Zbigniew Bielecki

Ultrasensitive laser spectroscopy for breath analysis

At present there are many reasons for seeking new methods and technologies that aim to develop new and more perfect sensors for different chemical compounds. However, the main reasons are safety ensuring and health care. In the paper, recent advances in the human breath analysis by the use of different techniques are presented. We have selected non-invasive ones ensuring detection of pathogenic changes at a molecular level. The presence of certain molecules in the human breath is used as an indicator of a specific disease. Thus, the analysis of the human breath is very useful for health monitoring. We have shown some examples of diseases’ biomarkers and various methods capable of detecting them. Described methods have been divided into non-optical and optical methods. The former ones are the following: gas chromatography, flame ionization detection, mass spectrometry, ion mobility spectrometry, proton transfer reaction mass spectrometry, selected ion flow tube mass spectrometry. In recent twenty years, the optical methods have become more popular, especially the laser techniques. They have a great potential for detection and monitoring of the components in the gas phase. These methods are characterized by high sensitivity and good selectivity. The spectroscopic sensors provide the opportunity to detect specific gases and to measure their concentration either in a sampling place or a remote one. Multipass spectroscopy, cavity ring-down spectroscopy, and photo-acoustic spectroscopy were characterised in the paper as well.

Detection of optical radiation

An overview of the important techniques for detection of optical radiation from the ultraviolet, through visible to infrared spectral regions is presented. At the beginning single-point devices are considered. Next, different application circuits used in direct detection systems together with elucidation of the design of front-end circuits and discussion of their performance are presented. Third part of the paper is devoted to advanced techniques including coherent detection. Finally, the updated information devoted to readout of signals from detector arrays and focal plane arrays is included. It is shown that detector focal plane technology has revolutionized many kinds of imaging in the past 25 years.

Towards optoelectronic detection of explosives

Detection of explosives is an important challenge for contemporary science and technology of security systems. We present an application of NOx sensors equipped with concentrator in searching of explosives. The sensors using CRDS with blue — violet diode lasers (410 nm) as well as with QCL lasers (5.26 μm and 4.53 μm) are described. The detection method is based either on reaction of the sensors to the nitrogen oxides emitted by explosives or to NOx produced during thermal decomposition of explosive vapours. For TNT, PETN, RDX, and HMX the detection limit better than 1 ng has been achieved.

Cavity ring down spectroscopy: detection of trace amounts of substance

We describe several applications of cavity ring-down spectroscopy (CRDS) for trace matter detection. NO2 sensor was constructed in our team using this technique and blue-violet lasers (395–440 nm). Its sensitivity is better than single ppb. CRDS at 627 nm was used for detection of NO3. Successful monitoring of N2O in air requires high precision mid-infrared spectroscopy. These sensors might be used for atmospheric purity monitoring as well as for explosives detection. Here, the spectroscopy on sharp vibronic molecular resonances is performed. Therefore the single mode lasers which can be tuned to selected molecular lines are used. Similarly, the spectroscopy at 936 nm was used for sensitive water vapour detection. The opportunity of construction of H2O sensor reaching the sensitivity about 10 ppb is also discussed.

Cavity enhanced spectroscopy for NO2 detection

We present an experiment on detection of nitrogen dioxide in free air using cavity enhanced spectroscopy. As a light source a blue pulsed diode laser was applied, while the output signal was detected with a photomultiplier. The absorber concentration was found by investigation of the optical resonator quality. It was done by determination of decay time of radiation pulse trapped in the cavity. Also the measurement of the phase shift between the output signal and modulation signal was used as the alternative method. The detection limit better than 1 ppb was demonstrated. The aim of this experiment was to study potential application of cavity enhanced absorption spectroscopy for construction of fully optoelectronic NO2 detector which could replace the commonly used chemical detectors.

Detection of disease markers in human breath with laser absorption spectroscopy

Abstract Number of trace compounds (called biomarkers), which occur in human breath, provide an information about individual feature of the body, as well as on the state of its health. In this paper we present the results of experiments about detection of certain biomarkers using laser absorption spectroscopy methods of high sensitivity. For NO, OCS, C2H6, NH3, CH4, CO and CO(CH3)2 an analysis of the absorption spectra was performed. The influence of interferents contained in exhaled air was considered. Optimal wavelengths of the detection were found and the solutions of the sensors, as well as the obtained results were presented. For majority of the compounds mentioned above the detection limits applicable for medicine were achieved. The experiments showed that the selected optoelectronic techniques can be applied for screening devices providing early diseases detection.

Infrared detection module for optoelectronic sensors

The paper presents the new infrared detection module developed at the VIGO System Ltd. Its high sensitivity of was achieved by both matching the IR detector to the preamp and minimizing noises. High sensitivity of the detector was achieved by using photodiodes with immersion lens. Immersion lens enables optimization of the detector area, decreasing detector capacity and time constant. Detector noise was reduced as a result of photodiode cooling by means of a thermoelectric cooler and reverse biasing. Developed module is dedicated to NOx optoelectronic sensors operates basing on Cavity Enhanced Absorption Spectroscopy technique.

Application of an optical parametric generator to cavity enhanced experiment

The paper presents an application of an optical parametric generator (OPG) for cavity enhanced absorption spectroscopy (CEAS) technique to nitric oxide (NO) detection. The principle of this method is based on an injection of a radiation beam into an optical cavity at a very small angle. The radiation is multiple reflected inside the resonator equipped with spherical and high reflectance mirrors. After each reflection a part of the radiation leaves the optical cavity due to residual transmission of mirrors. In the case of NO detection the laser emitting at around 5.26 μm was applied. During investigation of CEAS system with OPG, two-lenses collimator was required to improve OPG beam divergence. The Ge and ZnSe lenses were used. Thanks to this decrease of about three times in beam diameter was achieved (at the distance of 1 m from source). It make it possible to measure output signal from the CEAS optical cavity.

Time resolved FTIR study of spectral tuning and thermal dynamics of mid-IR QCLs

The aim of this paper is to address some of the aspects of thermal management of QCLs. Results include electrical and spectral characterization of the devices. Results show shift of QCL emission mode towards lower wavenumbers during the pulse. Characteristics were registered at different temperatures of operation and driving conditions. Registered shift rates depend on operating temperature, being the highest at room temperature. Based on spectral tuning results, temperature increase rates for different modes of operations were evaluated, delivering information on thermal dynamics of investigated devices.

NO and N 2 O detection employing cavity enhanced technique

The article describes an application of cavity enhanced absorption spectroscopy for nitric oxide and nitrous oxide detection. Both oxides are important greenhouse gases that are of large influence on environment, living organisms and human health. These compounds are also biomarkers of some human diseases. They determine the level of acid rain, and can be used for characterization of specific explosive materials. Therefore the sensitive detectors of these gases are of great importance for many applications: from routine air monitoring in industrial and intensive traffic areas, to detection of explosives in airports, finally for medicine investigation, for health care, etc. Our compact detection system provides opportunity for simultaneous measure of both NO and N2O concentration at ppb level. Its sensitivity is comparable with sensitivities of instruments based on other methods, e.g. gas chromatography or mass spectrometry.