a single-mode quantum cascade distributed-feedback laser, which was operated in pulsed mode at moderate duty cycle and slightly below room temperature. Temperature tuning resulted in a typical wavelength range of 3 cm 21 at a linewidth of 0.2 cm 21 . The setup was based on a Herriott multipass arrangement around the PA cell; the cell was equipped with a radial 16-microphone array to increase sensitivity. Despite the relatively small average laser power, the ammonia detection limit was 300 parts in 10 9 by volume.
Extensions of quartz-enhanced photoacoustic spectroscopy
2009
The goal of this thesis was to perform quartz-enhanced photoacoustic spectroscopy (QEPAS) on trace concentrations of NH 3 in the 1.53 pm region with a DFB laser without the use of a resonating cavity. I analyzed the process of QEPAS both analytically and experimentally. First, absorption spectroscopy was performed with a 1.55 pm DFB laser on the 1558.033 nm absorption line of H 13 C 12 N. The wavelength of the laser radiation was then modulated, and the spectral components of the absorbance were analyzed. In addition, low concentrations of NH 3 were generated through the use of a vaccuum system, and absorption spectoscopy was performed on these samples. A tuning fork was also characterized. Photoacoustic signals were ultimately not realized, however, plans for future work are mentioned.