Quartz-Enhanced Photoacoustic Spectroscopy-Based Acetone and Ammonia Measurements from Human Breath Near 8 μm Wavelength Band.

Human breath gas analysis is a noninvasive disease diagnostic approach used to identify different pathological conditions in the human body. Monitoring breath acetone (CHO) and ammonia (NH) as biomarkers is vital in diagnosing diabetes mellitus and liver disorders, respectively. In this article, the quartz-enhanced photoacoustic spectroscopy (QEPAS) technique is proposed and demonstrated for measuring CHO and NH in human exhaled breath samples.

Optical Biosensors for the Diagnosis of COVID-19 and Other Viruses-A Review.

The sudden outbreak of the COVID-19 pandemic led to a huge concern globally because of the astounding increase in mortality rates worldwide. The medical imaging computed tomography technique, whole-genome sequencing, and electron microscopy are the methods generally used for the screening and identification of the SARS-CoV-2 virus. The main aim of this review is to emphasize the capabilities of various optical techniques to facilitate not only the timely and effective diagnosis of the virus but also to apply its potential toward therapy in the field of virology.

Dual-wavelength absorption technique for dryness measurement of wet steam.

This paper presents a dual-wavelength absorption-based approach for measuring and validating the steam dryness fraction of wet steam. A thermally insulated steam cell with a temperature-controlled measurement window (up to 200°C) is designed and fabricated to minimize condensation during water vapor measurements at different operating pressures (1-10 bars). Water vapor's measurement sensitivity and accuracy are limited due to other absorbing and non-absorbing species in wet steam.

Laser-Induced Breakdown Spectroscopy Combined with Temporal Plasma Analysis of C Molecular Emission for Carbon Analysis in Coal.

A benchtop laser-induced breakdown spectroscopy is demonstrated to determine the elemental carbon content present in raw coal used for combustion in power plants. The spectral intensities of molecular CN and C emission are measured together with the atomic carbon (C) and other inorganic elements (Si, Fe, Mg, Al, Ca, Na, and K) in the laser-induced breakdown spectroscopy spectrum of coal. The emission persistence time of C molecule emission is measured from the coal plasma generated by a nanosecond laser ablation with a wavelength of 266 nm in the Ar atmosphere.

Advances in Mid-Infrared Spectroscopy-Based Sensing Techniques for Exhaled Breath Diagnostics.

Human exhaled breath consists of more than 3000 volatile organic compounds, many of which are relevant biomarkers for various diseases. Although gas chromatography has been the gold standard for volatile organic compound (VOC) detection in exhaled breath, recent developments in mid-infrared (MIR) laser spectroscopy have led to the promise of compact point-of-care (POC) optical instruments enabling even single breath diagnostics. In this review, we discuss the evolution of MIR sensing technologies with a special focus on photoacoustic spectroscopy, and its application in exhaled breath biomarker detection.

Off-Resonance Photoacoustic Spectroscopy Technique for Multi-Gas Sensing in Biogas Plants.

An off-resonance broadband photoacoustic spectroscopy (PAS) technique with a supercontinuum laser (SCL) in the near-infrared range is demonstrated for biogas measurements with different biomass matrices. The PAS sensor system has been calibrated with known concentrations of methane (CH), carbon dioxide (CO), water vapor (HO vapor), and hydrogen sulfide (HS). A laboratory-scale bioreactor was set up to monitor CH and CO generation using the SCL-PA sensor system.

Off-resonant photoacoustic spectroscopy for analysis of multicomponent gas mixtures at high concentrations using broadband vibrational overtones of individual gas species.

The broadband photoacoustic spectroscopy (PAS) technique is proposed and demonstrated for measurement of CH, CO, and HO vapor in the 1.6 to 2.0 μm wavelength region.

KTN-based high-speed axial and lateral scanning technique for an optical coherence tomography system and application to dental imaging.

A high-speed 840 nm based polarization-sensitive time domain optical coherence tomography (PSOCT) technique is proposed and demonstrated based on the quadratic electro-optic property of potassium tantalate niobate (KTN) crystals. A longitudinal (axial) scanning depth of ≈10  μm is obtained for an applied AC voltage of 600 V, at 1000 Hz and temperature maintained around 40°C. The OCT system with the KTN-based electro-optic delay line combined with a linear actuation is extended to image an early dental demineralization.

Glucose sensing in oral mucosa simulating phantom using differential absorption based frequency domain low-coherence interferometry.

The superluminescent diode based differential absorption frequency domain low-coherence interferometry (FD-DALCI) technique is proposed and demonstrated for sensing physiological concentrations of glucose (0-250 mg/dl) in oral mucosa simulating phantoms (intralipid of concentrations 0.25-0.50%) with wavelengths at 1589 and 1310 nm.

Development of UV-ionization based trace differential mobility sensor for acetone and hexane.

Clinical studies in recent times confirm feasibility of using trace concentrations of volatile organic compounds (VOC) in human exhale air as potential bio-markers for a variety of disease states. A Differential Mobility Sensor (DMS) with dual ultra-violet (UV) photo-ionization source is proposed and demonstrated for measurement of trace amounts of VOC gases in human exhale air. Experimental work performed with the DMS using high frequency asymmetrical waveform field for detection of trace concentrations of acetone and hexane with a few carrier gases including air, CO2 and O2 is discussed.

Development of an electro-optically tuned optical coherence tomography system for imaging dental lesions.

A conventional optical coherence tomography (OCT) system was set up in-house to image early dental caries, identify gap formation in the bonding interface for restoration and secondary caries. Two-dimensional images of tooth samples was obtained and dental defect were identified. A novel electro-optic tuning system is proposed in order to improve scanning speed and to perform noiseless imaging.

Gas sensors based on superluminescent diodes for combustion monitoring.

Application of fiber-coupled superluminescent diodes with a wideband optical source for the detection of various gases is reported. Superluminescent diodes with two different wavelengths around 760 and 1530 nm are used for O(2) and NH(3) gas sensing, respectively. The technique allows multiple-gas sensing for combustion monitoring.

Multiwavelength distributed-feedback dye laser array and its application to spectroscopy.

A multiwavelength, multistripe tunable laser array is proposed, and its application to absorption spectroscopy is demonstrated. Laser waveguides doped with Rhodamine 6 G dye were integrated on a plastic chip, and simultaneous output at different wavelengths was obtained by use of a distributed-feedback technique. A very low threshold of 3 muJ was attained, and spectrally narrowed output (<0.

Tuning of a Ti3+:sapphire laser by an electro-optic beam deflection method.

A wavelength-switching method for tuning a self-injection-seeded Ti3+:sapphire laser that uses an electro-optic beam deflection technique is reported. A LiNbO3 prism was employed in a tuning arm of the dual-cavity Ti3+:sapphire laser, and wavelength tuning of approximately 94 pm was attained by altering the deflection angle with the application of an electric field of 10 kV/cm to the prism. The spectral characteristics of the output laser were mainly determined by the diffraction grating in the dual-cavity laser, and the electro-optic prism just behaved as a light-beam deflector for the wavelength tuning purpose.

Feasibility of nonlinear Raman lidar based on stimulated Raman gain spectroscopy without a tunable laser.

A novel technique of lidar for atmospheric gas detection by use of stimulated Raman gain spectroscopy without any tunable laser is proposed. Detection sensitivity and detectable range are estimated on the basis of the lidar equation for CO2, CH4, and H2 in the atmosphere. The feasibility study clearly shows that the technique has a potential for application to lidar and that, in addition, the construction of the system is simpler than those of traditional differential absorption lidars.