Laser spectroscopy for breath analysis : towards clinical implementation

Detection and analysis of volatile compounds in exhaled breath represents an attractive tool for monitoring the metabolic status of a patient and disease diagnosis, since it is non-invasive and fast. Numerous studies have already demonstrated the benefit of breath analysis in clinical settings/applications and encouraged multidisciplinary research to reveal new insights regarding the origins, pathways, and pathophysiological roles of breath components. Many breath analysis methods are currently available to help explore these directions, ranging from mass spectrometry to laser-based spectroscopy and sensor arrays. This review presents an update of the current status of optical methods, using near and mid-infrared sources, for clinical breath gas analysis over the last decade and describes recent technological developments and their applications. The review includes: tunable diode laser absorption spectroscopy, cavity ring-down spectroscopy, integrated cavity output spectroscopy, cavity-enhanced absorption spectroscopy, photoacoustic spectroscopy, quartz-enhanced photoacoustic spectroscopy, and optical frequency comb spectroscopy. A SWOT analysis (strengths, weaknesses, opportunities, and threats) is presented that describes the laser-based techniques within the clinical framework of breath research and their appealing features for clinical use.Peer reviewe

Optical Gas Sensing: Media, Mechanisms and Applications

Optical gas sensing is one of the fastest developing research areas in laser spectroscopy. Continuous development of new coherent light sources operating especially in the Mid-IR spectral band (QCL—Quantum Cascade Lasers, ICL—Interband Cascade Lasers, OPO—Optical Parametric Oscillator, DFG—Difference Frequency Generation, optical frequency combs, etc.) stimulates new, sophisticated methods and technological solutions in this area. The development of clever techniques in gas detection based on new mechanisms of sensing (photoacoustic, photothermal, dispersion, etc.) supported by advanced applied electronics and huge progress in signal processing allows us to introduce more sensitive, broader-band and miniaturized optical sensors. Additionally, the substantial development of fast and sensitive photodetectors in MIR and FIR is of great support to progress in gas sensing. Recent material and technological progress in the development of hollow-core optical fibers allowing low-loss transmission of light in both Near- and Mid-IR has opened a new route for obtaining the low-volume, long optical paths that are so strongly required in laser-based gas sensors, leading to the development of a novel branch of laser-based gas detectors. This Special Issue summarizes the most recent progress in the development of optical sensors utilizing novel materials and laser-based gas sensing techniques

Trace gas sensing using DFB laser and QCL with miniaturized 3D-printed photoacoustic gas cells

Miniaturized 3D-printed photoacoustic trace gas sensors are presented, targeting gas species with absorption features in the telecommunications band as well as the mid-infrared with recovered gas concentrations down to the parts-per-billion range

Semiconductor Infrared Devices and Applications

Infrared (IR) technologies—from Herschel’s initial experiment in the 1800s to thermal detector development in the 1900s, followed by defense-focused developments using HgCdTe—have now incorporated a myriad of novel materials for a wide variety of applications in numerous high-impact fields. These include astronomy applications; composition identifications; toxic gas and explosive detection; medical diagnostics; and industrial, commercial, imaging, and security applications. Various types of semiconductor-based (including quantum well, dot, ring, wire, dot in well, hetero and/or homo junction, Type II super lattice, and Schottky) IR (photon) detectors, based on various materials (type IV, III-V, and II-VI), have been developed to satisfy these needs. Currently, room temperature detectors operating over a wide wavelength range from near IR to terahertz are available in various forms, including focal plane array cameras. Recent advances include performance enhancements by using surface Plasmon and ultrafast, high-sensitivity 2D materials for infrared sensing. Specialized detectors with features such as multiband, selectable wavelength, polarization sensitive, high operating temperature, and high performance (including but not limited to very low dark currents) are also being developed. This Special Issue highlights advances in these various types of infrared detectors based on various material systems

Fiber Lasers and Their Medical Applications

Advancing of photonics, aided with fruitful and abundant experimental and theoretical studies, over the last four decades has brought about the invention of a large variety of lasers. Among them one of the most popular types is a fiber laser, which is a variation of the standard solid-state laser, with the medium being a clad fiber waveguide structure and different dopants inside core serve as a gain media. They were derived from erbium-doped fiber amplifiers, which are still important component for telecommunications. Since discovery, fiber laser has become a natural choice for many uses, primarily because of the physical characteristics of fiber waveguide structure. Their rapid progress may show how excellent they really are. Although fiber lasers are today widely used in various research and industrial areas, one of the most meaningful applications of fiber laser technology has been through its use in medicine. A wide variety of wavelengths generated by fiber lasers as well as the diversity of physical mechanisms employed in pulse generation also additionally underpins the flexibility of fiber laser technology. This study is devoted to background technology of fiber lasers in the light of medical applications. Basic physics and theories of optical fibers and their important properties are introduced

III–V-on-silicon photonic integrated circuits for spectroscopic sensing in the 2–4 μm wavelength range

The availability of silicon photonic integrated circuits (ICs) in the 2-4 mu m wavelength range enables miniature optical sensors for trace gas and bio-molecule detection. In this paper, we review our recent work on III-V-on-silicon waveguide circuits for spectroscopic sensing in this wavelength range. We first present results on the heterogeneous integration of 2.3 mu m wavelength III-V laser sources and photodetectors on silicon photonic ICs for fully integrated optical sensors. Then a compact 2 mu m wavelength widely tunable external cavity laser using a silicon photonic IC for the wavelength selective feedback is shown. High-performance silicon arrayed waveguide grating spectrometers are also presented. Further we show an on-chip photothermal transducer using a suspended silicon-on-insulator microring resonator used for mid-infrared photothermal spectroscopy

Pushing the physical limits of infrared chemical imaging: intravascular photoacoustic & mid-infrared photothermal

Providing molecular fingerprint information, vibrational spectroscopy is a powerful tool for chemical analysis. In the mid-infrared window, FT-IR spectroscopy and microscopy have been routinely used for sample characterization. In the near-IR window, near-infrared spectroscopy has been widely used for tissue analysis and for the detection of lipids in the arterial walls. Yet, these traditional linear spectroscopies have intrinsic limitations. FT-IR spectroscopy suffers from a poor spatial resolution and strong water absorption for the study of living systems. Near-infrared spectroscopy avoids water absorption, yet it suffers from a poor, millimeter-scale spatial resolution in tissue analysis. My thesis focuses on breaking these limitations through photoacoustic and photothermal detection approaches. The first part of my thesis is on improving the spatial resolution in catheter-based intravascular photoacoustic (IVPA) imaging. By near-infrared excitation of lipids and acoustic detection, IVPA allows depth-resolved identification of lipid-laden atherosclerotic plaque. Thus far, most IVPA endoscopes use multimode fibers, which do not allow tight focusing of photons. Recent experiments on pulse propagation in multimode graded-index fibers have shown a nonlinear improvement in beam quality. Here, we harness this nonlinear phenomenon for the fiber-delivery of nanosecond laser pulses. We built a photoacoustic catheter 1.4 mm outer diameter, offering a lateral resolution as fine as 30 μm within a depth range of 2.5 mm. Such resolution is one order of magnitude better than current multi-mode fiber-based intravascular photoacoustic catheters. At the same time, the delivered pulse energy can reach as high as 20 μJ, which is two orders of magnitude higher than that of an optical resolution photoacoustic endoscope built with single-mode fiber. These improvements are expected to promote the biomedical application of photoacoustic endoscopes which require both high resolution and high pulse energy. Based on the technical advances, my thesis work further demonstrated longitudinal imaging of the same plaque in the same living animal. Recently developed mid-infrared photothermal (MIP) microscopy overcomes the limitations in FT-IR microscopy by probing the IR absorption-induced photothermal effect using visible light. MIP microscopy yields sub-micrometer spatial resolution with high spectral fidelity and much-reduced water background. The second part of my thesis work pushes the physical limits of MIP microscopy in aspects of detection sensitivity and imaging speed using two approaches. First, taking advantage of the interference scattering effect, the scattering signal from the sample can be greatly enhanced. Together with the relatively large infrared absorption coefficient, the sensitivity of the infrared spectrum is greatly improved, and single virus detection is achieved. Second, by using fluorescence as a thermo-sensitive probe, the temperature raise by infrared absorption can be retrieved in a more efficient way and much higher imaging speed and sensitivity are thus accomplished

Micromachined Optical and Acoustic Waveguide Systems for Advance Sensing and Imaging Applications

Evolving from the IC fabrication processes, micromachining technologies allow mass production of 2D or 3D microstructures, which are otherwise difficult to achieve with traditional machining techniques. In this research, novel micromachining processes have been developed to enable new micro optical and acoustic waveguide systems for advanced optical sensing and acoustic imaging applications. The investigated applications include non-invasive cancer detection inside human body, in-field soil characterization, and time-delayed and multiplexed ultrasound and photoacoustic tomography. Micromachining technology enables miniaturized optical waveguide system for efficient light transmission. The small size and light-guiding capabilities are particularly useful for optical sensing at places deep inside the human body or underground. Two micromachined optical waveguide systems were fabricated and tested. The first one was used to conduct oblique incidence diffuse reflectance spectroscopy (OIDRS) for the determination of tumor margins on human pancreas specimens. The second one was used to conduct visible-near-infrared diffuse reflectance spectroscopy (VNIR-DRS) for extracting the compositional information of soil samples. Micromachining technology also makes it possible to utilize single-crystalline silicon as a structural material for acoustic wave propagation. It enables the development of high-performance integrated acoustic circuits and allows direct acoustic signal processing and control. The acoustic properties and propagation inside silicon waveguides were characterized, and the acoustic signal processing using micromachined acoustic waveguide system was investigated. Based on the results, two acoustic waveguide systems were designed and constructed. The first system utilized micromachined acoustic delay lines to passively delay acoustic signal thereby reducing the required transceivers and processing electronics; while the second system employed micromachined acoustic multiplexer to actively control the transmission of acoustic signals. Both techniques are expected to provide new solutions to reduce the complexity and cost of the acoustic receiver systems in ultrasound and photoacoustic imaging

Fundamental Review to Ozone Gas Sensing Using Optical Fibre Sensors

The manuscript is a review of basic essentials to ozone gas sensing with optical methods. Optical methods are employed to monitor optical absorption, emission, reflectance and scattering of gas samples at specific wavelengths of light spectrum. In the light of their importance in numerous disciplines in analytical sciences, necessary integral information that serves both as a basis and reference material for intending researchers and others in the field is inevitable. This review provides insight into necessary essentials to gas sensing with optical fibre sensors. Ozone gas is chosen as a reference gas. Simulation results for ozone gas absorption cross section in the ultraviolet (UV) region of the spectrum using spectralcalc.com simulation have also been included