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We discuss a novel method of tunable diode laser sensor calibration using an in-line reference gas cell. The technique employs wavelength modulation spectroscopy at higher harmonics to simultaneously probe the sample and reference spectra.
Retrieval of atmospheric vertical profiles of five molecules from spectra recorded with 60MHz resolution external cavity quantum cascade laser heterodyne radiometer and 600MHz resolution Fourier Transform Spectrometer are analyzed to compare instruments' performances.
Nitric oxide sensing based on a 3.5 m Herriott cell-enhanced Faraday rotation spectrometer is reported. A minimum detection limit of 3.2 ppb/Hz1/2 is achieved using NO R(8.5)e transition at 1906.14cm−1 and 100 Gauss field.
A multi-pass cell enclosed by rare-earth magnets has been developed for sensitive FRS spectroscopy of oxygen. The FRS signals are generated by laser wavelength modulation and detected using a balanced photodetector and lock-in amplifier.
We demonstrated the tuning of the self-oscillation frequency of an external cavity VCSEL using drive current. This frequency tuning occurs for all cavity lengths constructed; however, the degree of frequency tuning correlates with cavity length.
Quantum Cascade lasers based on continuum-to-continuum design enable external cavity tuning over 340 cm−1 in pulsed mode operation at 15°C. Strong gain suppression over 320cm−1 is attributed to strong coupling between the laser transitions.
A phase sensitive signal detection scheme for molecular spectroscopy based on chirped laser dispersion spectroscopy (CLaDS) is presented. We demonstrate application to sensitive remote sensing of trace gases using a 5.2 μm quantum cascade laser.
We compare theoretical model simulations based on the HITRAN database with experimental data for the sensing of O2 using novel balanced Herriott multipass Faraday Rotation Spectroscopy. A detection limit of 10 ppm is achieved.
We report on the development of a Faraday rotation spectroscopy instrument using a DFB diode laser operating at 2.8 μm for the hydroxyl (OH) radical detection with a 1a detection limit of 8.2×108 OH radicals/cm3.
We present an active wavelength control method which ensures that all wavelength-selective elements of an external cavity semiconductor laser are spectrally aligned and the diffraction grating equation accurately predicts the laser operating frequency.
We have developed a compact sensor system for environmental CO2 studies based on quantum cascade laser. The sensor targets the strongest fundamental CO2 ro-vibrational band at 4.24μm and requires only 8mm optical path to provide sensitivity of 2 ppm.
An automatic external-cavity laser system for efficient testing of unmounted quantum cascade laser (QCL) bars has been developed. QCLs emitting at 3.45μm and broadband gain media with ∼344 cm1 tunability at 4.4μm have been studied.
In the short space of 15years since their first demonstration, quantum cascade lasers have become the most useful sources of tunable mid-infrared laser radiation. This Letter describes these developments in laser technology and the burgeoning applications of quantum cascade lasers to infrared spectroscopy. We foresee the potential application of quantum cascade lasers in other areas of chemical physics...
We describe the development of a Faraday Rotation Spectroscopic trace-gas sensor for quantification of molecular oxygen. Static magnetic field and balanced detection of polarization rotation is proposed for high precision and ultra-low power operation.
We demonstrate a wireless, portable CO2 sensor based on laser absorption spectroscopy. Allan variance for long run tests yielded Gaussian noise limited operation up to 100 seconds with ultimate minimum detection limit of 5.1×10-7.
Detailed noise analysis and system optimization of a DFB-QCL based Faraday rotation spectroscopic system for Nitric Oxide sensing is reported. New strategies for improvements of the ultimate sensitivity will be discussed.
We performed spectroscopy of methane using a broadly tunable external cavity interband cascade laser (EC-ICL). A miniaturized EC-ICL design for field applications, with improved anti-reflection and high-reflection coatings and new EC tuning mechanism, is presented.
A spectroscopic detection of molecular dispersion based on frequency-chirped laser is presented. Unlike non-linear direct absorption methods yielding line saturation, this method provides linear signal response and accuracy over a wide range of sample concentrations.
A Quantum Cascade laser design based on “continuum-to-bound” transitions with several strongly coupled upper laser states is demonstrated, which enables external cavity tuning over 190 cm-1 in pulsed mode operation at 0°C.
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