Wavelength Scanning Research Articles

A DFB-LD Internal Temperature Fluctuation Analysis in a TDLAS System for Gas Detection

The temperature fluctuations inside commercially distributed feedback laser diode were experimentally measured and analyzed in detail in this study. In tunable diode laser absorption spectroscopy based gas sensing systems, the temperature of the laser source is usually fixed and a current signal is used to drive the laser for wavelength scanning or modulation. Even if the laser is controlled by a robust temperature controller, the internal temperature still fluctuates due to the delayed response of the temperature controller when rapidly changing the drive current. These temperature fluctuations result in distortions in the measured absorption signals which can be effectively suppressed by limiting the drive current modulation to the resonance frequency of the temperature control proportional-integral-derivative loop. This study demonstrates a reduction in the temperature dependent absorption distortions and improves the detection uncertainty using this technique.

Relating glaucomatous visual field loss to retinal oxygen delivery and metabolism.

To test the hypothesis that visual field (VF) loss is associated with decreased retinal blood flow, oxygen delivery and metabolism, and with increased retinal oxygen extraction fraction (OEF) in glaucomatous individuals. Glaucomatous subjects underwent automated perimetry, dual wavelength scanning laser ophthalmoscopy and Doppler optical coherence tomography imaging in order to measure mean deviation, central retinal arterial and venous diameter equivalents (CRAE and CRVE), oxygen saturation levels and total retinal blood flow (TRBF), respectively. Retinal oxygen delivery, metabolism and extraction fraction were derived from measurements of oxygen saturation and blood flow. Twenty eyes of 14 subjects were included in the study. Mean deviation was on average -13.76±8.70 dB. Mean CRAE and CRVE were 126±28 and 191±35μm, respectively. Mean TRBF and oxygen delivery were 34.3± 11.7μl/min and 6.5±2.6μl O2 /min, respectively. Mean oxygen metabolism and extraction fraction were 2.1±0.94μl O2 /min and 0.34±0.15, respectively. Visual field (VF) loss was associated with reduced CRAE and CRVE, TRBF and oxygen delivery and associated with increased OEF. Combined measurements of retinal blood flow and oxygen saturation in glaucomatous individuals suggest VF loss is associated with impaired oxygen delivery and augmented OEF.

Super-resolution reconstruction of speckle phase in depth-resolved wavelength scanning interference using the total least-squares analysis.

Depth-resolved wavelength scanning interferometry (DRWSI) is a tomographic imaging tool that employs phase measurement to visualize micro-displacement inside a sample. It is well known that the depth resolution of DRWSI is restricted by a wavelength scanning range. Recently, a nonlinear least-squares analysis (NLS) algorithm was proposed to overcome the limitation of the wavelength scanning range to achieve super-resolution; however, the NLS failed to measure speckle surfaces owing to the sensibility of initial values. To the best of our knowledge, the improvement of depth resolution on measuring a speckle surface remains an open issue for DRWSI. For this study, we redesigned the signal processing algorithm for DRWSI to refine the depth resolution when considering the case of speckle phase measurement. It is mathematically shown that the DRWSI's signal is derived as a model of total least-squares analysis (TLSA). Subsequently, a super-resolution of the speckle phase map was obtained using a singular value decomposition. Further, a numerical simulation to measure the micro-displacements for speckle surfaces was performed to validate the TLSA, and the results show that it can precisely reconstruct the displacements of layers whose depth distance is 5μm. This study thus provides an opportunity to improve the DRWSI's depth resolution.

The Interrogation of Quasi-Distributed Optical FBG Sensing System Through Adopting a Wavelength-Tunable Fiber Chaotic Laser

Wavelength scanning- and optical time domain reflectometer (OTDR)-based methods have been widely used as sensor interrogation schemes for quasi-distributed fiber Bragg grating (FBG) sensing systems. However, wavelength scanning based technique mainly provides the information of wavelength shift at each FBG sensor, whereas it does not have the locating ability. For OTDR-based technique, the spatial resolution is typically several meters, which is not sufficient for high-resolution sensor locating where a centimeter resolution is usually required. Moreover, both of these two interrogation techniques lack the ability of real-time fiber fault monitoring. To address these problems, a novel interrogation technique for quasi-distributed optical FBG sensors based on a wavelength-tunable fiber chaotic laser is proposed and experimentally demonstrated. In the proposed technique, the wavelength shift at each FBG sensor can be obtained through differentially calculating the cross-correlation peaks at two separate wavelength of input light. The positions of FBG sensors can also be determined by the delay time of the corresponding cross-correlation peak. The proposed technique has the advantages of wide wavelength tunable range (40 nm in our works), tunable strain-sensing sensitivity, stability against source power fluctuation, and capability of interrogating both identical and wavelength division multiplexing-based FBG arrays. Strain sensing experiments show a sensitivity of up to 0.0076 dB/ μ ϵ in the range of 0∼1200 μ ϵ with a good linearity. At the same time, a spatial resolution of 18.86 cm is demonstrated in the real-time fiber fault monitoring, which can be further improved with a higher sampling rate.

High-speed refractive index sensing system based on Fourier domain mode locked laser.

A high-speed refractive index sensing system based on the Fourier domain mode locked laser (FDML) and a microfiber Bragg grating (mFBG) is theoretically studied and experimentally demonstrated. Unlike traditional physical parameter sensing systems, which directly use the FDML as the wavelength scanning source and the optical sensor as the spectra shaping component, we inserted an mFBG into the FDML cavity in order to generate time domain pulse signals used for sensing. The wavelength shift in optical frequency domain is converted into time domain pulse drift. The sensitivity of the proposed refractive index (RI) sensing system is improved by two orders of magnitude, compared with the wavelength monitoring method. The scanning speed is as high as 43 kHz. Moreover, the sensitivity curve can be adjusted by tuning the direct current voltage. The nonlinear sensitivity and linear sensitivity with RI can be achieved.

Real-time dynamic strain sensing in optical fibers using artificial neural networks.

We propose to use artificial neural networks (ANNs) for raw measurement data interpolation and signal shift computation and to demonstrate advantages for wavelength-scanning coherent optical time domain reflectometry (WS-COTDR) and dynamic strain distribution measurement along optical fibers. The ANNs are trained with synthetic data to predict signal shifts from wavelength scans. Domain adaptation to measurement data is achieved, and standard correlation algorithms are outperformed. First and foremost, the ANN reduces the data analysis time by more than two orders of magnitude, making it possible for the first time to predict strain in real-time applications using the WS-COTDR approach. Further, strain noise and linearity of the sensor response are improved, resulting in more accurate measurements. ANNs also perform better for low signal-to-noise measurement data, for a reduced length of correlation input (i.e., extended distance range), and for coarser sampling settings (i.e., extended strain scanning range). The general applicability is demonstrated for distributed measurement of ground movement along a dark fiber in a telecom cable. The presented ANN-based techniques can be employed to improve the performance of a wide range of correlation or interpolation problems in fiber sensing data analysis and beyond.

A new calibration implementation for Doppler Coherence Imaging Spectroscopy

A new widely tunable, continuous-wave laser named C-Wave enables direct calibration at the unshifted, center-of-mass wavelength for most plasma lines in the range between 450 and 650 nm for Doppler Coherence Imaging Spectroscopy. It also provides the ability to scan around each desired wavelength over a small range of ±50pm, thus enabling an easy way to translate the measured phase difference ΔΦ of the diagnostic to the desired Doppler line shift Δλ, that corresponds to the physical parameter of interest, the particle velocity of an observed plasma species.A first wavelength scan of the C-Wave laser ±50pm around a single plasma line of interest, C III at 464.881 nm, is presented and compared to a simulated wavelength scan. It demonstrates not only the C-Wave capability as a Doppler CIS calibration source, but also its potential to immensely simplify Doppler CIS analysis for nearly all visible plasma lines of interest.

Laser frequency locking and intensity normalization in wavelength modulation spectroscopy for sensitive gas sensing.

A novel method for laser frequency locking and intensity normalization in wavelength modulation spectroscopy (WMS)-based gas sensor system is reported. The center spacing between two second harmonic peaks demodulated from the rising and falling edges of a scanning triangular wave (for wavelength scan) is employed as a frequency locking reference. Amplitude of the directly acquired sine signal (for wavelength modulation) in the spectral region far away from the absorption feature is employed as an intensity normalization reference. A 50 ppm CH4:N2 sample sealed in a multi-pass cell at 1 atm was employed as the target analyte for demonstration. The frequency locking significantly improves measurement accuracy, and the introduced intensity normalization method realized a ~3 times SNR improvement as compared to the commonly used 1f normalization method under frequency locking conditions. A minimum measurement precision of ~2.5 ppbv was achieved with a normalized noise equivalent absorption coefficient of 1.8 × 10-9 cm-1Hz-1/2.

Near-infrared methane sensor based on a distributed feedback laser

In this article, a near-infrared methane detection system using tunable diode laser absorption spectroscopy technology was designed and implemented. The distributed feedback laser was driven by a self-developed temperature and current controller to allow scanning the selected absorption wavelength at 1654 nm. Laser temperature fluctuation was lower than 0.01%, and the output emission wavelength was linear and stable. The emitted beam passed a reflective gas chamber and was received by the Indium Gallium Arsenide photodiode detector. Through a data acquisition card, a digital lock-in amplifier was developed to extract the second harmonics with real-time monitoring and adjustment. Based on Allan deviation analysis, the limit of detection was about 48 ppm with a path length of 30 cm, at an integration time of 6 s. The experimental results revealed a maximum detection error of less than 3% at a gas concentration higher than 100 ppm. The fluctuations rates in long-term (9 hr) stability measurements for 1 × 103 ppm and 1 × 104 ppm methane samples were 0.8% and 0.48%, respectively, indicating good stability for the sensor. In the control module design, compared with previous reports on methane detection systems, the current system uses a self-developed temperature controller, a current driver and a signal processor, to allow real-time display and adjustments. The potential for adjustable wavelength scanning is available for multi-gas detection based on a single detection system.

Optical design of a multi-channel narrow-band imager for Lyman ultraviolet observation of diffuse sources.

This paper describes a novel optical design for a multi-channel narrow-band imager observing at the Lyman ultraviolet wavelengths. As one of the key instruments onboard the Census of Warm-Hot Intergalactic Medium, Accretion, and Feedback Explorer space mission, the imager is designed to map the neutral hydrogen Lyman-α line emissions from the intergalactic medium and nearby galaxies. The optical design features an instantaneous field of view (FOV) of 20arc min in diameter and a moderate and adjustable spectral resolution of 500-2000. A highly dispersive monochromator system is used to split the incident light into several wavelength channels, each with a full-field imaging capability and adjustable bandwidth, and the ensuing imaging optics form the individual channel images on different areas of the same microchannel plate detector. Channel wavelengths are tunable and a continuous wavelength scanning across the entire band of interest is proposed, which yields spectrally resolved 3D images with moderate spectral resolutions.

基于电流扫描波长响应函数直接确定正弦波扫描波长调制光谱中DFB激光器的相对波长响应

基于电流扫描波长响应函数直接确定正弦波扫描波长调制光谱中DFB激光器的相对波长响应

SINTESIS DAN UJI AKTIVITAS ANTIBAKTERI SENYAWA TURUNAN AMOKSISILIN TERHADAP Escherichia coli

Amoxicillin derivate compounds from the reaction of amoxicillin with p-aminophenol are synthesized compounds by reacting amoxicillin and p-aminophenol. . Escherichia coli is a flora normal bacteria that can causing infectious diseases. This research aimed to determine the antibiotic activity of amoxicillin derivat compound (amoxicillin with p-aminophenol) on the growth of E. coli. This research was conducted using the disc diffusion method. amoxicillin derivat compound (amoxicillin with p-aminophenol) were characterized by organoleptic test, melting point determination, pH test determination, Rf value, and maximum wavelength. The results of the organoleptic test showed that amoxicillin derivates from amoxicillin and p-aminophenol reaction is crystal powder, dark brown and bit bitter. Melting point of amoxicillin derivates from amoxicillin and p-aminophenol reaction was 160oC. pH test of amoxicillin derivates from amoxicillin and p-aminophenol reaction was 6,5. Rf value of amoxicillin derivates from amoxicillin and p-aminophenol reaction was 0,79. The results of UV wavelength scanning showed that amoxicillin derivates from amoxicillin and p-aminophenol reaction at 295 nm. Antibiotic activity showed by the clear zone form around the paper disk. The results showed that E. coli was resistant to pure amoxicillin. Amoxicillin derivat compound (amoxicillin with p-aminophenol) with concentrations of 100% and 12,5% have the largest inhibitory zones (6,33 mm) compared with concentrations of 50% and 25%, 5,33 and 6,00 mm respectively. Based on these results it can be concluded that derivat compound of amoxicillin (amoxicillin with p-aminophenol) has antibiotic activity against the growth of E. coli that has been resistant to pure amoxicillin. Keywords : Derivate compound of amoxicillin, Escherichia coli, antibiotic activity

Stability indicating high-performance thin layer chromatography method for estimation of ascorbic acid in Hibiscus sabdariffa L. aqueous extract

Background: High performance thin layer chromatography (HPTLC) has become a routine analysis technique due to its advantages of low operating cost, high sample throughput and need minimum sample clean up. Aim: To develop and validate an accurate, specific, repeatable and stability-indicating HPTLC method for the determination of ascorbic acid in presence of their degradation products for assessment of stability of the ascorbic acid in Hibiscus sabdariffa L. preparations. Methods: Chromatographic sample separations employed thin layer chromatography plates (20 cm x10 cm) pre-coated with silica gel 60 F254 as a stationary phase. Solvent system consisted of acetone: toluene: water: glacial acetic acid (26:4:4:1 v/v) while scanning wavelength of 269 nm was used. Ascorbic acid was subjected to stress degradation conditions i.e. oxidation, dry heat treatment, photo degradation and hydrolysis under different PH. Method was validated according to international council for harmonisation guidelines. Results: Peaks of products formed were well resolved with different Rf values. The linear regression data for the calibration plots showed good linear relationship with r2 = 0.9912 in the concentration range 2-4 µg/ml. The mean value slope and intercept were -531.72 and 8040.22 respectively. Conclusion: A rapid, simple, accurate and specific HPTLC method for determination of ascorbic acid in Hibiscus sabdariffa L. preparations was developed and validated. In addition, this method separated all the degradants from stress conditions showing that it is a stability indicating method. The developed method could now be used in quality control of H. sabdariffa herb products.

Spatially resolved LAAS/OES diagnostics of a free-burning Ar arc: measurements of excited atom densities

Spatially resolved optical diagnostics are applied to a free-burning DC arc in argon at atmospheric pressure. Densities of metastable and resonance -atoms are measured by laser atomic absorption spectroscopy (LAAS). The novel LAAS design allowed for an extended range of wavelength scan covering the complete Stark broadened line profile (∼ nm). High spatial resolution of 0.2 mm allowed measurements of atom densities and line profiles in the regions of high-temperature gradients. Besides absorbing -states, the radiating -states were measured using optical emission spectroscopy (OES). Results of the LAAS and OES measurements are compared with the nonequilibrium collisional-radiative model. Measurement of metastable states in the non-radiating regions near the cathode reveals the existence of a ‘collar’ effect. The interpretation of the effect with a focus on transport of resonance radiation is given, quantitative agreement between simulations and experiment is reached.

A Free-Space Interferometer for Phase-Delay Measurements in Integrated Optical Devices in Degenerate Pump-and-Probe Experiments

The authors report on a free-space interferometer for simultaneous phase and transmittance measurements of an optical signal in an integrated photonic circuit during degenerate pump-and-probe experiments. Differentiation of the weak probe signal from the strong pump relies on a lock-in amplifier. The interferometer shows high flexibility in terms of operating wavelengths, tested devices, and optical powers; it works with any integrated optical device provided with optical input–output channels; it can operate both with high input power (up to 100 mW at the sample input port) and low output power ( $ at the detection stage). Measuring both the transmittance and the phase of the optical signal allows using the phasor representation in the analysis. A dynamic operating mode allows to perform power and/or wavelength scan of the input signal, obtaining transmittance and phase spectra of the tested device. Remote control of the system and insulation from the external environment brings to more stable operating conditions. Characterization of the system properties with photonic-integrated structures (waveguide and ring resonator) is reported, with observed phase stability as high as 0.25°/min and average phase noise below 1°.

Macrophage uptake switches on OCT contrast of superparamagnetic nanoparticles for imaging of atherosclerotic plaques.

BackgroundOptical coherence tomography (OCT) is an intravascular, high-resolution imaging technique that is used to characterize atherosclerotic plaques. However, the identification of macrophages as important markers of inflammation and plaque vulnerability remains difficult. Here, we investigate whether the uptake of very small iron oxide particles (VSOP) in macrophages, that cluster in phagolysosomes and allow high-quality magnetic resonance imaging (MRI) of atherosclerotic plaques, and uptake of ferumoxytol nanoparticles enhance detection of macrophages by OCT.Materials and methodsRAW 264.7 macrophage cells were incubated with VSOP (1 and 2 mM Fe) that have been clinically tested and ferumoxytol (8.9 mM Fe) that is approved for iron deficiency treatment and currently investigated as an MRI contrast agent. The light scattering of control macrophages, nanoparticle-labeled macrophages (2,000,000 in 500 µL) and nanoparticle suspensions was measured in synchronous wavelength scan mode using a fluorescence spectrophotometer. For OCT analyses, pellets of 8,000,000 non-labeled, VSOP-labeled and ferumoxytol-labeled RAW 264.7 macrophages were imaged and analyzed on an OPTIS™ OCT imaging system.ResultsIncubation with 1 and 2 mM VSOP resulted in uptake of 7.1±1.5 and 12±1.5 pg Fe per cell, which increased the backscattering of the macrophages in spectrophotometry 2.5- and 3.6-fold, whereas incubation with 8.9 mM Fe ferumoxytol resulted in uptake of 6.6±2 pg Fe per cell, which increased the backscattering 1.5-fold at 700 nm. In contrast, backscattering of non-clustered nanoparticles in suspension was negligible. Accordingly, OCT imaging could visualize significantly increased backscattering and signal attenuation of nanoparticle-labeled macrophages in comparison with controls.ConclusionWe conclude that VSOP and, to a lesser extent, ferumoxytol increase light scattering and attenuation when taken up by macrophages and can serve as a multimodal imaging probe for MRI and OCT to improve macrophage detection in atherosclerotic plaques by OCT in the future.

Fluorescence Multiplexing with Spectral Imaging and Combinatorics.

Ultraviolet-to-infrared fluorescence is a versatile and accessible assay modality but is notoriously hard to multiplex due to overlap of wide emission spectra. We present an approach for fluorescence called multiplexing using spectral imaging and combinatorics (MuSIC). MuSIC consists of creating new independent probes from covalently linked combinations of individual fluorophores, leveraging the wide palette of currently available probes with the mathematical power of combinatorics. Probe levels in a mixture can be inferred from spectral emission scanning data. Theory and simulations suggest MuSIC can increase fluorescence multiplexing ∼4-5 fold using currently available dyes and measurement tools. Experimental proof-of-principle demonstrates robust demultiplexing of nine solution-based probes using ∼25% of the available excitation wavelength window (380-480 nm), consistent with theory. The increasing prevalence of white lasers, angle filter-based wavelength scanning, and large, sensitive multianode photomultiplier tubes make acquisition of such MuSIC-compatible data sets increasingly attainable.

High-fidelity cavity soliton generation in crystalline AlN micro-ring resonators.

Chip-scale mode-locked dissipative Kerr solitons have been realized on various materials platforms, making it possible to achieve a miniature, highly coherent frequency comb source with high repetition rates. Aluminum nitride (AlN), an appealing nonlinear optical material having both Kerr (χ3), and Pockels (χ2) effects, has immerse potential for comb self-referencing without the need for external harmonic generators. However, cavity soliton states have not yet been achieved in AlN microresonators. Here, we demonstrate mode-locked Kerr cavity soliton generation in a crystalline AlN microring resonator. By utilizing ultrafast tuning of the pump frequency through single-sideband modulation, in combination with an optimized wavelength scan and pump power-ramp patterns, we can deterministically elongate a ∼400 ns short-lived soliton to a time span as long as we wish to hold it.

Distortion-tolerated high-speed FBG demodulation method using temporal response of high-gain photodetector

Abstract A distortion-tolerated fiber Bragg grating (FBG) demodulation method for high-gain or high-speed sensing is proposed. The temporal response of photodetector (PD) on FBG reflection spectrum for different electric gains and wavelength scanning frequencies is investigated theoretically and experimentally. Simulation results show that high electric gains and high wavelength scanning frequencies will induce a tailed distortion on the right side of the FBG reflection peak output by the PD. A temporal response function of PD is presented to fit the peak with distortion and determine the peak position on FBG reflection spectrum. Experiments with varying degrees of FBG acquisition distortion are carried out. Compared with the traditional Gaussian fitting method, the measurement error of the temporal-response based method is limited within ±1.777 pm and the standard deviation is less than 0.940 pm, which are respectively improved by 6.87 times and 4.38 times at least.

Modified wavelength scanning interferometry for simultaneous tomography and topography of the cornea with Fourier domain optical coherence tomography.

Visual acuity is dependent on corneal shape and size. A minor variation in surface geometry can cause a deformation of corneal geometry, which affects its optical performance. In this work we demonstrate an algorithm for the simultaneous measurement of corneal tomography and topography with a traditional point-scanning Fourier domain optical coherence tomography (FD-OCT) system. A modified wavelength scanning interferometry (mWSI) algorithm enabled topographical evaluation of the surface with nanometer-scale resolution, which is superior to the micrometer-scale resolution of traditional OCT structural imaging. We validated the technique with an optically flat mirror, standard roughness gauges, and atomic force microscopy (AFM). The mirror results show nanometer-scale sensitivity (~3.5 nm), and the mWSI measurements were in good agreement (error ~5%) with the specifications of the roughness comparator and AFM, demonstrating the accuracy of the technique. Following validation, the measurements were made on pig corneas in situ at various artificially controlled intraocular pressures (IOP) and before and after cross-linking (CXL). The results show that the mean surface roughness increased by ~65% after removal of the epithelium in preparation for CXL but did not change as a function of IOP. The demonstrated method could be used for simultaneous measurement of tissue tomography with micrometer-precision and topography with nanometer-precision.