The Experts below are selected from a list of 354 Experts worldwide ranked by ideXlab platform
Shilong Pan - One of the best experts on this subject based on the ideXlab platform.
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ultrahigh resolution and wideband optical vector analysis for arbitrary responses
Optics Letters, 2018Co-Authors: Shifeng Liu, Min Xue, Shilong PanAbstract:An ultrahigh-resolution and wideband optical vector analyzer (OVA) with the simplest architecture, to the best of our knowledge, is proposed and demonstrated based on chirped optical double-sideband (ODSB) modulation in a single-drive Mach-Zehnder modulator (MZM). To distinguish the magnitude and phase information carried by the two sidebands in the ODSB signal, a two-step Measurement, in which biasing, respectively, the MZM at two different points is applied. Because no optical filtering is required in the scheme, the optical carrier can be located at any wavelength that is suitable for accurate Measurement, e.g., close to the notch of a notch response or within the passband of a bandpass response, so the proposed OVA has the capability to measure an arbitrary response. An experiment is carried out, which achieves the magnitude and phase responses of a programmable optical processor with bandpass, notch, or falling-edge responses. The Measurement Bandwidth is 134 GHz, and the Measurement resolution is 1.12 MHz.
K Pierz - One of the best experts on this subject based on the ideXlab platform.
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time domain optoelectronic vector network analysis on coplanar waveguides
IEEE Transactions on Microwave Theory and Techniques, 2015Co-Authors: Mark Bieler, Heiko Fuser, K PierzAbstract:The development of a one-port laser-based vector network analyzer (VNA) is described. Measurements are carried out in the time domain using a femtosecond laser for the generation and detection of ultrashort voltage pulses on a coplanar waveguide (CPW). The accurate separation of voltage signals propagating in forward and backward directions, being one of the key tasks of vector network analysis, is achieved by measuring voltage pulses at different positions on the CPW. This separation technique even works in the case of temporally overlapping forward and backward propagating signals. With this laser-based VNA, a frequency spacing of 500 MHz, a Measurement Bandwidth of approximately 500 GHz, and a dynamic range of more than 40 dB are obtained. As an application example, the laser-based VNA is used to realize an ultra-broadband voltage pulse standard.
Ronald K Hanson - One of the best experts on this subject based on the ideXlab platform.
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ultra sensitive spectroscopy of oh radical in high temperature transient reactions
Optics Letters, 2018Co-Authors: Shengkai Wang, Ronald K HansonAbstract:The hydroxyl (OH) radical is arguably the most important transient radical in high-temperature gas-phase combustion reactions, yet it is very difficult to measure because of its high reactivity and, thus, short lifetime and low concentration. This work reports the development of a novel method for ultra-sensitive, quantitative, and microsecond-resolved detection of OH based on UV frequency-modulation spectroscopy (FMS). To the best of the authors’ knowledge, this is the first FMS demonstration in the near-UV spectral region for detection of short-lived radical species. Shot-noise-limited detection was achieved at an optical power of 25 mW. A proof-of-concept experiment in a tabletop H2O/He microwave discharge cell has reached a 1σ minimum detectable absorbance (MDA) of less than 2×10−4 over 1 MHz Measurement Bandwidth. High-temperature OH Measurement was demonstrated in a 15 cm diameter shock tube, where a typical MDA of 3.0×10−4 was achieved at 1330 K, 0.38 atm, and 1 MHz. These preliminary results have outperformed the previous best MDA by more than a factor of 3; further improvement by another order of magnitude is anticipated, following the strategies outlined at the end of this Letter. The current method paves the path to parts per billion (ppb) -level OH detection capability and offers prospects to significantly advance fundamental combustion research by enabling direct observation of OH formation and scavenging kinetics during key stages of fuel oxidation that were inaccessible with previous methods.
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wavelength modulation spectroscopy near 1 4 µm for Measurements of h2o and temperature in high pressure and temperature gases
Measurement Science and Technology, 2014Co-Authors: Christopher S Goldenstein, R. Mitchell Spearrin, Ian A Schultz, Jay B. B. Jeffries, Ronald K HansonAbstract:The development, validation and demonstration of a two-color tunable diode laser (TDL) absorption sensor for Measurements of temperature and H2O in high-pressure and high-temperature gases are presented. This sensor uses first-harmonic-normalized wavelength-modulation spectroscopy with second-harmonic detection (WMS-2f/1f) to account for non-absorbing transmission losses and emission encountered in harsh, high-pressure environments. Two telecommunications-grade TDLs were used to probe H2O absorption transitions near 1391.7 and 1469.3 nm. The lasers were frequency-multiplexed and modulated at 160 and 200 kHz to enable a Measurement Bandwidth up to 30 kHz along a single line-of-sight. In addition, accurate Measurements are enabled at extreme conditions via an experimentally derived spectroscopic database. This sensor was validated under low-absorbance (<0.05) conditions in shock-heated H2O–N2 mixtures at temperatures and pressures from 700 to 2400 K and 2 to 25 atm. There, this sensor recovered the known temperature and H2O mole fraction with a nominal accuracy of 2.8% and 4.7% RMS, respectively. Lastly, this sensor resolved expected transients with high Bandwidth and high precision in a reactive shock tube experiment and a pulse detonation combustor.
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secondary diaphragm thickness effects and improved pressure Measurements in an expansion tube
AIAA Journal, 2014Co-Authors: Victor A Miller, Mirko Gamba, Godfrey M Mungal, Ronald K HansonAbstract:T HE aim of this Technical Note is to present practical considerations for measuring pressure in an expansion-tube flow facility; some aspects of this work can be applied to pressure Measurement strategies in other impulse (e.g., reflected shock tunnel) or continuous flow facilities that may suffer from similar issues. We assume that the reader is familiar with the terminology and general operating principles regarding expansion tubes; formore information regarding expansion tubes, please refer to the seminal work of Trimpi [1]. In many studies relevant to aerospace engineering, propulsion, and fluid mechanics, pressure Measurement is often a diagnostic of primary interest [2–7], but obtaining high-quality (i.e., high signalto-noise, or SNR) pressure Measurements can be a challenge in expansion-tube facilities (or other impulse facilities). Because of the short test times in impulse facilities, high-Bandwidth pressure transducers are necessary to capture transients of interest, but as we show in this work, certain transducer architectures are more susceptible to noise than others. Analog or digital signal processing can be used to filter some noise from the Measurements, but at the expense of Measurement Bandwidth or accuracy; thus, the engineer must compromise between Bandwidth and SNR to acquire reliable pressure Measurements. Practical information regarding the acquisition of optimal (i.e., high SNR) pressure Measurements in impulse facilities is sparse; however, some articles do provide useful details of implementation, for example Dufrene et al. [8] present specifics of pressure instrumentation in an expansion-tube facility, and Beresh et al. [9] report on the response characteristics of a variety of pressure transducers. Expansion-tube facilities also produce a contaminated freestream flow due to the presence of the secondary diaphragm; the primary shock wave may reflect off the secondary diaphragm [10], and secondary diaphragm fragments of a broad range of sizes are entrained in the test gas [11]. We have found that diaphragm fragments impacting the structure in which pressure transducers are mounted can have a significant, adverse effect on pressure Measurement quality. An example of this effect is presented in Fig. 1, which shows a pressure time history alongwith a schlieren image taken at the instant in time when a diaphragm fragment impacts the model that houses the pressure transducers. The shadowed shape in the schlieren image is a flat platewith a pitot-pressure transducer (PCB113A26)mounted above the plate in a conical housing; directly below the pitot opening, a wall-mounted transducer (PCB 112A22) simultaneously measures the wall static pressure. (We will interpret these pressure traces in Sec. III.A, but for now, we only demonstrate the level of noise in the two traces.) The displayed still schlieren image is taken from a high-speed schlieren video that captures the full event during a test. A diaphragm fragment can be seen impacting the top of the model, at which time both pressure traces become extremely noisy. We have also observed the spontaneous eruption of noise in pressure time histories in many other tests, and generally, the time at which the pressure traces become noisy varies from shot to shot, and the onset of noise never occurs before the arrival of the test gas. These introductory observations suggest that diaphragm fragments impacting the model are a major source of noise in these pressure Measurements. To test the hypothesis that diaphragm fragment impacts are a source of noise in pressure Measurements, we make pressure Measurements as a function of secondary diaphragm thickness, expecting thinner diaphragms (and less massive fragments) to cause less noise. Two types of pressure transducers are also tested, two different piezoelectric sensors and two different piezoresistive sensors, and the noise characteristics of each sensor are compared. As a secondary objective, we also test whether the secondary diaphragm thickness affects test-gas conditions as inferred from shock speed Measurements. Last, a practical solution for minimizing noise in piezoelectric transducers is provided.
Paul C Beard - One of the best experts on this subject based on the ideXlab platform.
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large area laser scanning optical resolution photoacoustic microscopy using a fibre optic sensor
Biomedical Optics Express, 2018Co-Authors: Thomas J Allen, Olumide Ogunlade, Edward Z Zhang, Paul C BeardAbstract:A laser scanning optical resolution photoacoustic microscopy (LS OR-PAM) system based on a stationary fibre optic sensor is described. The sensor comprises an optically resonant interferometric polymer cavity formed on the tip of a rounded single mode optical fibre. It provides low noise equivalent pressure (NEP = 68.7 Pa over a 20 MHz Measurement Bandwidth), a broad Bandwidth that extends to 80 MHz and a near omnidirectional response. The latter is a significant advantage, as it allows large areas (>1cm2) to be imaged without the need for translational mechanical scanning offering the potential for fast image acquisition. The system provides a lateral resolution of 8 µm, an axial resolution of 21 µm, and a field of view up to 10 mm × 10 mm. To demonstrate the system, in vivo 3D structural images of the microvasculature of a mouse ear were obtained, showing single capillaries overlaying larger vessels as well as functional images revealing blood oxygen saturation.
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a fabry perot fiber optic ultrasonic hydrophone for the simultaneous Measurement of temperature and acoustic pressure
Journal of the Acoustical Society of America, 2009Co-Authors: Paul Morris, Edward Z Zhang, A Hurrell, Adam Shaw, Paul C BeardAbstract:A dual sensing fiber-optic hydrophone that can make simultaneous Measurements of acoustic pressure and temperature at the same location has been developed for characterizing ultrasound fields and ultrasound-induced heating. The transduction mechanism is based on the detection of acoustically- and thermally-induced thickness changes in a polymer film Fabry–Perot interferometer deposited at the tip of a single mode optical fiber. The sensor provides a peak noise-equivalent pressure of 15 kPa (at 5 MHz, over a 20 MHz Measurement Bandwidth), an acoustic Bandwidth of 50 MHz, and an optically defined element size of 10 μm. As well as measuring acoustic pressure, temperature changes up to 70 °C can be measured, with a resolution of 0.34 °C. To evaluate the thermal Measurement capability of the sensor, Measurements were made at the focus of a high-intensity focused ultrasound (HIFU) field in a tissue mimicking phantom. These showed that the sensor is not susceptible to viscous heating, is able to withstand high i...
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backward mode multiwavelength photoacoustic scanner using a planar fabry perot polymer film ultrasound sensor for high resolution three dimensional imaging of biological tissues
Applied Optics, 2008Co-Authors: Edward Z Zhang, Jan Laufer, Paul C BeardAbstract:A multiwavelength backward-mode planar photoacoustic scanner for 3D imaging of soft tissues to depths of several millimeters with a spatial resolution in the tens to hundreds of micrometers range is described. The system comprises a tunable optical parametric oscillator laser system that provides nanosecond laser pulses between 600 and 1200 nm for generating the photoacoustic signals and an optical ultrasound mapping system based upon a Fabry-Perot polymer film sensor for detecting them. The system enables photoacoustic signals to be mapped in 2D over a 50 mm diameter aperture in steps of 10 microm with an optically defined element size of 64 microm. Two sensors were used, one with a 22 microm thick polymer film spacer and the other with a 38 mum thick spacer providing -3 dB acoustic Bandwidths of 39 and 22 MHz, respectively. The measured noise equivalent pressure of the 38 microm sensor was 0.21 kPa over a 20 MHz Measurement Bandwidth. The instrument line-spread function (LSF) was measured as a function of position and the minimum lateral and vertical LSFs found to be 38 and 15 microm, respectively. To demonstrate the ability of the system to provide high-resolution 3D images, a range of absorbing objects were imaged. Among these was a blood vessel phantom that comprised a network of blood filled tubes of diameters ranging from 62 to 300 microm immersed in an optically scattering liquid. In addition, to demonstrate the applicability of the system to spectroscopic imaging, a phantom comprising tubes filled with dyes of different spectral characteristics was imaged at a range of wavelengths. It is considered that this type of instrument may provide a practicable alternative to piezoelectric-based photoacoustic systems for high-resolution structural and functional imaging of the skin microvasculature and other superficial structures.
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characterization of a polymer film optical fiber hydrophone for use in the range 1 to 20 mhz a comparison with pvdf needle and membrane hydrophones
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, 2000Co-Authors: Paul C Beard, A Hurrell, T N MillsAbstract:A small aperture wideband ultrasonic optical fiber hydrophone is described. The transduction mechanism is based on the detection of acoustically induced changes in the optical thickness of a 25-/spl mu/m thick parylene polymer film acting as a low finesse Fabry Perot (FP) interferometer that is deposited directly onto the end of a single mode optical fiber. The acoustic performance compares favorably with that of PVDF needle and membrane hydrophones with a peak noise-equivalent-pressure (without signal averaging) of 10 kPa over a 25-MHz Measurement Bandwidth, a wideband response to 20 MHz, and a near omnidirectional performance at 10 MHz. The dynamic range was 60 dB with an upper limit of linear detection of 11 MPa and a temporal stability of <5% over a period of 20 h. The hydrophone can also measure temperature changes with a resolution of 0.065/spl deg/C, offering the prospect of making simultaneous acoustic pressure and temperature Measurements. The transduction parameters of the FP sensing element were measured, yielding an ultrasonic acoustic phase sensitivity of 0.075 rad/MPa and a temperature phase sensitivity of 0.077 rad//spl deg/C. The ability to achieve high acoustic sensitivity with small element sizes and to repeatably fabricate rugged sensor downleads using polymer deposition techniques suggests that this type of hydrophone can provide a practical alternative to piezoelectric hydrophone technology.
Shifeng Liu - One of the best experts on this subject based on the ideXlab platform.
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ultrahigh resolution and wideband optical vector analysis for arbitrary responses
Optics Letters, 2018Co-Authors: Shifeng Liu, Min Xue, Shilong PanAbstract:An ultrahigh-resolution and wideband optical vector analyzer (OVA) with the simplest architecture, to the best of our knowledge, is proposed and demonstrated based on chirped optical double-sideband (ODSB) modulation in a single-drive Mach-Zehnder modulator (MZM). To distinguish the magnitude and phase information carried by the two sidebands in the ODSB signal, a two-step Measurement, in which biasing, respectively, the MZM at two different points is applied. Because no optical filtering is required in the scheme, the optical carrier can be located at any wavelength that is suitable for accurate Measurement, e.g., close to the notch of a notch response or within the passband of a bandpass response, so the proposed OVA has the capability to measure an arbitrary response. An experiment is carried out, which achieves the magnitude and phase responses of a programmable optical processor with bandpass, notch, or falling-edge responses. The Measurement Bandwidth is 134 GHz, and the Measurement resolution is 1.12 MHz.
