Water-vapor detection using asynchronous THz sampling

The use of a fiber-coupled terahertz (THz) transmitter/receiver pair for spectroscopic detection of water vapor is investigated. Transmission signals of an alumina cylinder demonstrate that the measurement approach can be applied in a windowless ceramic combustor. First, a conventional commercial transmitter/receiver pair is used to make measurements for frequencies to 1.25 THz. Water-vapor absorption is clearly evident within the alumina transparency window and is readily modeled using existing databases. A variety of data-acquisition schemes is possible using THz instrumentation. To assess signal-collection techniques, a prototype THz transmitter/receiver pair is then used with the asynchronous optical-sampling (ASOPS) technique to obtain asynchronous THz-sampling signals to 1 THz without the need for an optomechanical delay line. Two mode-locked Ti:sapphire lasers operating at slightly different repetition rates are used for pumping the transmitter and receiver independently to permit a complete time-domain THz signal to be recorded. The resulting repetitive phase walkout is demonstrated by collecting power spectra of room air that exhibit water-vapor absorption.

Mid-infrared spectroscopy on skin using a silver halide fibre probe in vivo

BACKGROUND/AIM

Mid-infrared spectroscopy is a versatile method for in vivo investigation of skin after topical treatment with skin care products.

METHODS

FTIR-spectrometer (Bruker Optics) with a flexible silver halide fibre probe (Infrared Fiber Sensors).

RESULTS

Absorbance spectra from 700 to 3000 cm(-1) have been recorded to gain information about proteins (amide-I and amide-II vibrations at 1650 and 1550 cm(-1)), esters (1740 cm(-1)), carboxylic acid (1710 cm(-1)), polyalcohols (1050 cm(-1)) and hydrocarbons (CH(n) vibrations at 2800-3000 cm(-1)).

CONCLUSIONS

Using the particular light guide, we were able to measure for the first time the effects of lip care products on lips directly. Furthermore, water binding and glycerol content of the skin could be determined simultaneously, as well as the replenishment of lipids by lipid-enriched bath oil.

Infrared photodetectors in heterostructure nanowires

We report on spectrally resolved photocurrent measurements on single self-assembled nanowire heterostructures. The wires, typically 3 microm long with an average diameter of 85 nm, consist of InAs with a 1 microm central part of InAsP. Two different sets of wires were prepared with phosphorus contents of 15+/-3% and 35+/-3%, respectively, as determined by energy-dispersive spectroscopy measurements made in transmission electron microscopy. Ohmic contacts are fabricated to the InAs ends of the wire using e-beam lithography. The conduction band offset between the InAs and InAsP regions virtually removes the dark current through the wires at low temperature. In the optical experiments, interband excitation in the phosphorus-rich part of the wires results in a photocurrent with threshold energies of about 0.65 and 0.82 eV, respectively, in qualitative agreement with the expected band gap of the two compositions. Furthermore, a strong polarization dependence is observed with an order of magnitude larger photocurrent for light polarized parallel to the wire than for light polarized perpendicular to the wire. We believe that these wires form promising candidates as nanoscale infrared polarization-sensitive photodetectors.

Infrared imaging of the nanometer-thick accumulation layer in organic field-effect transistors

We report on infrared (IR) spectromicroscopy of the electronic excitations in nanometer-thick accumulation layers in field-effect transistor (FET) devices based on poly(3-hexylthiophene). IR data allows us to explore the charge injection landscape and uncovers the critical role of the gate insulator in defining relevant length scales. This work demonstrates the unique potential of IR spectroscopy for the investigation of physical phenomena at the nanoscale occurring at the semiconductor-insulator interface in FET devices.

Tunable ultrafast infrared/visible laser to probe vibrational dynamics

A tunable, ultrafast (approximately 100 fs-approximately 1 ps) laser system generating mid-IR (3-10 microm) and UV/visible (392-417 nm, 785-835 nm) radiation is described and its output characterized. The system is designed to explore vibrational dynamics in the condensed phase in a direct, two-pulse, time-resolved manner, using Raman spectroscopy as the probe. To produce vibrational resolution, probe pulses are spectrally narrowed by use of a long doubling crystal. Frequency-resolved optical gating is used to evaluate beam characteristics. An effective method for determining the temporal overlap of the pump and probe pulses for a one-color, 400 nm configuration is illustrated. Representative results from studies of heme and paranitroaniline vibrational dynamics illustrate the effectiveness of the visible pump-visible probe portion of the system in illuminating fast structure and energy dynamics.

Multiple-scattering extended X-ray absorption fine structure analysis of nanostructured iron(III) oxide in the pore system of mesoporous carbon CMK-1

This work is devoted to the EXAFS analysis of nanostructured iron(III) oxide synthesized inside the pore system of mesoporous carbon CMK-1. A detailed study of the recording, preparation and evaluation of data recorded in fluorescence mode at the iron K-edge with and without multiple scattering is shown. The results obtained show that the local structure of Fe3+ inside nanostructured iron(III) oxide is different to that of the bulk material. Due to the small particle size, data analysis is much more difficult and data preparation more complex. Incorporating multiple scattering paths in the Fourier transforms and back-transforms during data evaluation gives structural insights that cannot be obtained using other spectroscopic methods, and this technique was used to draw conclusions about the first four coordination spheres of the nanostructured iron(III) oxide.

Use of Surface Enhanced Infrared Absorption Spectroscopy (SEIRA) to probe the functionality of a protein monolayer

We present a novel infrared method to investigate the functionality of a protein monolayer tethered to a metal substrate. The approach employs Surface Enhanced Infrared Absorption Spectroscopy (SEIRAS), which renders high surface sensitivity by enhancing the signal of the adsorbed protein by up to approximately 2 orders of magnitude. We demonstrate that the electrochemically induced absorption changes of a cytochrome c monolayer can be observed with excellent signal-to-noise ratio when the protein is adhered to a modified gold surface. To probe membrane proteins, a concept is introduced for the oriented incorporation into solid supported lipid bilayers. Recombinant cytochrome c oxidase solubilized in detergent is immobilized on a chemically modified gold surface via the affinity of its histidine (His)-tag to a nickel-chelating nitro-triacetic acid (NTA) surface. The protein monolayer is reconstituted into the lipid environment by detergent removal. Changing the orientation of the protein with respect to the metal surface is achieved by inserting the His-tag on either side of the membrane protein surface. Orientational control is mandatory for experiments in which electrons are injected from the electrode into the protein. The presented methodology opens new avenues to study the mechanism of the biomedically relevant class of electron and voltage-gated proteins on the atomic level.

The measurement technique of human's bio-signals

A disaster like a big earthquake usually brings many destroyed buildings and many sufferers are generated in the disaster area. In this situation, sometimes a rescue person encounters a second disaster. This is the big problem to rescue sufferers. In order to avoid a second disaster, many kind of rescue robots are being developed. These robots can find sufferers and rescue them. However, they cannot measure the sufferer's condition at the disaster area. If the sufferer's condition becomes clear before rescue, the rescue efficiency will improve. Therefore, we are developing a rescue robot that can measure some vital signs of sufferer and send measured data to the medical doctor who is in safety place. In this paper, we will describe about a developed method that can measure the pulse and the arterial blood oxygen saturation degree (SPO2) by easy way. We think that these methods will be powerful and useful to rescue sufferers.

Tissue-like phantoms for near-infrared fluorescence imaging system assessment and the training of surgeons

We demonstrate how to construct calibrated, stable, and inexpensive tissue-like phantoms for near-IR (NIR) fluorescence imaging applications. The bulk phantom material is composed of gelatin, intralipid, hemoglobin, and indocyanine green (ICG). Absorbance, scatter, background fluorescence, and texture can be tuned as desired. NIR fluorescent inclusions are comprised of ICG-labeled polystyrene divinylbenzene beads and Pam78-labeled hydroxyapatite crystals. The former mimic tumor masses of controllable size and contrast agent concentration, and the latter mimic microcalcifications in breast cancer. NIR-fluorescent inclusions can be positioned precisely in phantoms, with one or more regions having different optical properties, and their position can be verified independently using microcomputed tomography. We demonstrate how these phantoms can be used to calibrate and compare imaging systems, and to train surgeons to operate under NIR fluorescence image guidance.

Design and implementation of a multifrequency near-infrared diffuse optical tomography system

The design and implementation of a multifrequency and multispectral diffuse optical tomography system is described. Four wavelengths are utilized: 665, 785, 808, and 830 nm. The system is based on a network analyzer, which provides rf modulation signals for the laser diodes, as well as measures the amplitude and the phase of the detected signals. Six different modulation frequencies ranging from 110 to 280 MHz are used. The details of instrumentation, calibration, data acquisition, and performance of the system are given. A finite element algorithm is used to solve the diffusion equation, and an inverse solver based on this forward solver is implemented to calculate the absorption and scattering maps from the acquired data. Data acquisition for one wavelength is completed in less than 2.5 min for a single modulation frequency. The measurement repeatability is 0.5% in ac intensity and 0.2 deg in phase. The performance of the system is evaluated with phantom studies. A multifrequency reconstruction algorithm is used, in which a single absorption and scattering image pair is obtained using the whole dataset obtained at different modulation frequencies. It is shown that the multifrequency reconstruction approach provides superior image quality compared to the single frequency counterpart.

A frequency-modulated quantum-cascade laser for spectroscopy of CH4 and N2O isotopomers

We report the development of a novel laser spectrometer for high-sensitivity detection of methane and nitrous oxide. The system relies on a quantum-cascade laser source emitting wavelength of around 8.06 microm, where strong fundamental absorption bands occur for the considered species and their isotopomers. The detection technique is based on audio-frequency and radio-frequency modulation of laser radiation. First experimental tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of (13)C/(12)C, (18)O/(16)O, (17)O/(16)O and (15)N/(14)N isotope ratios.

A chemometric analysis for evaluation of early-stage cartilage degradation by infrared fiber-optic probe spectroscopy

In vivo identification of early-stage cartilage degradation could positively impact disease progression in osteoarthritis, but to date remains a challenge. The primary goal of this study was to develop an infrared fiber-optic probe (IFOP) chemometric method using partial least squares (PLS1) to objectively determine the degree of cartilage degradation. Arthritic human tibial plateaus (N = 61) were obtained during knee replacement surgery and analyzed by IFOP. IFOP data were collected from multiple regions of each specimen and the cartilage graded according to the Collins Visual Grading Scale of 0, 1, 2, or 3. These grades correspond to cartilage morphology that displayed normal, swelling or softening, superficially slight fibrillation, and deeper fibrillation or serious fibrillation, respectively. The model focused on detecting early cartilage degradation and therefore utilized data from grades 0, 1, and 2. The best PLS1 calibration utilized the spectral range 1733-984 cm(-1), and independent validation of the model utilizing 206 spectra to create a model and 105 independent test spectra resulted in a correlation between the predicted and actual Collins grade of R2 = 0.8228 with a standard error of prediction of 0.258 with a PLS1 rank of 15 PLS factors. A preliminary PLS1 calibration that utilized a cross-validation technique to investigate the possibility of correlation with histological tissue grade (33 spectra from 18 tissues) resulted in R2 = 0.8408 using only eight PLS factors, a very encouraging outcome. Thus, the groundwork for use of IFOP-based chemometric determination of early cartilage degradation has been established.

Carbon isotopomers measurement using mid-IR tunable laser sources

Recent developments of two mid-infrared tunable laser spectrometers dedicated to carbon isotope ratio determination are presented. First, a field deployable quantum cascade laser-based sensor is described, along with line selection strategy for (13/12)CO(2) ratio measurements. Secondly, an instrument architecture based on difference frequency generation is presented. The analyses of fundamental limitations, specifically temperature and pressure stability, and water vapor collision broadening, are detailed.

Time resolved simultaneous detection of 14NO and 15NO via mid-infrared cavity leak-out spectroscopy

We present a ring-down absorption spectrometer based on a continuous-wave CO laser in the mid-infrared spectral region near lambda = 5 microm. Using a linear ring-down cavity (length: 0.5 m) with high reflective mirrors (R = 99.988 %), we observed a noise-equivalent absorption coefficient of 3 x 10(-10) cm(-1)Hz(-1/2). This corresponds to a noise-equivalent concentration of 800 parts per trillion (ppt) for (14)NO and 40 ppt for (15)NO in 1 s averaging time. We achieve a time resolution of 1 s which allows time resolved simultaneous detection of the two N isotopes. The delta(15)N value was obtained with a precision of +/-1.2 per thousand in a sample with a NO fraction of 11 ppm. The simultaneous detection enables the use of (15)NO as a tracer molecule for endogenous biomedical processes.

A new concept for sensitive in situ stable isotope ratio infrared spectroscopy based on sample modulation

Diode-laser absorption spectroscopy finds increasing applications in the emerging field of stable isotope research. To meet the requirements of the water isotopes measurement challenge in environmental research, ways have to be found to cope with the present limitations of spectroscopic systems. In this article, we discuss an approach based on the Stark effect in molecular spectra to reduce the influence of time-dependent, unwanted background structures generally superimposed on the desired signal from the spectral feature under investigation. A road map to high-sensitivity isotopic ratio measurements of water isotopes is presented. On the basis of an Allan Variance analysis of measured data, the detection limits have been calculated as a function of the integration time. To achieve the required optical density of about 6 x 10(-7) for H(2)(17)O measurements, the duty cycle has to be optimized and the implementation of a sample modulation within an optical multipass cell is a promising approach to increase the stability of spectroscopic instrumentation required for ecosystem research and airborne atmospheric platforms.

Major influence of oxygen supply on 13CO2:12CO2 ratio measurement by nondispersive isotope-selective infrared spectroscopy

BACKGROUND

The nondispersive isotope-selective infrared spectroscopy (NDIRS) is a valid method for the measurement of the 13CO2:12CO2 ratio in breath samples. Methodical influences have to be considered to obtain valid results.

AIM

To evaluate the effect of oxygen supply to patients on the measurement of 13C:12C ratio in breath samples by NDIRS.

METHODS

Breath samples of 26 healthy volunteers were taken before, immediately after, and 5 minutes after inhalation of 100% oxygen via a continuous positive air pressure (CPAP) mask. Analysis of breath samples was performed by NDIRS.

RESULTS

Delta per thousand before oxygen inhalation was -25.8 +/- 0.2. Immediately after 5 minutes of 100% oxygen inhalation, delta per thousand increased to -14.8 +/- 0.5 (delta over baseline [DOB] 11.0 +/- 0.4) and after additional 5 minutes of room air inhalation, delta per thousand normalized to -25.6 +/- 0.2 (DOB 0.2 +/- 0.1).

CONCLUSIONS

Oxygen supply to patients and, therefore, changes in gas composition in breath samples clearly influence 13CO2 measurement by NDIRS. This has to be taken into account in the clinical setting. Thus, oxygen supply during measurement of exhaled 13CO2 by NDIRS has to be avoided or maintained at a strictly constant level.

Tunable laser diode system for noninvasive blood glucose measurements

Optical sensing of glucose would allow more frequent monitoring and tighter glucose control for people with diabetes. The key to a successful optical noninvasive measurement of glucose is the collection of an optical spectrum with a very high signal-to-noise ratio in a spectral region with significant glucose absorption. Unfortunately, the optical throughput of skin is low due to absorption and scattering. To overcome these difficulties, we have developed a high-brightness tunable laser system for measurements in the 2.0-2.5 microm wavelength range. The system is based on a 2.3 microm wavelength, strained quantum-well laser diode incorporating GaInAsSb wells and AlGaAsSb barrier and cladding layers. Wavelength control is provided by coupling the laser diode to an external cavity that includes an acousto-optic tunable filter. Tuning ranges of greater than 110 nm have been obtained. Because the tunable filter has no moving parts, scans can be completed very quickly, typically in less than 10 ms. We describe the performance of the present laser system and avenues for extending the tuning range beyond 400 nm.

Improved infrared spectrophotometer for point-of-care patient 13C-urea breath testing in the primary care setting

The 13C-urea breath test provides non-invasive testing for Helicobacter pylori infection with the possibility of analysis at the point of care. Point of care tests require accurate and efficient desktop instrumentation.

OBJECTIVE

To compare results obtained from a new infrared spectrophotometer (10 kg, 2 min sample measurement) to the previously approved UBiT-IR300 (22.5 kg, 5-6 min sample measurement).

DESIGN AND METHODS

Adults underwent urea breath testing; breath samples were analyzed using the new and the predicate instruments.

RESULTS

There were 220 adults enrolled (age range 18-74 years; M/F = 35:65); with 86 UBT positive and 134 negative cases. The overall agreement between instruments was 99.6% (95% C.I. = 97.6 to 99.9); the positive agreement was 100%.

CONCLUSION

Technical performance of the new instrument was excellent.

Extraction of depth-dependent signals from time-resolved reflectance in layered turbid media

We try a new approach with near-IR time-resolved spectroscopy, to separate optical signals originated in the upper layer from those in the lower layer and to selectively determine the absorption coefficient (mu(a)) of each layer in a two-layered turbid medium. The difference curve in the temporal profiles of light attenuation between a target and a reference medium is divided into segments along the time axis, and a slope of each segment is calculated to determine the depth-dependent mu(a). The depth-dependent mu(a) values are estimated under various conditions in which mu(a) and the reduced scattering coefficient (mu(s)') of each layer are changed with a Monte Carlo simulation and in phantom experiments. Temporal variation of them represents the difference in mu(a) between two layers when mu(s)' of a reference is the same as that of the upper layer of the target. The discrepancies between calculated mu(a) and the real mu(a) depend on the ratio of the real mu(a) of the upper layer to that of the lower layer, and our approach enables us to estimate the ratio of mu(a) between the two layers. These results suggest the potential that mu(a) of the lower layer can be determined by our procedure.

Diffuse optical measurement of blood flow in breast tumors

Blood flow contrast between tumor and normal tissues in patients with malignant and benign breast cancer was measured by diffuse optical correlation methods. The measurements were carried out with a hand-held optical probe that was manually scanned over the tumor-bearing breast. Increased blood flow was observed in tumor regions relative to healthy tissue, and control subjects did not exhibit significant blood flow heterogeneity. The measurements introduce a new optical contrast for diffuse optical mammography.

Multiwavelength laser light transmission of hollow optical fiber from the visible to the mid-infrared

We report on low-loss multiwavelength laser delivery of hollow optical fiber in a wide wavelength region, from the visible to the infrared. Improved methods of liquid-phase coating were used to fabricate the hollow fiber with inner films of a silver and a cyclic olefin polymer (COP) layer. The surface roughness of the silver layer was reduced dramatically by pretreatment on the inner glass surface with an SnCl2 solution. The COP layer roughness was also decreased by using an ambient atmosphere of tetrahydrofuran (THF) solvent during the COP layer formation. Owing to the smooth surfaces, hollow fiber with optimum COP film thickness for CO2 laser light simultaneously yields low losses for a Er:YAG laser and a red pilot beam. The power durability of CO2 and Er:YAG lasers, as well as the loss properties for the pilot beam, is demonstrated.

Measurements and quality assessments of near-infrared plasma glucose spectra in the combination band region using a scanning filter spectrometer

Near-infrared measurements of glucose in human plasma are performed using a custom, rapid, high-throughput filter-based spectrometer covering a spectral range between 2080 and 2315 nm. Quality of the measured glucose signals is quantified through the use of two figures of merit: selectivity and limit of detection. Selectivity measures the uniqueness of the glucose spectrum from among the interfering spectra. Limit of detection measures the smallest glucose concentration change detectable. The proposed system, which includes the spectroscopic hardware and a spectral preprocessing algorithm, is shown to produce a selectivity value of 0.57, with zero being nonselective and one being fully selective, and a limit of detection value of 2.2 mM. Prediction of an independent dataset is also performed using net analyte signal-based and partial least-squares multivariate calibration techniques, which produce standard error of prediction values of 1.14 and 1.45 mM, respectively.

Video-rate near-infrared optical tomography using spectrally encoded parallel light delivery

A novel parallel source implementation approach to near-infrared tomography is demonstrated through spectral encoding of the light delivery. This new technique allows many sources to be input into the tissue at the same time, and a high-resolution spectrometer is used to spatially spread out the signals from each spectrally encoded source. The parallel sampling of all sources at all detection locations renders rapid imaging. Acquisition of complete tomographic data sets at a video rate of 35 frames/s is achieved for imaging of a 6.35 mm diameter inclusion with an absorption coefficient of 0.01 mm(-1) and a reduced scattering coefficient of 1.5 mm(-1) that is moving along a circular path inside a 1% Intralipid solution.

Local infrared microspectroscopy with subwavelength spatial resolution with an atomic force microscope tip used as a photothermal sensor

We describe a new method of infrared microspectroscopy. It is intended for performing chemical mapping of various objects with subwavelength lateral resolution by using the infrared vibrational signature characterizing different molecular species. We use the photothermal expansion effect, detected by an atomic force microscope tip, probing the local transient deformation induced by an infrared pulsed laser tuned at a sample absorbing wavelength. We show that this new tool opens the way for measuring and identifying spectroscopic contrasts not accessible by far-field or near-field optical methods and with a subwavelength lateral resolution.

Initial electron donor and acceptor in isolated Photosystem II reaction centers identified with femtosecond mid-IR spectroscopy

Despite the apparent similarity between the plant Photosystem II reaction center (RC) and its purple bacterial counterpart, we show in this work that the mechanism of charge separation is very different for the two photosynthetic RCs. By using femtosecond visible-pump-mid-infrared probe spectroscopy in the region of the chlorophyll ester and keto modes, between 1,775 and 1,585 cm(-1), with 150-fs time resolution, we show that the reduction of pheophytin occurs on a 0.6- to 0.8-ps time scale, whereas P+, the precursor state for water oxidation, is formed after approximately 6 ps. We conclude therefore that in the Photosystem II RC the primary charge separation occurs between the "accessory chlorophyll" Chl(D1) and the pheophytin on the so-called active branch.