David Thomazy

Modulation cancellation method for measurements of small temperature differences in a gas

An innovative spectroscopic technique based on balancing and cancellation of modulated signals induced by two excitation sources is reported. For its practical implementation, we used quartz-enhanced photoacoustic spectroscopy as an absorption-sensing technique and applied the new approach to measure small temperature differences between two gas samples. The achieved sensitivity was 30 mK in 17 s. A theoretical sensitivity analysis is presented, and the applicability of this method to isotopic measurements is discussed.

Compact portable QEPAS multi-gas sensor

A quartz-enhanced photoacoustic spectroscopy (QEPAS) based multi-gas sensor was developed to quantify concentrations of carbon monoxide (CO), hydrogen cyanide (HCN), hydrogen chloride (HCl), and carbon dioxide (CO2) in ambient air. The sensor consists of a compact package of dimensions 25cm x 25cm x 10cm and was designed to operate at atmospheric pressure. The HCN, CO2, and HCl measurement channels are based on cw, C-band telecommunication-style packaged, fiber-coupled diode lasers, while the CO channel uses a TO can-packaged Sb diode laser as an excitation source. Moreover, the sensor incorporates rechargeable batteries and can operate on batteries for at least 8 hours. It can also operate autonomously or interact with another device (such as a computer) via a RS232 serial port. Trace gas detection limits of 7.74ppm at 4288.29cm-1 for CO, 450ppb at 6539.11 cm-1 for HCN, 1.48ppm at 5739.26 cm-1 for HCl and 97ppm at 6361.25 cm-1 for CO2 for a 1sec average time, were demonstrated.

Real time ammonia detection in exhaled human breath with a quantum cascade laser based sensor

Quantum cascade laser based breath sensor platform for medical applications employing a quartz-enhanced photoacoustic spectroscopy technique is reported. The detection sensitivity for exhaled ammonia is at ≪10 ppbv level with 1 s time resolution.

Recent advances in infrared semiconductor based chemical sensing technologies

Recent advances in the development of sensors based on the use of quantum cascade lasers (QCLs) for the sensitive, selective detection, quantification and monitoring of both small and large molecular gas species with resolved and unresolved spectroscopic features respectively will be reported

Novel spherical mirror multipass cells with improved spot pattern density for gas sensing

We describe simulations of novel patterns in spherical two-mirror axially-aligned multipass cells typically used in Herriott configuration for gas sensing. Mirror spot fill factors are increased dramatically, while still avoiding beam overlap.

Modulation cancellation method for laser spectroscopy

We report on novel methods employing a modulation cancellation technique which result in a significantly increase in the sensitivity and accuracy of trace gas detectors. This method can be applied for isotopomer abundance quantification, temperature measurements and the detection of large molecules.

Modulation cancellation method (MOCAM) in modulation spectroscopy

An innovative spectroscopic technique based on balancing and cancellation of modulated signals induced by two excitation sources. We used quartz enhanced photoacoustic spectroscopy (QEPAS) in a 2f wavelength modulation mode as an absorption sensing technique and employed a modulation cancelation approach for spectroscopic measurements of small temperature differences in a gas mixture and detection of broadband absorbers. We demonstrated measurement of small temperature differences in a C2H2/N2gas mixture with a sensitivity of 30 mK in 17 sec and detection of hydrazine, a broadband absorbing chemical species, down to concentration of 1 part per million in volume in 1 sec. In both cases we used near-infrared laser diodes and selected overtone transitions.nuscrip

Latest developments for low-power infrared laser-based trace gas sensors for sensor networks

Academic and industrial researchers require ultra-low power, compact laser based trace-gas sensor systems for the most demanding environmental and space-borne applications. Here the latest results from research projects addressing these applications will be discussed: 1) an ultra-compact CO2 sensor based on a continuous wave quantum cascade laser, 2) an ultra-sensitive Faraday rotation spectrometer for O2 detection, 3) a fully ruggedized compact and low-power laser spectrometer, and 4) a novel non-paraxial nonthin multipass cell. Preliminary tests and projection for performance of future sensors based on this technology is presented.

Optimization of microresonator parameters for a quartz-enhanced photoacoustic spectroscopy sensor

A Quartz-Enhanced Photoacoustic Spectroscopy based gas sensor was optimized to improve its compact spectrophone design and performance. The impact of a 2-tube microresonator geometry on the detected signal and signal to noise ratio (SNR) was investigated. Experimental studies demonstrate that the l=4.4mm long tubes (ID=0.5mm) result in a significantly enhanced SNR.

CW DFB RT diode laser based sensor for trace-gas detection of ethane using novel compact multipass gas absorption cell

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 laser diode absorption spectroscopy (TDLAS) and wavelength modulation spectroscopy (WMS) as the detection technique. TDLAS was performed with an ultra-compact 57.6 m effective optical path length innovative spherical multipass cell capable of 459 passes between two mirrors separated by 12.5 cm. For an interference free C2H6 absorption line located at 2976.8 cm-1 a 1σ minimum detection limit of 130 pptv with a 1 second lock-in amplifier time constant was achieved.