Search query: pulse package oscillation

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abstract: Pulse package oscillations in broad area semiconductor lasers subjected to short optical feedback are experimentally observed. The pulse package oscillation consists of a frequency component that corresponds to an external optical feedback loop with an envelop of periodic low frequency fluctuations. However, the periodicity induced by optical feedback does not always improve the time averaged beam profiles of the laser oscillations. We also investigated time averaged near field beam profiles in relation with the optical feedback dynamics.
author_names: Akira Takeda

Rui Shogenji

Junji Ohtsubo
title: Dynamics and pulse package oscillations in broad area semiconductor lasers with short optical feedback
year: 2012

abstract: ABSTRACT This paper reports on the processing of aluminium melt by pulse magneto oscillation (PMO) technology. The melt is divided into five layers using a layered isolation device and, after grinding and corrosion, the refining effects of equiaxed crystals are observed to decrease from the centre outwards. The electromagnetic force and flow velocity of the melt were simulated using the ANSYS package, and found to decrease in the same manner as crystal size; i.e. from the centre outwards. It was also found that the melt, treated by PMO, possessed an optimum characteristic length at which the flow velocity reaches a maximum value, thus improving the refining effect of the solidification structure of the melt.
author_names: Shumin Cheng

Yuyi Zhong

Zhishuai Xu

Ning Pei

Qi-jie Zhai

Yongyong Gong
title: Effect of flow on solidification structure of pure aluminium under pulse magneto oscillation
year: 2018

abstract: In this article, a transfer function based modelling is proposed to investigate voltage oscillation phenomena, i.e. over voltage at the motor terminal, associated with pulse width modulation (PWM) inverter fed motor drives with long feeding cables. As such, the long feeding cable is assumed to be a distortionless transmission line; then, a bounce diagram and time harmonic method are utilised to derive a simple model with a minimum computational burden that is easy to realise using the Matlab/Simulink software package. Furthermore, the model takes account of the inverter output and the motor terminal filters, which are commonly used to suppress the motor terminal over voltage. The model accuracy is verified by a comparison with the circuit oriented software, OrCAD/PSpice, simulation results.
author_names: Sang-Choel Lee

Ju H Park
title: Transfer function based modelling for voltage oscillation phenomena in PWM motor drives with long feeding cables
year: 2010

abstract: Although external cavity feedback with a grating is widely used to achieve a tunable high power narrow linewidth broad area diode laser (BAL) system, the dynamics of such a system is seldom studied. In this paper, the temporal dynamics of a tunable high power green external cavity diode laser system based on a GaN BAL and Littrow external cavity is investigated experimentally. The regular pulse package oscillation (PPO) is observed just above the threshold. The oscillating period of the pulse package decreases with the increasing injected current. As the current increases further, the pulse package oscillates irregularly, and finally changes to a chaotic state. The PPO is observed, for the first time to our knowledge, in a BAL with an external cavity grating feedback.
author_names: Mingjun Chi

Ole Bjarlin Jensen

Anders Kragh Hansen

Paul Michael Petersen
title: Dynamics of a green high power tunable external cavity broad area GaN diode laser
year: 2018

abstract: An impulse measurement device and analysis package was conceived, designed, constructed, tested, and demonstrated to be capable of: measuring nanoNewton seconds to milliNewton seconds of impulse due to laser ablation; being transported as carry on baggage; set up and tear down times of less than an hour; target exchange times of less than two minutes (targets can be ablated at multiple positions for thousands of shots) measurements in air and in vacuum; error of just a few percent; repeatability over a wide range of potential systematic error sources; and time between measurements, including ring down and analysis, of less than 30 seconds. The instrument consists of a cantilever (i.e. leaf spring) whose time dependent displacement/oscillation is measured and analyzed to determine the impulse imparted by a laser pulse to a target. These shapes are readily/commercially available, and any target material can be used, provided it can be fashioned in the form of a cantilever, or as a coating/film/tape, suita.
author_names: Kevin P Kremeyer

J L Lapeyre

Steven Hamann
title: Compact And Robust Laser Impulse Measurement Device, With Ultrashort Pulse Laser Ablation Results
year: 2008

abstract: An impulse measurement device and analysis package was conceived, designed, constructed, tested, and demonstrated to be capable of: measuring nanoNewton seconds to milliNewton seconds of impulse due to laser ablation; being transported as carry on baggage; set up and tear down times of less than an hour; target exchange times of less than two minutes (targets can be ablated at multiple positions for thousands of shots) measurements in air and in vacuum; error of just a few percent; repeatability over a wide range of potential systematic error sources; and time between measurements, including ring down and analysis, of less than 30 seconds. The instrument consists of a cantilever (i.e. leaf spring) whose time dependent displacement/oscillation is measured and analyzed to determine the impulse imparted by a laser pulse to a target. These shapes are readily/commercially available, and any target material can be used, provided it can be fashioned in the form of a cantilever, or as a coating/film/tape, suitable for mounting on a cantilever of known geometry. The instrument was calibrated both statically and dynamically, and measurements were performed on brass, steel, and Aluminum, using laser pulses of ~7ns, ~500ps, and ~500fs. The results agree well with those published in the literature, with surface effects, atmosphere, and pre /post pulses demonstrating interesting effects and indicating areas for further study. In addition to exploring space propulsion applications, measurements were performed to explore the strong beneficial effects of depositing lines of energy ahead of supersonic and hypersonic vehicles. This deposition creates a low density channel, through which a vehicle can travel with dramatically reduced drag. Temperature and pressure are both also reduced on the front surfaces of the vehicle, while density and pressure are increased at the vehicle base. When applied off center, this technique can be used to control the vehicle, employing the entire body as the control surface and eliminating the need for actuators. Numerical results for drag reduction, temperature reduction, and control forces are indicated here.
author_names: Kevin P Kremeyer
title: Ultrashort pulse lasers applied to propulsion/control in space and atmospheric flight
venue: High Power Laser Ablation
year: 2008

abstract: Different dynamic behaviors, such as regular pulse package oscillation, irregular pulse package oscillation, and chaos are observed in a green high power broad area GaN diode laser system with a grating external cavity feedback.
author_names: Mingjun Chi

Ole Bjarlin Jensen

Anders Kragh Hansen

Paul Michael Petersen
title: Dynamics of a green high power tunable broad area GaN diode laser with external cavity feedback
year: 2018

abstract: The temporal dynamics of a broad area diode laser with lateral mode selected long cavity feedback is studied experimentally. Different dynamics are observed when different lateral modes are selected. When the feedback mirror is aligned perfectly and high order modes are selected, in most of the cases, the output of the laser shows a periodic oscillation corresponding to a single roundtrip external cavity loop, but the dynamic behavior disappears in some case; when the zero order lateral mode is selected, periodic oscillation corresponding to a double roundtrip external cavity loop is observed. When the feedback mirror is aligned non perfectly, pulse package oscillation is observed, for the first time to our knowledge, in a diode laser with long cavity feedback.
author_names: Mingjun Chi

Paul Michael Petersen
title: Dynamics of a broad area diode laser with lateral mode selected long cavity feedback
year: 2014

abstract: The CoRoT evolution and seismic tools activity. ASTEC the Aarhus STellar Evolution Code. The FRANEC stellar evolutionary code. YREC: the Yale rotating stellar evolution code. The Geneva stellar evolution code. The Toulouse Geneva Evolution Code (TGEC) CESAM: a free code for stellar evolution calculations. The STAROX stellar evolution code. CLES, Code Liegeois d'Evolution Stellaire. The ATON 3.1 stellar evolutionary code. GARSTEC the Garching Stellar Evolution Code. PULSE: a finite element code for solving adiabatic nonradial pulsation equations. ADIPLS the Aarhus adiabatic oscillation package. Porto Oscillation Code (posc) Granada oscillation code (GraCo) NOSC: Nice OScillations Code. The OSCROX stellar oscillaton code. The Liege Oscillation code. filou oscillation code. LNAWENR linear nonadiabatic nonradial waves. Reference grids of stellar models and oscillation frequencies. Grids of stellar evolution models for asteroseismology (cesam posc) Grids of stellar models and frequencies with CLES LOSC. CoRoT/ESTA TASK 1 and TASK 3 comparison of the internal structure and seismic properties of representative stellar models. FRANEC versus CESAM predictions for selected CoRoT ESTA task 1 models. Thorough analysis of input physics in CESAM and CLES codes. Inter comparison of the g f and p modes calculated using different oscillation codes for a given stellar model. Concluding remarks and perspectives on the evolution and seismic tools activity (ESTA) of the CoRoT community.
author_names: Mario J P F G Monteiro
title: Evolution and seismic tools for stellar astrophysics
year: 2009

abstract: Asymptotic and numerical methods are used to highlight different types of dynamical behaviors that occur for the motion of a localized spike type solution to the singularly perturbed Gierer Meinhardt and Schnakenberg reaction diffusion models in a one dimensional spatial domain. Depending on the parameter range in these models, there can either be a slow evolution of a spike toward the midpoint of the domain, a sudden oscillatory instability triggered by a Hopf bifurcation leading to an intricate temporal oscillation in the height of the spike, or a pulse splitting instability leading to the creation of new spikes in the domain. Criteria for the onset of these oscillatory and pulse splitting instabilities are obtained through asymptotic and numerical techniques. A moving mesh numerical method is introduced to compute these different behaviors numerically, and results are compared with corresponding results computed using a method of lines based software package.
author_names: Wentao Sun

Tao Tang

Michael Jeffrey Ward

Juncheng Wei
title: Numerical Challenges for Resolving Spike Dynamics for Two One Dimensional Reaction Diffusion Systems
year: 2003