Continuous Wave Research Papers - Academia.edu (original) (raw)

An applications-oriented review of optical parametric amplifiers in fiber communications is presented. The emphasis is on parametric amplifiers in general and single pumped parametric amplifiers in particular. While a theoretical framework based on highly efficient four-photon mixing is provided, the focus is on the intriguing applications enabled by the parametric gain, such as all-optical signal sampling, time-demultiplexing, pulse generation, and wavelength conversion. As these amplifiers offer high gain and low noise at arbitrary wavelengths with proper fiber design and pump wavelength allocation, they are also candidate enablers to increase overall wavelength-division-multiplexing system capacities similar to the more well-known Raman amplifiers. Similarities and distinctions between Raman and parametric amplifiers will also be addressed. Since the first fiber-based parametric amplifier experiments providing net continuous-wave gain in the for the optical fiber communication applications interesting 1.5-m region were only conducted about two years ago, there is reason to believe that substantial progress may be made in the future, perhaps involving "holey fibers" to further enhance the nonlinearity and thus the gain. This together with the emergence of practical and inexpensive high-power pump lasers may in many cases prove fiber-based parametric amplifiers to be a desired implementation in optical communication systems.

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- Quantum Physics, Optical Communication System, Optical physics, Wavelength Conversion

The effect of operating parameters on the thrombolytic potency of ultrasound (US) is important for potential therapeutic applications, but is not fully understood. Fresh human whole-blood thrombi were exposed in vitro to focused US from a diagnostic transducer driven by an impulse generator via an amplifier to vary duration (10 to 60 min), intensity (7 to 90 W/cm 2 ), frequency (2 to 4.5 MHz), pulsed wave duty cycle (1:5 to 1:100 and continuous wave mode) and pulse length (100 to 400 s). Segments of thrombi (498 ؎ 73 mg) were submersed and insonated in saline solution. Thrombolytic efficiency was expressed as percentage loss of mass compared with controls (noninsonified thrombi). Ultrasound exposure achieved a significantly higher thrombolysis than no US, 56 ؎ 16 % vs. 29 ؎ 11 % (n ‫؍‬ 232, p < 10 ؊6 ). There was an exponential saturation-type correlation with duration of insonation (r 2 ‫؍‬ 0.64) and intensity (r 2 ‫؍‬ 0.97), an inverse correlation with US frequency at matched intensities (r 2 ‫؍‬ 0.76, p < 10 ؊5 ), a logarithmic relationship with duty cycle in pulsed mode (r 2 ‫؍‬ 0.86) and a modest direct effect of pulse length (r 2 ‫؍‬ 0.57, p < 10 ؊5 ). Thus, thrombolytic efficiency of US depends directly on duration, intensity, duty cycle and pulse length and inversely, on frequency. (

- by U. Nixdorff
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- Ultrasound, Ultrasonic therapy, Clinical Sciences, Thrombosis

The present study concerns laser surface alloying with silicon of mild steel substrate using a high-power continuous wave CO2 laser with an objective to improve wear resistance. The effect of surface remelting using nitrogen as shrouding environment (with and without graphite coating) on microhardness and wear resistance has also been evaluated. Laser surface alloying leads to formation of a defect free microstructure consisting of iron silicides in laser surface alloyed mild steel with silicon and a combination of silicides and nitrides when remelted in nitrogen. Carbon deposition prior to remelting leads to presence of a few martensite in the microstructure. A significant improvement in microhardness is achieved by laser surface alloying and remelting to a maximum of 800 VHN when silicon alloyed surface is melted using nitrogen shroud with carbon coating. A detailed wear study (against diamond) showed that a significant improvement in wear resistance is obtained with a maximum improvement when remelted in nitrogen atmosphere followed by carbon coating.

- by Jyotsna Dutta Majumdar
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- Engineering, Wear, Surface, CHEMICAL SCIENCES

This paper is a study on various electric signals, which were employed over the History of Communication Engineering in its main landmarks: the telegraph and the telephone. The signals are presented in their time and frequency domain representations. The historical order has been followed in the presentation: wired systems; spark gap wireless; continuous wave (CW) and amplitude modulation (AM); detection by rectification; and frequency modulation (FM). The analysis of these signals is meant to lead into a better understanding on the evolution of communication technology. The material presented in this work could be used to illustrate "Signals and Systems" and "Communication Systems" courses, taking advantage of its technical as well as historical contents.

- by Denise Consonni
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- Engineering, Computer Science, Education, Communication System

Terahertz radiation is increasingly being applied in new and evolving technologies applied in areas such as homeland security and medical imaging. Thus a timely assessment of the potential hazards and health effects of occupational and general population exposure to THz radiation is required. We applied continuous-wave (CW) 0.1 THz radiation (0.031 mW/ cm 2) to dividing lymphocytes for 1, 2 and 24 h and examined the changes in chromosome number of chromosomes 1, 10, 11 and 17 and changes in the replication timing of their centromeres using interphase fluorescence in situ hybridization (FISH). Chromosomes 11 and 17 were most vulnerable (about 30% increase in aneuploidy after 2 and 24 h of exposure), while chromosomes 1 and 10 were not affected. We observed changes in the asynchronous mode of replication of centromeres 11, 17 and 1 (by 40%) after 2 h of exposure and of all four centromeres after 24 h of exposure (by 50%). It is speculated that these effects are caused by radiation-induced lowfrequency collective vibrational modes of proteins and DNA. Our results demonstrate that exposure of lymphocytes in vitro to a low power density of 0.1 THz radiation induces genomic instability. These findings, if verified, may suggest that such exposure may result in an increased risk of cancer. ᭧ 2008 by Radiation Research Society METHODS Cultures Lymphocytes were isolated by UNI-SEP maxi (NovaMed Ltd., Jerusalem, Israel. Catalog no. U-10) from 20 ml of whole blood obtained by vacu

- by Alon Eliran
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- Radiation, Homeland Security, Low Frequency, Biological Sciences
- by Kevin Lehmann
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- Mechanical Engineering, Resonators, Applied Optics, Optical physics

An electrically pumped light source on silicon is a key element needed for photonic integrated circuits on silicon. Here we report an electrically pumped AlGaInAs-silicon evanescent laser architecture where the laser cavity is defined solely by the silicon waveguide and needs no critical alignment to the III-V active material during fabrication via wafer bonding. This laser runs continuous-wave (c.w.) with a threshold of 65 mA, a maximum output power of 1.8 mW with a differential quantum efficiency of 12.7 % and a maximum operating temperature of 40 °C. This approach allows for 100's of lasers to be fabricated in one bonding step, making it suitable for high volume, low-cost, integration. By varying the silicon waveguide dimensions and the composition of the III-V layer, this architecture can be extended to fabricate other active devices on silicon such as optical amplifiers, modulators and photo-detectors.

The thermal third order nonlinearity of a neutral density glass is measured using the Z-Scan method. The measurements are performed using two different laser configurations: a continuous wave laser at 532 nm and a femtosecond laser at 1060 nm. The measurements are used to determine the nonlinear refractive index, n 2 and the thermo-optical coefficient dt dn of the samples. The measurements in the two different laser configurations are in good agreement with the existing theory models.

- by I. Dancus and +1
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- Femtosecond Laser, Refractive Index, Continuous Wave

a b s t r a c t 70 cm long Yb 3 + -doped Y 3 Al 5 O 12 (Yb:YAG) single-crystal fibers of 1 and 0.4 mm diameters were grown by the micro-pulling-down method. The structural and optical characterizations of those fibers showed that they exhibited a perfect single crystalline structure and have a homogeneous distribution of the Yb 3 + ion in the YAG host. In diode-pumped laser operation, a continuous wave output power of 50 W at 1030 nm was demonstrated for 180 W of pump power at 940 nm, for 1 mm diameter fibers. For 0.4 mm diameter fibers, 28 W at 1030 nm for 100 W of incident pump at 940 nm power was achieved. To the best of our knowledge, these results are the highest laser power ever obtained with directly grown singlecrystal fibers.

- by Julien Didierjean and +1
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- Crystal Growth, Single Crystal Growth, Single Crystal, Continuous Wave

This communication reports on post-processing of continuous wave EPR spectra by a digital convolution with filter functions that are subjected to differentiation or the Kramers-Krö nig transform analytically. In case of differentiation, such a procedure improves spectral resolution in the higher harmonics enhancing the relative amplitude of sharp spectral features over the broad lines. At the same time high-frequency noise is suppressed through filtering. These features are illustrated on an example of a Lorentzian filter function that has a principal advantage of adding a known magnitude of homogeneous broadening to the spectral shapes. Such spectral distortion could be easily and accurately accounted for in the consequent least-squares data modeling. Application examples include calculation of higher harmonics from pure absorption echo-detected EPR spectra and resolving small hyperfine coupling that are unnoticeable in conventional first derivative EPR spectra. Another example involves speedy and automatic separation of fast and broad slow-motion components from spin-label EPR spectra without explicit simulation of the slow motion spectrum. The method is illustrated on examples of X-band EPR spectra of partially aggregated membrane peptides.

- by Alex Smirnov
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- Engineering, Data Modeling, High Frequency, Computer Simulation
- by Deepa Venkitesh
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- Engineering, Applied Physics, Optical Communication, Fiber Laser

This work presents simulation and measurement results of the vital sign parameters based on low-power microwave and millimeter-wave monitoring systems through Doppler radar techniques. The cardiac beating and the breathing of patients are examined. Three systems operating at 5.8 GHz, 24 GHz and 35 GHz, respectively, are designed, simulated, and fabricated. Using such three systems and applying signal processing techniques, measured signals obtained at distance up to 1 m from the patient of reference are presented. These results show that the heartbeat and the frequency of breath are well detected which validates our radar analysis and design approach. Performances (sensitivity, complexity, etc.) of the different systems are compared and studied, showing that the highest sensitivity detection can be achieved with the system at the highest frequency (35 GHz) in this case.

- by Lydia Chioukh
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- Cardiology, Signal Processing, Millimeter Wave Antennas, Patient Monitoring

Beat frequencies between the transverse modes of an unstabilized CW CO2 laser were studied by detecting the homodyne signals emitted by the laser. Frequency pulling was observed and a resulting mode spacing reduction of up to 8 percent was measured. The dependence of mode pulling on total gas pressure was measured and was found to be in fair agreement with theory. The observed effect is important in some laser tuning techniques where it leads to a reduction of the tuning range and a nonlinear dependence of the laser frequency on cavity length.

- by Mira Naftaly
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- Mechanical Engineering, Carbon Dioxide, Applied Optics, Optical physics
- by G. Fasching
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- Organic Semiconductor Laser, Terahertz, Quantum Well, Growth rate

We report 85 C continuous-wave electrically pumped operation of a 1528-nm vertical-cavity laser. An InP-In-GaAsP active region was wafer bonded to GaAs-AlGaAs mirrors, with a superlattice barrier to reduce defect density in the active... more

- by D. Lofgreen
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- Photonics, Optical physics, Electrical And Electronic Engineering, Superlattices

A novel approach to finding an approximate analytic solution to the Bloch equation is developed in this paper. The method is based on time scaling and averaging of the Bloch equation after transformation to a rotating frame of reference. In order to accomplish the scaling, a novel time scaled magnetisation vector is introduced. The resultant time scaled system is subsequently approximated through averaging, a technique that to the best of our knowledge, has not previously been applied in the nuclear magnetic resonance context. Our proposed method of approximating the solution to the Bloch equation is valid for continuous wave excitation as well as the traditional pulse excitation with an arbitrary envelope, making this a widely applicable technique unlike previously proposed methods. Comparison of the approximate analytic solution and simulation results clearly indicates that the error is negligible when the field inhomogeneities are small compared to the excitation field amplitude. Extremum seeking techniques may be applied to determine the optimal excitation, given the form of the approximate solution. This result is applicable to a range of research areas including nuclear magnetic resonance, magnetic resonance imaging and optical resonance problems.

Many solid state laser systems rely on transversemagnetic polarized 808-nm diode lasers, whose efficiency is limited by the transparency current of the quantum well and whose peak power is limited by facet failure. Using optimized epitaxial growth, low voltage designs, and optimized facet reflectivity, we demonstrate 70% power conversion efficiency at 80 W in 1-cm laser bars under continuous-wave (CW) test conditions. We assess peak power limits in single emitters and find that 100-m stripe lasers roll thermally under the CW condition at 13 W without failure, then reach >50 W under 300-ns pulse condition, where they fail at internal defects.

- by G. Erbert and +2
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- Epitaxial Growth, Solid State Laser, Organic Semiconductor Laser, Passive Cooling

The use of portable wireless technology has increased dramatically over the past few years. This increased use has caused a heightened concern for electromagnetic interference from wireless-enabled technologies, such as laptop computers and cellular phones to aircraft communication and navigation radios. Researchers at NASA Langley Research Center, United Airlines and Eagles Wings Incorporated, have tested and collected interference path loss data on a United Airlines out-of-service B737 aircraft near Victorville, CA. This paper summarizes the results found from the measured data sets as well as includes graphical representations of the interference path loss data on a B737 plane with different system antennas.

- by madiha jafri
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- Engineering, Computer Science, Electromagnetic Interference, Communication System
- by Graham Turnbull
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- Mechanical Engineering, Oscillations, Steady state, Optical physics

In this paper, the content of two laboratory courses developed at the Department of Electronics of the Technological Educational Institute of Crete, Greece, focused on optoelectronics and optical communications, respectively, is presented. Both of these laboratory courses were developed with the philosophy of introducing a research-oriented approach. Emphasis is given on handson experimentation. In such a way, students get a better understanding of the various theoretical concepts (generation of light through single mode Continuous Wave lasers, transmission of optical power, etc.), and become able to analyze and solve problems associated with photonics components and their integration to optical systems. Coupling of experimentation and research is facilitated with a Marie Curie EU-funded grant for the establishment of a Centre of Excellence via the transfer of knowledge in the scientific area of optoelectronics and lasers. Our approach is presented by referring to specific laboratory exercises, such as the experimental study of a variable optical attenuator developed for research purposes, the development of an X-ray high power x-pinch optolectronic device, etc.).

- by Giorgos S Liodakis
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- Optical Communication, Course Development, X Rays, Experimental Study

A new portable brain imaging device based on continuous-wave functional near-infrared spectrometry (fNIRS) is presented. The source-detector part is composed of a multi-wavelength LED and a silicon photodetector that are directly placed on the scalp of the subject. The dimensions of the proposed device are small, as it has to be mounted on the head of an adult person. Acquired data are transmitted in real-time to a laptop for post processing using Matlab. Timemultiplexed light is used to achieve a higher SNR while keeping the device safe for long-term wearing. Preliminary evaluation on adults gave the expected accuracy and compare well with fNIRS characteristics found in literature, that are collected from bulky equipment. With a noise figure of -47dB and a sampling rate of 23Hz, the presented device is appropriate to isolate hemodynamic variations, which are strongly related to local cerebral activity.

- by Mohamad Sawan
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- Brain Imaging, Neurophysiology, Near Infrared, Biomedical Imaging

The potential of a continuous-wave microwave transceiver as a tool for detecting breathing and heartbeat of people buried in snow has been experimentally evaluated. The breathing has been clearly detected through a 1.8-m-thick snow barrier as well as through the 1.2-m-thick roof of an igloo dugout to simulate the experimental conditions of a human being trapped under an avalanche.

- by Massimiliano Pieraccini
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- Remote Sensing, Geomatic Engineering, SNOW, Experimental Evaluation

Three different lasers were compared under the same conditions for their effectiveness at producing photodynamic damage to normal colon following sensitization with aluminium sulphonated phthalocyanine (A1SPc). One laser was an argon ion pumped continuous wave (CW) dye laser and the other two were pulsed at 10 kHz (copper vapour laser pumped dye laser, and 5 Hz (flashlamp pumped dye laser). The CW and 10 kHz laser were equally effective at producing damage. The 5 Hz laser failed to produce a photodynamic effect, although occasionally caused a photomechanical effect when the laser fibre was placed touching the colonic mucosa. Quantitative analysis suggests that the high energy pulses of the flashlamp pumped dye laser saturate A1SPc, so very little of the available energy can be used to produce a photodynamic effect, in contrast to the two other lasers which do not produce saturation conditions.

- by Hugh Barr
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- Biomedical Engineering, Photodynamic Therapy, Quantitative analysis, Copper

Abstract- An effective detector for use in humanitarian de-mining must respond to metal and non-metal mines; reliably discriminate mines from clutter and decoys with a low rate of false-positives; discriminate amongst differing mine types; be lightweight; and be affordable. To address these sometimes competing specifications, we have evaluated an innovative, multi-channel, continuous-wave, holographic radar (RASCAN) and high resolution metal detector

- by Pierluigi Falorni and +1
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- Water Supply, Agricultural Production, High Resolution, Landmine Detection

It has been suggested that low-level laser therapy (LLLT) can modulate inflammatory processes. The aim of this experiment was to investigate what effects red laser irradiation with two different wavelengths (660 nm and 684 nm) on carrageenan-induced rat paw edema and histology. Thirty two male Wistar rats were randomly divided into four groups. One group received a sterile saline injection, while inflammation was induced by a sub-plantar injection of carrageenan (1 mg/paw) in the three other groups. After 1 h, LLLT was administered to the paw in two of the carrageenan-injected groups. Continuous wave 660 nm and 684 nm red lasers respectively with mean optical outputs of 30 mW and doses of 7.5 J/cm 2 were used. The 660 nm and 684 nm laser groups developed significantly (p < 0.01) less edema (0.58 ml [SE ± 0.17] ml and 0.76 ml [SE ± 0.10] respectively) than the control group (1.67 ml [SE ± 0.19]) at 4 h after injections. Similarly, both laser groups showed a significantly lower number of inflammatory cells in the muscular and conjunctive sub-plantar tissues than the control group.

- by Regiane Albertini and +1
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- Photochemistry, Inflammation, Color, Semiconductor Lasers

Er 3+ /Yb 3 + codoped pyrochlore-type (Y 0.99-x Er 0.01 Yb x ) 2 Ti 2 O 7 (x =0, 2.5, 5.0, 7.5, 10.0 and 12.5 mol%) nanocrystals have been successfully prepared by the sol-gel process with citric acid as chelator. The samples annealed at 800°C for 1 h exhibit good crystallinity and narrow size distribution with average size of 20-30 nm. Upon 980 nm excitation at room temperature, green (at~525 and 545 nm) and red (at~660 nm) upconversion emissions were observed, which are ascribed to the ( 2 H 11/2 , 4 S 3/2 ) → 4 I 15/2 and 4 F 9/2 → 4 I 15/2 transitions, respectively. And also, it has been found that the annealing temperatures and the Yb 3 + ion doping concentrations have greatly influenced on the upconversion luminescence intensity. The results show that Y 2 Ti 2 O 7 is an excellent host material for efficient upconversion nanophosphors.

- by P. Gredin
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- Engineering, Materials Engineering, Chemical Engineering, Condensed Matter Physics

Scanning confocal microscopy using pulsed illumination is investigated theoretically and experimentally. The point-spreadfunction of a confocal microscope operating with pulsed illumination is derived and compared to its continuous wave counterpart. High aperture confocal images of scattering point-like objects are recorded with pulses of 220 fs, and with a continuous beam. The images are compared paying particular attention to differences in resolution and contrast. Whereas no significant change in resolution has been observed for pulsed mode, the contrast of scanning reflection microscopy is enhanced when pulsed operation is employed. For ultrashort transform-limited pulses (< 50 fs) a significant increase of resolution is predicted. This resolution increase amounts to 20% at a pulse duration of 10 fs.

- by Pekka Hänninen
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- Optics, Confocal Microscopy, Optical physics, Point Spread Function

This paper deals with the analysis of the effects of radio frequency conducted interfering signals (RFI) on integrated circuits (IC's). After reviewing the basic results of the susceptibility analysis of operational amplifiers and smart power integrated circuits, the behavior of several pin-to-pin compatible control IC's for PWM current-mode switching power supplies (SMPS) has been tested in the presence of both continuous wave interfering signals (CW) as well as of pulsed noise signals (underground condition). The tested ICs were selected between some common models available on the market. The variations of the primary functional parameters (inner voltage reference, switching frequency, etc.) are evaluated in different test conditions. The paper gives a comparative view of the results, focusing on the key macroscopic effects. 0-7803-7474-6/02/$17.00 ©2002 IEEE

The paper investigates the possibility of reverberating a shielded room by means of source mode stirring. The transmitting antenna position and orientation are randomly changed inside a sub-volume of the chamber. In general, antenna displacement can be achieved by a proper design of an array of antennas, where one or more antennas are activated at different time instants. This technique eliminates mechanical rotating paddles inside the chamber, and offers the advantage of a continuous wave (CW) operation with respect to the frequency stirring method. The preliminary experimental and simulated results encourage further investigation of the proposed technique.

- by Graziano Cerri and +1
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- Electrical And Electronic Engineering, Continuous Wave

We propose a theory and experimentally verify ultraflat comb generation by dual-sine-wave phase-only modulation. This novel approach requires a single optical element and is very practical and efficient in terms of both power budget and bandwidth. Using this approach, we have generated two optical spectra, one with 11 comb lines and 1.9-dB flatness and the other with 9 comb lines and 0.8-dB flatness.

The characteristic time constants of the relaxation dynamics of core-excited atoms have hitherto been inferred from the linewidths of electronic transitions measured by continuous-wave extreme ultraviolet or X-ray spectroscopy. Here we demonstrate that a laser-based sampling system, consisting of a few-femtosecond visible light pulse and a synchronized sub-femtosecond soft X-ray pulse, allows us to trace these dynamics directly in the time domain with attosecond resolution. We have measured a lifetime of 7:9 11:0 20:9 fs of M-shell vacancies of krypton in such a pump-probe experiment.

- by Matthias Uiberacker
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- Multidisciplinary, Nature, Time Resolved, Constant Time Delay

A transverse flow transversely excited (TFTE) CW CO 2 with a maximum output power about 15 kW has been developed. This is excited by pulser sustained DC discharge applied between a pair of multi-pins anodes and a common tubular cathode. Though the laser power in convective cooled CO 2 laser scales proportionally with the volumetric gas flow, it did not increase in this laser when the volumetric gas flow was increased by increasing the electrode separation keeping the flow velocity constant. The discharge voltage too remained almost unchanged with increase of the electrode separation. These observations are explained considering the electrical discharge being controlled by ionization instability. Laser materials processing applications often demand programming facilities for laser power modulation. A four-stage cascaded multilevel DC-DC converter-based high-frequency switch mode power supply has been developed to modulate the output power of the laser. Laser was operated up to 15 kW output power in four different modes viz. continuous wave mode, pulse periodic mode, single shot mode and processing velocity-dependent power mode with 1:2 kHz modulation bandwidth. We describe briefly the laser system, the SMPS, and the temporal behavior of laser beam.

- by Christ Paul
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- High Frequency, Power Supply, Optical physics, High Power

The use of a saturable absorber as a passive mode locker in a solid-state laser can introduce a tendency for Q-switched mode-locked operation. We have investigated the transition between the regimes of cw mode locking and Q-switched mode locking. Experimental data from Nd:YLF lasers in the picosecond domain and soliton mode-locked Nd:glass lasers in the femtosecond domain, both passively mode locked with semiconductor saturable absorber mirrors, were compared with predictions from an analytical model. The observed stability limits for the picosecond lasers agree well with a previously described model, while for soliton mode-locked femtosecond lasers we have developed an extended theory that takes into account nonlinear soliton-shaping effects and gain filtering.

We introduce a method for measuring the speed of sound dispersion. It combines a short pulse transmission followed by a long burst comprised of two frequencies, one being double that of the other. The method allows the determination of the speed of sound dispersion using a single transmission. To validate the method, the dispersion was first measured in plastic samples

- by Yehuda Agnon and +2
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- Physics, Ultrasound, Echocardiography, Clinical Sciences
- by Mohsen Shahinpoor
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- Engineering, Design, Laser produced plasma, X Rays

Continuous-wave (CW) radar is one of the earliest forms of radar, and it is also in widespread use today. The proximity fuze, developed at the Applied Physics Laboratory of Johns Hopkins University before and during World War II, is a prominent example of a CW radar. The CW concept still dominates the proximity fuze industry. The CW approach is also found in short-range radar applications such as radar altimeters and atmospheric probing radars. The CW signal is also useful in velocity-measuring radars such as airborne Doppler navigation radars, artillery muzzle velocity, and police radars. Relative to a pulsed signal, a continuous-wave signal is more difficult to intercept by an unprepared receiver, where by unprepared we imply that the receiver does not contain a filter (or correlator) matched to the signal expected. For this reason, CW waveforms are sometimes referred to as low probability of intercept (LPI) waveforms.

- by Eli Mozeson
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- Continuous Wave

Surface modification of AISI316 stainless steel by laser melting was investigated experimentally using 2 and 4 kW laser power emitted from a continuous wave CO 2 laser at different specimen scanning speeds ranged from 300 to 1500 mm/min. Also, an investigation is reported of the introduction of carbon into the same material by means of laser surface alloying, which involves pre-coating the specimen surfaces with graphite powder followed by laser melting. The aim of these treatments is to enhance corrosion resistance by the rapid solidification associated with laser melting and also to increase surface hardness without affecting the bulk properties by increasing the carbon concentration near the surface. Different metallurgical techniques such as optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used to characterize the microstructure of the treated zone. The microstructures of the laser melted zones exhibited a dendritic morphology with a very fine scale with a slight increase in hardness from 200 to 230 Hv. However, the laser alloyed samples with carbon showed microstructure consisting of g dendrite surrounded by a network of eutectic structures (g +carbide). A significant increase in hardness from 200 to 500 Hv is obtained. Corrosion resistance was improved after laser melting, especially in the samples processed at high laser power (4 kW). There was shift in I corr and E corr toward more noble values and a lower passive current density than that of the untreated materials. These improvements in corrosion resistance were attributed to the fine and homogeneous dendritic structure, which was found throughout the melted zones. The corrosion resistance of the carburized sample was lower than the laser melted sample.

Operation of an efficient continuous-wave (CW) thulium-doped fiber laser emitting at wavelength, = 2.31 m is reported. The fiber laser parameters are optimized with a view to ultimately producing a compact and efficient laser source for optical absorption based gas sensing. A number of fiber laser configurations are investigated to assess their suitability for narrow linewidth, tunable fiber laser operation emitting around = 2.3 m, which is a wavelength region of significant importance for hydrocarbon gas monitoring. Tuning ranges of 140 nm and linewidths of less than 210 MHz have been demonstrated with lasers with bulk external tuning grating. Preliminary hydrocarbon gas sensing investigation confirm the potential of this source for detection of ppb gas concentrations.

- by John Donegan and +1
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- Quantum Physics, Fiber Laser, Optical physics, Infrared

We review recent results on high-power, high-efficiency two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays emitting around 980nm. Selectively oxidized, bottom-emitting single VCSEL emitters with 51% power conversion efficiency were developed as the basic building block of these arrays. More than 230W of continuous-wave (CW) power is demonstrated from a ~5mm x 5mm array chip. In quasi-CW mode, smaller array chips exhibit 100W output power, corresponding to more than 3.5kW/cm 2 of power density. High-brightness arrays have also been developed for pumping fiber lasers, delivering a fiber output power of 40W. We show that many of the advantages of low-power single VCSEL devices such as reliability, wavelength stability, low-divergence circular beam, and low-cost manufacturing are preserved for these high-power arrays. VCSELs thus offer an attractive alternative to the dominant edge-emitter technology for many applications requiring compact high-power laser sources.

Vehicle detection and classification system is an important part of the Intelligent Transportation systems (ITS). Its function is to measure traffic parameters such as flow-rate, speed, and vehicle types, which are valuable information for applications of road surveillance, traffic signal control, road planning, and so on. This paper presents a novel low-cost vehicle detection and classification system which is based on a K-band unmodulated CW radar. This system utilizes time-frequency analysis, multi-threshold detection, and Hough Transform as the major signal processing methods to extract speed and shape information of vehicles from Doppler signature they generate. It can perform vehicle detection, speed measurement, and vehicle classification simultaneously. Experimental results show that the proposed system and algorithms can provide promising performance and accuracy.

- by I. Dancus and +1
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- Femtosecond Laser, Refractive Index, Continuous Wave

Synchronous pulse operation upon both source and bias RFs for inductively coupled plasma (ICP) etching system, having both dynamic matching networks and RF frequency-sweeping to ensure the lowest RF reflected power, is introduced for the first time. A superior performance of synchronous pulse operation to conventional continuous wave (cw) as well as source pulse operations is confirmed through plasma diagnostics by using Langmuir probe, plasma simulation by using hybrid plasma equipment model (HPEM) and etching performance. Significant reduction of RF power reflection during pulse operation as well as improvement of 35 nm gate critical dimension (CD) uniformity for sub-50 nm dynamic random access memory (DRAM) are achieved by adapting synchronous pulse plasma etching technology. It is definitely expected that synchronous pulse plasma system would have a great ability from a perspective of robustness on fabrication site, excellent gate CD controllability and minimization of plasma induced damage (PID) related device performance degradation. #

- by Samer Banna
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- Mathematical Sciences, Applied, Physical sciences, Radio Frequency

The optical fiber based supercontinuum source has recently become a significant scientific and commercial success, with applications ranging from frequency comb production to advanced medical imaging. This one-of-a-kind book explains the theory of fiber supercontinuum broadening, describes the diverse operational regimes and indicates principal areas of applications, making it a very important guide for researchers and graduate students. With contributions from major figures and groups who have pioneered ...

- by daniel nolan
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- Fiber Lasers, Fiber Laser, Dispersion, Amplified spontaneous emission

An innovative sensor technique has been developed to detect water leaks in supply pipes, especially in cases where the existing prevailing methods do not offer reliable solution, such as in PVC pipelines or for minor leaks. The presented system uses a Continuous Wave (CW) Doppler sensing unit operating at 2.45 GHz, consisting of a low power transmitter, a homodyne receiver and a digital signal processing unit. The operation principle is the detection of the Doppler frequency shift of the reflected electromagnetic wave by slightly moving water that leaks out of a pipe. A first prototype has already been developed and tested in test sites as well as in real water leaking conditions. The system has additionally been compared to the commercially available water leaking methods, verifying its reliability and accuracy in the detection of water leaks.

- by Angelos Amditis
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- Geophysics, Digital Signal Processing, Applied Geophysics, Electromagnetic Waves

Laser-cladding experiments have been performed with STELLITE 6 powder on mild steel substrates, using a 1.5 kW linearly polarized continuous wave CO 2 laser as a heat source. The clad height, the mass efficiency, the dimensions of the melt pool, as well as the global absorptivity, were measured as functions of the powder feed rate and the scanning speed. A quantitative analytical model of the process is proposed, based on the overall mass and energy balance. It allows the calculation of the mass efficiency and of the global absorptivity, taking into account the incorporation of the powder into the melt pool as well as the energy absorbed by the powder jet and the substrate. It successfully explains the experimental results and demonstrates the role played by the melt pool inclination with respect to the substrate. A processing diagram is given to find rapidly the optimal laser treatment conditions and the desired clad height. It is discussed with respect to the other limiting conditions of the process, the geometrical maximum powder efficiency, the porosity, the dilution, and the maximum power of the laser installation.

- by Amedee Zryd
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- Chemical Engineering, Energy Balance, Analytical Model, Laser Treatment
- by Simon Dimaio and +1
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- Geology, Remote Sensing, Digital Signal Processing, Ground Penetrating Radar

This paper strongly suggests that the microwave rationale behind modern-day SETI lore is suspect, and that our search for electromagnetic signals from extraterrestrial technical civilizations may be doomed to failure because we are 'tuned to the wrong frequencies'. The old idea that lasers would be better for interstellar communications is revisited. That optical transmissions might be superior for CETI/SETI has generally been discounted by the community. Indeed, there is very little in the literature about the optical approach, as its efficacy was more or less dismissed by SETI researchers some twenty years ago. The main reason that the laser approach to SETI has been given a bad 'press' is the assumption that ETIs lack the skills to target narrow optical beams into selected stars. This assumption of ineptitude is shown to be erroneous, and calls into question some aspects of the rationale for Microwave SETI. The detectability of both continuous wave and pulsed visible/infrared laser signals is described in some detail.

- by Narendra Dahotre
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- Engineering, Materials Science, Cell Adhesion, Surface Chemistry

The present study concerns in-depth analysis of the alloyed zone formed by laser gas alloying of Ti-6Al-4V by melting the surface using a continuous wave Diode laser using nitrogen shroud. A detailed structure-property-process parameters correlation has been undertaken to optimize the process parameters. The microstructure of the alloyed zone consists of dispersion of titanium nitrides in α-Ti matrix. The morphology and mass fraction of titanium nitride was found to vary with laser parameters (applied power and gas flow rate). Residual stress on the surface nitrided zone was found to vary with laser parameters, application of high power and low gas flow rate was found to be essential in reducing residual tensile stress. The microhardness and corrosion property of the alloyed zone were improved significantly as compared to as-received Ti-6Al-4V substrate.

- by Jyotsna Dutta Majumdar
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- Corrosion, Nitriding, Microstructures, Residual Stress