Shaping propagation invariant laser beams
NASA Astrophysics Data System (ADS)
Soskind, Michael; Soskind, Rose; Soskind, Yakov
2015-11-01
Propagation-invariant structured laser beams possess several unique properties and play an important role in various photonics applications. The majority of propagation invariant beams are produced in the form of laser modes emanating from stable laser cavities. Therefore, their spatial structure is limited by the intracavity mode formation. We show that several types of anamorphic optical systems (AOSs) can be effectively employed to shape laser beams into a variety of propagation invariant structured fields with different shapes and phase distributions. We present a propagation matrix approach for designing AOSs and defining mode-matching conditions required for preserving propagation invariance of the output shaped fields. The propagation matrix approach was selected, as it provides a more straightforward approach in designing AOSs for shaping propagation-invariant laser beams than the alternative technique based on the Gouy phase evolution, especially in the case of multielement AOSs. Several practical configurations of optical systems that are suitable for shaping input laser beams into a diverse variety of structured propagation invariant laser beams are also presented. The laser beam shaping approach was applied by modeling propagation characteristics of several input laser beam types, including Hermite-Gaussian, Laguerre-Gaussian, and Ince-Gaussian structured field distributions. The influence of the Ince-Gaussian beam semifocal separation parameter and the azimuthal orientation between the input laser beams and the AOSs onto the resulting shape of the propagation invariant laser beams is presented as well.
Vertical laser beam propagation through the troposphere
NASA Technical Reports Server (NTRS)
Minott, P. O.; Bufton, J. L.; Schaefer, W. H.; Grolemund, D. A.
1974-01-01
The characteristics of the earth's atmosphere and its effects upon laser beams was investigated in a series of balloon borne, optical propagation experiments. These experiments were designed to simulate the space to ground laser link. An experiment to determine the amplitude fluctuation, commonly called scintillation, caused by the atmosphere was described.
Safe Laser Beam Propagation for Interplanetary Links
NASA Technical Reports Server (NTRS)
Wilson, Keith E.
2011-01-01
Ground-to-space laser uplinks to Earth–orbiting satellites and deep space probes serve both as a beacon and an uplink command channel for deep space probes and Earth-orbiting satellites. An acquisition and tracking point design to support a high bandwidth downlink from a 20-cm optical terminal on an orbiting Mars spacecraft typically calls for 2.5 kW of 1030-nm uplink optical power in 40 micro-radians divergent beams.2 The NOHD (nominal ocular hazard distance) of the 1030nm uplink is in excess of 2E5 km, approximately half the distance to the moon. Recognizing the possible threat of high power laser uplinks to the flying public and to sensitive Earth-orbiting satellites, JPL developed a three-tiered system at its Optical Communications Telescope Laboratory (OCTL) to ensure safe laser beam propagation through navigational and near-Earth space.
Laser beam propagation in atmospheric turbulence
NASA Technical Reports Server (NTRS)
Murty, S. S. R.
1979-01-01
The optical effects of atmospheric turbulence on the propagation of low power laser beams are reviewed in this paper. The optical effects are produced by the temperature fluctuations which result in fluctuations of the refractive index of air. The commonly-used models of index-of-refraction fluctuations are presented. Laser beams experience fluctuations of beam size, beam position, and intensity distribution within the beam due to refractive turbulence. Some of the observed effects are qualitatively explained by treating the turbulent atmosphere as a collection of moving gaseous lenses of various sizes. Analytical results and experimental verifications of the variance, covariance and probability distribution of intensity fluctuations in weak turbulence are presented. For stronger turbulence, a saturation of the optical scintillations is observed. The saturation of scintillations involves a progressive break-up of the beam into multiple patches; the beam loses some of its lateral coherence. Heterodyne systems operating in a turbulent atmosphere experience a loss of heterodyne signal due to the destruction of coherence.
Laser beam shaping profiles and propagation.
Shealy, David L; Hoffnagle, John A
2006-07-20
We consider four families of functions--the super-Gaussian, flattened Gaussian, Fermi-Dirac, and super-Lorentzian--that have been used to describe flattened irradiance profiles. We determine the shape and width parameters of the different distributions, when each flattened profile has the same radius and slope of the irradiance at its half-height point, and then we evaluate the implicit functional relationship between the shape and width parameters for matched profiles, which provides a quantitative way to compare profiles described by different families of functions. We conclude from an analysis of each profile with matched parameters using Kirchhoff-Fresnel diffraction theory and M2 analysis that the diffraction patterns as they propagate differ by small amounts, which may not be distinguished experimentally. Thus, beam shaping optics is designed to produce either of these four flattened output irradiance distributions with matched parameters will yield similar irradiance distributions as the beam propagates.
Modeling beam propagation and frequency conversion for the beamlet laser
Auerbach, J.M.
1996-06-01
The development of the Beamlet laser has involved extensive and detailed modeling of laser performance and beam propagation to: (1) predict the performance limits of the laser, (2) select system configurations with higher performance, (3) analyze experiments and provide guidance for subsequent laser shots, and (4) design optical components and establish component manufacturing specifications. In contrast to modeling efforts of previous laser systems such as Nova, those for Beamlet include as much measured optical characterization data as possible. This article concentrates on modeling of beam propagation in the Beamlet laser system, including the frequency converter, and compares modeling predictions with experimental results for several Beamlet shots. It briefly describes the workstation-based propagation and frequency conversion codes used to accomplish modeling of the Beamlet.
CO2 laser beam propagation with ZnSe optics
NASA Astrophysics Data System (ADS)
Leong, K. H.; Liu, Yi; Holdridge, D. J.
Beam propagation characteristics of ZnSe optics used in kiloWatt power CO2 laser aided material processing applications are determined using the Prometec Laser Beam Analyzer. The laser used was a Rofin Sinar RS6000 CO2 laser with mode aperturing. Beam power varied from 500W to 6300W and beam modes used were TEM(sub 00), TEM(sub 01), TEM(sub 10), and TEM(sub 20). Both transmissive and reflective optics were examined. The ZnSe lenses tested included meniscus, diffractive, and cylindrical lenses of 5 in. focal length and a 10 in. focal length integrating lens. Reflective optics included an integrator and a 5 in. focal length parabolic mirror for welding. Parameters obtained included beam propagation profiles, intensity profiles, depth of focus, spot size, and back focal length. A subset of the data obtained is presented here. Details of the work will appear in a full length paper.
Characteristic of laser diode beam propagation through a collimating lens.
Xu, Qiang; Han, Yiping; Cui, Zhiwei
2010-01-20
A mathematical model of a laser diode beam propagating through a collimating lens is presented. Wave propagation beyond the paraxial approximation is studied. The phase delay of the laser diode wave in passing through the lens is analyzed in detail. The propagation optical field after the lens is obtained from the diffraction integral by the stationary phase method. The model is employed to predict the light intensity at various beam cross sections, and the computed intensity distributions are in a good agreement with the corresponding measurements.
Proceedings of the laser beam propagation in the atmosphere
Leader, J.C.
1983-01-01
Among the topics discussed are the atmospheric attenuation of laser radiation, the determination of atmospheric properties from lidar measurements, laser transmission measurement limitations due to correlated atmospheric effects, high spatial resolution studies of propagation, multiple scattering of laser beam propagation in clouds, the probability density of the irradiance in atmospheric turbulence, source statistics effects on irradiance scintillations in turbulence, and numerical solutions of the fourth-moment equation. Also discussed are the characteristics and effects of speckle propagation through turbulence, the application of random medium propagation theory to communication and radar system analyses, multiple scattering corrections to the Beer-Lambert Law, millimeter wave propagation through a clear atmosphere, endoatmospheric laser arrays for thermal blooming environments, the wavelength dependence of adaptive optics compensation, time-dependent thermal blooming in axial pipe flow, and turbulence-induced adaptive optics performance degradation.
Instability versus equilibrium propagation of a laser beam in plasma.
Lushnikov, Pavel M; Rose, Harvey A
2004-06-25
We obtain, for the first time, an analytic theory of the forward stimulated Brillouin scattering instability of a spatially and temporally incoherent laser beam that controls the transition between statistical equilibrium and nonequilibrium (unstable) self-focusing regimes of beam propagation. The stability boundary may be used as a comprehensive guide for inertial confinement fusion designs. Well into the stable regime, an analytic expression for the angular diffusion coefficient is obtained, which provides an essential correction to a geometric optic approximation for beam propagation.
Harmonic generation by circularly polarized laser beams propagating in plasma
Agrawal, Ekta; Hemlata,; Jha, Pallavi
2015-04-15
An analytical theory is developed for studying the phenomenon of generation of harmonics by the propagation of an obliquely incident, circularly polarized laser beam in homogeneous, underdense plasma. The amplitudes of second and third harmonic radiation as well as detuning distance have been obtained and their variation with the angle of incidence is analyzed. The amplitude of harmonic radiation increases with the angle of incidence while the detuning distance decreases, for a given plasma electron density. It is observed that the generated second and third harmonic radiation is linearly and elliptically polarized, respectively. The harmonic radiation vanishes at normal incidence of the circularly polarized laser beam.
Evolution of decentred laser beams propagating through atmospheric turbulence
NASA Astrophysics Data System (ADS)
Li, Xiaoqing; Ji, Xiaoling; Zhu, Wenyue
2012-07-01
The changes of the average intensity, the centre of beam gravity and the position of intensity maximum of decentred laser beams propagating through atmospheric turbulence are examined in detail. It is shown that the decentred intensity distribution is amended gradually with increasing the propagation distance and the strength of turbulence, and it becomes an off-axis Gaussian-like beam when the propagation distance and the strength of turbulence become large enough. The centre of beam gravity is independent of both the propagation distance and the strength of turbulence. On the other hand, there are two intensity maxima, and their positions are symmetrical around the propagation z-axis when the propagation distance z is small. With increasing z, there is only one intensity maximum. As z further increases, position of the intensity maximum is further shifted towards the z-axis. When z is large enough, the position of the intensity maximum is unchanged. The unchanged position of the intensity maximum moves further away from the z-axis with an increase in the refraction index structure constant, the decentred parameter and the waist width.
Experimental study of laser beam propagation in turbulent atmosphere
NASA Astrophysics Data System (ADS)
Yang, Chun-Ping; He, Wu-Guang; Wu, Jian
2009-05-01
Intensity of atmospheric turbulence may overly affect bit error rate for a ground-based laser wireless communication system, so it is necessary to measure of atmospheric turbulence intensity and fluctuation of image centroid while laser beam propagates in turbulent atmosphere. In this paper, an experiment system is set up based on theory of light transmission in turbulent atmosphere. In the system, a laser named Nd : YAG is used horizontally to emit a laser beam with wavelength 1.06 μm on a platform at the height of 1.5 m. Three infrared CCD cameras are set at 200 m, 300 m(or 600 m) and 1000 m far from laser, which are applied to receive laser facula images from Lambertian boards, respectively. A lot of laser facula images are collected within some serial days under different periods of time every day, and hundreds of image frames are gathered at a time by making use of this experiment device. Fluctuation of image centroid is computed with these image frames, and the structure constant of atmospheric refractive index (C 2n) is also derived. Finally, a comparison is made between aforementioned C2n and those derived by meteorology factors.
Propagation modeling results for narrow-beam undersea laser communications
NASA Astrophysics Data System (ADS)
Fletcher, Andrew S.; Hardy, Nicholas D.; Hamilton, Scott A.
2016-03-01
Communication links through ocean waters are challenging due to undersea propagation physics. Undersea optical communications at blue or green wavelengths can achieve high data rates (megabit- to gigabit-per-second class links) despite the challenging undersea medium. Absorption and scattering in ocean waters attenuate optical signals and distort the waveform through dense multipath. The exponential propagation loss and the temporal spread due to multipath limit the achievable link distance and data rate. In this paper, we describe the Monte Carlo modeling of the undersea scattering and absorption channel. We model photon signal attenuation levels, spatial photon distributions, time of arrival statistics, and angle of arrival statistics for a variety of lasercom scenarios through both clear and turbid water environments. Modeling results inform the design options for an undersea optical communication system, particularly illustrating the advantages of narrow-beam lasers compared to wide beam methods (e.g. LED sources). The modeled pupil plane and focal plane photon arrival distributions enable beam tracking techniques for robust pointing solutions, even in highly scattering harbor waters. Laser communication with collimated beams maximizes the photon transfer through the scattering medium and enables spatial and temporal filters to minimize waveform distortion and background interference.
Tao, Rumao; Si, Lei; Ma, Yanxing; Zhou, Pu; Liu, Zejin
2012-08-10
The propagation properties of coherently combined truncated laser beam arrays with beam distortions through non-Kolmogorov turbulence are studied in detail both analytically and numerically. The analytical expressions for the average intensity and the beam width of coherently combined truncated laser beam arrays with beam distortions propagating through turbulence are derived based on the combination of statistical optics methods and the extended Huygens-Fresnel principle. The effect of beam distortions, such as amplitude modulation and phase fluctuation, is studied by numerical examples. The numerical results reveal that phase fluctuations have significant influence on the spreading of coherently combined truncated laser beam arrays in non-Kolmogorov turbulence, and the effects of the phase fluctuations can be negligible as long as the phase fluctuations are controlled under a certain level, i.e., a>0.05 for the situation considered in the paper. Furthermore, large phase fluctuations can convert the beam distribution rapidly to a Gaussian form, vary the spreading, weaken the optimum truncation effects, and suppress the dependence of spreading on the parameters of the non-Kolmogorov turbulence.
Laser Beam Propagation Through Inhomogeneous Media with Shock-Like Profiles: Modeling and Computing
NASA Technical Reports Server (NTRS)
Adamovsky, Grigory; Ida, Nathan
1997-01-01
Wave propagation in inhomogeneous media has been studied for such diverse applications as propagation of radiowaves in atmosphere, light propagation through thin films and in inhomogeneous waveguides, flow visualization, and others. In recent years an increased interest has been developed in wave propagation through shocks in supersonic flows. Results of experiments conducted in the past few years has shown such interesting phenomena as a laser beam splitting and spreading. The paper describes a model constructed to propagate a laser beam through shock-like inhomogeneous media. Numerical techniques are presented to compute the beam through such media. The results of computation are presented, discussed, and compared with experimental data.
NASA Astrophysics Data System (ADS)
Kapranov, Vitaliy; Tugaenko, Vjatcheslav; Marakasov, Dmitrii; Kudryavtsev, Andrei
2015-11-01
In this paper, we describe an experimental setup for laser beam propagation along a horizontal urban path that can be useful for applications such as wireless power transfer or free-space laser communications. This setup can be used for experiments in different atmosphere conditions. Part of obtained results from experiments for 1064 nm laser beam is presented.
Propagation characteristics of a Gaussian laser beam in plasma with modulated collision frequency
Wang Ying; Yuan Chengxun; Zhou Zhongxiang; Gao Ruilin; Li Lei; Du Yanwei
2012-08-15
The propagation characteristics of a Gaussian laser beam in cold plasma with the electron collision frequency modulated by laser intensity are presented. The nonlinear dynamics of the ponderomotive force, which induce nonlinear self-focusing as opposed to spatial diffraction, are considered. The effective dielectric function of the Drude model and complex eikonal function are adopted in deriving coupled differential equations of the varying laser beam parameters. In the framework of ponderomotive nonlinearity, the frequency of electron collision in plasmas, which is proportional to the spatial electron density, is strongly interrelated with the laser beam propagation characteristics. Hence, the propagation properties of the laser beam and the modulated electron collision frequency distribution in plasma were studied and explained in depth. Employing this self-consistent method, the obtained simulation results approach practical conditions, which is of significance to the study of laser-plasma interactions.
NASA Astrophysics Data System (ADS)
Zinchik, Alexander A.; Muzychenko, Yana B.
2015-06-01
This paper discusses theoretical and experimental results of the investigation of light beams that retain their intensity structure during propagation and focusing. Spiral laser beams are a family of laser beams that preserve the structural stability up to scale and rotation with the propagation. Properties of spiral beams are of practical interest for laser technology, medicine and biotechnology. Researchers use a spiral beams for movement and manipulation of microparticles. Functionality laser manipulators can be significantly enhanced by using spiral beams whose intensity remains invariable. It is well known, that these beams has non-zero orbital angular momentum. Spiral beams have a complicated phase distribution in cross section. In this paper we investigate the structural stability of the laser beams having a spiral phase structure by passing them through an inhomogeneous phase medium. Laser beam is passed through a medium is characterized by a random distribution of phase in the range 0..2π. The modeling was performed using VirtualLab 5.0 (manufacturer LightTrans GmbH). Compared the intensity distribution of the spiral and ordinary laser beam after the passage of the inhomogeneous medium. It is shown that the spiral beams exhibit a significantly better structural stability during the passage phase heterogeneous environments than conventional laser beams. The results obtained in the simulation are tested experimentally. Experimental results show good agreement with the theoretical results.
Excitation of Accelerating Plasma Waves by Counter-propagating Laser Beams
Gennady Shvets; Nathaniel J. Fisch; and Alexander Pukhov
2001-08-30
Generation of accelerating plasma waves using two counter-propagating laser beams is considered. Colliding-beam accelerator requires two laser pulses: the long pump and the short timing beam. We emphasize the similarities and differences between the conventional laser wakefield accelerator and the colliding-beam accelerator (CBA). The highly nonlinear nature of the wake excitation is explained using both nonlinear optics and plasma physics concepts. Two regimes of CBA are considered: (i) the short-pulse regime, where the timing beam is shorter than the plasma period, and (ii) the parametric excitation regime, where the timing beam is longer than the plasma period. Possible future experiments are also outlined.
Aksenov, Valerii P; Kolosov, Valeriy V; Pogutsa, Cheslav E
2014-06-10
The propagation of laser beams having orbital angular momenta (OAM) in the turbulent atmosphere is studied numerically. The variance of random wandering of these beams is investigated with the use of the Monte Carlo technique. It is found that, among various types of vortex laser beams, such as the Laguerre-Gaussian (LG) beam, modified Bessel-Gaussian beam, and hypergeometric Gaussian beam, having identical initial effective radii and OAM, the LG beam occupying the largest effective volume in space is the most stable one.
NASA Astrophysics Data System (ADS)
Mossoulina, O. A.; Kirilenko, M. S.; Khonina, S. N.
2016-08-01
We use radial Fractional Fourier transform to model vortex laser beams propagation in optical waveguides with parabolic dependence of the refractive index. To overcome calculation difficulties at distances proportional to a quarter of the period we use varied calculation step. Numerical results for vortex modes superposition propagation in a parabolic optical fiber show that the transverse beam structure can be changed significantly during the propagation. To provide stable transverse distribution input scale modes should be in accordance with fiber parameters.
Wang Ying; Yuan Chengxun; Gao Ruilin; Zhou Zhongxiang
2012-10-15
Theoretical investigations of a Gaussian laser beam propagating in relativistic plasmas have been performed with the WKB method and complex eikonal function. We consider the relativistic nonlinearity induced by intense laser beam, and present the relativistically generalized forms of the plasma frequency and electron collision frequency in plasmas. The coupled differential equations describing the propagation variations of laser beam are derived and numerically solved. The obtained simulation results present the similar variation tendency with experiments. By changing the plasma density, we theoretically analyze the feasibility of using a plasmas slab of a fixed thickness to compress the laser beam-width and acquire the focused laser intensity. The present work complements the relativistic correction of the electron collision frequency with reasonable derivations, promotes the theoretical approaching to experiments and provides effective instructions to the practical laser-plasma interactions.
Plan for Safe Laser Beam Propagation from the Optical Communications Telescope Laboratory
NASA Astrophysics Data System (ADS)
Wilson, K. E.; Roberts, W. T.; Garkanian, V.; Battle, F.; Leblanc, R.; Hemmati, H.; Robles, P.
2002-10-01
JPL is building a state-of-the-art Optical Communications Telescope Laboratory (OCTL) to perform research and development of laser beam propagation and signal detection technologies to meet NASA's future needs for high-bandwidth communications from Earth-orbiting and deep-space probes. Laser beam propagation between ground and space is regulated by several government agencies -- regulation that is significant when propagating high-brightness, Q-switched laser beams that will be used for uplinking commands to deep-space probes and as an acquisition, pointing, and tracking beacon for downlink optical communication. To ensure safe laser operation and beam propagation from the OCTL, JPL has identified a four-tier safety system. The safety system starts with safe beam propagation within the OCTL, extends to safe beam propagation through the air and into space, and is designed to meet the requirements of State (California Occupational Safety and Health Administration) and Federal agencies (Federal Aviation Administration and the U.S. Space Command's Laser Clearinghouse).
Propagation of high-power partially coherent fibre laser beams in a real environment
NASA Astrophysics Data System (ADS)
Tao, Ru-Mao; Si, Lei; Ma, Yan-Xing; Zou, Yong-Chao; Zhou, Pu
2011-09-01
The propagation performance of high-power partially coherent fibre laser beams in a real environment is investigated and the theoretical model of a high-power fibre laser propagating in a real environment is established. The influence of a collimating system and thermal blooming is considered together with atmospheric turbulence and mechanical jitter. The laser energy concentration of partially coherent beams in the far field is calculated and analysed based on the theoretical model. It is shown that the propagation performance of partially coherent beams depends on the collimating system, atmospheric turbulence, mechanical jitter and thermal blooming. The propagation performance of partially coherent beams and fully coherent beams is studied and the results show that partially coherent beams are less sensitive to the influence of thermal blooming, which results in that the energy degeneration for partially coherent beams is only 50% of that for fully coherent beams. Both partially coherent beams and fully coherent beams become less sensitive to thermal blooming when the average structural constant of the refraction index fluctuations increases to 1.7 × 10-14m-2/3. The investigation presents a reference for applications of a high-power fibre laser system.
Laser beam propagation through turbulence and adaptive optics for beam delivery improvement
NASA Astrophysics Data System (ADS)
Nicolas, Stephane
2015-10-01
We report results from numerical simulations of laser beam propagation through atmospheric turbulence. In particular, we study the statistical variations of the fractional beam energy hitting inside an optical aperture placed at several kilometer distance. The simulations are performed for different turbulence conditions and engagement ranges, with and without the use of turbulence mitigation. Turbulence mitigation is simulated with phase conjugation. The energy fluctuations are deduced from time sequence realizations. It is shown that turbulence mitigation leads to an increase of the mean energy inside the aperture and decrease of the fluctuations even in strong turbulence conditions and long distance engagement. As an example, the results are applied to a high energy laser countermeasure system, where we determine the probability that a single laser pulse, or one of the pulses in a sequence, will provide a lethal energy inside the target aperture. Again, turbulence mitigation contributes to increase the performance of the system at long-distance and for strong turbulence conditions in terms of kill probability. We also discuss a specific case where turbulence contributes to increase the pulse energy within the target aperture. The present analysis can be used to evaluate the performance of a variety of systems, such as directed countermeasures, laser communication, and laser weapons.
Effects of laser beam propagation and saturation on the spatial shape of sodium laser guide stars.
Marc, Fabien; Guillet de Chatellus, Hugues; Pique, Jean-Paul
2009-03-30
The possibility to produce diffraction-limited images by large telescopes through Adaptive Optics is closely linked to the precision of measurement of the position of the guide star on the wavefront sensor. In the case of laser guide stars, many parameters can lead to a strong distortion on the shape of the LGS spot. Here we study the influence of both the saturation of the sodium layer excited by different types of lasers, the spatial quality of the laser mode at the ground and the influence of the atmospheric turbulence on the upward propagation of the laser beam. Both shape and intensity of the LGS spot are found to depend strongly on these three effects with important consequences on the precision on the wavefront analysis. PMID:19333251
Effects of laser beam propagation and saturation on the spatial shape of sodium laser guide stars.
Marc, Fabien; Guillet de Chatellus, Hugues; Pique, Jean-Paul
2009-03-30
The possibility to produce diffraction-limited images by large telescopes through Adaptive Optics is closely linked to the precision of measurement of the position of the guide star on the wavefront sensor. In the case of laser guide stars, many parameters can lead to a strong distortion on the shape of the LGS spot. Here we study the influence of both the saturation of the sodium layer excited by different types of lasers, the spatial quality of the laser mode at the ground and the influence of the atmospheric turbulence on the upward propagation of the laser beam. Both shape and intensity of the LGS spot are found to depend strongly on these three effects with important consequences on the precision on the wavefront analysis.
NASA Astrophysics Data System (ADS)
Hartmann, Rainer; Pflaum, Christoph; Graupeter, Thomas
2015-03-01
We developed a complex physical model for simulating laser amplifiers to numerically analyze birefringence effects. This model includes pump configuration, thermal lensing effects, birefringence, and beam propagation in the laser amplifier. Temperature, deformation, and stress inside the laser crystal were calculated using a three-dimensional finite element analysis (FEA). The pump configuration is simulated using a three-dimensional ray tracing or an approximation based on super-Gaussian functions. Our simulations show the depolarization of a linearly polarized electromagnetic wave in a cylindrical laser crystal. These simulations were performed using a three-dimensional full vectorial beam propagation method (VBPM). Stress induced birefringence can be compensated well for moderate pumping powers. High power amplification requires sensitive alignment. Our simulation technique calculates the influence of the photo-elastic effect inside the laser crystal accurately. Detailed knowledge about beam waist and depolarization is needed to develop compensation techniques for high power output beams with low depolarization losses.
Laser beam propagation through an atmospheric transitional and turbulent boundary layer
NASA Astrophysics Data System (ADS)
Katz, Richard A.; Manzur, Tariq
2015-05-01
This study investigates laser beam propagation through an atmospheric boundary layer near the ocean surface. Objectives of this research are to ascertain feasibility limits for achieving maximum energy efficiency at extended ranges in the face of atmospheric and other distortions as the laser beam penetrates through transitional (anisotropic) and turbulent (isotropic) boundary layer regimes. Various aspects of turbulence modeling of laser beam propagation near the ocean surface are discussed including: Kolmogorov's model of atmospheric turbulence, parameterized structure functions (e.g., velocity and temperature gradients, gradients in refractive index) and other important factors affecting near surface propagation such as humidity, aerosols, and wave slap. Various preliminary modeled propagation results are shown, and a new methodology is proposed for improving existing model estimates with new time domain measurement procedures.
Analysis of birefringence effects in laser crystals by full vectorial beam propagation method
NASA Astrophysics Data System (ADS)
Hartmann, Rainer; Pflaum, Christoph; Graupeter, Thomas
2014-05-01
Modern laser technology demands powerful numerical tools to predict the efficiency of laser configurations. Birefringence has a strong influence on the beam quality and output power of a laser amplifier. We developed a complex physical model for simulating laser amplifiers and analyzing the birefringence effects. This model includes pump configuration, thermal lensing effects, birefringence, and beam propagation in the laser amplifier. The pump configuration is simulated using a complete three-dimensional ray tracing or by an approximation based on super-Gaussian functions. For an accurate modeling of the thermal lensing effect, the deformation of the end faces and the polarization dependent index of refraction was taken into account. Temperature, deformation and stress inside the laser crystal were calculated by a three-dimensional finite element analysis (FEA). In particular, the refractive index was accurately calculated by considering its temperature dependency and the photo elastic effect. This refractive index was used in the simulation of laser beam propagation through an amplifier. These simulations were performed by a complete three-dimensional vectorial beam propagation method (VBPM). The advantage of VBPM is that it can be applied to a polarization dependent index of refraction. This is important when taking into account the birefringence obtained by the photo elastic effect inside the laser crystal. The beam propagation method is based on finite elements on block structured grids as well as a Crank-Nicolson approximation in the propagation direction (FE-BPM). Reflecting boundaries were eliminated by introducing a perfect matching layer (PML). Simulation results show that a complete three-dimensional simulation model was useful in analyzing and optimizing high power laser amplifiers. The value of our model lies in the fact that it can take into account the crystal cut direction. Based on this the birefringence for simulating the laser beam quality and
Propagation of a laser beam in a time-varying waveguide. [plasma heating for controlled fusion
NASA Technical Reports Server (NTRS)
Chapman, J. M.; Kevorkian, J.
1978-01-01
The propagation of an axisymmetric laser beam in a plasma column having a radially parabolic electron density distribution is reported. For the case of an axially uniform waveguide it is found that the basic characteristics of alternating focusing and defocusing beams are maintained. However, the intensity distribution is changed at the foci and outer-beam regions. The features of paraxial beam propagation are discussed with reference to axially varying waveguides. Laser plasma coupling is considered noting the case where laser heating produces a density distribution radially parabolic near the axis and the energy absorbed over the focal length of the plasma is small. It is found that: (1) beam-propagation stability is governed by the relative magnitude of the density fluctuations existing in the axial variation of the waveguides due to laser heating, and (2) for beam propagation in a time-varying waveguide, the global instability of the propagation is a function of the initial fluctuation growth rate as compared to the initial time rate of change in the radial curvature of the waveguide.
NASA Astrophysics Data System (ADS)
Leader, J. C.
1983-01-01
Among the topics discussed are the atmospheric attenuation of laser radiation, the determination of atmospheric properties from lidar measurements, laser transmission measurement limitations due to correlated atmospheric effects, high spatial resolution studies of propagation, multiple scattering of laser beam propagation in clouds, the probability density of the irradiance in atmospheric turbulence, source statistics effects on irradiance scintillations in turbulence, and numerical solutions of the fourth-moment equation. Also discussed are the characteristics and effects of speckle propagation through turbulence, the application of random medium propagation theory to communication and radar system analyses, multiple scattering corrections to the Beer-Lambert Law, millimeter wave propagation through a clear atmosphere, endoatmospheric laser arrays for thermal blooming environments, the wavelength dependence of adaptive optics compensation, time-dependent thermal blooming in axial pipe flow, and turbulence-induced adaptive optics performance degradation.
NASA Astrophysics Data System (ADS)
Peng, Yufeng; Peng, Fang; Han, Junpeng
2013-02-01
Based on the laser field from a positive confocal unstable resonator, considering the influence of thermal distortion of the internal resonator mirror on the annular beam, the propagation characteristics of the annular beam through turbulent atmosphere are investigated by means of the fast Fourier transform algorithm (FFT). The intensity distributions of the output laser far-field are obtained to analyze the propagation characteristics of laser annular beam through the turbulent atmosphere, which is a function about different propagation distances. The results show that the peak intensity of the laser pattern becomes depressed and the spread of the far field diagram patterns is broadened under the increasing of the transmission distance and the thermal distortion of the laser resonator. β-parameter and strehl ratio are introduced to estimate the annular beam quality characteristics. It is found that the annular beam through strong turbulence influences much less obviously than the annular beam through weak turbulence on the quality characteristics with thermal distortion. In the same atmospheric conditions with a certain distance, the greater the mirror thermal distortion is, the worse the annular beam quality characteristics is.
Efficient propagation of ultra-intense laser beam in dense plasma
Habara, H.; Ivancic, S.; Anderson, K.; Haberberger, D.; Iwawaki, T.; Stoeckl, C.; Tanaka, K. A.; Uematsu, Y.; Theobald, W.
2015-04-29
Ultra intense laser propagation in extended, dense plasma is investigated through optical and proton probing. When a >1 kJ, 10 ps laser propagates into a long-density scale length plasma, channel formation was observed up to 0.6 _{nc} from the analysis of optical probe images. The proton track analysis shows the formation of strong electric and magnetic fields along the plasma channel, which may lead to the observed collimated electron beam on the laser axis. These results are promising for the feasibility of the direct irradiation scheme of fast ignition.
Green (2(omega)) Laser Beam propagation in high-temperature Hohlraum Plasmas
Niemann, C; Berger, R; Divol, L; Froula, D H; Jones, O S; Kirkwood, R K; Meezan, N; Moody, J; Ross, J S; Suter, L; Glenzer, S H
2007-10-26
We demonstrate propagation and small backscatter losses of a frequency-doubled (2{omega}) laser beam interacting with inertial confinement fusion hohlraum plasmas. The electron temperature of 3.3 keV, approximately a factor of two higher than achieved in previous experiments with open geometry targets, approaches plasma conditions of high-fusion yield hohlraums. In this new temperature regime, we measure 2{omega} laser beam transmission approaching 80% with simultaneous backscattering losses of less than 10%. These findings suggests that good laser coupling into fusion hohlraums using 2{omega} light is possible.
Green frequency-doubled laser-beam propagation in high-temperature hohlraum plasmas.
Niemann, C; Berger, R L; Divol, L; Froula, D H; Jones, O; Kirkwood, R K; Meezan, N; Moody, J D; Ross, J; Sorce, C; Suter, L J; Glenzer, S H
2008-02-01
We demonstrate propagation and small backscatter losses of a frequency-doubled (2omega) laser beam interacting with inertial confinement fusion hohlraum plasmas. The electron temperature of 3.3 keV, approximately a factor of 2 higher than achieved in previous experiments with open geometry targets, approaches plasma conditions of high-fusion yield hohlraums. In this new temperature regime, we measure 2omega laser-beam transmission approaching 80% with simultaneous backscattering losses of less than 10%. These findings suggest that good laser coupling into fusion hohlraums using 2omega light is possible.
Green Frequency-Doubled Laser-Beam Propagation in High-Temperature Hohlraum Plasmas
Niemann, C.; Berger, R. L.; Divol, L.; Froula, D. H.; Jones, O.; Kirkwood, R. K.; Meezan, N.; Moody, J. D.; Ross, J.; Sorce, C.; Suter, L. J.; Glenzer, S. H.
2008-02-01
We demonstrate propagation and small backscatter losses of a frequency-doubled (2{omega}) laser beam interacting with inertial confinement fusion hohlraum plasmas. The electron temperature of 3.3 keV, approximately a factor of 2 higher than achieved in previous experiments with open geometry targets, approaches plasma conditions of high-fusion yield hohlraums. In this new temperature regime, we measure 2{omega} laser-beam transmission approaching 80% with simultaneous backscattering losses of less than 10%. These findings suggest that good laser coupling into fusion hohlraums using 2{omega} light is possible.
Hermite-cosine-Gaussian laser beam and its propagation characteristics in turbulent atmosphere.
Eyyuboğlu, Halil Tanyer
2005-08-01
Hermite-cosine-Gaussian (HcosG) laser beams are studied. The source plane intensity of the HcosG beam is introduced and its dependence on the source parameters is examined. By application of the Fresnel diffraction integral, the average receiver intensity of HcosG beam is formulated for the case of propagation in turbulent atmosphere. The average receiver intensity is seen to reduce appropriately to various special cases. When traveling in turbulence, the HcosG beam initially experiences the merging of neighboring beam lobes, and then a TEM-type cosh-Gaussian beam is formed, temporarily leading to a plain cosh-Gaussian beam. Eventually a pure Gaussian beam results. The numerical evaluation of the normalized beam size along the propagation axis at selected mode indices indicates that relative spreading of higher-order HcosG beam modes is less than that of the lower-order counterparts. Consequently, it is possible at some propagation distances to capture more power by using higher-mode-indexed HcosG beams.
Beam Propagation For The Laser Inertial Confinement Fusion-Fission Energy Engine
Wilks, S C; Cohen, B I; Latkowski, J F; Williams, E A
2008-12-16
Several potential issues concerning laser-beam propagation thorough the LIFE target chambers are addressed. It is found that the absorption due to inverse Bremsstrahlung limits the gas density to approximately 2 {micro}g/cc of xenon gas. A comparison to prior calculations suggests that this results in acceptable first wall heating.
Evolution of branch points for a laser beam propagating through an uplink turbulent atmosphere.
Ge, Xiao-Lu; Liu, Xuan; Guo, Cheng-Shan
2014-03-24
Evolution of branch points in the distorted optical field is studied when a laser beam propagates through turbulent atmosphere along an uplink path. Two categories of propagation events are mainly explored for the same propagation height: fixed wavelength with change of the turbulence strength and fixed turbulence strength with change of the wavelength. It is shown that, when the beam propagates to a certain height, the density of the branch-points reaches its maximum and such a height changes with the turbulence strength but nearly remains constant with different wavelengths. The relationship between the density of branch-points and the Rytov number is also given. A fitted formula describing the relationship between the density of branch-points and propagation height with different turbulence strength and wavelength is found out. Interestingly, this formula is very similar to the formula used for describing the Blackbody radiation in physics. The results obtained may be helpful for atmospheric optics, astronomy and optical communication.
Pérez, Darío G; Funes, Gustavo
2012-12-01
Under the Geometrics Optics approximation is possible to estimate the covariance between the displacements of two thin beams after they have propagated through a turbulent medium. Previous works have concentrated in long propagation distances to provide models for the wandering statistics. These models are useful when the separation between beams is smaller than the propagation path-regardless of the characteristics scales of the turbulence. In this work we give a complete model for these covariances, behavior introducing absolute limits to the validity of former approximations. Moreover, these generalizations are established for non-Kolmogorov atmospheric models.
Propagation of a laser beam in a plasma
NASA Technical Reports Server (NTRS)
Chapman, J. M.; Kevorkian, J.; Steinhauer, L. C.; Vagners, J.
1975-01-01
This paper shows that for a nonabsorbing medium with a prescribed index of refraction, the effects of beam stability, line focusing, and beam distortion can be predicted from simple ray optics. When the paraxial approximation is used, diffraction effects are examined for Gaussian, Lorentzian, and square beams. Most importantly, it is shown that for a Gaussian beam, diffraction effects can be included simply by adding imaginary solutions to the paraxial ray equations. Also presented are several procedures to extend the paraxial approximation so that the solution will have a domain of validity of greater extent.
Excitation of Accelerating Plasma Waves by Counter-Propagating Laser Beams
Shvets, Gennady; Fisch, Nathaniel J; Pukhov, Alexander
2002-04-05
The conventional approach to exciting high phase velocity waves in plasmas is to employ a laser pulse moving in the direction of the desired particle acceleration. Photon downshifting then causes momentum transfer to the plasma and wave excitation. Novel approaches to plasma wake excitation, colliding-beam accelerator (CBA), which involve photon exchange between the long and short counter-propagating laser beams, are described. Depending on the frequency detuning Dw between beams and duration tL of the short pulse, there are two approaches to CBA. The first approach assumes tL ª 2/wp. Photons exchanged between the beams deposit their recoil momentum in the plasma driving the plasma wake. Frequency detuning between the beams determines the direction of the photon exchange, thereby controlling the phase of the plasma wake. This phase control can be used for reversing the slippage of the accelerated particles with respect to the wake. A variation on the same theme, super-beatwave accelerator, is also described. In the second approach, a short pulse with tL >> 2/wp1 detuned by Dw ~ 2wp from the counter-propagating beam is employed. While parametric excitation of plasma waves by the electromagnetic beatwave at 2wp of two co-propagating lasers was first predicted by Rosenbluth and Liu [M.N. Rosenbluth, C.S. Liu, Phys. Rev. Lett. 29 (1972) 701], it is demonstrated that the two excitation beams can be counter-propagating. The advantages of using this geometry (higher instability growth rate, insensitivity to plasma inhomogeneity) are explained, and supporting numerical simulations presented.
Sheikh, Mumtaz; Riza, Nabeel A
2010-06-01
To the best of our knowledge, we propose the first motion-free laser beam propagation analyzer with a hybrid design using a digital micromirror device (DMD) and a liquid electronically controlled variable focus lens (ECVFL). Unlike prior analyzers that require profiling the beam at multiple locations along the light propagation axis, the proposed analyzer profiles the beam at the same plane for multiple values of the ECVFL focal length, thus eliminating beam profiler assembly motion. In addition to measuring standard Gaussian beam parameters, the analyzer can also be used to measure the M(2) beam propagation parameter of a multimode beam. Proof-of-concept beam parameter measurements with the proposed analyzer are successfully conducted for a 633 nm laser beam. Given the all-digital nature of the DMD-based profiling and all-analog motion-free nature of the ECVFL beam focus control, the proposed analyzer versus prior art promises better repeatability, speed, and reliability.
Experimental determination of thermal turbulence effects on a propagating laser beam
NASA Astrophysics Data System (ADS)
Ndlovu, Sphumelele C.; Chetty, Naven
2015-08-01
The effect of turbulence on propagating laser beams has been a subject of interest since the evolution of lasers back in 1959. In this work, an inexpensive and reliable technique for producing interferograms using a point diffraction interferometer (PDI) was considered to experimentally study the turbulence effects on a laser beam propagating through air. The formed interferograms from a propagating beamwere observed and digitally processed to study the strength of atmospheric turbulence. This technique was found to be sensitive enough to detect changes in applied temperature with distance between the simulated turbulence and laser path. These preliminary findings indicated that we can use a PDI method to detect and localise atmospheric turbulence parameters. Such parameters are very important for use in the military (defence laser weapons) and this is vital for South Africa (SA) since it has natural resources, is involved in peace keeping and mediation for other countries, and hence must have a strong defence system that will be able to locate, detect and destroy incoming missiles and other threatening atmospheric systems in order to protect its environment and avoid the initiation of countermeasures on its land.
2D Self-Similar Profile for Laser Beam Propagation in Medium with Saturating Multi-Photon Absorption
NASA Astrophysics Data System (ADS)
Trofimov, Vyacheslav A.; Lysak, Tatiana M.; Zakharova, Irina G.
2016-02-01
We study a self-similar mode of 2D laser beam propagation in media with multiphoton absorption (MA) taking into account a resonant nonlinearity and nonlinear absorption saturating. An analytical solution of the corresponding equations describing the problems under consideration is derived using an eigenvalue problem method generalization for soliton- like solution finding. The developed solution is used as incident beam profile and phase front for computer simulation of the 2D laser beam propagation. In particular, we demonstrate numerically that the laser beam propagation in a self-similar mode occurs within a certain distance, which depends on medium properties. Under certain relations between the nonlinear absorption and resonant nonlinearity, and cubic nonlinear response, we observe the super long distance of the beam propagation without any beam profile distributions.
A self-consistent model of stripe geometry lasers based on the beam propagation method
Meissner, P.; Patzak, E.; Yevick, D.
1984-08-01
Using the propagating beam technique to solve Maxwell's equations together with a shooting method solution to the carrier diffusion equation, the authors develop an iterative, self-consistent procedure for determing the properties of stripe geometry lasers. This procedure allows the authors to calculate the power-current characteristics, differential quantum efficiencies, gain distributions and near and far fields over a wide range of currents at and above threshold. Far above threshold, as expected, that symmetric and antisymmetric transverse modes can lase simultaneously.
Propagation of a laser-driven relativistic electron beam inside a solid dielectric
NASA Astrophysics Data System (ADS)
Sarkisov, G. S.; Ivanov, V. V.; Leblanc, P.; Sentoku, Y.; Yates, K.; Wiewior, P.; Chalyy, O.; Astanovitskiy, A.; Bychenkov, V. Yu.; Jobe, D.; Spielman, R. B.
2012-09-01
Laser probe diagnostics: shadowgraphy, interferometry, and polarimetry were used for a comprehensive characterization of ionization wave dynamics inside a glass target induced by a laser-driven, relativistic electron beam. Experiments were done using the 50-TW Leopard laser at the University of Nevada, Reno. We show that for a laser flux of ˜2 × 1018 W/cm2 a hemispherical ionization wave propagates at c/3 for 10 ps and has a smooth electron-density distribution. The maximum free-electron density inside the glass target is ˜2 × 1019 cm-3, which corresponds to an ionization level of ˜0.1%. Magnetic fields and electric fields do not exceed ˜15 kG and ˜1 MV/cm, respectively. The electron temperature has a hot, ringlike structure with a maximum of ˜0.7 eV. The topology of the interference phase shift shows the signature of the “fountain effect”, a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields driven by laser. The very low ionization observed after the laser heating pulse suggests a fast recombination on the sub-ps time scale.
Propagation of a laser-driven relativistic electron beam inside a solid dielectric.
Sarkisov, G S; Ivanov, V V; Leblanc, P; Sentoku, Y; Yates, K; Wiewior, P; Chalyy, O; Astanovitskiy, A; Bychenkov, V Yu; Jobe, D; Spielman, R B
2012-09-01
Laser probe diagnostics: shadowgraphy, interferometry, and polarimetry were used for a comprehensive characterization of ionization wave dynamics inside a glass target induced by a laser-driven, relativistic electron beam. Experiments were done using the 50-TW Leopard laser at the University of Nevada, Reno. We show that for a laser flux of ∼2 × 10(18) W/cm2 a hemispherical ionization wave propagates at c/3 for 10 ps and has a smooth electron-density distribution. The maximum free-electron density inside the glass target is ∼2 × 10(19) cm-3, which corresponds to an ionization level of ∼0.1%. Magnetic fields and electric fields do not exceed ∼15 kG and ∼1 MV/cm, respectively. The electron temperature has a hot, ringlike structure with a maximum of ∼0.7 eV. The topology of the interference phase shift shows the signature of the "fountain effect", a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields driven by laser. The very low ionization observed after the laser heating pulse suggests a fast recombination on the sub-ps time scale. PMID:23031038
Propagation of a laser-driven relativistic electron beam inside a solid dielectric.
Sarkisov, G S; Ivanov, V V; Leblanc, P; Sentoku, Y; Yates, K; Wiewior, P; Chalyy, O; Astanovitskiy, A; Bychenkov, V Yu; Jobe, D; Spielman, R B
2012-09-01
Laser probe diagnostics: shadowgraphy, interferometry, and polarimetry were used for a comprehensive characterization of ionization wave dynamics inside a glass target induced by a laser-driven, relativistic electron beam. Experiments were done using the 50-TW Leopard laser at the University of Nevada, Reno. We show that for a laser flux of ∼2 × 10(18) W/cm2 a hemispherical ionization wave propagates at c/3 for 10 ps and has a smooth electron-density distribution. The maximum free-electron density inside the glass target is ∼2 × 10(19) cm-3, which corresponds to an ionization level of ∼0.1%. Magnetic fields and electric fields do not exceed ∼15 kG and ∼1 MV/cm, respectively. The electron temperature has a hot, ringlike structure with a maximum of ∼0.7 eV. The topology of the interference phase shift shows the signature of the "fountain effect", a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional particle-in-cell (PIC) computer simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields driven by laser. The very low ionization observed after the laser heating pulse suggests a fast recombination on the sub-ps time scale.
Stimulated Raman scattering of laser in a plasma in the presence of a co-propagating electron beam
Parashar, J.
2013-12-15
A relativistic electron beam co-propagating with a high power laser in plasma is shown to add to the growth of the stimulated Raman back scattering of the laser. The growth rate is sensitive to phase matching of electron beam with the plasma wave. In the case of phase mismatch, the growth rate drops by an order. The energy spread of the electron beam significantly reduces the effectiveness of the beam on the stimulated Raman process.
Hanson, Frank; Lasher, Mark
2010-06-01
We characterize and compare the effects of turbulence on underwater laser propagation with theory. Measurements of the coupling efficiency of the focused beam into a single-mode fiber are reported. A simple tip-tilt control system, based on the position of the image centroid in the focal plane, was shown to maintain good coupling efficiency for a beam radius equal to the transverse coherence length, r(0). These results are relevant to high bandwidth communication technology that requires good spatial mode quality.
Propagation of Laser-Driven Relativistic Electron Beam inside Solid Dielectric
NASA Astrophysics Data System (ADS)
Sarkisov, G. S.; Jobe, D.; Spielman, R.; Ivanov, V. V.; Leblanc, P.; Sentoku, Y.; Yates, K.; Wiewior, P.; Bychenkov, V. Yu.
2011-10-01
Laser probing diagnostics shadowgraphy, interferometry and polarimetry was used for comprehensive characterization of ionization wave dynamics inside glass target induced by laser-driven relativistic electron beam. Experiment was done using 50-TW Leopard laser at University of Nevada Reno. It has been shown that for laser flax ~2 ×1018W/cm2 hemispheric ionization wave propagates with c/3 speed has smooth electron density distribution, absorbing probing green beam in 2-10 times. Maximum of free-electron density inside glass target is ~2x1019cm-3, which correspond to ionization ~0.1%. Magnetic and electric fields do not exceed ~15 kG and ~1 MV/cm. Electron temperature has hot-ring structure with maximum 0.1-0.5 eV. The topology of the interference phase shift shows the signature of the ``fountain effect'', a narrow electron beam that fans out from the propagation axis and heads back to the target surface. Two-dimensional PIC-simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields. The very low ionization, ~0.1%, observed after the heating pulse suggests a fast recombination at the sub-ps time scale. Work was supported by the DOE/NNSA under UNR grant DE-FC52-06NA27616 and grant DE-PS02-08ER08-16.
Acceleration and Compression of Charged Particle Bunches Using Counter-Propagating Laser Beams
G. Shvets; N. J. Fisch; A. Pukhov
2000-10-17
The nonlinear interaction between counter-propagating laser beams in a plasma results in the generation of large (enhanced) plasma wakes. The two beams need to be slightly detuned in frequency, and one of them has to be ultra-short (shorter than a plasma period). Thus produced wakes have a phase velocity close to the speed of light and can be used for acceleration and compression of charged bunches. The physical mechanism responsible for the enhanced wake generation is qualitatively described and compared with the conventional laser wakefield mechanism. The authors also demonstrate that, depending on the sign of the frequency difference between the lasers, the enhanced wake can be used as a ``snow-plow'' to accelerate and compress either positively or negatively charged bunches. This ability can be utilized in an electron-positron injector.
Nonlinear propagation of a randomized laser beam through an expanding plasma.
Myatt, J; Pesme, D; Hüller, S; Maximov, A; Rozmus, W; Capjack, C E
2001-12-17
We present simulations of the interaction of a random phase plate laser beam with an underdense, expanding plasma for conditions typical of recent LULI experiments. We use a new code that describes the paraxial propagation of the laser, accounting for the nonlinear evolution of the plasma in an isothermal fluid description with weakly collisional electrons. The transmitted light, in excellent agreement with experiment, is shown to be strongly redshifted as a result of self-phase modulation due to self-focusing. PMID:11736585
NASA Astrophysics Data System (ADS)
Gurdev, Ljuan; Dreischuh, Tanja; Vankov, Orlin; Bliznakova, Irina; Avramov, Lachezar; Stoyanov, Dimitar
2014-06-01
The possibility is studied to develop a straightforward analytical approach to the determination of the optical properties of liquid turbid media having forward-peaked scattering indicatrices. The approach is based on investigating the in-depth behavior of the radius and the axial intensity of a laser radiation beam propagating through the turbid medium. Based on the small-angle approximation, the detected forward-propagating light power spatial distribution, at relatively small or large optical depths along the beam axis, is obtained asymptotically in analytical form allowing one to derive relatively simple expressions of the extinction, reduced-scattering and absorption coefficients and the anisotropy factor of the medium through the characteristics of the propagating light beam. Preliminary experiments have also been performed, using Intralipid dilutions of different relatively low concentrations and measuring the cross-sectional radial distribution of the detected light power at different depths along the beam axis. The corresponding on-axis detected light power profiles have been measured independently as well. The experimental results are consistent with the analytical expressions obtained that allow one to estimate the optical coefficients and the anisotropy factor of the investigated media on the basis of the measured beam characteristics. The values obtained are near those predicted by other researchers.
Controlled Ion Acceleration in Two Crossed Laser Beams Propagating in Plasmas
NASA Astrophysics Data System (ADS)
Tataronis, J. A.; Petržílka, V.; Krlín, L.
2003-10-01
Electron acceleration occurs in a single plane laser beam that is in the presence of a secondary perpendicularly propagating plane laser beam with a randomized phase. As the accelerated electrons are pushed away, they leave the heavier ions behind, producing thereby a charge separation electrostatic field and consequent ion flows. The power flux carried by the accelerated ions can be controlled by varying the intensity of the secondary beam. Results of a numerical study of this control process are presented here. The laser beam parameters chosen for the computations of the primary electron acceleration match the parameters available at the Prague Asterix Laser System (PALS)^1. For the modeling, we use an advanced version of our 3-d two-fluid numerical code^2, originally developed for the analysis of fast electron generation and subsequent ion acceleration in front of lower hybrid wave launchers in large tokamaks. [2pt] ^1K. Jungwirth et al., Phys. Plasmas 8, 2495 (2001). [2pt] ^2V. Petržílka et al., Proc. 29th EPS Conference, Montreux, June 2002, paper 2.105.
Stimulated Raman scattering and nonlinear focusing of high-power laser beams propagating in water.
Hafizi, B; Palastro, J P; Peñano, J R; Gordon, D F; Jones, T G; Helle, M H; Kaganovich, D
2015-04-01
The physical processes associated with propagation of a high-power (power > critical power for self-focusing) laser beam in water include nonlinear focusing, stimulated Raman scattering (SRS), optical breakdown, and plasma formation. The interplay between nonlinear focusing and SRS is analyzed for cases where a significant portion of the pump power is channeled into the Stokes wave. Propagation simulations and an analytical model demonstrate that the Stokes wave can re-focus the pump wave after the power in the latter falls below the critical power. It is shown that this novel focusing mechanism is distinct from cross-phase focusing. The phenomenon of gain-focusing discussed here for propagation in water is expected to be of general occurrence applicable to any medium supporting nonlinear focusing and stimulated Raman scattering.
Stimulated Raman scattering and nonlinear focusing of high-power laser beams propagating in water
NASA Astrophysics Data System (ADS)
Hafizi, B.; Palastro, J. P.; Peñano, J. R.; Gordon, D. F.; Jones, T. G.; Helle, M. H.; Kaganovich, D.
2015-04-01
The physical processes associated with propagation of a high-power (power > critical power for self-focusing) laser beam in water include nonlinear focusing, stimulated Raman scattering (SRS), optical breakdown and plasma formation. The interplay between nonlinear focusing and SRS is analyzed for cases where a significant portion of the pump power is channeled into the Stokes wave. Propagation simulations and an analytical model demonstrate that the Stokes wave can re-focus the pump wave after the power in the latter falls below the critical power. It is shown that this novel focusing mechanism is distinct from cross-phase focusing. While discussed here in the context of propagation in water, the gain-focusing phenomenon is general to any medium supporting nonlinear focusing and stimulated forward Raman scattering.
Stimulated Raman scattering and nonlinear focusing of high-power laser beams propagating in water.
Hafizi, B; Palastro, J P; Peñano, J R; Gordon, D F; Jones, T G; Helle, M H; Kaganovich, D
2015-04-01
The physical processes associated with propagation of a high-power (power > critical power for self-focusing) laser beam in water include nonlinear focusing, stimulated Raman scattering (SRS), optical breakdown, and plasma formation. The interplay between nonlinear focusing and SRS is analyzed for cases where a significant portion of the pump power is channeled into the Stokes wave. Propagation simulations and an analytical model demonstrate that the Stokes wave can re-focus the pump wave after the power in the latter falls below the critical power. It is shown that this novel focusing mechanism is distinct from cross-phase focusing. The phenomenon of gain-focusing discussed here for propagation in water is expected to be of general occurrence applicable to any medium supporting nonlinear focusing and stimulated Raman scattering. PMID:25831383
Turbulence distance for laser beams propagating through non-Kolmogorov turbulence.
Huang, Yongping; Zhang, Bin
2013-11-01
Based on the second-order moments and the non-Kolmogorov turbulence spectrum, the general analytical expression for the turbulence distance of laser beams propagating through non-Kolmogorov turbulence is derived, which depends on the non-Kolmogorov turbulence parameters including the generalized exponent parameter α, inner scale l(0), and outer scale L(0) and the initial second-order moments of the beams at the plane of z=0. Taking the partially coherent Hermite-Gaussian linear array (PCHGLA) beam as an illustrative example, the effects of non-Kolmogorov turbulence and array parameters on the turbulence distance are discussed in detail. The results show that the turbulence distance z(Mx)(α) of PCHGLA beams through non-Kolmogorov turbulence first decreases to a dip and then increases with increasing α, and the value of z(Mx)(α) increases with increasing beam number and beam order and decreasing coherence parameter, meaning less influence of non-Kolmogorov turbulence on partially coherent array beams than that of fully coherent array beams and a single partially coherent beam. However, the value of z(Mx)(α) for PCHGLA beams first increases nonmonotonically with the increasing of the relative beam separation x0' for x0'≤1 and increases monotonically as x0' increases for x0'>1. Moreover, the variation behavior of the turbulence distance with the generalized exponent parameter, inner scale, and outer scale of the turbulence and the beam number is similar, but different with the relative beam separation for coherent and incoherent combination cases.
Ideal laser-beam propagation through high-temperature ignition Hohlraum plasmas.
Froula, D H; Divol, L; Meezan, N B; Dixit, S; Moody, J D; Neumayer, P; Pollock, B B; Ross, J S; Glenzer, S H
2007-02-23
We demonstrate that a blue (3omega, 351 nm) laser beam with an intensity of 2 x 10(15) W cm(-2) propagates nearly within the original beam cone through a millimeter scale, T(e)=3.5 keV high density (n(e)=5 x 10(20) cm(-3)) plasma. The beam produced less than 1% total backscatter at these high temperatures and densities; the resulting transmission is greater than 90%. Scaling of the electron temperature in the plasma shows that the plasma becomes transparent for uniform electron temperatures above 3 keV. These results are consistent with linear theory thresholds for both filamentation and backscatter instabilities inferred from detailed hydrodynamic simulations. This provides a strong justification for current inertial confinement fusion designs to remain below these thresholds.
Purohit, Gunjan Rawat, Priyanka; Chauhan, Prashant; Mahmoud, Saleh T.
2015-05-15
This article presents higher-order paraxial theory (non-paraxial theory) for the ring ripple formation on an intense Gaussian laser beam and its propagation in plasma, taking into account the relativistic-ponderomotive nonlinearity. The intensity dependent dielectric constant of the plasma has been determined for the main laser beam and ring ripple superimposed on the main laser beam. The dielectric constant of the plasma is modified due to the contribution of the electric field vector of ring ripple. Nonlinear differential equations have been formulated to examine the growth of ring ripple in plasma, self focusing of main laser beam, and ring rippled laser beam in plasma using higher-order paraxial theory. These equations have been solved numerically for different laser intensities and plasma frequencies. The well established experimental laser and plasma parameters are used in numerical calculation. It is observed that the focusing of the laser beams (main and ring rippled) becomes fast in the nonparaxial region by expanding the eikonal and other relevant quantities up to the fourth power of r. The splitted profile of laser beam in the plasma is observed due to uneven focusing/defocusing of the axial and off-axial rays. The growths of ring ripple increase when the laser beam intensity increases. Furthermore, the intensity profile of ring rippled laser beam gets modified due to the contribution of growth rate.
NASA Astrophysics Data System (ADS)
Aksenov, V. P.; Dudorov, V. V.; Kolosov, V. V.
2016-08-01
Using a numerical simulation, we investigate the possibility of synthesising vortex laser beams with a variable orbital angular momentum by a hexagonal array of fibre lasers under a phase control of individual subapertures of the array. We report the requirements to the parameters of the device generating a vortex beam (number and size of subapertures, as well as their mutual arrangement). The propagation dynamics of synthesised vortex beams is compared with that of conventional Laguerre-Gaussian beams in free space and in a turbulent atmosphere. The spectral properties of the synthesised beam, represented as a superposition of different azimuthal modes, are determined during its propagation in free space. The energy and statistical parameters of the synthesised and Laguerre-Gaussian vortex beams are shown to coincide with increasing propagation distance in a turbulent medium.
X-ray laser beam propagation in double-foil targets
NASA Astrophysics Data System (ADS)
Boswell, B.; Shvarts, D.; Boehly, T.; Yaakobi, B.
1990-02-01
Refraction effects on the gain of an x-ray laser propagating in a convex (lateral) plasma density profile have been studied previously. Here the corresponding case of concave density profile is studied theoretically. Experimentally, the convex profile is obtained by irradiating a single (exploding) foil target; the concave case can be realized by various two-beam irradiation configurations. Such geometries have been studied experimentally at the Laboratory for Laser Energetics (LLE) [SPIE Proceedings (SPIE, Bellingham, WA, 1987), Vol. 831, Paper 40, p. 283; Paper 42, p. 305]. The concave profile has a waveguiding effect on the propagation of the x-ray laser and can reduce the deleterious effects of refraction. The output power, its dependence on the length of the amplifying medium, and its angular distribution are studied and compared with the convex profile case. An amplifier mode (in which a collimated beam is incident on an amplifying medium) is compared with an amplified spontaneous emission mode (where spontaneous emission sources exist throughout the amplifying medium).
0.351 micron Laser Beam propagation in High-temperature Plasmas
Froula, D; Divol, L; Meezan, N; Ross, J; Berger, R L; Michel, P; Dixit, S; Rekow, V; Sorce, C; Moody, J D; Neumayer, P; Pollock, B; Wallace, R; Suter, L; Glenzer, S H
2007-12-10
A study of the laser-plasma interaction processes have been performed in plasmas that are created to emulate the plasma conditions in indirect drive inertial confinement fusion targets. The plasma emulator is produced in a gas-filled hohlraum; a blue 351-nm laser beam propagates along the axis of the hohlraum interacting with a high-temperature (T{sub e} = 3.5 keV), dense (n{sub e} = 5 x 10{sup 20}cm{sup -3}), long-scale length (L {approx} 2 mm) plasma. Experiments at these conditions have demonstrated that the interaction beam produces less than 1% total backscatter resulting in transmission greater than 90% for laser intensities less than I < 2 x 10{sup 15} W-cm{sup -2}. The bulk plasma conditions have been independently characterized using Thomson scattering where the peak electron temperatures are shown to scale with the hohlraum heater beam energy in the range from 2 keV to 3.5 keV. This feature has allowed us to determine the thresholds for both backscattering and filamentation instabilities; the former measured with absolutely calibrated full aperture backscatter and near backscatter diagnostics and the latter with a transmitted beam diagnostics. A plasma length scaling is also investigated extending our measurements to 4-mm long high-temperature plasmas. At intensities I < 5 x 10{sup 14} W-cm{sup -2}, greater than 80% of the energy in the laser is transmitted through a 5-mm long, high-temperature (T{sub e} > 2.5 keV) high-density (n{sub e} = 5 x 10{sup 20} w-cm{sup -3}) plasma. Comparing the experimental results with detailed gain calculations for the onset of significant laser scattering processes shows a stimulated Brillouin scattering threshold (R=10%) for a linear gain of 15; these high temperature, low density experiments produce plasma conditions comparable to those along the outer beams in ignition hohlraum designs. By increasing the gas fill density (n{sub e} = 10{sup 21} cm{sup -3}) in these targets, the inner beam ignition hohlraum conditions are
Shu, Hong; Mokhov, Sergiy; Zeldovich, Boris Ya; Bass, Michael
2009-01-01
A further extension of the iteration method for beam propagation calculation is presented that can be applied for volume Bragg gratings (VBGs) with extremely large grating strength. A reformulation of the beam propagation formulation is presented for analyzing the reflection of a laser beam by a deformed VBG. These methods will be shown to be very accurate and efficient. A VBG with generic z-dependent distortion has been analyzed using these methods.
Sokolovskii, G S; Dyudelev, V V; Losev, S N; Butkus, M; Soboleva, K K; Sobolev, A I; Deryagin, A G; Kuchinskii, V I; Sibbet, V; Rafailov, E U
2013-05-31
We study the peculiarities of the formation of Bessel beams in semiconductor lasers with a high propagation parameter M{sup 2}. It is shown that the propagation distance of the Bessel beam is determined by the divergence of the quasi-Gaussian beam with high M{sup 2} rather than the geometric parameters of the optical scheme. It is demonstrated that technologically inevitable rounding of the axicon tip leads to a significant increase in the transverse dimension of the central part of the Bessel beam near the axicon. (semiconductor lasers. physics and technology)
Turbulence effects on high energy laser beam propagation in the atmosphere.
Yahel, R Z
1990-07-20
A simple phenomenological model for the interaction of a high energy laser (HEL) beam with atmospheric turbulence is presented. According to this model the temperature power spectrum becomes non-Kolmogorov. The refractive index structure constant C(2)(n) is replaced by another quantity C(2)(n,eff) which is space dependent, C(2)(n,eff) = C(2)(n) (1 + mid R:nablaT/ partial differentialtheta / partial differentialzmid R:(2)) (provided ( partial differentialtheta )/( partial differentialz) not equal 0). Here DeltaT is the local temperature gradient in the crosswind direction, while ( partial differentialtheta )/( partial differentialz) is the vertical potential temperature gradient in the atmosphere. Numerical simulations of HEL beam propagation were performed including effects of this model. Implications of the results are discussed.
Challenges of laser beam propagation near/within marine boundary layer
NASA Astrophysics Data System (ADS)
Manzur, Tariq; Katz, Richard A.; Olson, Joshua
2015-05-01
Marine atmospheric condition plays a critical role on imaging, laser beam propagation, and optical communication of the commercial and military platform. In Military platforms, ships and sailors must be able to defend and communicate with other maritime platform in sometimes volatile and hostile regions around the globe. Naval combatants need defensive and offensive capabilities against a variety of potential threats - many coming at low altitude, UAV, USV etc. High energy lasers (HELs) are currently in development, which have sufficient power levels (~100 kW) to destroy/disable most types of threats. Though target engagement and energy delivery are challenging, a HEL weapon can engage targets at the speed of light, does not require physical ammunition, and is able to run for hours at a time.
NASA Astrophysics Data System (ADS)
Labaune, Christine; Fuchs, Julien; Depierreux, Sylvie; Baldis, Hector; Pesme, Denis; Myatt, Jason; Hüller, Stefan; Laval, Guy; Tikhonchuk, Vladimir
2000-10-01
Experiments with the six-beam laser facility at Laboratoire pour l'Utilisation des lasers Intenses (LULI) have demonstrated simultaneous and correlated large angular beam spreading and spectral broadening, on the red side of the spectra, of a RPP laser beam after its propagation through an underdense plasma.. At the highest intensities, the beam initial aperture is widely broadened (the F.W.H.M. aperture is increased by a factor 2) and its bandwidth increases from <0.1 A to more than 10 A. Results showing the effect of the plasma electron density, laser intensity and polarization smoothing will be presented. The increase of spatial and temporal incoherence of the laser beam is discussed following recent numerical simulations.
Dios, Federico; Recolons, Jaume; Rodríguez, Alejandro; Batet, Oscar
2008-02-01
Temporal analysis of the irradiance at the detector plane is intended as the first step in the study of the mean fade time in a free optical communication system. In the present work this analysis has been performed for a Gaussian laser beam propagating in the atmospheric turbulence by means of computer simulation. To this end, we have adapted a previously known numerical method to the generation of long phase screens. The screens are displaced in a transverse direction as the wave is propagated, in order to simulate the wind effect. The amplitude of the temporal covariance and its power spectrum have been obtained at the optical axis, at the beam centroid and at a certain distance from these two points. Results have been worked out for weak, moderate and strong turbulence regimes and when possible they have been compared with theoretical models. These results show a significant contribution of beam wander to the temporal behaviour of the irradiance, even in the case of weak turbulence. We have also found that the spectral bandwidth of the covariance is hardly dependent on the Rytov variance.
Monte Carlo simulations of converging laser beam propagating in turbid media with parallel computing
NASA Astrophysics Data System (ADS)
Wu, Di; Lu, Jun Q.; Hu, Xin H.; Zhao, S. S.
1999-11-01
Due to its flexibility and simplicity, Monte Carlo method is often used to study light propagation in turbid medium where the photons are treated like classic particles being scattered and absorbed randomly based on a radiative transfer theory. However, due to the need of large number of photons to produce statistically significance results, this type of calculations requires large computing resources. To overcome such difficulty, we implemented parallel computing technique into our Monte Carlo simulations. The algorithm is based on the fact that the classic particles are uncorrelated, and the trajectories of multiple photons can be tracked simultaneously. When a beam of focused light incident to the medium, the incident photons are divided into groups according to the available processes on a parallel machine and the calculations are carried out in parallel. Utilizing PVM (Parallel Virtual Machine, a parallel computing software), the parallel programs in both C and FORTRAN are developed on the massive parallel computer Cray T3E at the North Carolina Supercomputer Center and a local PC-cluster network running UNIX/Sun Solaris. The parallel performances of our codes have been excellent on both Cray T3E and the PC clusters. In this paper, we present results on a focusing laser beam propagating through a highly scattering and diluted solution of intralipid. The dependence of the spatial distribution of light near the focal point on the concentration of intralipid solution is studied and its significance is discussed.
Propagation of hypergeometric laser beams in a medium with a parabolic refractive index
NASA Astrophysics Data System (ADS)
Kotlyar, V. V.; Kovalev, A. A.; Nalimov, A. G.
2013-12-01
An expression to describe the complex amplitude of a family of paraxial hypergeometric laser beams propagating in a parabolic-index fiber is proposed. A particular case of a Gaussian optical vortex propagating in a parabolic-index fiber is studied. Under definite parameters, the Gaussian optical vortices become the modes of the medium. This is a new family of paraxial modes derived for the parabolic-index medium. A wide class of solutions of nonparaxial Helmholtz equations that describe modes in a parabolic refractive index medium is derived in the cylindrical coordinate system. As the solutions derived are proportional to Kummer’s functions, only those of them which are coincident with the nonparaxial Laguerre-Gaussian modes possess a finite energy, meaning that they are physically implementable. A definite length of the graded-index fiber is treated as a parabolic lens, and expressions for the numerical aperture and the focal spot size are deduced. An explicit expression for the radii of the rings of a binary lens approximating a parabolic-index lens is derived. Finite-difference time-domain simulation has shown that using a binary parabolic-index microlens with a refractive index of 1.5, a linearly polarized Gaussian beam can be focused into an elliptic focal spot which is almost devoid of side-lobes and has a smaller full width at half maximum diameter of 0.45 of the incident wavelength.
Standoff spectroscopy via remote generation of a backward-propagating laser beam
Hemmer, Philip R.; Miles, Richard B.; Polynkin, Pavel; Siebert, Torsten; Sokolov, Alexei V.; Sprangle, Phillip; Scully, Marlan O.
2011-01-01
In an earlier publication we demonstrated that by using pairs of pulses of different colors (e.g., red and blue) it is possible to excite a dilute ensemble of molecules such that lasing and/or gain-swept superradiance is realized in a direction toward the observer. This approach is a conceptual step toward spectroscopic probing at a distance, also known as standoff spectroscopy. In the present paper, we propose a related but simpler approach on the basis of the backward-directed lasing in optically excited dominant constituents of plain air, N2 and O2. This technique relies on the remote generation of a weakly ionized plasma channel through filamentation of an ultraintense femtosecond laser pulse. Subsequent application of an energetic nanosecond pulse or series of pulses boosts the plasma density in the seed channel via avalanche ionization. Depending on the spectral and temporal content of the driving pulses, a transient population inversion is established in either nitrogen- or oxygen-ionized molecules, thus enabling a transient gain for an optical field propagating toward the observer. This technique results in the generation of a strong, coherent, counterpropagating optical probe pulse. Such a probe, combined with a wavelength-tunable laser signal(s) propagating in the forward direction, provides a tool for various remote-sensing applications. The proposed technique can be enhanced by combining it with the gain-swept excitation approach as well as with beam shaping and adaptive optics techniques. PMID:21297033
Modeling laser beam diffraction and propagation by the mode-expansion method.
Snyder, James J
2007-08-01
In the mode-expansion method for modeling propagation of a diffracted beam, the beam at the aperture can be expanded as a weighted set of orthogonal modes. The parameters of the expansion modes are chosen to maximize the weighting coefficient of the lowest-order mode. As the beam propagates, its field distribution can be reconstructed from the set of weighting coefficients and the Gouy phase of the lowest-order mode. We have developed a simple procedure to implement the mode-expansion method for propagation through an arbitrary ABCD matrix, and we have demonstrated that it is accurate in comparison with direct calculations of diffraction integrals and much faster.
NASA Astrophysics Data System (ADS)
Calhoun, William R., III
One of the most recent advancements in laser technology is the development of ultrashort pulsed femtosecond lasers (FSLs). FSLs are improving many fields due to their unique extreme precision, low energy and ablation characteristics. In the area of laser medicine, ophthalmic surgeries have seen very promising developments. Some of the most commonly performed surgical operations in the world, including laser-assisted in-situ keratomileusis (LASIK), lens replacement (cataract surgery), and keratoplasty (cornea transplant), now employ FSLs for their unique abilities that lead to improved clinical outcome and patient satisfaction. The application of FSLs in medical therapeutics is a recent development, and although they offer many benefits, FSLs also stimulate nonlinear optical effects (NOEs), many of which were insignificant with previously developed lasers. NOEs can change the laser characteristics during propagation through a medium, which can subsequently introduce unique safety concerns for the surrounding tissues. Traditional approaches for characterizing optical effects, laser performance, safety and efficacy do not properly account for NOEs, and there remains a lack of data that describe NOEs in clinically relevant procedures and tissues. As FSL technology continues to expand towards new applications, FSL induced NOEs need to be better understood in order to ensure safety as FSL medical devices and applications continue to evolve at a rapid pace. In order to improve the understanding of FSL-tissue interactions related to NOEs stimulated during laser beam propagation though corneal tissue, research investigations were conducted to evaluate corneal optical properties and determine how corneal tissue properties including corneal layer, collagen orientation and collagen crosslinking, and laser parameters including pulse energy, repetition rate and numerical aperture affect second and third-harmonic generation (HG) intensity, duration and efficiency. The results of
Multiple-scattering analysis of laser-beam propagation in the atmosphere and through obscurants
Zardecki, A.; Gerstl, S.A.W.
1983-01-01
The general purpose, discrete-ordinates transport code TWOTRAN is applied to describe the propagation and multiple scattering of a laser beam in a nonhomogeneous aerosol medium. For the medium composed of smoke, haze, and a rain cloud, the problem of the target detectability in a realistic atmospheric scenario is addressed and solved. The signals reflected from the target vs the signals scattered from the smoke cloud are analyzed as a function of the smoke concentration. By calculating the average intensity and a correction factor in the x-y and r-z geometries, the consistency of the rectangular and cylindrical geometry models is assessed. Received power for a detector with a small field of view is computed on a sphere of 1-km radius around the laser source for the Air Force Geophysics Laboratory rural aerosol model with extinction coefficients of 4 km/sup -1/ and 10 km/sup -1/. This computation allows us to study the received power as a function of the angle between the detector and source axes. The correction factor describing the multiple-scattering enhancement with respect to the simple Lambert-Beer law is introduced, and its calculation is employed to validate the use of the small-angle approximation for the transmissometer configuration. An outline of the theory for a finite field of view detector is followed by numerical results pertaining to the received power and intensity for various aerosol models. Recommendations regarding future work are also formulated.
NASA Astrophysics Data System (ADS)
Pikuz, T.; Faenov, A.; Magnitskiy, S.; Nagorskiy, N.; Tanaka, M.; Ishino, M.; Nishikino, M.; Kando, M.; Kato, Y.; Kawachi, T.
2016-03-01
There is a significant interest in developing the coherent table-top X-ray lasers. Advent of plasma-based transient collisional excitation x-ray laser and particular, injection of coherent seeded beam, especially high-order harmonics, has tremendously improved the spatial coherence of such lasers, what allowed them to be the same widely used as synchrotron sources. Here we report experimental founding of unknown interference structure in a spatial profile of the output beam of the two-stage plasma X-ray laser. That allowed us experimental and theoretical discovering a new phenomenon consisted in a generation of phase-matched coherent point source in a laser plasma media by propagated X-ray laser seeded beam. This phenomenon could extend the applications of such x-ray lasers. For explanation of the observed phenomenon a new method of solving the standard system of Maxwell-Bloch equations has been developed. It was found that the interference pattern in the output laser beam was formed due to an emergence of phase-matched coherent virtual point source in the XRL amplifier and could be treated as the first observation of mirage phenomenon, analogous to the optical mirage, but in X-rays. The obtained results bring new comprehension into the physical nature of amplification of X-ray radiation in laser-induced plasma amplifiers and opening new opportunities for X-ray interferometry, holography and other applications, which requiring multiple rigidly phased sources of coherent radiation.
NASA Astrophysics Data System (ADS)
Zhao, Chenglong; LeBrun, Thomas W.
2015-08-01
Gold nanoparticles (GNP) have wide applications ranging from nanoscale heating to cancer therapy and biological sensing. Optical trapping of GNPs as small as 18 nm has been successfully achieved with laser power as high as 855 mW, but such high powers can damage trapped particles (particularly biological systems) as well heat the fluid, thereby destabilizing the trap. In this article, we show that counter propagating beams (CPB) can successfully trap GNP with laser powers reduced by a factor of 50 compared to that with a single beam. The trapping position of a GNP inside a counter-propagating trap can be easily modulated by either changing the relative power or position of the two beams. Furthermore, we find that under our conditions while a single-beam most stably traps a single particle, the counter-propagating beam can more easily trap multiple particles. This (CPB) trap is compatible with the feedback control system we recently demonstrated to increase the trapping lifetimes of nanoparticles by more than an order of magnitude. Thus, we believe that the future development of advanced trapping techniques combining counter-propagating traps together with control systems should significantly extend the capabilities of optical manipulation of nanoparticles for prototyping and testing 3D nanodevices and bio-sensing.
Jha, Pallavi; Agrawal, Ekta
2014-05-15
An analytical study of second harmonic generation due to interaction an intense, p-polarized laser beam propagating obliquely in homogeneous underdense plasma, in the mildly relativistic regime, has been presented. The efficiency of the second harmonic radiation as well as its detuning length has been obtained and their variation with the angle of incidence is analyzed. It is shown that, for a given plasma electron density, the second harmonic efficiency increases with the angle of incidence while the detuning length decreases. The second harmonic amplitude vanishes at normal incidence of the laser beam.
Chen, Yu-Jen; Lin, Yu-Sung; Jiang, I-Min; Tsai, Ming-Shan
2008-03-17
This study investigates the optical nonlinearity of beam propagation in homogeneously aligned nematic liquid crystal (NLC) cells at a temperature close to the nematic-isotropic temperature (TNI). The undulate propagation mode with convergent and divergent loops appearing alternately is reported and the thermally enhanced optical reorientation nonlinearity at the focus is described. The optically induced phase transition exists along the pump beam direction. With the application of the conscopic technique, the arrangements of LC at the focus are proposed in this study. Results of this study demonstrate that the evolution of the LC configuration was affected by the pump beam based on the analysis of conoscopic patterns.
NASA Astrophysics Data System (ADS)
Katz, Richard A.; Manzur, Tariq
2016-05-01
In this paper, we draw attention to the requirements for obtaining measurement data essential to accurate modeling and prediction of atmospheric laser beam propagation at heights 10 meters or less above the ocean surface. This is an atmospheric zone we call the marine boundary layer. There are numerous models and applications for optical beam propagation in the upper atmosphere that based on the Kolmogorov Theory of Turbulence. However, close to the ocean surface standard procedures for measuring and modeling the effects of boundary layer turbulence may no longer apply. In addition to classical measurement procedures, we suggest a new methodology and measurement procedures for exploration of beam propagation and the ensuing dynamics within the marine boundary layer.[1,2
Severe Self-induced Beam Distortion in Laboratory Simulated Laser Propagation at 10.6 micro.
Buser, R G; Rohde, R S
1973-02-01
Precision irradiance profiles have been determined for horizontally slewing high power laser beams through stationary absorbing gaseous media for the case of strong beam-medium interaction coupled with strong heating. Results are compared with the predictions of existing theoretical models concerning thermally induced lens effects in the presence of cross winds. Bending of the beam into the wind by beam slewing and intensification is found in reasonable agreement with the theory; for the observed overall beam spread, induced flow, turbulent tail, and concomitant beam breakup, no satisfactory theoretical treatment is available.
Kumar, Subodh; Singh, Ram Kishor Sharma, R. P.
2015-10-15
Terahertz (THz) generation by beating of two co-axial Gaussian laser beams, propagating in ripple density plasma, has been studied when both ponderomotive and relativistic nonlinearities are operative. When the two lasers co-propagate in rippled density plasma, electrons acquire a nonlinear velocity at beat frequency in the direction transverse to the direction of propagation. This nonlinear oscillatory velocity couples with the density ripple to generate a nonlinear current, which in turn generates THz radiation at the difference frequency. The necessary phase matching condition is provided by the density ripple. Relativistic ponderomotive focusing of the two lasers and its effects on yield of the generated THz amplitude have been discussed. Numerical results show that conversion efficiency of the order of 10{sup −3} can be achieved in the terahertz radiation generation with relativistic ponderomotive focusing.
Slow-motion acquisition of laser beam profiles after propagation through gun blast
NASA Astrophysics Data System (ADS)
Kay, Armin V.
1991-07-01
Degradation of laser beam quality by special effects is considered to be of increasing importance for investigations concerning combat field communications. An 8-bit transient memory device has been developed which allows storing of a series of up to 15 laser beam intensity profiles using a CCD linear array of 1754 diodes with a spatial resolution of 10 micrometers . The shortest time interval between consecutive profiles amounts to 2 ms. Data reduction of the measured profiles can be achieved by best fit of a Gaussian normal distribution with four parameters representing bias level, peak amplitude, width (FWHM), and peak position. This procedure was applied to helium-neon-laser radiation after transmission through the gas blast expanding from a powder gun. Two different experimental arrangements have been realized so far. The first one comprises a large vessel which limits the expansion of the combustion products from a 20 mm-bore gun, and the laser beam traverses the barrel axis in front of the muzzle. The second set-up allows free gas blast expansion from a 40 mm-bore gun, the laser beam being adjusted parallel to the barrel axis. For both cases, the time behavior of beam extinction, broadening and wandering is reported. Absorption and scattering of radiation by shock waves, turbulent structures and aerosols in the exhaust cause considerable temporary alterations: peak intensity attenuation down to 0.1 beam width reaching up to twice its initial value, and beam deflection up to 2 mrad.
Propagation instabilities of high-intensity laser-produced electron beams.
Tatarakis, M; Beg, F N; Clark, E L; Dangor, A E; Edwards, R D; Evans, R G; Goldsack, T J; Ledingham, K W D; Norreys, P A; Sinclair, M A; Wei, M-S; Zepf, M; Krushelnick, K
2003-05-01
Measurements of energetic electron beams generated from ultrahigh intensity laser interactions (I>10(19) W/cm(2)) with dense plasmas are discussed. These interactions have been shown to produce very directional beams, although with a broad energy spectrum. In the regime where the beam density approaches the density of the background plasma, we show that these beams are unstable to filamentation and "hosing" instabilities. Particle-in-cell simulations also indicate the development of such instabilities. This is a regime of particular interest for inertial confinement fusion applications of these beams (i.e., "fast ignition").
Sepehri Javan, N.; Adli, F.
2013-06-15
The present study is devoted to investigation of the nonlinear dynamics of an intense laser beam interacting with a hot magnetized electron-positron plasma. Propagation of the intense circularly polarized laser beam along an external magnetic field is studied using a relativistic two-fluid model. A modified nonlinear Schrödinger equation is derived based on the quasi-neutral approximation, which is valid for hot plasma. Light envelope solitary waves and modulation instability are studied, for one-dimensional case. Using a three-dimensional model, spatial-temporal development of laser pulse is investigated. Occurrence of some nonlinear phenomena such as self-focusing, self-modulation, light trapping, and filamentation of laser pulse is discussed. Also the effect of external magnetic field and plasma temperature on the nonlinear evolution of these phenomena is studied.
Deepak, A; Farrukh, U O; Zardecki, A
1982-02-01
An approach is outlined for computing the different orders of scattering in any medium that possesses a phase function with a strong forward peak. Computations are done for the case of a Gaussian laser beam incident on such a medium. The formulation adopted does reproduce the natural divergence of general Gaussian beams without the need to assume the presence of point sources or the need to assume perfectly collimated beams within the region of interest. Results are discussed for the case of water cloud particles with a strongly forward-peaked phase function for the incident laser radiation.
Willingale, L.; Nagel, S. R.; Thomas, A. G. R.; Bellei, C.; Dangor, A. E.; Kaluza, M. C.; Kamperidis, C.; Kneip, S.; Krushelnick, K.; Mangles, S. P. D.; Nilson, P. M.; Najmudin, Z.; Clarke, R. J.; Heathcote, R.; Lopes, N.; Nazarov, W.
2009-03-27
Experiments were performed to investigate the propagation of a high intensity (I{approx}10{sup 21} W cm{sup -2}) laser in foam targets with densities ranging from 0.9n{sub c} to 30n{sub c}. Proton acceleration was used to diagnose the interaction. An improvement in proton beam energy and efficiency is observed for the lowest density foam (n{sub e}=0.9n{sub c}), compared to higher density foams. Simulations show that the laser beam penetrates deeper into the target due to its relativistic propagation and results in greater collimation of the ensuing hot electrons. This results in the rear surface accelerating electric field being larger, increasing the efficiency of the acceleration. Enhanced collimation of the ions is seen to be due to the self-generated azimuthal magnetic and electric fields at the rear of the target.
On the control of filamentation of intense laser beams propagating in underdense plasma
Williams, E A
2005-10-21
In indirect drive ICF ignition designs, the laser energy is delivered into the hohlraum through the laser entrance holes (LEH), which are sized as small as practicable to minimize X-ray radiation losses. On the other hand, deleterious laser plasma processes, such as filamentation and stimulated back-scatter, typically increase with laser intensity. Ideally, therefore, the laser spot shape should be a close fit to the LEH, with uniform (envelope) intensity in the spot and minimal energy at larger radii spilling onto the LEH material. This keeps the laser intensity as low as possible consistent with the area of the LEH aperture and the power requirements of the design. This can be achieved (at least for apertures significantly larger than the laser's aberrated focal spot) by the use of custom-designed phase plates. However, outfitting the 192 beam (National Ignition facility) NIF laser with multiple sets of phase plates optimized for a variety of different LEH aperture sizes is an expensive proposition. It is thus important to assess the impact on laser-plasma interaction processes of using phase plates with a smaller than optimum focal spot (or even no phase plates at all!) and then de-focusing the beam to expand it to fill the LEH and lower its intensity. We find significant effects from the lack of uniformity of the laser envelope out of the focal plane, from changes in the characteristic sizes of the laser speckle, and on the efficacy of additional polarization and/or SSD beam smoothing. We quantify these effects with analytic estimates and simulations using our laser plasma interaction code pF3D.
Laserna, J J; Reyes, R Fernández; González, R; Tobaria, L; Lucena, P
2009-06-01
We report on an experimental study of the effect of atmospheric turbulence on laser induced breakdown spectroscopy (LIBS) measurements. The characteristics of the atmosphere dictate specific performance constraints to this technology. Unlike classical laboratory LIBS systems where the distance to the sample is well known and characterized, LIBS systems working at several tens of meters to the target have specific atmospheric propagation conditions that cause the quality of the LIBS signals to be affected to a significant extent. Using a new LIBS based sensor system fitted with a nanosecond laser emitting at 1064 nm, propagation effects at distances of up to 120 m were investigated. The effects observed include wander and scintillation in the outgoing laser beam and in the return atomic emission signal. Plasmas were formed on aluminium targets. Average signal levels and signal fluctuations are measured so the effect of atmospheric turbulence on LIBS measurements is quantified.
Srisungsitthisunti, Pornsak; Ersoy, Okan K; Xu, Xianfan
2009-01-01
Light diffraction by volume Fresnel zone plates (VFZPs) is simulated by the Hankel transform beam propagation method (Hankel BPM). The method utilizes circularly symmetric geometry and small step propagation to calculate the diffracted wave fields by VFZP layers. It is shown that fast and accurate diffraction results can be obtained with the Hankel BPM. The results show an excellent agreement with the scalar diffraction theory and the experimental results. The numerical method allows more comprehensive studies of the VFZP parameters to achieve higher diffraction efficiency.
Laser induced bubbles inside liquids: Transient optical properties and effects on a beam propagation
Lazic, V.; Carpanese, M.; Jovicevic, S.
2012-07-30
Light transmission through a laser formed bubble (LFB) following ablation of a metallic target inside water was studied. During the early expansion and late collapsing phases, the refraction index n{sub b} of the hot high-pressure vapor bubble is higher than 1.23 and close to that of the surrounding liquid. The cavity growth lowers n{sub b} down to 1.00 and causes strong defocusing of the incident laser beam with consequent enlargement of the ablation crater diameter, here overcoming factor two. Inhomogeneous water vapor clustering inside the cool expanded bubble further perturbs the light transmission and induces irregular ablation by the successive laser pulse.
Influence of sea-air interface on upward laser beam propagation
NASA Astrophysics Data System (ADS)
Zhou, Tian-hua; He, Yan; Zhu, Xiao-lei; Chen, Wei-biao
2013-08-01
The roughness of sea surface affects the optical property of the exiting upward laser, which constrains the application of the LIDAR and Laser Communication in ocean. The paper designs one pool test to study the influence of sea-air interfaces and develops a corresponding geometric optical model. It analyzes the optical property of the upward laser through the sea-air interface systematic. Results show that the roughness of wavy sea surface will affect beam spreading, pointing and scintillation when transmitting through the boundary. Further, experiment results in one water tank with man-made wave show that the incident angle and divergence angle are very important to the upward laser on the real-time and statistics change. Selecting one appropriate incident angle and divergence angle will get one stabilized performance, which is useful to the laser practical application on the marine areas.
Guo, Q L; Liang, B L; Wang, Y; Deng, G Y; Jiang, Y H; Zhang, S H; Fu, G S; Simmonds, P J
2014-10-01
The propagation characteristics of a focused laser beam in a SBN:75 photorefractive crystal strongly depend on the signal-to-background intensity ratio (R=I_{s}/I_{b}) under reverse external electric field. In the range 20>R>0.05, the laser beam shows enhanced self-defocusing behavior with increasing external electric field, while it shows self-focusing in the range 0.03>R>0.01. Spatial solitons are observed under a suitable reverse external electric field for R=0.025. A theoretical model is proposed to explain the experimental observations, which suggest a new type of soliton formation due to "enhancement" not "screening" of the external electrical field.
A phase screen model for simulating numerically the propagation of a laser beam in rain
Lukin, I P; Rychkov, D S; Falits, A V; Lai, Kin S; Liu, Min R
2009-09-30
The method based on the generalisation of the phase screen method for a continuous random medium is proposed for simulating numerically the propagation of laser radiation in a turbulent atmosphere with precipitation. In the phase screen model for a discrete component of a heterogeneous 'air-rain droplet' medium, the amplitude screen describing the scattering of an optical field by discrete particles of the medium is replaced by an equivalent phase screen with a spectrum of the correlation function of the effective dielectric constant fluctuations that is similar to the spectrum of a discrete scattering component - water droplets in air. The 'turbulent' phase screen is constructed on the basis of the Kolmogorov model, while the 'rain' screen model utiises the exponential distribution of the number of rain drops with respect to their radii as a function of the rain intensity. Theresults of the numerical simulation are compared with the known theoretical estimates for a large-scale discrete scattering medium. (propagation of laser radiation in matter)
Analytic models for beam propagation and far-field patterns in slab and bow-tie x-ray lasers
Chandler, E.A.
1994-06-01
Simplified analytic models for beam propagation in slab and bow-tie x-ray lasers yield convenient expressions that provide both a framework for guidance in computer modeling and useful approximates for experimenters. In unrefracted bow-tie lasers, the laser shape in conjunction with the nearly-exponential weighting of rays according to their length produces a small effective aperture for the signal. We develop an analytic expression for the aperture and the properties of the far-field signal. Similarly, we develop the view that the far-field pattern of refractive slab lasers is the result of effective apertures that are created by the interplay of refraction and exponential amplification. We present expressions for the size of this aperture as a function of laser parameters as well as for the intensity and position of the far-field lineout. This analysis also yields conditions for the refraction limit in slab lasers and an estimate for the signal loss due to refraction.
Analytical approach of laser beam propagation in the hollow polygonal light pipe.
Zhu, Guangzhi; Zhu, Xiao; Zhu, Changhong
2013-08-10
An analytical method of researching the light distribution properties on the output end of a hollow n-sided polygonal light pipe and a light source with a Gaussian distribution is developed. The mirror transformation matrices and a special algorithm of removing void virtual images are created to acquire the location and direction vector of each effective virtual image on the entrance plane. The analytical method is demonstrated by Monte Carlo ray tracing. At the same time, four typical cases are discussed. The analytical results indicate that the uniformity of light distribution varies with the structural and optical parameters of the hollow n-sided polygonal light pipe and light source with a Gaussian distribution. The analytical approach will be useful to design and choose the hollow n-sided polygonal light pipe, especially for high-power laser beam homogenization techniques.
Gaussian-Beam Laser-Resonator Program
NASA Technical Reports Server (NTRS)
Cross, Patricia L.; Bair, Clayton H.; Barnes, Norman
1989-01-01
Gaussian Beam Laser Resonator Program models laser resonators by use of Gaussian-beam-propagation techniques. Used to determine radii of beams as functions of position in laser resonators. Algorithm used in program has three major components. First, ray-transfer matrix for laser resonator must be calculated. Next, initial parameters of beam calculated. Finally, propagation of beam through optical elements computed. Written in Microsoft FORTRAN (Version 4.01).
Weil, Bradley S.; Wetherington, Jr., Grady R.
1985-01-01
Laser beam monitoring systems include laser-transparent plates set at an angle to the laser beam passing therethrough and light sensor for detecting light reflected from an object on which the laser beam impinges.
Viering, Kirsten; Medellin, David; Mo, Jianyong; Raizen, Mark G
2012-11-01
We report on an experimental method to align a laser beam to a cloud of atoms trapped in a magneto-optical trap (MOT). We show how balanced lock-in detection leads to a very sensitive method to align the laser beam to the atoms in the plane perpendicular to the propagation direction. This provides a very reliable and fast way of aligning laser beams to atoms trapped in a MOT.
Independent assessment of laser power beaming options
NASA Technical Reports Server (NTRS)
Ponikvar, Donald R.
1992-01-01
Technical and architectural issues facing a laser power beaming system are discussed. Issues regarding the laser device, optics, beam control, propagation, and lunar site are examined. Environmental and health physics aspects are considered.
NASA Technical Reports Server (NTRS)
Manning, Robert M.
2012-01-01
The method of moments is used to define and derive expressions for laser beam deflection and beam radius broadening for high-energy propagation through the Earth s atmosphere. These expressions are augmented with the integral invariants of the corresponding nonlinear parabolic equation that describes the electric field of high-energy laser beam to propagation to yield universal equations for the aforementioned quantities; the beam deflection is a linear function of the propagation distance whereas the beam broadening is a quadratic function of distance. The coefficients of these expressions are then derived from a thin screen approximation solution of the nonlinear parabolic equation to give corresponding analytical expressions for a target located outside the Earth s atmospheric layer. These equations, which are graphically presented for a host of propagation scenarios, as well as the thin screen model, are easily amenable to the phase expansions of the wave front for the specification and design of adaptive optics algorithms to correct for the inherent phase aberrations. This work finds application in, for example, the analysis of beamed energy propulsion for space-based vehicles.
NASA Astrophysics Data System (ADS)
Lukin, I. P.; Rychkov, D. S.; Falits, A. V.; Lai, Kin S.; Liu, Min R.
2009-09-01
The method based on the generalisation of the phase screen method for a continuous random medium is proposed for simulating numerically the propagation of laser radiation in a turbulent atmosphere with precipitation. In the phase screen model for a discrete component of a heterogeneous 'air—rain droplet' medium, the amplitude screen describing the scattering of an optical field by discrete particles of the medium is replaced by an equivalent phase screen with a spectrum of the correlation function of the effective dielectric constant fluctuations that is similar to the spectrum of a discrete scattering component — water droplets in air. The 'turbulent' phase screen is constructed on the basis of the Kolmogorov model, while the 'rain' screen model utilises theexponential distribution of the number of rain drops with respect to their radii as a function of the rain intensity. Theresults of the numerical simulation are compared with the known theoretical estimates for a large-scale discrete scattering medium.
NASA Technical Reports Server (NTRS)
Ulrich, Peter B. (Editor); Wilson, Leroy E. (Editor)
1991-01-01
Consideration is given to turbulence at the inner scale, modeling turbulent transport in laser beam propagation, variable wind direction effects on thermal blooming correction, realistic wind effects on turbulence and thermal blooming compensation, wide bandwidth spectral measurements of atmospheric tilt turbulence, remote alignment of adaptive optical systems with far-field optimization, focusing infrared laser beams on targets in space without using adaptive optics, and a simplex optimization method for adaptive optics system alignment. Consideration is also given to ground-to-space multiline propagation at 1.3 micron, a path integral approach to thermal blooming, functional reconstruction predictions of uplink whole beam Strehl ratios in the presence of thermal blooming, and stability analysis of semidiscrete schemes for thermal blooming computation.
The RADLAC beam propagation experiment
Frost, C.A.; Shope, S.L.; Mazarakis, M.G.; Poukey, J.W.; Wagner, J.S.; Turman, B.N.; Crist, C.E. ); Welch, D.R.; Struve, K.W. )
1992-01-01
The most recent RADLAC experiments studied propagation and hose stability of a high current beam propagating in the atmosphere, and confirmed the convective nature of the hose instability. The unique combination of high beam current and extremely small initial perturbation, allowed saturation of the hose instability to be observed for the first time. Data on high current propagation was needed because the current scaling is more complex than energy scaling. It was important to collect data at atmospheric pressure to insure that subtle air chemistry effects such as avalanche did not distort the experiment. With this philosophy, the results should be directly scaleable to applications at higher energy.
The RADLAC beam propagation experiment
Frost, C.A.; Shope, S.L.; Mazarakis, M.G.; Poukey, J.W.; Wagner, J.S.; Turman, B.N.; Crist, C.E.; Welch, D.R.; Struve, K.W.
1992-06-01
The most recent RADLAC experiments studied propagation and hose stability of a high current beam propagating in the atmosphere, and confirmed the convective nature of the hose instability. The unique combination of high beam current and extremely small initial perturbation, allowed saturation of the hose instability to be observed for the first time. Data on high current propagation was needed because the current scaling is more complex than energy scaling. It was important to collect data at atmospheric pressure to insure that subtle air chemistry effects such as avalanche did not distort the experiment. With this philosophy, the results should be directly scaleable to applications at higher energy.
Spectral expansion method in problems of laser-beam propagation in the turbulent atmosphere.
Aksenov, V P; Mironov, V L
1978-11-01
A mixed spectral expansion over elementary spherical and plane waves is suggested for use as an approximate solution of the stochastic wave equation describing propagation of optical waves in a turbulent medium. In this case, the complex amplitude of an elementary plane wave is calculated as a solution of a shortened equation, considering only the phase fluctuations of this wave. It is shown that such an approximate solution uniformly approximates statistical moments of the field (up to the fourth order, inclusive) under arbitrary conditions of wave propagationin a turbulent medium and conditions of wave diffraction on the transmitting aperture.
Yi, Xiang; Li, Zan; Liu, Zengji
2015-02-20
In clean ocean water, the performance of a underwater optical communication system is limited mainly by oceanic turbulence, which is defined as the fluctuations in the index of refraction resulting from temperature and salinity fluctuations. In this paper, using the refractive index spectrum of oceanic turbulence under weak turbulence conditions, we carry out, for a horizontally propagating plane wave and spherical wave, analysis of the aperture-averaged scintillation index, the associated probability of fade, mean signal-to-noise ratio, and mean bit error rate. Our theoretical results show that for various values of the rate of dissipation of mean squared temperature and the temperature-salinity balance parameter, the large-aperture receiver leads to a remarkable decrease of scintillation and consequently a significant improvement on the system performance. Such an effect is more noticeable in the plane wave case than in the spherical wave case.
Yi, Xiang; Li, Zan; Liu, Zengji
2015-02-20
In clean ocean water, the performance of a underwater optical communication system is limited mainly by oceanic turbulence, which is defined as the fluctuations in the index of refraction resulting from temperature and salinity fluctuations. In this paper, using the refractive index spectrum of oceanic turbulence under weak turbulence conditions, we carry out, for a horizontally propagating plane wave and spherical wave, analysis of the aperture-averaged scintillation index, the associated probability of fade, mean signal-to-noise ratio, and mean bit error rate. Our theoretical results show that for various values of the rate of dissipation of mean squared temperature and the temperature-salinity balance parameter, the large-aperture receiver leads to a remarkable decrease of scintillation and consequently a significant improvement on the system performance. Such an effect is more noticeable in the plane wave case than in the spherical wave case. PMID:25968187
GAUSSIAN BEAM LASER RESONATOR PROGRAM
NASA Technical Reports Server (NTRS)
Cross, P. L.
1994-01-01
In designing a laser cavity, the laser engineer is frequently concerned with more than the stability of the resonator. Other considerations include the size of the beam at various optical surfaces within the resonator or the performance of intracavity line-narrowing or other optical elements. Laser resonators obey the laws of Gaussian beam propagation, not geometric optics. The Gaussian Beam Laser Resonator Program models laser resonators using Gaussian ray trace techniques. It can be used to determine the propagation of radiation through laser resonators. The algorithm used in the Gaussian Beam Resonator program has three major components. First, the ray transfer matrix for the laser resonator must be calculated. Next calculations of the initial beam parameters, specifically, the beam stability, the beam waist size and location for the resonator input element, and the wavefront curvature and beam radius at the input surface to the first resonator element are performed. Finally the propagation of the beam through the optical elements is computed. The optical elements can be modeled as parallel plates, lenses, mirrors, dummy surfaces, or Gradient Index (GRIN) lenses. A Gradient Index lens is a good approximation of a laser rod operating under a thermal load. The optical system may contain up to 50 elements. In addition to the internal beam elements the optical system may contain elements external to the resonator. The Gaussian Beam Resonator program was written in Microsoft FORTRAN (Version 4.01). It was developed for the IBM PS/2 80-071 microcomputer and has been implemented on an IBM PC compatible under MS DOS 3.21. The program was developed in 1988 and requires approximately 95K bytes to operate.
Laser beam modeling in optical storage systems
NASA Technical Reports Server (NTRS)
Treptau, J. P.; Milster, T. D.; Flagello, D. G.
1991-01-01
A computer model has been developed that simulates light propagating through an optical data storage system. A model of a laser beam that originates at a laser diode, propagates through an optical system, interacts with a optical disk, reflects back from the optical disk into the system, and propagates to data and servo detectors is discussed.
NASA Astrophysics Data System (ADS)
Golmohammady, Sh; Ghafary, B.
2016-06-01
In this study, generalized Stokes parameters of a phase-locked partially coherent flat-topped array beam based on the extended Huygens-Fresnel principle and the unified theory of coherence and polarization have been reported. Analytical formulas for 2 × 2 cross-spectral density matrix elements, and consequently Stokes parameters of a phase-locked partially coherent flat-topped array beam propagating through the turbulent atmosphere have been formulated. Effects of many physical attributes such as wavelength, turbulence strength, flatness order and other source parameters on the Stokes parameters, and therefore spectral degree of polarization upon propagation have been studied thoroughly. The behaviour of the spectral degree of coherence of a delineated beam for different source conditions has been investigated. It can be shown that four generalized Stokes parameters increase by raising the flatness order at the same propagation distance. Increasing the number of beams leads to a decrease in the Stokes parameters to zero slowly. The results are of utmost importance for optical communications.
NASA Astrophysics Data System (ADS)
Golmohammady, Sh; Ghafary, B.
2016-06-01
In this study, generalized Stokes parameters of a phase-locked partially coherent flat-topped array beam based on the extended Huygens–Fresnel principle and the unified theory of coherence and polarization have been reported. Analytical formulas for 2 × 2 cross-spectral density matrix elements, and consequently Stokes parameters of a phase-locked partially coherent flat-topped array beam propagating through the turbulent atmosphere have been formulated. Effects of many physical attributes such as wavelength, turbulence strength, flatness order and other source parameters on the Stokes parameters, and therefore spectral degree of polarization upon propagation have been studied thoroughly. The behaviour of the spectral degree of coherence of a delineated beam for different source conditions has been investigated. It can be shown that four generalized Stokes parameters increase by raising the flatness order at the same propagation distance. Increasing the number of beams leads to a decrease in the Stokes parameters to zero slowly. The results are of utmost importance for optical communications.
Controlling Second Harmonic Efficiency of Laser Beam Interactions
NASA Technical Reports Server (NTRS)
Barnes, Norman P. (Inventor); Walsh, Brian M. (Inventor); Reichle, Donald J. (Inventor)
2011-01-01
A method is provided for controlling second harmonic efficiency of laser beam interactions. A laser system generates two laser beams (e.g., a laser beam with two polarizations) for incidence on a nonlinear crystal having a preferred direction of propagation. Prior to incidence on the crystal, the beams are optically processed based on the crystal's beam separation characteristics to thereby control a position in the crystal along the preferred direction of propagation at which the beams interact.
IBEX - annular beam propagation experiment
Mazarakis, M G; Miller, R B; Shope, S L; Poukey, J W; Ramirez, J J; Ekdahl, C A; Adler, R J
1983-01-01
IBEX is a 4-MV, 100-kA, 20-ns cylindrical isolated Blumlein accelerator. In the experiments reported here, the accelerator is fitted with a specially designed foilless diode which is completely immersed in a uniform magnetic field. Several diode geometries have been studied as a function of magnetic field strength. The beam propagates a distance of 50 cm (approx. 10 cyclotron wavelengths) in vacuum before either striking a beam stop or being extracted through a thin foil. The extracted beam was successfully transported 60 cm downstream into a drift pipe filled either with 80 or 640 torr air. The main objectives of this experiment were to establish the proper parameters for the most quiescent 4 MV, 20 to 40 kA annular beam, and to compare the results with available theory and numerical code simulations.
NASA Technical Reports Server (NTRS)
Bufton, Jack L.; Harding, David J.; Ramos-Izquierdo, Luis
1993-01-01
Laser altimetry provides a high-resolution, high-accuracy method for measurement of the elevation and horizontal variability of Earth-surface topography. The basis of the measurement is the timing of the round-trip propagation of short-duration pulses of laser radiation between a spacecraft and the Earth's surface. Vertical resolution of the altimetry measurement is determined primarily by laser pulsewidth, surface-induced spreading in time of the reflected pulse, and the timing precision of the altimeter electronics. With conventional gain-switched pulses from solid-state lasers and sub-nsec resolution electronics, sub-meter vertical range resolution is possible from orbital attitudes of several hundred kilometers. Horizontal resolution is a function of laser beam footprint size at the surface and the spacing between successive laser pulses. Laser divergence angle and altimeter platform height above the surface determine the laser footprint size at the surface, while laser pulse repetition-rate, laser transmitter beam configuration, and altimeter platform velocity determine the space between successive laser pulses. Multiple laser transitters in a singlaltimeter instrument provide across-track and along-track coverage that can be used to construct a range image of the Earth's surface. Other aspects of the multi-beam laser altimeter are discussed.
Yousefi, Masoud; Golmohammady, Shole; Mashal, Ahmad; Kashani, Fatemeh Dabbagh
2015-11-01
In this paper, on the basis of the extended Huygens-Fresnel principle, a semianalytical expression for describing on-axis scintillation index of a partially coherent flat-topped (PCFT) laser beam of weak to moderate oceanic turbulence is derived; consequently, by using the log-normal intensity probability density function, the bit error rate (BER) is evaluated. The effects of source factors (such as wavelength, order of flatness, and beam width) and turbulent ocean parameters (such as Kolmogorov microscale, relative strengths of temperature and salinity fluctuations, rate of dissipation of the mean squared temperature, and rate of dissipation of the turbulent kinetic energy per unit mass of fluid) on propagation behavior of scintillation index, and, hence, on BER, are studied in detail. Results indicate that, in comparison with a Gaussian beam, a PCFT laser beam with a higher order of flatness is found to have lower scintillations. In addition, the scintillation index and BER are most affected when salinity fluctuations in the ocean dominate temperature fluctuations.
Yousefi, Masoud; Golmohammady, Shole; Mashal, Ahmad; Kashani, Fatemeh Dabbagh
2015-11-01
In this paper, on the basis of the extended Huygens-Fresnel principle, a semianalytical expression for describing on-axis scintillation index of a partially coherent flat-topped (PCFT) laser beam of weak to moderate oceanic turbulence is derived; consequently, by using the log-normal intensity probability density function, the bit error rate (BER) is evaluated. The effects of source factors (such as wavelength, order of flatness, and beam width) and turbulent ocean parameters (such as Kolmogorov microscale, relative strengths of temperature and salinity fluctuations, rate of dissipation of the mean squared temperature, and rate of dissipation of the turbulent kinetic energy per unit mass of fluid) on propagation behavior of scintillation index, and, hence, on BER, are studied in detail. Results indicate that, in comparison with a Gaussian beam, a PCFT laser beam with a higher order of flatness is found to have lower scintillations. In addition, the scintillation index and BER are most affected when salinity fluctuations in the ocean dominate temperature fluctuations. PMID:26560913
Yu, Hao; Rossi, Giammarco; Braglia, Andrea; Perrone, Guido
2016-08-10
The paper presents the development of a tool based on a back-propagation artificial neural network to assist in the accurate positioning of the lenses used to collimate the beam from semiconductor laser diodes along the so-called fast axis. After training using a Gaussian beam ray-equivalent model, the network is capable of indicating the tilt, decenter, and defocus of such lenses from the measured field distribution, so the operator can determine the errors with respect to the actual lens position and optimize the diode assembly procedure. An experimental validation using a typical configuration exploited in multi-emitter diode module assembly and fast axis collimating lenses with different focal lengths and numerical apertures is reported.
Yu, Hao; Rossi, Giammarco; Braglia, Andrea; Perrone, Guido
2016-08-10
The paper presents the development of a tool based on a back-propagation artificial neural network to assist in the accurate positioning of the lenses used to collimate the beam from semiconductor laser diodes along the so-called fast axis. After training using a Gaussian beam ray-equivalent model, the network is capable of indicating the tilt, decenter, and defocus of such lenses from the measured field distribution, so the operator can determine the errors with respect to the actual lens position and optimize the diode assembly procedure. An experimental validation using a typical configuration exploited in multi-emitter diode module assembly and fast axis collimating lenses with different focal lengths and numerical apertures is reported. PMID:27534506
NASA Technical Reports Server (NTRS)
Mcdermid, I. S.
1984-01-01
Train of prisms and optical stop separate fundamental beam of laser from second and higher order harmonics of beam produced in certain crystals and by stimulated Raman scattering in gases and liquids.
Laser propagation in underdense plasmas: Scaling arguments
Garrison, J.C.
1993-05-01
The propagation of an intense laser beam in the underdense plasma is modelled by treating the plasma as a relativistic, zero temperature, charged fluid. For paraxial propagation and a sufficiently underdense plasma ({omega}p/{omega} {much_lt} 1), a multiple-scales technique is used to expand the exact equations in powers of the small parameter {theta} {equivalent_to} {omega}p/{omega}. The zeroth order equations are used in a critical examination of previous work on this problem, and to derive a scaling law for the threshold power required for cavitation.
Meteorological effects on laser propagation for power transmission
NASA Technical Reports Server (NTRS)
Beverly, R. E., III
1982-01-01
An examination of possible laser operating parameters for power transmission to earth from solar power satellites is presented, with particular attention paid to assuring optimal delivery at midlatitudes. The degradation of beam efficiency due to molecular scattering, molecular absorption, aerosol scattering, and aerosol absorption during beam propagation through the atmosphere can be alleviated by judicious choice of wavelength windows, elevating the receptor sites, using a vertical propagation path, or by hole boring, i.e., vaporizing the aerosol particles in the beam path. Analyses are given for the beam propagation through fog, haze, clouds, and snow using various transitions. Only weapons-quality lasers are seen as being capable of boring through clouds and aerosols, employing a CW beam with superimposed pulses at high power densities. It is concluded that further short wavelength transmission experiments be performed to demonstrate transmission feasibility with the CW/pulsed mode of beam propagation.
Kashani, Fatemeh Dabbagh; Yousefi, Masoud
2016-08-10
In this research, based on an analytical expression for cross-spectral density (CSD) matrix elements, coherence and polarization properties of phase-locked partially coherent flat-topped (PCFT) radial array laser beams propagating through weak oceanic turbulence are analyzed. Spectral degrees of coherence and polarization are analytically calculated using CSD matrix elements. Also, the effective width of spatial degree of coherence (EWSDC) is calculated numerically. The simulation is done by considering the effects of source parameters (such as radius of the array setup's circle, effective width of the spectral degree of coherence, and wavelength) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature and salinity fluctuations, Kolmogorov micro-scale, and rate of dissipation of the mean squared temperature) in detail. Results indicate that any change in the amount of turbulence factors that increase the turbulence power reduces the EWSDC significantly and causes the reduction in the degree of polarization, and occurs at shorter propagation distances but with smaller magnitudes. In addition, being valid for all conditions, the degradation rate of the EWSDC of Gaussian array beams are more in comparison with the PCFT ones. The simulation and calculation results are shown by graphs.
Kashani, Fatemeh Dabbagh; Yousefi, Masoud
2016-08-10
In this research, based on an analytical expression for cross-spectral density (CSD) matrix elements, coherence and polarization properties of phase-locked partially coherent flat-topped (PCFT) radial array laser beams propagating through weak oceanic turbulence are analyzed. Spectral degrees of coherence and polarization are analytically calculated using CSD matrix elements. Also, the effective width of spatial degree of coherence (EWSDC) is calculated numerically. The simulation is done by considering the effects of source parameters (such as radius of the array setup's circle, effective width of the spectral degree of coherence, and wavelength) and turbulent ocean factors (such as the rate of dissipation of the turbulent kinetic energy per unit mass of fluid and relative strength of temperature and salinity fluctuations, Kolmogorov micro-scale, and rate of dissipation of the mean squared temperature) in detail. Results indicate that any change in the amount of turbulence factors that increase the turbulence power reduces the EWSDC significantly and causes the reduction in the degree of polarization, and occurs at shorter propagation distances but with smaller magnitudes. In addition, being valid for all conditions, the degradation rate of the EWSDC of Gaussian array beams are more in comparison with the PCFT ones. The simulation and calculation results are shown by graphs. PMID:27534473
Diagnostics for the ATA beam propagation experiments
Fessenden, T.J.; Atchison, W.L.; Barletta, W.A.
1981-11-01
This report contains a discussion of the diagnostics required for the beam propagation experiment to be done with the ATA accelerator. Included are a list of the diagnostics needed; a description of the ATA experimental environment; the status of beam diagnostics available at Livermore including recent developments, and a prioritized list of accelerator and propagation diagnostics under consideration or in various stages of development.
NASA Technical Reports Server (NTRS)
Beverly, R. E., III
1980-01-01
The primary emphasis of this research activity was to investigate the effect of the environment on laser power transmission/reception from space to ground. Potential mitigation techniques to minimize the environment effect by a judicious choice of laser operating parameters was investigated. Using these techniques, the availability of power at selected sites was determined using statistical meteorological data for each site.
Kasner, William H.; Racki, Daniel J.; Swenson, Clark E.
1984-01-01
A plurality of pivotal reflectors direct a high-power laser beam onto a workpiece, and a rotatable reflector is movable to a position wherein it intercepts the beam and deflects a major portion thereof away from its normal path, the remainder of the beam passing to the pivotal reflectors through an aperture in the rotating reflector. A plurality of targets are movable to positions intercepting the path of light traveling to the pivotal reflectors, and a preliminary adjustment of the latter is made by use of a low-power laser beam reflected from the rotating reflector, after which the same targets are used to make a final adjustment of the pivotal reflectors with the portion of the high-power laser beam passed through the rotating reflector.
ERIC Educational Resources Information Center
Jodoin, Ronald E.
1979-01-01
Investigates the effect of the nonuniform irradiance across a laser beam on diffraction of the beam, specifically the Fraunhofer diffraction of a laser beam with a Gaussian irradiance profile as it passes through a circular aperture. (GA)
Propagation-invariant beams with quantum pendulum spectra: from Bessel beams to Gaussian beam-beams.
Dennis, Mark R; Ring, James D
2013-09-01
We describe a new class of propagation-invariant light beams with Fourier transform given by an eigenfunction of the quantum mechanical pendulum. These beams, whose spectra (restricted to a circle) are doubly periodic Mathieu functions in azimuth, depend on a field strength parameter. When the parameter is zero, pendulum beams are Bessel beams, and as the parameter approaches infinity, they resemble transversely propagating one-dimensional Gaussian wave packets (Gaussian beam-beams). Pendulum beams are the eigenfunctions of an operator that interpolates between the squared angular momentum operator and the linear momentum operator. The analysis reveals connections with Mathieu beams, and insight into the paraxial approximation.
NASA Technical Reports Server (NTRS)
Box, M. A.; Deepak, A.
1981-01-01
The propagation of photons in a medium with strongly anisotropic scattering is a problem with a considerable history. Like the propagation of electrons in metal foils, it may be solved in the small-angle scattering approximation by the use of Fourier-transform techniques. In certain limiting cases, one may even obtain analytic expressions. This paper presents some of these results in a model-independent form and also illustrates them by the use of four different phase-function models. Sample calculations are provided for comparison purposes
Laser beam scintillation beyond the turbulent atmosphere A numerical computation
NASA Technical Reports Server (NTRS)
Bufton, J. L.; Taylor, L. S.
1976-01-01
The extended Huygens-Fresnel formulation for propagation through turbulence is used to examine scintillation of a finite laser beam. The method is demonstrated analytically for propagation beyond a weak Gaussian phase screen. A numerical integration technique is used to extend the results to a more realistic turbulence model. Results are compared with existing Gaussian beam propagation theory.
Laser steering of particle beams: Refraction and reflection ofparticle beams
Esarey, Eric; Katsouleas, T.; Mori, W.B.; Dodd, E.; Lee, S.; Hemker, R.; Clayton, C.; Joshi, C.
1999-11-01
The co-propagation of an intense particle beam with an ionizing laser beam in a working gas/plasma is considered. When the axes of the laser and particle beam are not aligned, then asymmetric plasma lensing results in a net dipole field acting on the particle beam. The particle beam can be steered or bent (as well as focused) by steering the laser. An analogy is made between the bending of the particle beam by collective effects at a plasma boundary and the refraction or reflection of light at an interface. This mechanism of particle steering may be of interest in applications for which permanent magnets are inconvenient of a fast turn on is required. 3-D particle-in-cell simulations and relevance to a recent experiment are discussed.
Single element laser beam shaper
Zhang, Shukui; Michelle D. Shinn
2005-09-13
A single lens laser beam shaper for converting laser beams from any spatial profile to a flat-top or uniform spatial profile. The laser beam shaper includes a lens having two aspheric surfaces. The beam shaper significantly simplifies the overall structure in comparison with conventional 2-element systems and therefore provides great ease in alignment and reduction of cost.
Atmospheric propagation and combining of high-power lasers.
Nelson, W; Sprangle, P; Davis, C C
2016-03-01
In this paper, we analyze beam combining and atmospheric propagation of high-power lasers for directed-energy (DE) applications. The large linewidths inherent in high-power fiber and slab lasers cause random phase and intensity fluctuations that occur on subnanosecond time scales. Coherently combining these high-power lasers would involve instruments capable of precise phase control and operation at rates greater than ∼10 GHz. To the best of our knowledge, this technology does not currently exist. This presents a challenging problem when attempting to phase lock high-power lasers that is not encountered when phase locking low-power lasers, for example, at milliwatt power levels. Regardless, we demonstrate that even if instruments are developed that can precisely control the phase of high-power lasers, coherent combining is problematic for DE applications. The dephasing effects of atmospheric turbulence typically encountered in DE applications will degrade the coherent properties of the beam before it reaches the target. Through simulations, we find that coherent beam combining in moderate turbulence and over multikilometer propagation distances has little advantage over incoherent combining. Additionally, in cases of strong turbulence and multikilometer propagation ranges, we find nearly indistinguishable intensity profiles and virtually no difference in the energy on the target between coherently and incoherently combined laser beams. Consequently, we find that coherent beam combining at the transmitter plane is ineffective under typical atmospheric conditions.
Atmospheric propagation and combining of high-power lasers.
Nelson, W; Sprangle, P; Davis, C C
2016-03-01
In this paper, we analyze beam combining and atmospheric propagation of high-power lasers for directed-energy (DE) applications. The large linewidths inherent in high-power fiber and slab lasers cause random phase and intensity fluctuations that occur on subnanosecond time scales. Coherently combining these high-power lasers would involve instruments capable of precise phase control and operation at rates greater than ∼10 GHz. To the best of our knowledge, this technology does not currently exist. This presents a challenging problem when attempting to phase lock high-power lasers that is not encountered when phase locking low-power lasers, for example, at milliwatt power levels. Regardless, we demonstrate that even if instruments are developed that can precisely control the phase of high-power lasers, coherent combining is problematic for DE applications. The dephasing effects of atmospheric turbulence typically encountered in DE applications will degrade the coherent properties of the beam before it reaches the target. Through simulations, we find that coherent beam combining in moderate turbulence and over multikilometer propagation distances has little advantage over incoherent combining. Additionally, in cases of strong turbulence and multikilometer propagation ranges, we find nearly indistinguishable intensity profiles and virtually no difference in the energy on the target between coherently and incoherently combined laser beams. Consequently, we find that coherent beam combining at the transmitter plane is ineffective under typical atmospheric conditions. PMID:26974640
Optical chirped beam amplification and propagation
Barty, Christopher P.
2004-10-12
A short pulse laser system uses dispersive optics in a chirped-beam amplification architecture to produce high peak power pulses and high peak intensities without the potential for intensity dependent damage to downstream optical components after amplification.
Propagation properties of cylindrical sinc Gaussian beam
NASA Astrophysics Data System (ADS)
Eyyuboğlu, Halil T.; Bayraktar, Mert
2016-09-01
We investigate the propagation properties of cylindrical sinc Gaussian beam in turbulent atmosphere. Since an analytic solution is hardly derivable, the study is carried out with the aid of random phase screens. Evolutions of the beam intensity profile, beam size and kurtosis parameter are analysed. It is found that on the source plane, cylindrical sinc Gaussian beam has a dark hollow appearance, where the side lobes also start to emerge with increase in width parameter and Gaussian source size. During propagation, beams with small width and Gaussian source size exhibit off-axis behaviour, losing the dark hollow shape, accumulating the intensity asymmetrically on one side, whereas those with large width and Gaussian source size retain dark hollow appearance even at long propagation distances. It is seen that the beams with large widths expand more in beam size than the ones with small widths. The structure constant values chosen do not seem to alter this situation. The kurtosis parameters of the beams having small widths are seen to be larger than the ones with the small widths. Again the choice of the structure constant does not change this trend.
Intense laser propagation in sapphire
NASA Astrophysics Data System (ADS)
Tate, Jennifer L.
When a sufficiently energetic short laser pulse propagates through a medium it can generate an explosive increase in bandwidth leading to the creation of white light; this is known as supercontinuum generation (SCG). Although it is frequently referred to as a single process, SCG is actually the result of many different parallel and competing processes. In this work we investigate the contribution of the individual physical processes underlying the SCG effect, focusing specifically on Raman processes and plasma formation in sapphire. For our experiments we use an amplified Ti:sapphire laser system producing nearly transform limited 60 fs pulses at 800 nm. Typical pulse energies for the experiments are 1--3 muJ/pulse. Using a new experimental technique, the spectrally resolved interferometric double pump, we study the contribution of non-instantaneous Raman effects. We see two distinct Raman contributions in sapphire which are much stronger than indicated in previous work. One Raman process has a period of approximately 185 fs and is related to an available optical phonon; the second Raman process has a period of 20 fs and is related to defect states caused by an oxygen vacancy in the sapphire crystal. Data from the same experiment show that the SCG light is not phase stable at low excitation energies, but that the phase stability is restored and saturates with increasing laser intensity. In a separate experiment we investigate the dynamics of plasma formation using a pump-probe technique. We observe that in sapphire both the formation and the decay of the plasma occur over time scales much longer than predicted by current theory. The plasma rise time is ˜225 fs, while the decay time is ˜150 ps; we also observe that these values do not depend on input pulse energy. In addition to these experiments, we perform a numerical integration of the extended (3 + 1) dimensional nonlinear Schrodinger equation, which models the propagation of a short laser pulse through a
A laser beam quality definition based on induced temperature rise.
Miller, Harold C
2012-12-17
Laser beam quality metrics like M(2) can be used to describe the spot sizes and propagation behavior of a wide variety of non-ideal laser beams. However, for beams that have been diffracted by limiting apertures in the near-field, or those with unusual near-field profiles, the conventional metrics can lead to an inconsistent or incomplete description of far-field performance. This paper motivates an alternative laser beam quality definition that can be used with any beam. The approach uses a consideration of the intrinsic ability of a laser beam profile to heat a material. Comparisons are made with conventional beam quality metrics. An analysis on an asymmetric Gaussian beam is used to establish a connection with the invariant beam propagation ratio. PMID:23263122
A laser beam quality definition based on induced temperature rise.
Miller, Harold C
2012-12-17
Laser beam quality metrics like M(2) can be used to describe the spot sizes and propagation behavior of a wide variety of non-ideal laser beams. However, for beams that have been diffracted by limiting apertures in the near-field, or those with unusual near-field profiles, the conventional metrics can lead to an inconsistent or incomplete description of far-field performance. This paper motivates an alternative laser beam quality definition that can be used with any beam. The approach uses a consideration of the intrinsic ability of a laser beam profile to heat a material. Comparisons are made with conventional beam quality metrics. An analysis on an asymmetric Gaussian beam is used to establish a connection with the invariant beam propagation ratio.
Propagation of ultrashort laser pulses through water.
Li, Jianchao; Alexander, Dennis R; Zhang, Haifeng; Parali, Ufuk; Doerr, David W; Bruce, John C; Wang, Hao
2007-02-19
In this paper, propagation of ultrashort pulses through a long 3.5 meter water channel was studied. Of particular interest was the attenuation of the beam at various lengths along the variable path length and to find an explanation of why the attenuation deviates from typical Beer Lambert law around 3 meters for ultrashort laser pulse transmission. Laser pulses of 10 fs at 75 MHz, 100 fs at 80 MHz and 300 fs at 1 KHz were employed to investigate the effects of pulse duration, spectrum and repetition rate on the attenuation after propagating through water up to 3 meters. Stretched pulse attenuation measurements produced from 10 fs at a frequency of 75 MHz were compared with the 10 fs attenuation measurements. Results indicate that the broad spectrum of the ultrashort pulse is the dominant reason for the observed decrease in attenuation after 3 meters of travel in a long water channel. The repetition rate is found not to play a significant role at least for the long pulse scenario in this reported attenuation studies. PMID:19532433
Repositioning and steering laser beam power via coherent combination of multiple Airy beams.
Zhang, Ze; Ye, Zhuoyi; Song, Daohong; Zhang, Peng; Chen, Zhigang
2013-12-10
We study numerically and experimentally laser coherent combination (LCC) with multiple one- or two-dimensional Airy beams. It is shown that the method of LCC using Airy beams leads to a higher combining efficiency and a better feature of propagation than that using conventional Gaussian beams. Based on such coherent Airy beams combination, we propose a laser steering approach that could achieve large-angle beam steering (over 0.6°) without the need of using any mechanical steering component.
Dickson, Richard K.
2010-09-07
A quick insert and release laser beam guard panel clamping apparatus having a base plate mountable on an optical table, a first jaw affixed to the base plate, and a spring-loaded second jaw slidably carried by the base plate to exert a clamping force. The first and second jaws each having a face acutely angled relative to the other face to form a V-shaped, open channel mouth, which enables wedge-action jaw separation by and subsequent clamping of a laser beam guard panel inserted through the open channel mouth. Preferably, the clamping apparatus also includes a support structure having an open slot aperture which is positioned over and parallel with the open channel mouth.
NASA Technical Reports Server (NTRS)
Hinkley, E. D., Jr.
1981-01-01
Instrument uses infrared absorption to determine methane concentration in liquid natural gas vapor. Two sensors measure intensity of 3.39 mm laser beam after it passes through gas; absorption is proportional to concentration of methane. Instrument is used in modeling spread of LNG clouds and as leak detector on LNG carriers and installations. Unit includes wheels for mobility and is both vertically and horizontally operable.
Laser beam pulse formatting method
Daly, T.P.; Moses, E.I.; Patterson, R.W.; Sawicki, R.H.
1994-08-09
A method for formatting a laser beam pulse using one or more delay loops is disclosed. The delay loops have a partially reflective beam splitter and a plurality of highly reflective mirrors arranged such that the laser beam pulse enters into the delay loop through the beam splitter and circulates therein along a delay loop length defined by the mirrors. As the laser beam pulse circulates within the delay loop a portion thereof is emitted upon each completed circuit when the laser beam pulse strikes the beam splitter. The laser beam pulse is thereby formatted into a plurality of sub-pulses. The delay loops are used in combination to produce complex waveforms by combining the sub-pulses using additive waveform synthesis. 8 figs.
Laser beam pulse formatting method
Daly, Thomas P.; Moses, Edward I.; Patterson, Ralph W.; Sawicki, Richard H.
1994-01-01
A method for formatting a laser beam pulse (20) using one or more delay loops (10). The delay loops (10) have a partially reflective beam splitter (12) and a plurality of highly reflective mirrors (14) arranged such that the laser beam pulse (20) enters into the delay loop (10) through the beam splitter (12) and circulates therein along a delay loop length (24) defined by the mirrors (14). As the laser beam pulse (20) circulates within the delay loop (10) a portion thereof is emitted upon each completed circuit when the laser beam pulse (20) strikes the beam splitter (12). The laser beam pulse (20) is thereby formatted into a plurality of sub-pulses (50, 52, 54 and 56). The delay loops (10) are used in combination to produce complex waveforms by combining the sub-pulses (50, 52, 54 and 56) using additive waveform synthesis.
Synchronous characterization of semiconductor microcavity laser beam.
Wang, T; Lippi, G L
2015-06-01
We report on a high-resolution double-channel imaging method used to synchronously map the intensity- and optical-frequency-distribution of a laser beam in the plane orthogonal to the propagation direction. The synchronous measurement allows us to show that the laser frequency is an inhomogeneous distribution below threshold, but that it becomes homogeneous across the fundamental Gaussian mode above threshold. The beam's tails deviations from the Gaussian shape, however, are accompanied by sizeable fluctuations in the laser wavelength, possibly deriving from manufacturing details and from the influence of spontaneous emission in the very low intensity wings. In addition to the synchronous spatial characterization, a temporal analysis at any given point in the beam cross section is carried out. Using this method, the beam homogeneity and spatial shape, energy density, energy center, and the defects-related spectrum can also be extracted from these high-resolution pictures.
Synchronous characterization of semiconductor microcavity laser beam.
Wang, T; Lippi, G L
2015-06-01
We report on a high-resolution double-channel imaging method used to synchronously map the intensity- and optical-frequency-distribution of a laser beam in the plane orthogonal to the propagation direction. The synchronous measurement allows us to show that the laser frequency is an inhomogeneous distribution below threshold, but that it becomes homogeneous across the fundamental Gaussian mode above threshold. The beam's tails deviations from the Gaussian shape, however, are accompanied by sizeable fluctuations in the laser wavelength, possibly deriving from manufacturing details and from the influence of spontaneous emission in the very low intensity wings. In addition to the synchronous spatial characterization, a temporal analysis at any given point in the beam cross section is carried out. Using this method, the beam homogeneity and spatial shape, energy density, energy center, and the defects-related spectrum can also be extracted from these high-resolution pictures. PMID:26133832
NASA Technical Reports Server (NTRS)
Motamedi, M. E.; Andrews, A. P.; Gunning, W. J.
1993-01-01
Agile beam steering is a critical requirement for airborne and space based LIDAR and optical communication systems. Design and test results are presented for a compact beam steering device with low inertia which functions by dithering two complementary (positive and negative) binary optic microlens arrays relative to each other in directions orthogonal to the direction of light propagation. The miniaturized system has been demonstrated at scan frequencies as high as 300 Hz, generating a 13 x 13 spot array with a total field of view of 2.4 degrees. The design is readily extendable to a 9.5 degree field of view and a 52 x 52 scan pattern. The system is compact - less than 2 in. on a side. Further size reductions are anticipated.
Propagation of focused and multibeam laser energy in biological tissue.
Fowler, A J; Menguc, M P
2000-10-01
The results of a Monte Carlo simulation of laser beam propagation in turbid media are presented. The study was performed to determine whether using a focused beam or multiple beams instead of a single collimated beam could improve subsurface laser energy delivery in biological tissue. A parametric study was carried out to determine both the laser fluence at a target depth and the ratio of fluence at the target over surface fluence as a function of tissue properties and the mode of energy delivery. It was found that the reduced scattering coefficient was the primary determinant as to whether multibeam or focused beam delivery could be effective. A focused beam was found to be extremely effective in increasing fluence at the target if the dimensionless reduced scattering coefficient was less than 2. The delivered fluence, however, was found to be extremely sensitive to tissue properties. A five-beam laser system was found to be less effective at increasing fluence at the target than a focused beam; but the fluence delivered by a five-beam system was far less sensitive to tissue properties, thereby making accurate dosimetry more feasible.
Reciprocity breaking during nonlinear propagation of adapted beams through random media.
Palastro, J P; Peñano, J; Nelson, W; DiComo, G; Helle, M; Johnson, L A; Hafizi, B
2016-08-22
Adaptive optics (AO) systems rely on the principle of reciprocity, or symmetry with respect to the interchange of point sources and receivers. These systems use the light received from a low power emitter on or near a target to compensate phase aberrations acquired by a laser beam during linear propagation through random media. If, however, the laser beam propagates nonlinearly, reciprocity is broken, potentially undermining AO correction. Here we examine the consequences of this breakdown, providing the first analysis of AO applied to high peak power laser beams. While discussed for general random and nonlinear media, we consider specific examples of Kerr-nonlinear, turbulent atmosphere.
Reciprocity breaking during nonlinear propagation of adapted beams through random media.
Palastro, J P; Peñano, J; Nelson, W; DiComo, G; Helle, M; Johnson, L A; Hafizi, B
2016-08-22
Adaptive optics (AO) systems rely on the principle of reciprocity, or symmetry with respect to the interchange of point sources and receivers. These systems use the light received from a low power emitter on or near a target to compensate phase aberrations acquired by a laser beam during linear propagation through random media. If, however, the laser beam propagates nonlinearly, reciprocity is broken, potentially undermining AO correction. Here we examine the consequences of this breakdown, providing the first analysis of AO applied to high peak power laser beams. While discussed for general random and nonlinear media, we consider specific examples of Kerr-nonlinear, turbulent atmosphere. PMID:27557166
Propagation of a general-type beam through a truncated fractional Fourier transform optical system.
Zhao, Chengliang; Cai, Yangjian
2010-03-01
Paraxial propagation of a general-type beam through a truncated fractional Fourier transform (FRT) optical system is investigated. Analytical formulas for the electric field and effective beam width of a general-type beam in the FRT plane are derived based on the Collins formula. Our formulas can be used to study the propagation of a variety of laser beams--such as Gaussian, cos-Gaussian, cosh-Gaussian, sine-Gaussian, sinh-Gaussian, flat-topped, Hermite-cosh-Gaussian, Hermite-sine-Gaussian, higher-order annular Gaussian, Hermite-sinh-Gaussian and Hermite-cos-Gaussian beams--through a FRT optical system with or without truncation. The propagation properties of a Hermite-cos-Gaussian beam passing through a rectangularly truncated FRT optical system are studied as a numerical example. Our results clearly show that the truncated FRT optical system provides a convenient way for laser beam shaping.
Characterizing the beam properties of terahertz quantum-cascade lasers
NASA Astrophysics Data System (ADS)
Richter, H.; Rothbart, N.; Hübers, H.-W.
2014-08-01
Terahertz quantum-cascade lasers (QCLs) are very promising radiation sources for many scientific and commercial applications. Shaping and characterizing the beam profile of a QCL is crucial for any of these applications. Usually the beam profile should be as close as possible to a fundamental Gaussian TEM00 mode. In order to completely characterize the laser beam the power and the wavefront have to be measured. We describe methods for characterizing the beam properties of QCLs. Several QCLs with single-plasmon waveguide and emission frequencies between 2 and 5 THz are investigated. The beam profiles of these lasers are shaped into almost fundamental Gaussian modes using dedicated lenses. The beam propagation factor M2 is as low as 1.2. The wavefront is measured along the axis of propagation with a THz Hartmann sensor. Its curvature behaves as expected for a Gaussian beam. The applied methods can be transferred to any other THz beam.
Simulation of laser propagation in a turbulent atmosphere.
Frehlich, R
2000-01-20
The split-step Fourier-transform algorithm for numerical simulation of wave propagation in a turbulent atmosphere is refined to correctly include the effects of large-scale phase fluctuations that are important for imaging problems and many beam-wave problems such as focused laser beams and beam spreading. The results of the improved algorithm are similar to the results of the traditional algorithm for the performance of coherent Doppler lidar and for plane-wave intensity statistics because the effects of large-scale turbulence are less important. The series solution for coherent Doppler lidar performance converges slowly to the results from simulation. PMID:18337906
Synchronous characterization of semiconductor microcavity laser beam
Wang, T. Lippi, G. L.
2015-06-15
We report on a high-resolution double-channel imaging method used to synchronously map the intensity- and optical-frequency-distribution of a laser beam in the plane orthogonal to the propagation direction. The synchronous measurement allows us to show that the laser frequency is an inhomogeneous distribution below threshold, but that it becomes homogeneous across the fundamental Gaussian mode above threshold. The beam’s tails deviations from the Gaussian shape, however, are accompanied by sizeable fluctuations in the laser wavelength, possibly deriving from manufacturing details and from the influence of spontaneous emission in the very low intensity wings. In addition to the synchronous spatial characterization, a temporal analysis at any given point in the beam cross section is carried out. Using this method, the beam homogeneity and spatial shape, energy density, energy center, and the defects-related spectrum can also be extracted from these high-resolution pictures.
Rippled beam free electron laser amplifier
Carlsten, Bruce E.
1999-01-01
A free electron laser amplifier provides a scalloping annular electron beam that interacts with the axial electric field of a TM.sub.0n mode. A waveguide defines an axial centerline and, a solenoid arranged about the waveguide produces an axial constant magnetic field within the waveguide. An electron beam source outputs a annular electron beam that interacts with the axial magnetic field to have an equilibrium radius and a ripple radius component having a variable radius with a ripple period along the axial centerline. An rf source outputs an axial electric field that propagates within the waveguide coaxial with the electron beam and has a radial mode that interacts at the electron beam at the equilibrium radius component of the electron beam.
Energy transfer between laser beams crossing in ignition hohlraums
Michel, P; Divol, L; Williams, E A; Thomas, C A; Callahan, D A; Weber, S; Haan, S W; Salmonson, J D; Dixit, S; Hinkel, D E; Edwards, M J; MacGowan, B J; Lindl, J D; Glenzer, S H; Suter, L J
2008-10-03
The full scale modeling of power transfer between laser beams crossing in plasmas is presented. A new model was developed, allowing calculation of the propagation and coupling of pairs of laser beams with their associated plasma wave in three dimensions. The full laser beam smoothing techniques used in ignition experiments are modeled, and their effects on crossed-beam energy transfer is investigated. A shift in wavelength between the beams can move the instability off resonance and reduce the transfer, hence preserving the symmetry of the capsule implosion.
Laser beam alignment apparatus and method
Gruhn, Charles R.; Hammond, Robert B.
1981-01-01
The disclosure relates to an apparatus and method for laser beam alignment. Thermoelectric properties of a disc in a laser beam path are used to provide an indication of beam alignment and/or automatic laser alignment.
Laser beam alignment apparatus and method
Gruhn, C.R.; Hammond, R.B.
The disclosure related to an apparatus and method for laser beam alignment. Thermoelectric properties of a disc in a laser beam path are used to provide an indication of beam alignment and/or automatic laser alignment.
NASA Astrophysics Data System (ADS)
Gouesbet, Gérard; Lock, James A.
2016-07-01
When dealing with light scattering and propagation of an electromagnetic beam, there are essentially two kinds of expansions which have been used to describe the incident beam (i) a discrete expansion involving beam shape coefficients and (ii) a continuous expansion in terms of an angular spectrum of plane waves. In this paper, we demonstrate that the angular spectrum decomposition readily leads to two important consequences, (i) laser light beams travel in free space with an effective velocity that is smaller than the speed of light c, and (ii) the optical theorem does not hold for arbitrary shaped beams, both in the case of electromagnetic waves and scalar waves, e.g. quantum and acoustical waves.
Propagation of a cosh-Gaussian beam through an optical system in turbulent atmosphere.
Chu, Xiuxiang
2007-12-24
The propagation of a cosh-Gaussian beam through an arbitrary ABCD optical system in turbulent atmosphere has been investigated. The analytical expressions for the average intensity at any receiver plane are obtained. As an elementary example, the average intensity and its radius at the image plane of a cosh-Gaussian beam through a thin lens are studied. To show the effects of a lens on the average intensity and the intensity radius of the laser beam in turbulent atmosphere, the properties of a collimated cosh-Gaussian beam and a focused cosh-Gaussian beam for direct propagation in turbulent atmosphere are studied and numerically calculated. The average intensity profiles of a cosh-Gaussian beam through a lens can have a shape similar to that of the initial beam for a longer propagation distance than that of a collimated cosh-Gaussian beam for direct propagation. With the increment in the propagation distance, the average intensity radius at the image plane of a cosh-Gaussian beam through a thin lens will be smaller than that at the focal plane of a focused cosh-Gaussian beam for direct propagation. Meanwhile, the intensity distributions at the image plane of a cosh-Gaussian beam through a lens with different w(0) and Omega(0) are also studied.
Phased laser array for generating a powerful laser beam
Holzrichter, John F.; Ruggiero, Anthony J.
2004-02-17
A first injection laser signal and a first part of a reference laser beam are injected into a first laser element. At least one additional injection laser signal and at least one additional part of a reference laser beam are injected into at least one additional laser element. The first part of a reference laser beam and the at least one additional part of a reference laser beam are amplified and phase conjugated producing a first amplified output laser beam emanating from the first laser element and an additional amplified output laser beam emanating from the at least one additional laser element. The first amplified output laser beam and the additional amplified output laser beam are combined into a powerful laser beam.
Image processing techniques for laser propagation through atmospheric turbulence
NASA Astrophysics Data System (ADS)
Belichki, Sara B.; Splitter, Landon J.; Andrews, Larry C.; Phillips, Ronald L.; Coffaro, Joseph T.; Panich, Michael G.
2014-06-01
In order to better understand laser beam propagation through the analysis of the fluctuations in scintillation data, images from a 30 frame per second monochrome camera are utilized. Scintillation is the effect of atmospheric turbulence which is known to disrupt and alter the intensity and formation of a laser signal as it propagates through the atmosphere. To model and understand this phenomenon, recorded video output of a laser upon a target screen is inspected to determine how much of an effect the atmospheric turbulence has disrupted the laser signal as it has been propagated upon a set distance. The techniques of data processing outlined in this paper moves toward a software-based approach of determining the effects of propagation and detection of a laser based on the visual fluctuations caused by the scintillation effect. With the aid of such visual models, this paper examines the idea of implementing mathematical models via software that is then validated by the gathered video data taken at Kennedy Space Center.
Laser-induced propagation and destruction of amyloid beta fibrils.
Yagi, Hisashi; Ozawa, Daisaku; Sakurai, Kazumasa; Kawakami, Toru; Kuyama, Hiroki; Nishimura, Osamu; Shimanouchi, Toshinori; Kuboi, Ryoichi; Naiki, Hironobu; Goto, Yuji
2010-06-18
The amyloid deposition of amyloid beta (Abeta) peptides is a critical pathological event in Alzheimer disease (AD). Preventing the formation of amyloid deposits and removing preformed fibrils in tissues are important therapeutic strategies against AD. Previously, we reported the destruction of amyloid fibrils of beta(2)-microglobulin K3 fragments by laser irradiation coupled with the binding of amyloid-specific thioflavin T. Here, we studied the effects of a laser beam on Abeta fibrils. As was the case for K3 fibrils, extensive irradiation destroyed the preformed Abeta fibrils. However, irradiation during spontaneous fibril formation resulted in only the partial destruction of growing fibrils and a subsequent explosive propagation of fibrils. The explosive propagation was caused by an increase in the number of active ends due to breakage. The results not only reveal a case of fragmentation-induced propagation of fibrils but also provide insights into therapeutic strategies for AD.
THz Generation and Propagation Using Femtosecond Laser
NASA Astrophysics Data System (ADS)
Jeon, Tae-In
There are several methods to generate and detect THz electromagnetic radiation whose frequency lies between the microwave and infrared regions of the spectrum. For example photoconductive switching, optical rectification, photomixing, Quantum cascade lasers, and free electrons laser are widely used methods to generate THz beam.
Qin, Zhiyuan; Tao, Rumao; Zhou, Pu; Xu, Xiaojun; Liu, Zejin
2013-11-20
Based on partially coherent Bessel-Gaussian beams (BGBs), the coherence evolution of the partially coherent beams carrying optical vortices in non-Kolmogorov turbulence is investigated in detail. The analytical formulas for the spatial coherence length of partially coherent BGBs with optical vortices in non-Kolmogorov turbulence have been derived by using the combination of a coherence superposition approximation of decentered Gaussian beams and the extended Huygens-Fresnel principle. The influences of beam and turbulence parameters on spatial coherence are investigated by numerical examples. Numerical results reveal that the coherence of the partially coherent laser beam with vortices is independent of the optical vortices, and the spatial correlation length of the beams does not decrease monotonically during propagation in non-Kolmogorov turbulence. Within a certain propagation distance, the coherence of the partially coherent beam will improve, and the improvement of the coherence of the partially coherent beams is closely related to the beam and turbulence parameters.
Tests for assessing beam propagation algorithms
NASA Astrophysics Data System (ADS)
Stone, Bryan D.
2011-10-01
Given a beam propagation algorithm, whether it is a commercial implementation or some other in-house or research implementation, it is not trivial to determine whether it is suitable either for a wide range of applications or even for a specific application. In this paper, we describe a range of tests with "known" results; these can be used to exercise beam propagation algorithms and assess their robustness and accuracy. Three different categories of such tests are discussed. One category is tests of self-consistency. Such tests often rely on symmetry to make guarantees about some aspect of the resulting field. While passing such tests does not guarantee correct results in detail, they can nonetheless point towards problems with an algorithm when they fail, and build confidence when they pass. Another category of tests compares the complex field to values that have been experimentally measured. While the experimental data is not always known in precisely, and the experimental setup might not always be accessible, these tests can provide reasonable quantitative comparisons that can also point towards problems with the algorithm. The final category of tests discussed is those for which the propagated complex field can be computed independently. The test systems for this category tend to be relatively simple, such as diffraction through apertures in free space or in the pupil of an ideal imaging system. Despite their relative simplicity, there are a number of advantages to these tests. For example, they can provide quantitative measures of accuracy. These tests also allow one to develop an understanding of how the execution time (or similarly, memory usage) scales as the region-of-interest over which one desires the field is changed.
Radiative trapping in intense laser beams
NASA Astrophysics Data System (ADS)
Kirk, J. G.
2016-08-01
The dynamics of electrons in counter-propagating, circularly polarized laser beams are shown to exhibit attractors whose ability to trap particles depends on the ratio of the beam intensities and a single parameter describing radiation reaction. Analytical expressions are found for the underlying limit cycles and the parameter range in which they are stable. In high-intensity optical pulses, where radiation reaction strongly modifies the trajectories, the production of collimated gamma-rays and the initiation of non-linear cascades of electron-positron pairs can be optimized by a suitable choice of the intensity ratio.
Radiative trapping in intense laser beams
NASA Astrophysics Data System (ADS)
Kirk, J. G.
2016-08-01
The dynamics of electrons in counter-propagating, circularly polarized laser beams are shown to exhibit attractors whose ability to trap particles depends on the ratio of the beam intensities and a single parameter describing radiation reaction. Analytical expressions are found for the underlying limit cycles and the parameter range in which they are stable. In high-intensity optical pulses, where radiation reaction strongly modifies the trajectories, the production of collimated gamma-rays and the initiation of non-linear cascades of electron–positron pairs can be optimized by a suitable choice of the intensity ratio.
Unresonant interaction of laser beams with microdroplets
NASA Astrophysics Data System (ADS)
Pascu, M. L.; Popescu, G. V.; Ticos, C. M.; Andrei, I. R.
2012-03-01
The interaction of distilled water microdroplets (volumes of 3-4μl) with pulsed laser beams emitted at 532nm is described. At 532nm the distilled water absorption is very low and the interaction of a water bead with the laser radiation is dominated by unresonant phenomena. Following the collision of the laser beam with a microdroplet in suspended/ hanging/pendant position in air, deformations and mechanical vibrations of the droplets are produced. The conditions in which the droplets lose material as a consequence of the impact with laser beams are also explored. The effects produced on the droplet were studied pulse by pulse and depend on: droplet's content, beam wavelength, power and focusing conditions, irradiation geometry and adhesion of the bead to the capillary on which it is suspended. The laser pulses energies were varied in four steps: 0.25mJ, 0.4mJ, 0.7mJ and 1mJ. The pulse full time width was 5ns and the typical focus diameter on the droplet was 90Î¼m; the beam had a relatively low divergence around the focus point. The microdroplets and the modification/evolution of their shapes are visualised by recordings performed at 10kframes/second. Following a microdroplet interaction with the laser beam one may also produce at a controlled moment in time nanodroplets propagating at high (probably supersonic) speeds and microdroplets propagating at slower speeds. One may also produce pendant droplets of smaller dimensions than the initial one as well as micro/nano gas bubbles in the pendant droplet's material/volume. In a second set of experiment was recorded at high speed the behaviour of the microdroplets of Rhodamine 6G in distilled water at resonant interaction with similar laser pulses, at the same power levels. The optical phenomena considering that the microdroplets contents are Newtonian liquids which dominate the beads behaviour at interaction with the laser beams, are discussed.
Split step solution in the iteration of the beam propagation method for analyzing Bragg gratings.
Shu, Hong
2009-08-20
The split step method is applied to the iteration of the beam propagation method for analyzing the reflection of a laser beam by a volume Bragg grating. The application of the split step method is made possible by a way to properly treat the grating coupling terms in the paraxial wave equations. This method is demonstrated to be accurate in addition to efficient and robust. After this modification, the iteration of the beam propagation method is suitable for analyzing finite beams in volume Bragg gratings, for which the grating strength might be large. It is also suitable for analyzing Bragg gratings with nonuniform grating structures.
Controllable laser ion beam generation
NASA Astrophysics Data System (ADS)
Kamiyama, D.; Takano, M.; Nagashima, T.; Barada, D.; Gu, Y. J.; Li, X. F.; Kong, Q.; Wang, P. X.; Kawata, S.
2016-05-01
In intense-laser plasma interaction, several issues still remain to be solved for a future laser particle acceleration. In this paper we focus on a bunching of ion beam, which is preaccelerated by a strong electric field generated in a laser plasma interaction. In this study, a nearcritical-density plasma target is illuminated by an intense short laser pulse. A moving strong inductive electric field is generated inside of the target. We have successfully obtained a bunched ion beam in our particle-in-cell simulations in this paper.
Atmospheric effects on CO2 laser propagation
NASA Technical Reports Server (NTRS)
Murty, S. S. R.; Bilbro, J. W.
1978-01-01
An investigation was made of the losses encountered in the propagation of CO2 laser radiation through the atmosphere, particularly as it applies to the NASA/Marshall Space Flight Center Pulsed Laser Doppler System. As such it addresses three major areas associated with signal loss: molecular absorption, refractive index changes in a turbulent environment, and aerosol absorption and scattering. In particular, the molecular absorption coefficients of carbon dioxide, water vapor, and nitrous oxide are calculated for various laser lines in the region of 10.6 mu m as a function of various pressures and temperatures. The current status in the physics of low-energy laser propagation through a turbulent atmosphere is presented together with the analysis and evaluation of the associated heterodyne signal power loss. Finally, aerosol backscatter and extinction coefficients are calculated for various aerosol distributions and the results incorporated into the signal-to-noise ratio equation for the Marshall Space Flight Center system.
Fisher, R.A.; Wilson, L.E.
1989-01-01
Various papers on nonlinear optical beam manipulation and high-energy beam propagation through the atmosphere are presented. Individual topics addressed include: suppression of Raman amplification using large Stokes seeds, review of multiple-short-pulse SBS experiments and theory, laser-induced gratings for beam manipulation in a gas, considerations for computing realistic atmospheric distortion parameter profiles, effect of turbulent diffusion on laser propagation, use of multiple photon processes in krypton for laser guiding of electron beams, effect of ionization on intense electron beam propagation in low-pressure media, lidar measurements of the troposphere and middle atmosphere, seasonal and diurnal changes in cloud obscuration to visible and IR energy transmission, new cloud composite climatologies using meteorological satellite imagery, effect of neutral atmospheric structure on beam propagation, small-scale electron density fluctuations in a disturbed ionospheric environment, and SDIO radio frequency communications in a structured environment.
Helicopter engine exhaust rotor downwash effects on laser beams
NASA Astrophysics Data System (ADS)
Henriksson, Markus; Sjöqvist, Lars; Seiffer, Dirk
2015-10-01
The hot exhaust gases from engines on helicopters are pushed down by the rotor in a turbulent flow. When the optical path of a laser beam or optical sensor passes through this region severe aberrations of the optical field may result. These perturbations will lead to beam wander and beam distortions that can limit the performance of optical countermeasure systems. To quantify these effects the Italian Air Force Flight Test Centre hosted a trial for the "Airborne platform effects on lasers and warning sensors" (ALWS) EDA-project. Laser beams were propagated from the airport control tower to a target screen in a slant path with the helicopter hovering over this path. Collimated laser beams at 1.55-, 2- and 4.6-μm wavelength were imaged with high speed cameras. Large increases in beam wander and beam divergence were found, with beam wander up to 200 μrad root-mean-square and increases in beam divergence up to 1 mrad. To allow scaling to other laser beam parameters and geometries formulas for propagation in atmospheric turbulence were used even though the turbulence may not follow Kolmogorov statistics. By assuming that the plume is short compared to the total propagation distance the integrated structure parameter through the plume could be calculated. Values in the range 10-10 to 10-8 m1/3 were found when the laser beams passed through the exhaust gases below the helicopter tail. The integrated structure parameter values calculated from beam wander were consistently lower than those calculated from long term spot size, indicating that the method is not perfect but provides information about order of magnitudes. The measured results show that the engine exhaust for worst case beam directions will dominate over atmospheric turbulence even for kilometer path lengths from a helicopter at low altitude. How severe the effect is on system performance will depend on beam and target parameters.
Positron Beam Propagation in a Meter Long Plasma Channel
Marsh, K.A.; Blue, B.E.; Clayton, C.E.; Joshi, C.; Mori, W.B.; Decker, F.-J.; Hogan, M.J.; Iverson, R.; O'Connell, C.; Raimondi, P.; Siemann, Robert H.; Walz, D.; Katsouleas, T.C.; Muggli, P.; /Southern California U.
2008-03-17
Recent experiments and simulations have shown that positron beams propagating in plasmas can be focused and also create wakes with large accelerating gradients. For similar parameters, the wakes driven by positron beams are somewhat smaller compared to the case of an electron beam. Simulations have shown that the wake amplitude can be increased if the positron beam is propagated in a hollow plasma channel (Ref. 1). This paper, compares experimentally, the propagation and beam dynamics of a positron beam in a meter scale homogeneous plasma, to a positron beam hollow channel plasma. The results show that positron beams in hollow channels are less prone to distortions and deflections. Hollow channels were observed to guide the positron beam onto the channel axis. Beam energy loss was also observed implying the formation of a large wake amplitude. The experiments were carried out as part of the E-162 plasma wakefield experiments at SLAC.
Propagation of a radial phased-locked Lorentz beam array in turbulent atmosphere.
Zhou, Guoquan
2011-11-21
A radial phased-locked (PL) Lorentz beam array provides an appropriate theoretical model to describe a coherent diode laser array, which is an efficient radiation source for high-power beaming use. The propagation of a radial PL Lorentz beam array in turbulent atmosphere is investigated. Based on the extended Huygens-Fresnel integral and some mathematical techniques, analytical formulae for the average intensity and the effective beam size of a radial PL Lorentz beam array are derived in turbulent atmosphere. The average intensity distribution and the spreading properties of a radial PL Lorentz beam array in turbulent atmosphere are numerically calculated. The influences of the beam parameters and the structure constant of the atmospheric turbulence on the propagation of a radial PL Lorentz beam array in turbulent atmosphere are discussed in detail.
Propagation of optical beams in two transverse gradient index media
NASA Astrophysics Data System (ADS)
Martín-Ruiz, A.; Martín-Heredia, J.; Ruiz-Ochoa, L. A.; Chan-López, E.
2016-05-01
We investigate the propagation of optical beams in two gradient index inhomogeneous media. The Green's function for paraxial propagation in an inhomogeneous medium is derived as a Feynman path integral involving summation over real rays. We use a simple method based on discontinuous functions, which is similar to that used in General Relativity when studying metric discontinuities across an hypersurface, to study the propagation in two transverse refractive index gradients which are coupled in the propagation direction. We show that this method is consistent with the geometric-optics ray theory, and then with the definition of the coupled Green's function. The propagation of Gaussian beams in two homogeneous media with different refractive indices is analyzed. We also study the propagation of Airy beams in two media with different linear transverse refractive index gradients. We demonstrate that by controlling the gradient strength of the media it is possible to reduce to zero their acceleration, yielding an Airy beam that propagates linearly.
Long-distance Bessel beam propagation through Kolmogorov turbulence.
Birch, Philip; Ituen, Iniabasi; Young, Rupert; Chatwin, Chris
2015-11-01
Free-space optical communication has the potential to transmit information with both high speed and security. However, since it is unguided it suffers from losses due to atmospheric turbulence and diffraction. To overcome the diffraction limits the long-distance propagation of Bessel beams is considered and compared against Gaussian beam properties. Bessel beams are shown to have a number of benefits over Gaussian beams when propagating through atmospheric turbulence.
Reciprocity breaking during nonlinear propagation of adapted beams through random media
NASA Astrophysics Data System (ADS)
Palastro, J. P.; Peñano, J.; Nelson, W.; DiComo, G.; Helle, M.; Johnson, L. A.; Hafizi, B.
2016-08-01
Adaptive optics (AO) systems rely on the principle of reciprocity, or symmetry with respect to the interchange of point sources and receivers. These systems use the light received from a low power emitter on or near a target to compensate profile aberrations acquired by a laser beam during linear propagation through random media. If, however, the laser beam propagates nonlinearly, reciprocity is broken, potentially undermining AO correction. Here we examine the consequences of this breakdown. While discussed for general random and nonlinear media, we consider specific examples of Kerr-nonlinear, turbulent atmosphere.
A finite element beam propagation method for simulation of liquid crystal devices.
Vanbrabant, Pieter J M; Beeckman, Jeroen; Neyts, Kristiaan; James, Richard; Fernandez, F Anibal
2009-06-22
An efficient full-vectorial finite element beam propagation method is presented that uses higher order vector elements to calculate the wide angle propagation of an optical field through inhomogeneous, anisotropic optical materials such as liquid crystals. The full dielectric permittivity tensor is considered in solving Maxwell's equations. The wide applicability of the method is illustrated with different examples: the propagation of a laser beam in a uniaxial medium, the tunability of a directional coupler based on liquid crystals and the near-field diffraction of a plane wave in a structure containing micrometer scale variations in the transverse refractive index, similar to the pixels of a spatial light modulator.
NASA Astrophysics Data System (ADS)
Fahrbach, Florian O.; Rohrbach, Alexander
2012-01-01
Laser beams that can self-reconstruct their initial beam profile even in the presence of massive phase perturbations are able to propagate deeper into inhomogeneous media. This ability has crucial advantages for light sheet-based microscopy in thick media, such as cell clusters, embryos, skin or brain tissue or plants, as well as scattering synthetic materials. A ring system around the central intensity maximum of a Bessel beam enables its self-reconstruction, but at the same time illuminates out-of-focus regions and deteriorates image contrast. Here we present a detection method that minimizes the negative effect of the ring system. The beam's propagation stability along one straight line enables the use of a confocal line principle, resulting in a significant increase in image contrast. The axial resolution could be improved by nearly 100% relative to the standard light-sheet techniques using scanned Gaussian beams, while demonstrating self-reconstruction also for high propagation depths.
Fahrbach, Florian O; Rohrbach, Alexander
2012-01-17
Laser beams that can self-reconstruct their initial beam profile even in the presence of massive phase perturbations are able to propagate deeper into inhomogeneous media. This ability has crucial advantages for light sheet-based microscopy in thick media, such as cell clusters, embryos, skin or brain tissue or plants, as well as scattering synthetic materials. A ring system around the central intensity maximum of a Bessel beam enables its self-reconstruction, but at the same time illuminates out-of-focus regions and deteriorates image contrast. Here we present a detection method that minimizes the negative effect of the ring system. The beam's propagation stability along one straight line enables the use of a confocal line principle, resulting in a significant increase in image contrast. The axial resolution could be improved by nearly 100% relative to the standard light-sheet techniques using scanned Gaussian beams, while demonstrating self-reconstruction also for high propagation depths.
Laser processing with specially designed laser beam
NASA Astrophysics Data System (ADS)
Asratyan, A. A.; Bulychev, N. A.; Feofanov, I. N.; Kazaryan, M. A.; Krasovskii, V. I.; Lyabin, N. A.; Pogosyan, L. A.; Sachkov, V. I.; Zakharyan, R. A.
2016-04-01
The possibility of using laser systems to form beams with special spatial configurations has been studied. The laser systems applied had a self-conjugate cavity based on the elements of copper vapor lasers (LT-5Cu, LT-10Cu, LT-30Cu) with an average power of 5, 10, or 30 W. The active elements were pumped by current pulses of duration 80-100 ns. The duration of laser generation pulses was up to 25 ns. The generator unit included an unstable cavity, where one reflector was a special mirror with a reflecting coating. Various original optical schemes used were capable of exploring spatial configurations and energy characteristics of output laser beams in their interaction with micro- and nanoparticles fabricated from various materials. In these experiments, the beam dimensions of the obtained zones varied from 0.3 to 5 µm, which is comparable with the minimum permissible dimensions determined by the optical elements applied. This method is useful in transforming a large amount of information at the laser pulse repetition rate of 10-30 kHz. It was possible to realize the high-precision micromachining and microfabrication of microscale details by direct writing, cutting and drilling (with the cutting width and through-hole diameters ranging from 3 to 100 µm) and produce microscale, deep, intricate and narrow grooves on substrate surfaces of metals and nonmetal materials. This system is used for producing high-quality microscale details without moving the object under treatment. It can also be used for microcutting and microdrilling in a variety of metals such as molybdenum, copper and stainless steel, with a thickness of up to 300 µm, and in nonmetals such as silicon, sapphire and diamond with a thickness ranging from 10 µm to 1 mm with different thermal parameters and specially designed laser beam.
Atmospheric propagation of high power laser radiation at different weather conditions
NASA Astrophysics Data System (ADS)
Pargmann, Carsten; Hall, Thomas; Duschek, Frank; Handke, Jürgen
2016-05-01
Applications based on the propagation of high power laser radiation through the atmosphere are limited in range and effect, due to weather dependent beam wandering, beam deterioration, and scattering processes. Security and defense related application examples are countermeasures against hostile projectiles and the powering of satellites and aircrafts. For an examination of the correlations between weather condition and laser beam characteristics DLR operates at Lampoldshausen a 130 m long free transmission laser test range. Sensors around this test range continuously monitor turbulence strength, visibility, precipitation, temperature, and wind speed. High power laser radiation is obtained by a TruDisk 6001 disk laser (Trumpf company) yielding a maximum output power of 6 kW at a wavelength of 1030 nm. The laser beam is expanded to 180 mm and focused along the beam path. Power and intensity distribution are measured before and after propagation, providing information about the atmospheric transmission and alterations of diameter and position of the laser beam. Backscattered laser light is acquired by a photo receiver. As a result, measurements performed at different weather conditions show a couple of correlations to the characteristics of the laser beam. The experimental results are compared to a numerical analysis. The calculations are based on the Maxwell wave equation in Fresnel approximation. The turbulence is considered by the introduction of phase screens and the "von Karman" spectrum.
Stable propagation of non-Gaussian beams in a multiple-pass cell.
Takasaki, T; Suda, A; Sato, K; Nagasaka, K; Tashiro, H
1997-05-20
To apply annular output beams emitted from an unstable resonator to a multiple-pass cell (MPC) for Raman conversion, we studied the mode-matching condition of non-Gaussian beams to a MPC using beam propagation analysis based on Laguerre-Gaussian functions. During transits of the MPC, the radial profile of an annular beam changes between annular and Airy patterns. Although such behavior indicates that it is impossible to achieve complete mode matching of an annular beam, we found a quasi-mode-matching condition under which the variation of beam size was minimized. The above theoretical analysis was verified experimentally using a CO(2) laser beam prepared for a para-hydrogen Raman laser. PMID:18253356
Propagation of Bessel and Airy beams through atmospheric turbulence.
Nelson, W; Palastro, J P; Davis, C C; Sprangle, P
2014-03-01
We investigate, through simulation, the modifications to Bessel and Airy beams during propagation through atmospheric turbulence. We find that atmospheric turbulence disrupts the quasi-non-diffracting nature of Bessel and Airy beams when the transverse coherence length (Fried parameter) nears the initial aperture diameter or diagonal, respectively. The turbulence-induced transverse phase distortion limits the effectiveness of Bessel and Airy beams for applications requiring propagation over long distances in the turbulent atmosphere.
Li, Wentao; Liu, Jiansheng; Wang, Wentao; Chen, Qiang; Zhang, Hui; Tian, Ye; Zhang, Zhijun; Qi, Rong; Wang, Cheng; Leng, Yuxin; Li, Ruxin; Xu, Zhizhan
2013-11-15
The multiple filaments formation process in the laser wakefield accelerator (LWFA) was observed by imaging the transmitted laser beam after propagating in the plasma of different density. During propagation, the laser first self-focused into a single filament. After that, it began to defocus with energy spreading in the transverse direction. Two filaments then formed from it and began to propagate independently, moving away from each other. We have also demonstrated that the laser multiple filamentation would lead to the multiple electron beams acceleration in the LWFA via ionization-induced injection scheme. Besides, its influences on the accelerated electron beams were also analyzed both in the single-stage LWFA and cascaded LWFA.
Propagation of intense short-pulse laser in homogeneous near-critical density plasmas
NASA Astrophysics Data System (ADS)
Habara, H.; Nakaguchi, S.; Uematsu, Y.; Baton, S. D.; Chen, S. N.; Fuchs, J.; Iwawaki, T.; MacDonald, M.; Nazarov, W.; Rousseaux, C.; Tanaka, K. A.
2016-05-01
Ultra intense laser light propagation in a homogeneous overdense plasma was investigated using a plastic foam target filling a polyimide tube. Laser propagation into overdense plasma was measured via Doppler red shift of the reflected laser light from the moving plasma at 0.3-0.4 of speed of light. We also observed strongly collimated electron beam possibly caused by the magnetic field surrounding the plasma channel, and high energy X-rays emitted via synchrotron radiation by the oscillating electrons inside the channel. These features imply that UIL propagates inside the overdense plasma as predicted in PIC calculation, and are very important for direct irradiation scheme of fast ignition.
Liu, Chuyu; Zhang, Shukui
2011-10-04
A single lens bullet-shaped laser beam shaper capable of redistributing an arbitrary beam profile into any desired output profile comprising a unitary lens comprising: a convex front input surface defining a focal point and a flat output portion at the focal point; and b) a cylindrical core portion having a flat input surface coincident with the flat output portion of the first input portion at the focal point and a convex rear output surface remote from the convex front input surface.
ERIC Educational Resources Information Center
Knotts, Michael
1993-01-01
Describes an inexpensive fog machine that is useful for photography and laser demonstrations. The apparatus uses liquid nitrogen to chill steam to make a fine mist safe for precision optics. The device can be made for around $50. (MVL)
Repeat scanning technology for laser ultrasonic propagation imaging
NASA Astrophysics Data System (ADS)
Lee, Jung-Ryul; Yenn Chong, See; Sunuwar, Nitam; Park, Chan Yik
2013-08-01
Laser ultrasonic scanning in combination with contact or non-contact sensors provides new paradigms in structural health management (SHM) and non-destructive in-process quality control (IPQC) for large composite structures. Wave propagation imaging technology based on laser ultrasonic scanning and fixed-point sensing shows remarkable advantages, such as minimal need for embedded sensors in SHM, minimum invasive defect visualization in IPQC and general capabilities of curved and complex target inspection, and temporal reference-free inspection. However, as with other SHM methods and non-destructive evaluation based on ultrasound, the signal-to-noise ratio (SNR) is a prevalent issue in real structural applications, especially with non-contact thin-composite sensing or with thick and heterogeneous composites. This study proposes a high-speed repeat scanning technique for laser ultrasonic propagation imaging (UPI) technology, which is realized with the scanning speed of 1 kHz of a Q-switched continuous wave laser, and precise control of the laser beam pulses for identical point scanning. As a result, the technique enables the achievement of significant improvement in the SNR to inspect real-world composite structures. The proposed technique provides enhanced results for impact damage detection in a 2 mm thick wing box made of carbon-fiber-reinforced plastic, despite the low sensitivity of non-contact laser ultrasonic sensing. A field-applicable pure laser UPI system has been developed using a laser Doppler vibrometer as the non-contact ultrasonic sensor. The proposed technique enables the visualization of the disbond defect in a 15 mm thick wind blade specimen made of glass-fiber-reinforced plastic, despite the high dissipation of ultrasound in the thick composite.
Real-time determination of laser beam quality by modal decomposition.
Schmidt, Oliver A; Schulze, Christian; Flamm, Daniel; Brüning, Robert; Kaiser, Thomas; Schröter, Siegmund; Duparré, Michael
2011-03-28
We present a real-time method to determine the beam propagation ratio M2 of laser beams. The all-optical measurement of modal amplitudes yields M2 parameters conform to the ISO standard method. The experimental technique is simple and fast, which allows to investigate laser beams under conditions inaccessible to other methods.
Scintillation reduction for combined Gaussian-vortex beam propagating through turbulent atmosphere
Berman, Gennady P; Gorshkov, V. N.; Torous, S. V.
2010-12-14
We numerically examine the spatial evolution of the structure of coherent and partially coherent laser beams (PCBs), including the optical vortices, propagating in turbulent atmospheres, The influence of beam fragmentation and wandering relative to the axis of propagation (z-axis) on the value of the scintillation index (SI) of the signal at the detector is analyzed. A method for significantly reducing the SI, by averaging the signal at the detector over a set of PCBs, is described, This novel method is to generate the PCBs by combining two laser beams - Gaussian and vortex beams, with different frequencies (the difference between these two frequencies being significantly smaller than the frequencies themselves). In this case, the SI is effectively suppressed without any high-frequency modulators.
Investigation of the accuracy of M2 measurement of CO2 laser beams
NASA Astrophysics Data System (ADS)
Ward, Brooke A.; Assa, Shlomo; Davis, Brian W.; Edwards, Christopher B.; Muys, Peter F.
1995-04-01
The propagation parameters of CO2 laser beams have been investigated using second moment and knife-edge width measurement techniques. The characteristics of two laser types have been measured: a low power stabilized single frequency instrument and a prototype 3 kW laser. The propagation parameters have been estimated by using two commercial beam analyzing instruments: a rotating drum knife-edge device and a 2D array scanner. The propagation of errors through the analysis procedures has been investigated. The experiments were designed to assess the viability of the draft ISO standard for the measurement of beam width and propagation characteristics of real laser beams. Uncertainties in the estimated beam parameters, resulting from the propagation of errors, are taken into account when assessing the relative merits of the width measurement procedures. It was found that, for the high quality laser beam investigated, there were some small but systematic variations in estimating the width of waists of subject laser beams. In the case of the lower quality, high power laser beam, both the knife-edge and second moment techniques produced estimates of the input beam waist properties that were within the experimental uncertainty limits but again some inconsistency was displayed. It is suggested that the source of the inconsistency is diffraction by hard-edge apertures in the beam path. Nevertheless, the ISO standard procedures are judged to be suitable for the measurement of important beam parameters with an accuracy that is sufficient for the majority of industrial applications.
Protective laser beam viewing device
Neil, George R.; Jordan, Kevin Carl
2012-12-18
A protective laser beam viewing system or device including a camera selectively sensitive to laser light wavelengths and a viewing screen receiving images from the laser sensitive camera. According to a preferred embodiment of the invention, the camera is worn on the head of the user or incorporated into a goggle-type viewing display so that it is always aimed at the area of viewing interest to the user and the viewing screen is incorporated into a video display worn as goggles over the eyes of the user.
Convolution approach for beam propagation in random media.
Wang, Fei; Korotkova, Olga
2016-04-01
A simple formula is derived for predicting transverse intensity distribution of coherent and partially coherent (Schell-model) scalar beams propagating in extended linear isotropic, homogeneous media with given power spectra of refractive index. The examples illustrate how the formula can be applied to different beams propagating in atmospheric and oceanic turbulence. Our result provides deep insight into the light-media interaction process and serves as a convenient analytical and/or numerical tool for analyzing beam propagation problems without performing lengthy evaluations.
Modeling of dynamic effects of a low power laser beam
NASA Technical Reports Server (NTRS)
Lawrence, George N.; Scholl, Marija S.; Khatib, AL
1988-01-01
Methods of modeling some of the dynamic effects involved in laser beam propagation through the atmosphere are addressed with emphasis on the development of simple but accurate models which are readily implemented in a physical optics code. A space relay system with a ground based laser facility is considered as an example. The modeling of such characteristic phenomena as laser output distribution, flat and curved mirrors, diffraction propagation, atmospheric effects (aberration and wind shear), adaptive mirrors, jitter, and time integration of power on target, is discussed.
Program Models A Laser Beam Focused In An Aerosol Spray
NASA Technical Reports Server (NTRS)
Barton, J. P.
1996-01-01
Monte Carlo analysis performed on packets of light. Program for Analysis of Laser Beam Focused Within Aerosol Spray (FLSPRY) developed for theoretical analysis of propagation of laser pulse optically focused within aerosol spray. Applied for example, to analyze laser ignition arrangement in which focused laser pulse used to ignite liquid aerosol fuel spray. Scattering and absorption of laser light by individual aerosol droplets evaluated by use of electromagnetic Lorenz-Mie theory. Written in FORTRAN 77 for both UNIX-based computers and DEC VAX-series computers. VAX version of program (LEW-16051). UNIX version (LEW-16065).
Unveiling the propagation dynamics of self-accelerating vector beams
Bar-David, Jonathan; Voloch-Bloch, Noa; Mazurski, Noa; Levy, Uriel
2016-01-01
We study theoretically and experimentally the varying polarization states and intensity patterns of self-accelerating vector beams. It is shown that as these beams propagate, the main intensity lobe and the polarization singularity gradually drift apart. Furthermore, the propagation dynamics can be manipulated by controlling the beams’ acceleration coefficients. We also demonstrate the self-healing dynamics of these accelerating vector beams for which sections of the vector beam are being blocked by an opaque or polarizing obstacle. Our results indicate that the self-healing process is almost insensitive for the obstacles’ polarization direction. Moreover, the spatial polarization structure also shows self- healing properties, and it is reconstructed as the beam propagates further beyond the perturbation plane. These results open various possibilities for generating, shaping and manipulating the intensity patterns and space variant polarization states of accelerating vector beams. PMID:27671745
Laser-Beam-Alignment Controller
NASA Technical Reports Server (NTRS)
Krasowski, M. J.; Dickens, D. E.
1995-01-01
In laser-beam-alignment controller, images from video camera compared to reference patterns by fuzzy-logic pattern comparator. Results processed by fuzzy-logic microcontroller, which sends control signals to motor driver adjusting lens and pinhole in spatial filter.
Electron beam pumped semiconductor laser
NASA Technical Reports Server (NTRS)
Hug, William F. (Inventor); Reid, Ray D. (Inventor)
2009-01-01
Electron-beam-pumped semiconductor ultra-violet optical sources (ESUVOSs) are disclosed that use ballistic electron pumped wide bandgap semiconductor materials. The sources may produce incoherent radiation and take the form of electron-beam-pumped light emitting triodes (ELETs). The sources may produce coherent radiation and take the form of electron-beam-pumped laser triodes (ELTs). The ELTs may take the form of electron-beam-pumped vertical cavity surface emitting lasers (EVCSEL) or edge emitting electron-beam-pumped lasers (EEELs). The semiconductor medium may take the form of an aluminum gallium nitride alloy that has a mole fraction of aluminum selected to give a desired emission wavelength, diamond, or diamond-like carbon (DLC). The sources may be produced from discrete components that are assembled after their individual formation or they may be produced using batch MEMS-type or semiconductor-type processing techniques to build them up in a whole or partial monolithic manner, or combination thereof.
Propagation of partially coherent pulsed beams in the spatiotemporal domain.
Wang, Li-gang; Lin, Qiang; Chen, Hong; Zhu, Shi-yao
2003-05-01
A generalized model to describe the spatiotemporal partially coherent pulsed beams is presented. The corresponding propagation formula is derived by using the partially coherent light theory. Based on this formula, we obtain a nonstationary generalized ABCD law (which illustrates the transformation of optical beams or pulses passing through media) to describe the spatiotemporal behavior of partially coherent Gaussian pulsed beams. The physical meaning of such generalized pulsed beams is discussed. An example to illustrate the application of this law is given. PMID:12786302
Propagation of electron and positron beams in long, dense plasmas
NASA Astrophysics Data System (ADS)
Muggli, Patric; Blue, Brent; Clayton, Chris; Decker, Franz-Joseph; Hogan, Mark; Hunag, Chengkun; Joshi, Chan; Katsouleas, Tom; Lu, Wei; Mori, Warren; O'Connell, Caollionn; Siemann, Robert; Walz, Dieter; Zhou, Miaomiao
2008-04-01
Electron beams with density larger than the plasma density can propagate through plasmas without significant emittance growth. The electron beam expels the plasma electrons from the bunch volume and propagate in a pure, uniform ion column. In contrast, positron beams attract plasma electrons that flow through the positron bunch. As a result the plasma focusing force is nonlinear, a charge halo forms around the bunch, and the bunch emittance grows. After some distance into the plasma, the bunch emittance reaches an approximately constant value, and the beam and the plasma focusing force reach a steady state. Experimental results obtained with electron and positron bunches, as well as numerical simulation results will be presented.
Symmetric neutralized ion beams: Production, acceleration, propagation, and applications
NASA Astrophysics Data System (ADS)
Hicks, Nathaniel Kenneth
This dissertation presents the first integrated experimental, computational, and theoretical research program on symmetric neutralized ion beams. A beam of this type is composed of positive and negative ions having equal charge-to-mass ratios, such that the beam has overall charge neutrality and its constituent ions respond symmetrically to electromagnetic forces. Under the right conditions, these beams may propagate undeflected across transverse magnetic fields due to beam polarization. Such propagation is studied here computationally, using a three-dimensional particle-in-cell code. Also, key theoretical differences between the propagation ability of these beams and that of beams consisting of positive ions and electrons are elucidated. An experimental method of producing a symmetric neutralized ion beam by merging together separate beams of positive and negative ions is demonstrated, and prototype collector hardware to diagnose the composition and energy distribution of the beam is developed. The ability of radio frequency quadrupole accelerators to simultaneously confine and accelerate the positive and negative ions of such a beam is demonstrated computationally and is confirmed experimentally, and a method to reestablish local charge neutrality in the beam after acceleration is conceived and simulated. The favorable scaling of such accelerators to small size and high frequency is illustrated. Finally, applications of the research to magnetic confinement fusion and topics for future study are presented.
Uncertainty Propagation for Terrestrial Mobile Laser Scanner
NASA Astrophysics Data System (ADS)
Mezian, c.; Vallet, Bruno; Soheilian, Bahman; Paparoditis, Nicolas
2016-06-01
Laser scanners are used more and more in mobile mapping systems. They provide 3D point clouds that are used for object reconstruction and registration of the system. For both of those applications, uncertainty analysis of 3D points is of great interest but rarely investigated in the literature. In this paper we present a complete pipeline that takes into account all the sources of uncertainties and allows to compute a covariance matrix per 3D point. The sources of uncertainties are laser scanner, calibration of the scanner in relation to the vehicle and direct georeferencing system. We suppose that all the uncertainties follow the Gaussian law. The variances of the laser scanner measurements (two angles and one distance) are usually evaluated by the constructors. This is also the case for integrated direct georeferencing devices. Residuals of the calibration process were used to estimate the covariance matrix of the 6D transformation between scanner laser and the vehicle system. Knowing the variances of all sources of uncertainties, we applied uncertainty propagation technique to compute the variance-covariance matrix of every obtained 3D point. Such an uncertainty analysis enables to estimate the impact of different laser scanners and georeferencing devices on the quality of obtained 3D points. The obtained uncertainty values were illustrated using error ellipsoids on different datasets.
Measurement system with high accuracy for laser beam quality.
Ke, Yi; Zeng, Ciling; Xie, Peiyuan; Jiang, Qingshan; Liang, Ke; Yang, Zhenyu; Zhao, Ming
2015-05-20
Presently, most of the laser beam quality measurement system collimates the optical path manually with low efficiency and low repeatability. To solve these problems, this paper proposed a new collimated method to improve the reliability and accuracy of the measurement results. The system accuracy controlled the position of the mirror to change laser beam propagation direction, which can realize the beam perpendicularly incident to the photosurface of camera. The experiment results show that the proposed system has good repeatability and the measuring deviation of M^{2} factor is less than 0.6%.
Measurement system with high accuracy for laser beam quality.
Ke, Yi; Zeng, Ciling; Xie, Peiyuan; Jiang, Qingshan; Liang, Ke; Yang, Zhenyu; Zhao, Ming
2015-05-20
Presently, most of the laser beam quality measurement system collimates the optical path manually with low efficiency and low repeatability. To solve these problems, this paper proposed a new collimated method to improve the reliability and accuracy of the measurement results. The system accuracy controlled the position of the mirror to change laser beam propagation direction, which can realize the beam perpendicularly incident to the photosurface of camera. The experiment results show that the proposed system has good repeatability and the measuring deviation of M^{2} factor is less than 0.6%. PMID:26192526
Beam profile measurement and evaluation of far field high energy laser
NASA Astrophysics Data System (ADS)
Yang, Pengling; Feng, Guobin; Wang, Zhenbao; Wang, Ping; Wu, Yong; Zhang, Jianmin; Cheng, Shaowu; Feng, Gang; Wang, Fei; Shao, Bibo
2015-05-01
The far field beam profile is of significant importance to the analysis of the atmospheric propagation effect and evaluation of the beam control capability, tracking and aiming precision of laser system. In the paper, technology of laser beam measurement such as mid-infrared laser detection at wide temperature range, power density attenuation, photoelectric and calorimetric compound method for laser measurement, synchronous detecting of multi-channel pulsed signal are introduced. A series of instrumented target with detector array are developed for laser beam power density distribution measurement at far field. The power in the bucket, strehl ratio, centroid and jitter of beam can be calculated from the measured results.
NASA Astrophysics Data System (ADS)
Rickenstorff, Carolina; Rodrigo, Jóse A.; Alieva, Tatiana
2016-04-01
Different applications such as astronomy, remote optical sensing and free space optical communications, among others, require both numerical and laboratory experimental simulations of beam propagation through turbulent atmosphere prior to an outdoor test. While rotating phase plates or hot chambers can be applied to such studies, they do not allow changing the atmospheric conditions and the propagation distance in situ. In contrast, the spatial light modulators (SLMs) are a flexible alternative for experimental turbulence simulation. In this work we consider an experimental setup comprising two SLMs for studying laser beam propagation in weak atmospheric turbulence. The changes of atmospheric conditions and propagation distances are properly achieved by the adjustment of the phase screens and the focal distances of digital lenses implemented in both SLMs. The proposed system can be completely automatized and all its elements are in fixed positions avoiding mechanical misalignment. Its design, propagation distance and atmospheric condition adjustment are provided. The setup performance is verified by numerical simulation of Gaussian beam propagation in the weak turbulence regime. The obtained parameters: scintillation index, beam wander and spreading are compared to their theoretical counterparts for different propagation distances and atmospheric conditions.
Propagation of a Gaussian beam in a nonhomogeneous plasma
Mazzucato, E.
1989-06-01
The asymptotic theory of Choudhary and Felsen on the propagation of scalar inhomogeneous waves in two-dimensional isotropic media is extended to the case of three-dimensional vector fields. The theory is applied to the propagation of Gaussian beams in nonhomogeneous media. The wave trajectory equations are then reformulated for anisotropic media and used for tracking a Gaussian beam in a tokamak plasma. 14 refs., 5 figs.
Electron-Beam Recombination Lasers
NASA Astrophysics Data System (ADS)
Rhoades, Robert Lewis
1992-01-01
The first known instance of electron-beam pumping of the 546.1 nm mercury laser is reported. This has been achieved using high-energy electrons to create intense ionization in a coaxial diode chamber containing a mixture of noble gases with a small amount of mercury vapor. Also reported are the results of a study of the 585.3 nm neon laser in He:Ne:Ar mixtures under similar experimental conditions. Both of these lasers are believed to be predominantly pumped by recombination. For the mercury laser, kinetic processes in the partially ionized plasma following the excitation pulse of high-energy electrons should favor the production of atomic mercury ions and molecular ions containing mercury. Subsequent recombination with electrons heavily favors the production of the 7^3S and 6^3 D states of Hg, of which 7^3S is the upper level of the reported laser. For the neon laser, the dominant recombining ion has been previously shown to be Ne_2^{+}. One of the dominant roles of helium in recombination lasers is inferred from the data for the neon laser at low helium concentrations. Helium appears to be necessary for the rapid relaxation of the electron energy which then increases the reaction rates for all known recombination processes thus increasing the pump rate into the upper state.
Enhanced propagation for relativistic laser pulses in inhomogeneous plasmas using hollow channels.
Fuchs, J; d'Humières, E; Sentoku, Y; Antici, P; Atzeni, S; Bandulet, H; Depierreux, S; Labaune, C; Schiavi, A
2010-11-26
The influence of long (several millimeters) and hollow channels, bored in inhomogeneous ionized plasma by using a long pulse laser beam, on the propagation of short, ultraintense laser pulses has been studied. Compared to the case without a channel, propagation in channels significantly improves beam transmission and maintains a beam quality close to propagation in vacuum. In addition, the growth of the forward-Raman instability is strongly reduced. These results are beneficial for the direct scheme of the fast ignitor concept of inertial confinement fusion as we demonstrate, in fast-ignition-relevant conditions, that with such channels laser energy can be carried through increasingly dense plasmas close to the fuel core with minimal losses.
Enhanced propagation for relativistic laser pulses in inhomogeneous plasmas using hollow channels.
Fuchs, J; d'Humières, E; Sentoku, Y; Antici, P; Atzeni, S; Bandulet, H; Depierreux, S; Labaune, C; Schiavi, A
2010-11-26
The influence of long (several millimeters) and hollow channels, bored in inhomogeneous ionized plasma by using a long pulse laser beam, on the propagation of short, ultraintense laser pulses has been studied. Compared to the case without a channel, propagation in channels significantly improves beam transmission and maintains a beam quality close to propagation in vacuum. In addition, the growth of the forward-Raman instability is strongly reduced. These results are beneficial for the direct scheme of the fast ignitor concept of inertial confinement fusion as we demonstrate, in fast-ignition-relevant conditions, that with such channels laser energy can be carried through increasingly dense plasmas close to the fuel core with minimal losses. PMID:21231391
Propagation characteristics of Bessel beams generated by continuous, incoherent light sources.
Altıngöz, Ceren; Yalızay, Berna; Akturk, Selcuk
2015-08-01
We investigate the propagation behavior of Bessel beams generated by incoherent, continuous light sources. We perform experiments with narrowband and broadband light emitting diodes, and, for comparison, with a laser diode. We observe that the formation of Bessel beams is affected minimally by temporal coherence, while spatial coherence determines the longitudinal evolution of the beam profile. With spatially incoherent beams, the fringe contrast is comparable to the coherent case at the beginning of the Bessel zone, while it completely fades away by propagation, turning into a cylindrical light pipe. Our results show that beam shaping methods can be extended to cases of limited spatial coherence, paving the way for potential new uses and applications of such sources.
Propagation characteristics of Bessel beams generated by continuous, incoherent light sources.
Altıngöz, Ceren; Yalızay, Berna; Akturk, Selcuk
2015-08-01
We investigate the propagation behavior of Bessel beams generated by incoherent, continuous light sources. We perform experiments with narrowband and broadband light emitting diodes, and, for comparison, with a laser diode. We observe that the formation of Bessel beams is affected minimally by temporal coherence, while spatial coherence determines the longitudinal evolution of the beam profile. With spatially incoherent beams, the fringe contrast is comparable to the coherent case at the beginning of the Bessel zone, while it completely fades away by propagation, turning into a cylindrical light pipe. Our results show that beam shaping methods can be extended to cases of limited spatial coherence, paving the way for potential new uses and applications of such sources. PMID:26367302
Bliss, E.S.; Peterson, R.L.; Salmon, J.T.; Thomas, R.A.
1992-11-01
The laser system described in the previous paper is used for experiments in which success requires tight tolerances on beam position, direction, and wavefront. Indeed, the optimum performance of the laser itself depends on careful delivery of copper laser light to the dye amplifiers, precise propagation of dye laser beams through restricted amplifier apertures, and accurate monitoring of laser power at key locations. This paper describes the alignment systems, wavefront correction systems, and laser diagnostics systems which ensure that the control requirements of both the laser and associated experiments are met. Because laser isotope separation processes utilize more than one wavelength, these systems monitor and control multiple wavelengths simultaneously.
Ponderomotive self-focusing of Gaussian laser beam in warm collisional plasma
Jafari Milani, M. R.; Niknam, A. R.; Farahbod, A. H.
2014-06-15
The propagation characteristics of a Gaussian laser beam through warm collisional plasma are investigated by considering the ponderomotive force nonlinearity and the complex eikonal function. By introducing the dielectric permittivity of warm unmagnetized plasma and using the WKB and paraxial ray approximations, the coupled differential equations defining the variations of laser beam parameters are obtained and solved numerically. Effects of laser and plasma parameters such as the collision frequency, the initial laser intensity and its spot size on the beam width parameter and the axis laser intensity distribution are analyzed. It is shown that, self-focusing of the laser beam takes place faster by increasing the collision frequency and initial laser spot size and then after some distance propagation the laser beam abruptly loses its initial diameter and vastly diverges. Furthermore, the modified electron density distribution is obtained and the collision frequency effect on this distribution is studied.
Turbulence-induced persistence in laser beam wandering.
Zunino, Luciano; Gulich, Damián; Funes, Gustavo; Pérez, Darío G
2015-07-01
We have experimentally confirmed the presence of long-memory correlations in the wandering of a thin Gaussian laser beam over a screen after propagating through a turbulent medium. A laboratory-controlled experiment was conducted in which coordinate fluctuations of the laser beam were recorded at a sufficiently high sampling rate for a wide range of turbulent conditions. Horizontal and vertical displacements of the laser beam centroid were subsequently analyzed by implementing detrended fluctuation analysis. This is a very well-known and widely used methodology to unveil memory effects from time series. Results obtained from this experimental analysis allow us to confirm that both coordinates behave as highly persistent signals for strong turbulent intensities. This finding is relevant for a better comprehension and modeling of the turbulence effects in free-space optical communication systems and other applications related to propagation of optical signals in the atmosphere.
Turbulence-induced persistence in laser beam wandering.
Zunino, Luciano; Gulich, Damián; Funes, Gustavo; Pérez, Darío G
2015-07-01
We have experimentally confirmed the presence of long-memory correlations in the wandering of a thin Gaussian laser beam over a screen after propagating through a turbulent medium. A laboratory-controlled experiment was conducted in which coordinate fluctuations of the laser beam were recorded at a sufficiently high sampling rate for a wide range of turbulent conditions. Horizontal and vertical displacements of the laser beam centroid were subsequently analyzed by implementing detrended fluctuation analysis. This is a very well-known and widely used methodology to unveil memory effects from time series. Results obtained from this experimental analysis allow us to confirm that both coordinates behave as highly persistent signals for strong turbulent intensities. This finding is relevant for a better comprehension and modeling of the turbulence effects in free-space optical communication systems and other applications related to propagation of optical signals in the atmosphere. PMID:26125388
Laser cutting silicon-glass double layer wafer with laser induced thermal-crack propagation
NASA Astrophysics Data System (ADS)
Cai, Yecheng; Yang, Lijun; Zhang, Hongzhi; Wang, Yang
2016-07-01
This study was aimed at introducing the laser induced thermal-crack propagation (LITP) technology to solve the silicon-glass double layer wafer dicing problems in the packaging procedure of silicon-glass device packaged by WLCSP technology, investigating the feasibility of this idea, and studying the crack propagation process of LITP cutting double layer wafer. In this paper, the physical process of the 1064 nm laser beam interact with the double layer wafer during the cutting process was studied theoretically. A mathematical model consists the volumetric heating source and the surface heating source has been established. The temperature and stress distribution was simulated by using finite element method (FEM) analysis software ABAQUS. The extended finite element method (XFEM) was added to the simulation as the supplementary features to simulate the crack propagation process and the crack propagation profile. The silicon-glass double layer wafer cutting verification experiment under typical parameters was conducted by using the 1064 nm semiconductor laser. The crack propagation profile on the fracture surface was examined by optical microscope and explained from the stress distribution and XFEM status. It was concluded that the quality of the finished fracture surface has been greatly improved, and the experiment results were well supported by the numerical simulation results.
Unified formalism for TE and TM beam propagators
NASA Astrophysics Data System (ADS)
Poladian, Leon; Ladouceur, Francois J.
1998-07-01
The unification of transverse electric (TE) and transverse magnetic (TM) beam propagation algorithms is made possible through a transformation which converts the wave equation for TM fields in planar waveguides into a form identical to the corresponding TE wave equation. The transformation can be applied to any smoothly varying waveguide. This transformation can be made independently of any paraxial or other approximations. Thus, any TE propagation algorithm can also be applied immediately to TM fields without additional approximations. This includes the classical fast Fourier transform beam propagator, which has not previously been applied successfully to TM propagation. We also specifically develop a Finite Difference Beam Propagation Method that applies to both TE and TM propagation in 1D (planar) geometry. Previous implementations for the TM case involve an approximation that in certain circumstances leads to severe errors (including the totally unphysical occurrence of field amplification). This is the first TM propagator which exactly conserves power. We also investigate the role of the reference background wavenumber (or index) and clarify its role as it is dynamically adapted. The algorithms proposed are easily adaptable to wide-angle beam propagators and to modern transparent boundary conditions. The extension of these ideas to rapidly varying structures (such as Bragg gratings) is also briefly discussed.
Shock wave and material vapour plume propagation during excimer laser ablation of aluminium samples
NASA Astrophysics Data System (ADS)
Jeong, S. H.; Greif, R.; Russo, R. E.
1999-10-01
A probe beam deflection technique was utilized to measure the propagation of a shock wave and material vapour plume generated during excimer laser ablation of aluminium samples. The measured transit time of the laser-induced shock wave was compared with the prediction based on an ideal blast-wave model, using the Sedov-Taylor solution. The prediction of the incident laser energy converted into the laser-induced gasdynamic flow utilizing this blast-wave model overestimated the efficiency, even under conditions when the measured shock-wave velocity follows the correct model relation. The propagation of material vapour was measured from the deflection of the probe beam at later times. The propagation velocity of material vapour ranged from 20-40 m s-1 with a greater velocity near the target surface.
Propagation of an Airy beam through the atmosphere.
Ji, Xiaoling; Eyyuboğlu, Halil T; Ji, Guangming; Jia, Xinhong
2013-01-28
In this paper, the effect of thermal blooming of an Airy beam propagating through the atmosphere is examined, and the effect of atmospheric turbulence is not considered. The changes of the intensity distribution, the centroid position and the mean-squared beam width of an Airy beam propagating through the atmosphere are studied by using the four-dimensional (4D) computer code of the time-dependent propagation of Airy beams through the atmosphere. It is shown that an Airy beam can't retain its shape and the structure when the Airy beam propagates through the atmosphere due to thermal blooming except for the short propagation distance, or the short time, or the low beam power. The thermal blooming results in a central dip of the center lobe, and causes the center lobe to spread and decrease. In contrast with the center lobe, the side lobes are less affected by thermal blooming, such that the intensity maximum of the side lobe may be larger than that of the center lobe. However, the cross wind can reduce the effect of thermal blooming. When there exists the cross wind velocity vx in x direction, the dependence of centroid position in x direction on vx is not monotonic, and there exists a minimum, but the centroid position in y direction is nearly independent of vx.
Optimization of Gaussian beam widths in acoustic propagation
NASA Astrophysics Data System (ADS)
Gordon, D. F.
1989-10-01
The use of Gaussian beams to compute wave propagation phenomena is a field of current interest and activity. Porter and Bucker (1987) supply an extensive list of references. More recent references can be found in Benites and Aki (1989). Gaussian beams can be traced as rays in range-dependent media providing not only propagation loss, but travel times, multipath structure, and frequency dependence. The well-known ray theory problems of caustics and shadow zones are treated automatically. A beam width minimization technique applied to a Gaussian beam model developed by Dr. H. P. Bucker, is outlined. Porter and Bucker (1987) gives the formulation upon which the techniques is built. A free parameter E is usually determined in a heuristic manner. Here, it is shown that the minimization of beam width assigns a precise value to E. Examples are given showing that the minimized beams give good propagation losses in some cases. A case also shown in the standard Gaussian beams give poor results and the minimized beams give even worse results. The problem appears to arise in beams that pass near boundaries. This problem will have to be corrected before a final judgment can be made on the validity of minimum-width beams.
Intense electron beam propagation across a magnetic field
Zhang, X.; Striffler, C.D.; Yao, R.L.; Destler, W.W.; Reiser, M.P.
1989-01-01
In this paper we consider the propagation of an intense electron-ion beam across an applied magnetic field. In the absence of the applied field, the beam system is in a Bennett equilibrium state that involves electrons with both large axial and thermal velocities and a cold stationary space-charge neutralizing ion species. Typical parameters under consideration are V{sub o} {approximately} 1 MV, I {approximately} 5 kA, T{sub e} {approximately} 100 keV, and beam radii {approximately} 1 cm. We find that in the intense beam regime, the propagation is limited due to space-charge depression caused by the deflection of the electron beam by the transverse field. This critical field is of the order of the peak self-magnetic field of the electron beam which is substantially higher than the single particle cut-off field. 8 refs., 3 figs.
Laser beam complex amplitude measurement by phase diversity.
Védrenne, Nicolas; Mugnier, Laurent M; Michau, Vincent; Velluet, Marie-Thérèse; Bierent, Rudolph
2014-02-24
The control of the optical quality of a laser beam requires a complex amplitude measurement able to deal with strong modulus variations and potentially highly perturbed wavefronts. The method proposed here consists in an extension of phase diversity to complex amplitude measurements that is effective for highly perturbed beams. Named camelot for Complex Amplitude MEasurement by a Likelihood Optimization Tool, it relies on the acquisition and processing of few images of the beam section taken along the optical path. The complex amplitude of the beam is retrieved from the images by the minimization of a Maximum a Posteriori error metric between the images and a model of the beam propagation. The analytical formalism of the method and its experimental validation are presented. The modulus of the beam is compared to a measurement of the beam profile, the phase of the beam is compared to a conventional phase diversity estimate. The precision of the experimental measurements is investigated by numerical simulations.
Propagation of Airy Gaussian vortex beams in uniaxial crystals
NASA Astrophysics Data System (ADS)
Weihao, Yu; Ruihuang, Zhao; Fu, Deng; Jiayao, Huang; Chidao, Chen; Xiangbo, Yang; Yanping, Zhao; Dongmei, Deng
2016-04-01
The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374108, 11374107, 10904041, and 11547212), the Foundation of Cultivating Outstanding Young Scholars of Guangdong Province, China, the CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, the National Training Program of Innovation and Entrepreneurship for Undergraduates (Grant No. 2015093), and the Science and Technology Projects of Guangdong Province, China (Grant No. 2013B031800011).
Propagation of Airy Gaussian vortex beams in uniaxial crystals
NASA Astrophysics Data System (ADS)
Weihao, Yu; Ruihuang, Zhao; Fu, Deng; Jiayao, Huang; Chidao, Chen; Xiangbo, Yang; Yanping, Zhao; Dongmei, Deng
2016-04-01
The propagation dynamics of the Airy Gaussian vortex beams in uniaxial crystals orthogonal to the optical axis has been investigated analytically and numerically. The propagation expression of the beams has been obtained. The propagation features of the Airy Gaussian vortex beams are shown with changes of the distribution factor and the ratio of the extraordinary refractive index to the ordinary refractive index. The correlations between the ratio and the maximum intensity value during the propagation, and its appearing distance have been investigated. Project supported by the National Natural Science Foundation of China (Grant Nos. 11374108, 11374107, 10904041, and 11547212), the Foundation of Cultivating Outstanding Young Scholars of Guangdong Province, China, the CAS Key Laboratory of Geospace Environment, University of Science and Technology of China, the National Training Program of Innovation and Entrepreneurship for Undergraduates (Grant No. 2015093), and the Science and Technology Projects of Guangdong Province, China (Grant No. 2013B031800011).
Pulsed electron beam propagation in argon and nitrogen gas mixture
NASA Astrophysics Data System (ADS)
Kholodnaya, G. E.; Sazonov, R. V.; Ponomarev, D. V.; Remnev, G. E.; Zhirkov, I. S.
2015-10-01
The paper presents the results of current measurements for the electron beam, propagating inside a drift tube filled in with a gas mixture (Ar and N2). The experiments were performed using the TEA-500 pulsed electron accelerator. The main characteristics of electron beam were as follows: 60 ns pulse duration, up to 200 J energy, and 5 cm diameter. The electron beam propagated inside the drift tube assembled of three sections. Gas pressures inside the drift tube were 760 ± 3, 300 ± 3, and 50 ± 1 Torr. The studies were performed in argon, nitrogen, and their mixtures of 33%, 50%, and 66% volume concentrations, respectively.
LASER PROFILE MEASUREMENTS OF AN H BEAM.
CONNOLLY,R.; CAMERON,P.; CUPOLO,J.; GRAU,M.; KESSELMAN,M.; LIAW,C.J.; SIKORA,R.
2001-06-18
A non-intercepting beam profile monitor for He beams is being developed at Brookhaven National Lab. An H{sup {minus}} ion has a first ionization potential of 0.75eV. Electrons can be removed from an H{sup {minus}} beam by passing light from a near-infrared laser through it. Experiments have been performed on the BNL linac to measure the transverse profile of a 750keV beam by using a Nd:YAG laser to photoneutralize narrow slices of the beam. The laser beam is scanned across the ion beam neutralizing the portion of the beam struck by the laser. The electrons are removed from the ion beam and the beam current notch is measured.
Scattering apodizer for laser beams
Summers, M.A.; Hagen, W.F.; Boyd, R.D.
1984-01-01
A method is disclosed for apodizing a laser beam to smooth out the production of diffraction peaks due to optical discontinuities in the path of the laser beam, such method comprising introduction of a pattern of scattering elements for reducing the peak intensity in the region of such optical discontinuities, such pattern having smoothly tapering boundaries in which the distribution density of the scattering elements is tapered gradually to produce small gradients in the distribution density, such pattern of scattering elements being effective to reduce and smooth out the diffraction effects which would otherwise be produced. The apodizer pattern may be produced by selectively blasting a surface of a transparent member with fine abrasive particles to produce a multitude of minute pits. In one embodiment, a scattering apodizer pattern is employed to overcome diffraction patterns in a multiple element crystal array for harmonic conversion of a laser beam. The interstices and the supporting grid between the crystal elements are obscured by the gradually tapered apodizer pattern of scattering elements.
Scattering apodizer for laser beams
Summers, Mark A.; Hagen, Wilhelm F.; Boyd, Robert D.
1985-01-01
A method is disclosed for apodizing a laser beam to smooth out the production of diffraction peaks due to optical discontinuities in the path of the laser beam, such method comprising introduction of a pattern of scattering elements for reducing the peak intensity in the region of such optical discontinuities, such pattern having smoothly tapering boundaries in which the distribution density of the scattering elements is tapered gradually to produce small gradients in the distribution density, such pattern of scattering elements being effective to reduce and smooth out the diffraction effects which would otherwise be produced. The apodizer pattern may be produced by selectively blasting a surface of a transparent member with fine abrasive particles to produce a multitude of minute pits. In one embodiment, a scattering apodizer pattern is employed to overcome diffraction patterns in a multiple element crystal array for harmonic conversion of a laser beam. The interstices and the supporting grid between the crystal elements are obscured by the gradually tapered apodizer pattern of scattering elements.
Optodynamics: dynamic aspects of laser beam-surface interaction
NASA Astrophysics Data System (ADS)
Možina, J.; Diaci, J.
2012-05-01
This paper presents a synthesis of the results of our original research in the area of laser-material interaction and pulsed laser material processing with a special emphasis on the dynamic aspects of laser beam-surface interaction, which include the links between the laser material removal and the resulting material motion. In view of laser material processing, a laser beam is not only considered as a tool but also as a generator of information about the material transformation. The information is retained and conveyed by different kinds of optically induced mechanical waves. Several generation/detection schemes have been developed to extract this information, especially in the field of non-destructive material evaluation. Blast and acoustic waves, which propagate in the air surrounding the work-piece, have been studied using microphone detection as well as various setups of the laser beam deflection probe. Stress waves propagating through the work-piece have been studied using piezoelectric transducers and laser interferometers.
Influence of laser array performance on spectrally combined beam
NASA Astrophysics Data System (ADS)
Wu, Zhen; Yang, Lei; Zhong, Zheqiang; Zhang, Bin
2016-10-01
Incoherent spectral beam combining (SBC) of multiple laser beams is accomplished along the emitters' arraying direction. Considering that the output beams from a laser array (LA) usually have deflection angles, positional displacements and divergence angles even after being collimated, a propagation model of SBC systems based on multilayer dielectric gratings has been built up. On the basis, properties of the spectrally combined beam affected by parameters of the LA have been discussed in detail. Simulation results show that with the increase in the deflection angle, both the power and the beam quality of the combined beam degrade dramatically. The positional displacement has little impact on the intensity distribution and the beam quality of combined beam but change the wavelength composition of the combined beam. The divergence angle strongly affects the intensity distribution and the beam quality of the combined beam. Additionally, the effect of the deflection angle on the output beam quality is more obvious and may shift the beam spot when comparing with that of the divergence angle.
High-current fast electron beam propagation in a dielectric target
Klimo, Ondrej; Tikhonchuk, V. T.; Debayle, A.
2007-01-15
Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10{sup 12} A cm{sup -2}. The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.
High-current fast electron beam propagation in a dielectric target.
Klimo, Ondrej; Tikhonchuk, V T; Debayle, A
2007-01-01
Recent experiments demonstrate an efficient transformation of high intensity laser pulse into a relativistic electron beam with a very high current density exceeding 10(12) A cm(-2). The propagation of such a beam inside the target is possible if its current is neutralized. This phenomenon is not well understood, especially in dielectric targets. In this paper, we study the propagation of high current density electron beam in a plastic target using a particle-in-cell simulation code. The code includes both ionization of the plastic and collisions of newborn electrons. The numerical results are compared with a relatively simple analytical model and a reasonable agreement is found. The temporal evolution of the beam velocity distribution, the spatial density profile, and the propagation velocity of the ionization front are analyzed and their dependencies on the beam density and energy are discussed. The beam energy losses are mainly due to the target ionization induced by the self-generated electric field and the return current. For the highest beam density, a two-stream instability is observed to develop in the plasma behind the ionization front and it contributes to the beam energy losses.
Cascaded injection resonator for coherent beam combining of laser arrays
Kireev, Vassili [Sunnyvale, CA; Liu, Yun; Protopopescu, Vladimir [Knoxville, TN; Braiman, Yehuda [Oak Ridge, TN
2008-10-21
The invention provides a cascaded injection resonator for coherent beam combining of laser arrays. The resonator comprises a plurality of laser emitters arranged along at least one plane and a beam sampler for reflecting at least a portion of each laser beam that impinges on the beam sampler, the portion of each laser beam from one of the laser emitters being reflected back to another one of the laser emitters to cause a beam to be generated from the other one of the laser emitters to the beam reflector. The beam sampler also transmits a portion of each laser beam to produce a laser output beam such that a plurality of laser output beams of the same frequency are produced. An injection laser beam is directed to a first laser emitter to begin a process of generating and reflecting a laser beam from one laser emitter to another laser emitter in the plurality. A method of practicing the invention is also disclosed.
Raman beam combining for laser brightness enhancement
Dawson, Jay W.; Allen, Graham S.; Pax, Paul H.; Heebner, John E.; Sridharan, Arun K.; Rubenchik, Alexander M.; Barty, Chrisopher B. J.
2015-10-27
An optical source capable of enhanced scaling of pulse energy and brightness utilizes an ensemble of single-aperture fiber lasers as pump sources, with each such fiber laser operating at acceptable pulse energy levels. Beam combining involves stimulated Raman scattering using a Stokes' shifted seed beam, the latter of which is optimized in terms of its temporal and spectral properties. Beams from fiber lasers can thus be combined to attain pulses with peak energies in excess of the fiber laser self-focusing limit of 4 MW while retaining the advantages of a fiber laser system of high average power with good beam quality.
Adaptive laser link reconfiguration using constraint propagation
NASA Technical Reports Server (NTRS)
Crone, M. S.; Julich, P. M.; Cook, L. M.
1993-01-01
This paper describes Harris AI research performed on the Adaptive Link Reconfiguration (ALR) study for Rome Lab, and focuses on the application of constraint propagation to the problem of link reconfiguration for the proposed space based Strategic Defense System (SDS) Brilliant Pebbles (BP) communications system. According to the concept of operations at the time of the study, laser communications will exist between BP's and to ground entry points. Long-term links typical of RF transmission will not exist. This study addressed an initial implementation of BP's based on the Global Protection Against Limited Strikes (GPALS) SDI mission. The number of satellites and rings studied was representative of this problem. An orbital dynamics program was used to generate line-of-site data for the modeled architecture. This was input into a discrete event simulation implemented in the Harris developed COnstraint Propagation Expert System (COPES) Shell, developed initially on the Rome Lab BM/C3 study. Using a model of the network and several heuristics, the COPES shell was used to develop the Heuristic Adaptive Link Ordering (HALO) Algorithm to rank and order potential laser links according to probability of communication. A reduced set of links based on this ranking would then be used by a routing algorithm to select the next hop. This paper includes an overview of Constraint Propagation as an Artificial Intelligence technique and its embodiment in the COPES shell. It describes the design and implementation of both the simulation of the GPALS BP network and the HALO algorithm in COPES. This is described using a 59 Data Flow Diagram, State Transition Diagrams, and Structured English PDL. It describes a laser communications model and the heuristics involved in rank-ordering the potential communication links. The generation of simulation data is described along with its interface via COPES to the Harris developed View Net graphical tool for visual analysis of communications
High-power, high-intensity laser propagation and interactions
Sprangle, Phillip; Hafizi, Bahman
2014-05-15
This paper presents overviews of a number of processes and applications associated with high-power, high-intensity lasers, and their interactions. These processes and applications include: free electron lasers, backward Raman amplification, atmospheric propagation of laser pulses, laser driven acceleration, atmospheric lasing, and remote detection of radioactivity. The interrelated physical mechanisms in the various processes are discussed.
Chu, Shu-Chun; Yang, Chao-Shun; Otsuka, Kenju
2008-11-24
This paper proposes a new scheme for generating vortex laser beams from a laser. The proposed system consists of a Dove prism embedded in an unbalanced Mach-Zehnder interferometer configuration. This configuration allows controlled construction of p x p vortex array beams from Ince-Gaussian modes, IG(e) (p,p) modes. An incident IG(e)(p,p) laser beam of variety order p can easily be generated from an end-pumped solid-state laser system with an off-axis pumping mechanism. This study simulates this type of vortex array laser beam generation, analytically derives the vortex positions of the resulting vortex array laser beams, and discusses beam propagation effects. The resulting vortex array laser beam can be applied to optical tweezers and atom traps in the form of two-dimensional arrays, or used to study the transfer of angular momentum to micro particles or atoms (Bose-Einstein condensate).
Propagation of flat-topped multi-Gaussian beams through a double-lens system with apertures.
Gao, Yanqi; Zhu, Baoqiang; Liu, Daizhong; Lin, Zunqi
2009-07-20
A general model for different apertures and flat-topped laser beams based on the multi-Gaussian function is developed. The general analytical expression for the propagation of a flat-topped beam through a general double-lens system with apertures is derived using the above model. Then, the propagation characteristics of the flat-topped beam through a spatial filter are investigated by using a simplified analytical expression. Based on the Fluence beam contrast and the Fill factor, the influences of a pinhole size on the propagation of the flat-topped multi-Gaussian beam (FMGB) through the spatial filter are illustrated. An analytical expression for the propagation of the FMGB through the spatial filter with a misaligned pinhole is presented, and the influences of the pinhole offset are evaluated.
Self-focusing and defocusing of Gaussian laser beams in plasmas with linear temperature ramp
Zhou Zhongxiang; Wang Ying; Yuan Chengxun; Du Yanwei
2011-07-15
The propagation characteristics of the Gaussian laser beam in plasmas in the presence of a linear electron temperature ramp have been investigated by taking the electron temperature as an individual variable. The ponderomotive force and collision have been considered as the mechanisms of nonlinearity. The second order differential equation of the dimensionless beam-width parameter has been acquired and solved with several initial electron temperatures and plus-minus temperature ramp parameters. The propagation regimes of laser beam are found to be sensitive with the selection of electron temperature. The linear temperature ramp breaks the stationary propagating mode and enhances the self-focusing or defocusing propagation properties. Results indicate the feasibility of extended propagation of focused laser beam in plasmas by modifying the electron temperature.
Long distance laser ultrasonic propagation imaging system for damage visualization
NASA Astrophysics Data System (ADS)
Lee, Jung-Ryul; Shin, He-Jin; Chia, Chen Ciang; Dhital, Dipesh; Yoon, Dong-Jin; Huh, Yong-Hak
2011-12-01
Wind turbine blade failure is the most prominent and common type of damage occurring in operating wind turbine systems. Conventional nondestructive testing systems are not available for in situ wind turbine blades. We propose a portable long distance ultrasonic propagation imaging (LUPI) system that uses a laser beam targeting and scanning system to excite, from a long distance, acoustic emission sensors installed in the blade. An examination of the beam collimation effect using geometric parameters of a commercial 2 MW wind turbine provided Lamb wave amplitude increases of 41.5 and 23.1 dB at a distance of 40 m for symmetrical and asymmetrical modes, respectively, in a 2 mm-thick stainless steel plate. With this improvement in signal-to-noise ratio, a feasibility study of damage detection was conducted with a 5 mm-thick composite leading edge specimen. To develop a reliable damage evaluation system, the excitation/sensing technology and the associated damage visualization algorithm are equally important. Hence, our results provide a new platform based on anomalous wave propagation imaging (AWPI) methods with adjacent wave subtraction, reference wave subtraction, reference image subtraction, and the variable time window amplitude mapping method. The advantages and disadvantages of AWPI algorithms are reported in terms of reference data requirements, signal-to-noise ratios, and damage evaluation accuracy. The compactness and portability of the proposed UPI system are also important for in-field applications at wind farms.
NASA Astrophysics Data System (ADS)
Malekshahi, Moslem; Dorranian, Davoud; Askari, Hassan Ranjbar
2014-12-01
In this paper, evolution of the spot size of the ultra short intense laser beam propagating in underdense magnetized cold plasma, taking into account the nonlinearity up to third order and the relativistic effect, has been studied. The plasma embedded in a constant external magnetic field that is set in the plane perpendicular to the electric field vector of the laser beam with different directions. The paraxial wave equation in plasma has been used and the source dependent expansion (SDE) method is employed to solve the equation. Using continuity equation and equation of motion for plasma electrons in the electric field of laser beam a set of equations for the evolution of laser beam structure in plasma is found. Results show that imposing the external magnetic field enhances self-focusing property of the laser beam. Taking into account the relativistic effect increases the effect of the external magnetic field on self-focusing of the laser beam. Increasing the angle between the laser beam magnetic field and external magnetic field will decrease the self-focusing property.
Separating Isotopes With Laser And Electron Beams
NASA Technical Reports Server (NTRS)
Trajmar, Sandor
1989-01-01
Need for second laser eliminated. In scheme for separation of isotopes, electrons of suitable kinetic energy ionize specific isotope excited by laser beam in magnetic field. Ionization by electron beams cheap and efficient in comparison to ionization by laser beams, and requires no special technical developments. Feasibility of new scheme demonstrated in selective ionization of Ba138, making possible separation of isotope from Ba isotopes of atomic weight 130, 132, 134, 135, 136, and 137.
Method for splitting low power laser beams
Pierscionek, B.K. )
1990-04-01
A new method for producing parallel rays from a laser beam using a cylindrical lens and pinholes is presented. This method can produce a greater number of emergent rays than using a {ital beam} {ital splitter}.
Diplexer for laser-beam heterodyne receiver
NASA Technical Reports Server (NTRS)
Koepf, G.
1981-01-01
Four prism interferometer superposes local oscillator beam on signal beam. Position of movable prism directs incident energy in both beams out one output port. Output port is spatially separated from input ports, and there is no limitation on size of frequency difference between laser beams.
Nonlinear effects in propagation of radiation of X-ray free-electron lasers
NASA Astrophysics Data System (ADS)
Nosik, V. L.
2016-05-01
Nonlinear effects accompanying the propagation of high-intensity beams of X-ray free-electron lasers are considered. It is shown that the X-ray wave field in the crystal significantly changes due to the formation of "hollow" atomic shells as a result of the photoelectric effect.
NASA Astrophysics Data System (ADS)
Xu, Yonggen; Li, Yude; Dan, Youquan; Du, Quan; Wang, Shijian
2016-07-01
The Wigner distribution function (WDF) has been used to study the propagation properties of partially coherent Laguerre Gaussian (PCLG) beams through atmospheric turbulence. Based on the extended Huygens-Fresnel principle, an analytical formula of the propagation matrixes in terms of the second-order moments of the WDF for PCLG Beams in the receiving plane is derived. And then the analytical formulae for the curvature radii of PCLG Beams propagating in turbulence are given by the second-order moments of the WDF. The numerical results indicate that the curvature radius of PCLG Beams changes more rapidly in turbulence than that in the free space. The influence of the transverse coherence width and the beam waist width on the curvature radius of PCLG Beams is obvious, while the laser wavelength and the inner scale of turbulence have a slight effect. The study results may be useful for remote sensing and free space optical communications.
NASA Astrophysics Data System (ADS)
Xu, Yonggen; Li, Yude; Dan, Youquan; Du, Quan; Wang, Shijian
2016-07-01
The Wigner distribution function (WDF) has been used to study the propagation properties of partially coherent Laguerre Gaussian (PCLG) beams through atmospheric turbulence. Based on the extended Huygens-Fresnel principle, an analytical formula of the propagation matrixes in terms of the second-order moments of the WDF for PCLG Beams in the receiving plane is derived. And then the analytical formulae for the curvature radii of PCLG Beams propagating in turbulence are given by the second-order moments of the WDF. The numerical results indicate that the curvature radius of PCLG Beams changes more rapidly in turbulence than that in the free space. The influence of the transverse coherence width and the beam waist width on the curvature radius of PCLG Beams is obvious, while the laser wavelength and the inner scale of turbulence have a slight effect. The study results may be useful for remote sensing and free space optical communications.
Impact of Atmospheric Turbulence on Beam Propagation
Strasburg, Jana D.; Harper, Warren W.; William E Thompson & Richard L Brunson
2004-09-08
A trailer-based sensor system has been developed for remote chemical sensing applications. The detection scheme utilizes quantum cascade lasers operating in the long-wave infrared. It has been determined that atmospheric turbulence is the dominating noise source for this system. For this application, horizontal path lengths vary from several hundred meters to several kilometers resulting in weak to moderate to strong turbulence conditions.
NASA Technical Reports Server (NTRS)
Wu, Janet P.
2003-01-01
Furthering pursuits in high bandwidth communications to future NASA deep space and neat-Earth probes, the Jet Propulsion Laboratory (JPL) is building the Optical communications Telescope Laboratory (OCTL) atop Table Mountain in Southern California. This R&D optical antenna will be used to develop optical communication strategies for future optical ground stations. Initial experiments to be conducted include propagating high-powered, Q-switched laser beams to retro-reflecting satellites. Yet laser beam propagation from the ground to space is under the cognizance of various government agencies, namely: the Occupational Safety and Health Administration (ISHA) that is responsible for protecting workforce personnel; the Federal Aviation Administration (FAA) responsible for protecting pilots and aircraft; and the Laser Clearinghouse of Space Command responsible for protecting space assets. To ensure that laser beam propagation from the OCTL and future autonomously operated ground stations comply with the guidelines of these organizations, JPL is developing a multi-tiered safety system that will meet the coordination, monitoring, and reporting functions required by the agencies. At Tier 0, laser operators will meet OSHA safety standards for protection and access to the high power lasers area will be restricted and interlocked. Tier 1, the area defined from the telescope dome out to a range of 3.4-km, will utilize long wave infrared camera sensors to alert operators of at risk aircraft in the FAA controlled airspace. Tier 2, defined to extend from 3.4-km out to the aircraft service ceiling in FAA airspace, will detect at risk aircraft by radar. Lastly, beam propagation into space, defined as Tier 3, will require coordination with the Laser Clearinghouse. A detailed description of the four tiers is presented along with the design of the integrated monitoring and beam transmission control system.
Wang, Fei; Toselli, Italo; Korotkova, Olga
2016-02-10
An optical system consisting of a laser source and two independent consecutive phase-only spatial light modulators (SLMs) is shown to accurately simulate a generated random beam (first SLM) after interaction with a stationary random medium (second SLM). To illustrate the range of possibilities, a recently introduced class of random optical frames is examined on propagation in free space and several weak turbulent channels with Kolmogorov and non-Kolmogorov statistics.
Wang, Fei; Toselli, Italo; Korotkova, Olga
2016-02-10
An optical system consisting of a laser source and two independent consecutive phase-only spatial light modulators (SLMs) is shown to accurately simulate a generated random beam (first SLM) after interaction with a stationary random medium (second SLM). To illustrate the range of possibilities, a recently introduced class of random optical frames is examined on propagation in free space and several weak turbulent channels with Kolmogorov and non-Kolmogorov statistics. PMID:26906385
Accuracy of laser beam center and width calculations.
Mana, G; Massa, E; Rovera, A
2001-03-20
The application of lasers in high-precision measurements and the demand for accuracy make the plane-wave model of laser beams unsatisfactory. Measurements of the variance of the transverse components of the photon impulse are essential for wavelength determination. Accuracy evaluation of the relevant calculations is thus an integral part of the assessment of the wavelength of stabilized-laser radiation. We present a propagation-of-error analysis on variance calculations when digitized intensity profiles are obtained by means of silicon video cameras. Image clipping criteria are obtained that maximize the accuracy of the computed result.
Analysis of the fluctuations of a laser beam due to thermal turbulence
NASA Astrophysics Data System (ADS)
Ndlovu, Sphumelele C.; Chetty, Naven
2014-07-01
A laser beam propagating in air and passing through a point diffraction interferometer (PDI) produces stable interferograms that can be used to extract wavefront data such as major atmospheric characteristics: turbulence strength, inner scale and outer scale of the refractive index. These parameters need to be taken into consideration when developing defense laser weapons since they can be affected by thermal fluctuations that are due to the changes in temperature in close proximity to the propagating beam and results in phase shifts that can be used to calculate the temperature which causes wavefront perturbations on a propagating beam.
Tian, Yuzhen; Guo, Jin; Wang, Rui; Wang, Tingfeng
2011-09-12
In order to research the statistical properties of Gaussian beam propagation through an arbitrary thickness random phase screen for adaptive optics and laser communication application in the laboratory, we establish mathematic models of statistical quantities, which are based on the Rytov method and the thin phase screen model, involved in the propagation process. And the analytic results are developed for an arbitrary thickness phase screen based on the Kolmogorov power spectrum. The comparison between the arbitrary thickness phase screen and the thin phase screen shows that it is more suitable for our results to describe the generalized case, especially the scintillation index.
Multimode laser beam analyzer instrument using electrically programmable optics
NASA Astrophysics Data System (ADS)
Marraccini, Philip J.; Riza, Nabeel A.
2011-12-01
Presented is a novel design of a multimode laser beam analyzer using a digital micromirror device (DMD) and an electronically controlled variable focus lens (ECVFL) that serve as the digital and analog agile optics, respectively. The proposed analyzer is a broadband laser characterization instrument that uses the agile optics to smartly direct light to the required point photodetectors to enable beam measurements of minimum beam waist size, minimum waist location, divergence, and the beam propagation parameter M2. Experimental results successfully demonstrate these measurements for a 500 mW multimode test laser beam with a wavelength of 532 nm. The minimum beam waist, divergence, and M2 experimental results for the test laser are found to be 257.61 μm, 2.103 mrad, 1.600 and 326.67 μm, 2.682 mrad, 2.587 for the vertical and horizontal directions, respectively. These measurements are compared to a traditional scan method and the results of the beam waist are found to be within error tolerance of the demonstrated instrument.
Multimode laser beam analyzer instrument using electrically programmable optics.
Marraccini, Philip J; Riza, Nabeel A
2011-12-01
Presented is a novel design of a multimode laser beam analyzer using a digital micromirror device (DMD) and an electronically controlled variable focus lens (ECVFL) that serve as the digital and analog agile optics, respectively. The proposed analyzer is a broadband laser characterization instrument that uses the agile optics to smartly direct light to the required point photodetectors to enable beam measurements of minimum beam waist size, minimum waist location, divergence, and the beam propagation parameter M(2). Experimental results successfully demonstrate these measurements for a 500 mW multimode test laser beam with a wavelength of 532 nm. The minimum beam waist, divergence, and M(2) experimental results for the test laser are found to be 257.61 μm, 2.103 mrad, 1.600 and 326.67 μm, 2.682 mrad, 2.587 for the vertical and horizontal directions, respectively. These measurements are compared to a traditional scan method and the results of the beam waist are found to be within error tolerance of the demonstrated instrument.
Experimental demonstration of coherent beam combining over a 7 km propagation path.
Weyrauch, Thomas; Vorontsov, Mikhail A; Carhart, Gary W; Beresnev, Leonid A; Rostov, Andrey P; Polnau, Ernst E; Liu, Jony Jiang
2011-11-15
We demonstrate coherent combining (phase locking) of seven laser beams emerging from an adaptive fiber-collimator array over a 7 km atmospheric propagation path using a target-in-the-loop (TIL) setting. Adaptive control of the piston and the tip and tilt wavefront phase at each fiber-collimator subaperture resulted in automatic focusing of the combined beam onto an unresolved retroreflector target (corner cube) with precompensation of quasi-static and atmospheric turbulence-induced phase aberrations. Both phase locking (piston) and tip-tilt control were performed by maximizing the target-return optical power using iterative stochastic parallel gradient descent (SPGD) techniques. The performance of TIL coherent beam combining and atmospheric mitigation was significantly increased by using an SPGD control variation that accounts for the round-trip propagation delay (delayed SPGD).
Beam Propagator for Weather Radars, Modules 1 and 2
2013-10-08
This program simulates the beam propagation of weather radar pulses under particular and realistic atmospheric conditions (without using the assumption of standard refraction conditions). It consists of two modules: radiosondings_refract_index_many.pro (MAIN MODULE) beam_propagation_function.pro(EXTERNAL FUNCTION) FOR THE MAIN MODULE, THE CODE DOES OUTPUT--INTO A FILE--THE BEAM HEIGHT AS A FUNCTION OF RANGE. THE RADIOSONDE INPUT FILES SHOULD BE ALREADY AVAILABLE BY THE USER. FOR EXAMPLE, RADIOSONDE OBSERVATION FILES CAN BE OBTAINED AT: RADIOSONDE OBSERVATIONS DOWNLOADED ATmore » "http://weather.uwyo.edu/upperair/soounding.html" OR "http://jervis.pyr.ec.gc.ca" THE EXTERNAL FUNCTION DOES THE ACTUAL COMPUTATION OF BEAM PROPAGATION. IT INCLUDES CONDITIONS OF ANOMALOUS PROPAGATION AND NEGATIVE ELEVATION ANGLES. THE EQUATIONS USED HERE WERE DERIVED BY EDWIN CAMPOS, BASED ON THE SNELL-DESCARTES LAW OF REFRACTION, CONSIDERING THE EARTH CURVATURE. THE PROGRAM REQUIRES A COMPILER FOR THE INTERACTIVE DATA LANGUAGE (IDL). DESCRIPTION AND VALIDATION DETAILS HAVE BEEN PUBLISHED IN THE PEER-REVIEWED SCIENTIFIC LITERATURE, AS FOLLOWS: Campos E. 2012. Estimating weather radar coverage over complex terrain, pp.26-32, peer reviewed, in Weather Radar and Hydrology, edited by Moore RJ, Cole SJ and Illingworth AJ. International Association of Hydrological Sciences (IAHS) Press, IAHS Publ. 351. ISBN 978-1-907161-26-1.« less
Beam Propagator for Weather Radars, Modules 1 and 2
Ortega, Edwin Campos
2013-10-08
This program simulates the beam propagation of weather radar pulses under particular and realistic atmospheric conditions (without using the assumption of standard refraction conditions). It consists of two modules: radiosondings_refract_index_many.pro (MAIN MODULE) beam_propagation_function.pro(EXTERNAL FUNCTION) FOR THE MAIN MODULE, THE CODE DOES OUTPUT--INTO A FILE--THE BEAM HEIGHT AS A FUNCTION OF RANGE. THE RADIOSONDE INPUT FILES SHOULD BE ALREADY AVAILABLE BY THE USER. FOR EXAMPLE, RADIOSONDE OBSERVATION FILES CAN BE OBTAINED AT: RADIOSONDE OBSERVATIONS DOWNLOADED AT "http://weather.uwyo.edu/upperair/soounding.html" OR "http://jervis.pyr.ec.gc.ca" THE EXTERNAL FUNCTION DOES THE ACTUAL COMPUTATION OF BEAM PROPAGATION. IT INCLUDES CONDITIONS OF ANOMALOUS PROPAGATION AND NEGATIVE ELEVATION ANGLES. THE EQUATIONS USED HERE WERE DERIVED BY EDWIN CAMPOS, BASED ON THE SNELL-DESCARTES LAW OF REFRACTION, CONSIDERING THE EARTH CURVATURE. THE PROGRAM REQUIRES A COMPILER FOR THE INTERACTIVE DATA LANGUAGE (IDL). DESCRIPTION AND VALIDATION DETAILS HAVE BEEN PUBLISHED IN THE PEER-REVIEWED SCIENTIFIC LITERATURE, AS FOLLOWS: Campos E. 2012. Estimating weather radar coverage over complex terrain, pp.26-32, peer reviewed, in Weather Radar and Hydrology, edited by Moore RJ, Cole SJ and Illingworth AJ. International Association of Hydrological Sciences (IAHS) Press, IAHS Publ. 351. ISBN 978-1-907161-26-1.
Propagation velocities of laser-produced plasmas from copper wire targets and water droplets
NASA Technical Reports Server (NTRS)
Song, Kyo-Dong; Alexander, Dennis R.
1994-01-01
Experiments were performed to determine the plasma propagation velocities resulting from KrF laser irradiation of copper wire target (75 microns diameter) and water droplets (75 microns diameter) at irradiance levels ranging from 25 to 150 GW/sq cm. Plasma propagation velocities were measured using a streak camera system oriented orthogonally to the high-energy laser propagation axis. Plasma velocities were studied as a function of position in the focused beam. Results show that both the shape of the plasma formation and material removal from the copper wire are different and depend on whether the targets are focused or slightly defocused (approximately = 0.5 mm movement in the beam axis). Plasma formation and its position relative to the target is an important factor in determining the practical focal point during high-energy laser interaction with materials. At irradiance of 100 GW/sq cm, the air plasma has two weak-velocity components which propagate toward and away from the incident laser while a strong-velocity component propagates away from the laser beam as a detonation wave. Comparison of the measured breakdown velocities (in the range of 2.22-2.27 x 10(exp 5) m/s) for air and the value calculated by the nonlinear breakdown wave theory at irradiance of 100 GW/sq cm showed a quantitative agreement within approximately 50% while the linear theory and Gaussian pulse theory failed. The detonation wave velocities of plasma generated from water droplets and copper wire targets for different focused cases were measured and analyzed theoretically. The propagation velocities of laser-induced plasma liquid droplets obtained by previous research are compared with current work.
Enhanced laser beam coupling to a plasma
Steiger, Arno D.; Woods, Cornelius H.
1976-01-01
Density perturbations are induced in a heated plasma by means of a pair of oppositely directed, polarized laser beams of the same frequency. The wavelength of the density perturbations is equal to one half the wavelength of the laser beams. A third laser beam is linearly polarized and directed at the perturbed plasma along a line that is perpendicular to the direction of the two opposed beams. The electric field of the third beam is oriented to lie in the plane containing the three beams. The frequency of the third beam is chosen to cause it to interact resonantly with the plasma density perturbations, thereby efficiently coupling the energy of the third beam to the plasma.
Kline, J L; Montgomery, D S; Flippo, K A; Johnson, R P; Rose, H A; Shimada, T; Williams, E A
2008-10-01
A short pulse (few picoseconds) laser probe provides high temporal resolution measurements to elucidate details of fast dynamic phenomena not observable with typical longer laser pulse probes and gated diagnostics. Such a short pulse laser probe (SPLP) has been used to measure filamentation of a random phase plate (RPP) smoothed laser beam in a gas-jet plasma. The plasma index of refraction due to driven density and temperature fluctuations by the RPP beam perturbs the phase front of a SPLP propagating at a 90 degree angle with respect to the RPP interaction beam. The density and temperature fluctuations are quasistatic on the time scale of the SPLP (approximately 2 ps). The transmitted near-field intensity distribution from the SPLP provides a measure of the phase front perturbation. At low plasma densities, the transmitted intensity pattern is asymmetric with striations across the entire probe beam in the direction of the RPP smoothed beam. As the plasma density increases, the striations break up into smaller sizes along the direction of the RPP beam propagation. The breakup of the intensity pattern is consistent with self-focusing of the RPP smoothed interaction beam. Simulations of the experiment using the wave propagation code, PF3D, are in qualitative agreement demonstrating that the asymmetric striations can be attributed to the RPP driven density fluctuations. Quantification of the beam breakup measured by the transmitted SPLP could lead to a new method for measuring self-focusing of lasers in underdense plasmas.
Spatial-temporal dynamics of broadband terahertz Bessel beam propagation
NASA Astrophysics Data System (ADS)
Semenova, V. A.; Kulya, M. S.; Bespalov, V. G.
2016-08-01
The unique properties of narrowband and broadband terahertz Bessel beams have led to a number of their applications in different fields, for example, for the depth of focusing and resolution enhancement in terahertz imaging. However, broadband terahertz Bessel beams can probably be also used for the diffraction minimization in the short-range broadband terahertz communications. For this purpose, the study of spatial-temporal dynamics of the broadband terahertz Bessel beams is needed. Here we present a simulation-based study of the propagating in non-dispersive medium broadband Bessel beams generated by a conical axicon lens. The algorithm based on scalar diffraction theory was used to obtain the spatial amplitude and phase distributions of the Bessel beam in the frequency range from 0.1 to 3 THz at the distances 10-200 mm from the axicon. Bessel beam field is studied for the different spectral components of the initial pulse. The simulation results show that for the given parameters of the axicon lens one can obtain the Gauss-Bessel beam generation in the spectral range from 0.1 to 3 THz. The length of non-diffraction propagation for a different spectral components was measured, and it was shown that for all spectral components of the initial pulse this length is about 130 mm.
NASA Astrophysics Data System (ADS)
Wu, Guohua; Dai, Wen; Tang, Hua; Guo, Hong
2015-02-01
Beam wander of random electromagnetic Gaussian-Shell model (EGSM) vortex beams propagating through atmospheric turbulence is investigated. We develop the expression for beam wander of random EGSM vortex beams in theory. The effects of topological charge, turbulence strength, initial spatially coherent length, transverse scale, and wavelength on beam wander are illustrated numerically. The numerical results show that vortex beams with both positive and negative topological charges have the same beam wander, decreasing the coherent length and decreasing the transverse scale, or increasing the topological charge, can decrease the beam wander. In free-space optical (FSO) communication, we can choose beams with smaller coherent length, smaller wavelength, and larger topological charge to reduce beam wander.
Stability of charged beam propagation through a relativistic hollow electron beam. Final report
Uhm, H.S.
1981-09-01
Stability properties of charged beam propagation through a relativistic hollow electron beam are investigated, in connection with present experimental applications in the collective particle accelerator. The stability analysis is carried out for long axial wavelength and low-frequency perturbations. A closed algebraic dispersion relation for coupled transverse oscillations is obtained for the solid and hollow beams with sharp-boundary density profiles. One of the most important features in the analysis is that the typical growth rate of the transverse oscillation is order of the hollow beam diocotron frequency, thereby severely limiting the solid beam propagation through a relativistic hollow electron beam. However, for a solid beam with a small radius, the fundamental mode perturbation (i.e., the dipole oscillation) is the most unstable mode.
Pulsed electron beam propagation in argon and nitrogen gas mixture
Kholodnaya, G. E.; Sazonov, R. V.; Ponomarev, D. V.; Remnev, G. E.; Zhirkov, I. S.
2015-10-15
The paper presents the results of current measurements for the electron beam, propagating inside a drift tube filled in with a gas mixture (Ar and N{sub 2}). The experiments were performed using the TEA-500 pulsed electron accelerator. The main characteristics of electron beam were as follows: 60 ns pulse duration, up to 200 J energy, and 5 cm diameter. The electron beam propagated inside the drift tube assembled of three sections. Gas pressures inside the drift tube were 760 ± 3, 300 ± 3, and 50 ± 1 Torr. The studies were performed in argon, nitrogen, and their mixtures of 33%, 50%, and 66% volume concentrations, respectively.
Self-focusing of Hermite-Gaussian laser beam with relativistic nonlinearity
Sharma, Prerana
2015-07-31
This paper presents an investigation of self-focusing of Hermite-Gaussian laser beams in plasma considering relativistic nonlinearity. The differential equations for beam width parameters are obtained using the usual Wentzel–Kramers–Brillouin and paraxial approximations. The nonlinearity in the dielectric constant is assumed to be aroused mainly due to the relativistic mass correction of electron. To highlight the nature of focusing, graphical results of the behavior of beam-width parameters with the dimensionless distance of propagation is presented. The numerical computation is completed by using Taylor series method. The present work is helpful to understand issues related to the beam propagation in laser plasma interaction experiments.
Microwave accelerator E-beam pumped laser
Brau, Charles A.; Stein, William E.; Rockwood, Stephen D.
1980-01-01
A device and method for pumping gaseous lasers by means of a microwave accelerator. The microwave accelerator produces a relativistic electron beam which is applied along the longitudinal axis of the laser through an electron beam window. The incident points of the electron beam on the electron beam window are varied by deflection coils to enhance the cooling characteristics of the foil. A thyratron is used to reliably modulate the microwave accelerator to produce electron beam pulses which excite the laser medium to produce laser pulse repetition frequencies not previously obtainable. An aerodynamic window is also disclosed which eliminates foil heating problems, as well as a magnetic bottle for reducing laser cavity length and pressures while maintaining efficient energy deposition.
Influence of periodic compressible vortices on laser beam intensity
NASA Astrophysics Data System (ADS)
Weston, C. P.
1982-12-01
This study explored the effect of narrow-band, vortex-induced density fluctuations on the beam quality of a laser propagated through the fluctuating flow. The research was a dual investigation. First, the ability to create and characterize 'tailored', fluctuating flows was explored. Second, the degradation of the laser beam due to these various flows was assessed. The flows of periodic vortices were created by cylindrical rods placed at the exit plane of a 1 cm by 10 cm rectangular free jet issuing air at M = .6. Reynolds number based on rod diameter varied from 4,600 to 110,000. Mean and fluctuating mass flux, total pressure and static pressure time histories of the flows were measured in order to derive fluid eddy passage frequency, eddy length and periodic density fluctuation data. Schlieren photographs were obtained for further assessment of the flow fields. A nominal 1 mW laser beam was propagated at two wavelengths transversely through the periodic portion of each flow. The far field beam cross-section was analyzed to determine beam intensity degradation. A Strehl ratio for each flow field was deduced from pseudo-quantitative data.
Vectorial rotating vortex Hankel laser beams
NASA Astrophysics Data System (ADS)
Kotlyar, Victor V.; Kovalev, Alexey A.; Soifer, Victor A.
2016-09-01
We propose a generalization of spherical waves in the form of linearly polarized beams with embedded optical vortices. The source of these beams is an infinitely narrow light ring with an infinitely small radius. These vectorial beams are obtained based on scalar Hankel beams discovered by the authors recently. We have derived explicit relations for complex amplitudes of all six components of vectorial vortex Hankel beams. A closed analytical expression for the axial projection of the orbital angular momentum density in far field has been obtained. We also showed that the intensity distribution of the electric vector rotates by 90 degrees upon the beam propagation in near field.
Development of laser beam injection system for the Edge Thomson Scattering (ETS) in ITER
NASA Astrophysics Data System (ADS)
Yatsuka, E.; Hatae, T.; Suitoh, S.; Ohara, M.; Hagita, K.; Inoue, K.; Bassan, M.; Walsh, M.; Itami, K.
2016-01-01
This paper focuses on the design and development of the laser injection system for the ITER Edge Thomson Scattering system (ETS). The ITER ETS achieves a temporal resolution of 100 Hz by firing two 50 Hz laser beams alternatively. The use of dual lasers enables us to perform the Thomson scattering measurements at a temporal resolution of 50 Hz in case that one of the laser systems stops functioning. A new type of beam combiner was developed to obtain a single beam that is collinear and fixed linearly polarized from two laser beams using a motor-driven rotating half-wave plate. The rotating half-wave plate method does not induce misalignment even if the rotating mechanism malfunctions. The combined beam is relayed from the diagnostic hall to the plasma using mirror optics and is absorbed at the beam dump integrated on the inner blanket. The beam alignment system was designed to direct the laser beam onto the center of the beam dump head. The beam position at the beam dump is monitored by four alignment laser beams which propagate parallel to the diagnostic Nd:YAG laser beam and imaging systems installed outside the diagnostic port.
Beam Stop For High-Power Lasers
NASA Technical Reports Server (NTRS)
Mcdermid, Iain S.; Williamson, William B.
1990-01-01
Graphite/aluminum plate absorbs most of light. Beam stop fits on standard optical mounting fixture. Graphite plate thick enough to absorb incident laser beam but thin enough to transfer heat quickly to heat sink. Device used for variety of blocking purposes. For example, blocks laser beam after it passes through experimental setup, or at each stage of setup so stages checked and tested in sequence. Negligible reflectance of device is valuable safety feature, protecting both users and equipment from reflections.
Coherence delay augmented laser beam homogenizer
Rasmussen, P.; Bernhardt, A.
1993-06-29
The geometrical restrictions on a laser beam homogenizer are relaxed by ug a coherence delay line to separate a coherent input beam into several components each having a path length difference equal to a multiple of the coherence length with respect to the other components. The components recombine incoherently at the output of the homogenizer, and the resultant beam has a more uniform spatial intensity suitable for microlithography and laser pantogography. Also disclosed is a variable aperture homogenizer, and a liquid filled homogenizer.
Coherence delay augmented laser beam homogenizer
Rasmussen, Paul; Bernhardt, Anthony
1993-01-01
The geometrical restrictions on a laser beam homogenizer are relaxed by ug a coherence delay line to separate a coherent input beam into several components each having a path length difference equal to a multiple of the coherence length with respect to the other components. The components recombine incoherently at the output of the homogenizer, and the resultant beam has a more uniform spatial intensity suitable for microlithography and laser pantogography. Also disclosed is a variable aperture homogenizer, and a liquid filled homogenizer.
Hollow circular-truncated cone resonator and its hollow variable biconical laser beam
NASA Astrophysics Data System (ADS)
Liu, Jinglun; Chen, Mei; Wang, Qionghua; Sun, Nianchun
2014-05-01
To obtain a hollow variable biconical laser beam (HVBLB), a CO2 laser having a hollow circular-truncated cone resonator (HCTCR) is presented. This HCTCR comprises a rotationally symmetric total-reflecting concave mirror at the bottom, a rotationally symmetric part-reflecting convex mirror at the top, and a hollow circular-truncated cone discharge tube at the middle. The cross section of this generated biconical laser beam changes from annulus to circular to annulus and the size of this cross section from big to small to large as the propagation distance increases. So, a kind of laser beam with variable center intensity from zero to peak value to zero is obtained and is known as HVBLB. Due to the inclusion of part of the hollow laser beam (HLB) and solid laser beam, this HVBLB requires no additional beam-shaping element and has broad applications such as optical trapping and commercial manufacturing.
Robotics For High Power Laser Beam Manipulation
NASA Astrophysics Data System (ADS)
Watson, Henry E.
1989-03-01
The research and development programs in manufacturing science at The Pennsylvania State University have a major emphasis on laser materials processing technology development. A major thrust of this program is the development of an intelligent robotic system which can manipulate a laser beam in three dimension with the precision required for welding. The robot is called LARS for Laser Articulated Robotic System. A gantry based robot was selected as the foundation for LARS and the system is divided into five major subsystems: robot, electronic control, vision, workhead, beam transport, and software. An overview of the Laser Robotics program including laser materials processing research programs will be provided.
Potential converter for laser-power beaming
NASA Technical Reports Server (NTRS)
Walker, Gilbert H.; Williams, Michael D.; Schuster, Gregory L.; Iles, Peter A.
1991-01-01
Future space missions, such as those associated with the Space Exploration Initiative (SEI), will require large amounts of power for operation of bases, rovers, and orbit transfer vehicles. One method for supplying this power is to beam power from a spaced based or Earth based laser power station to a receiver where laser photons can be converted to electricity. Previous research has described such laser power stations orbiting the Moon and beaming power to a receiver on the surface of the Moon by using arrays of diode lasers. Photovoltaic converters that can be efficiently used with these diode lasers are described.
Method and apparatus for timing of laser beams in a multiple laser beam fusion system
Eastman, Jay M.; Miller, Theodore L.
1981-01-01
The optical path lengths of a plurality of comparison laser beams directed to impinge upon a common target from different directions are compared to that of a master laser beam by using an optical heterodyne interferometric detection technique. The technique consists of frequency shifting the master laser beam and combining the master beam with a first one of the comparison laser beams to produce a time-varying heterodyne interference pattern which is detected by a photo-detector to produce an AC electrical signal indicative of the difference in the optical path lengths of the two beams which were combined. The optical path length of this first comparison laser beam is adjusted to compensate for the detected difference in the optical path lengths of the two beams. The optical path lengths of all of the comparison laser beams are made equal to the optical path length of the master laser beam by repeating the optical path length adjustment process for each of the comparison laser beams. In this manner, the comparison laser beams are synchronized or timed to arrive at the target within .+-.1.times.10.sup.-12 second of each other.
NASA Astrophysics Data System (ADS)
Jeong, S. H.; Greif, R.; Russo, R. E.
1998-05-01
Propagation of the shock wave generated during pulsed laser heating of aluminum targets was measured utilizing a probe beam deflection technique. The transit time of the laser-generated shock wave was compared with that predicted from the Sedov-Taylor solution for an ideal spherical blast wave. It was found that the most important parameters for the laser-generated shock wave to be consistent with the theoretically predicted propagation are the ambient pressure and the laser beam spot size. The prediction for laser energy conversion into the laser-induced vapor flow using the Sedov-Taylor solution overestimated the energy coupling efficiency, indicating a difference between a laser-induced gas-dynamic flow and an ideal blast wave.
Grech, M.; Riazuelo, G.; Pesme, D.; Weber, S.; Tikhonchuk, V. T.
2009-04-17
A statistical model for forward stimulated-Brillouin scattering is developed for a spatially incoherent, monochromatic, laser beam propagating in a plasma. The threshold above which the laser beam spatial incoherence cannot prevent the coherent growth of forward stimulated-Brillouin scattering is computed. It is found to be well below the threshold for self-focusing. Three-dimensional simulations confirm its existence and reveal the onset of beam spray above it. From these results, we propose a new figure of merit for the control of propagation through a plasma of a spatially incoherent laser beam.
Emission and Propagation Properties of Midinfrared Quantum Cascade Lasers
Krishnaswami, Kannan; Bernacki, Bruce E.; Cannon, Bret D.; Ho, Nicolas; Anheier, Norman C.
2008-02-15
We report divergence, astigmatism and M^{2} measurements of quantum cascade lasers (QCL) with an emission wavelength of 8.77 mum. Emission profiles from the QCL facet showed divergence angles of 62° and 32° FWHM ± 2° for the fast and slow axes, respectively. The observation of far field structure superimposed on the fast axes profiles was attributed to the position of the QCL die with respect to the edge of the laser submount, emphasizing the need for careful placement. Two diffraction-limited Germanium aspheric microlenses were designed and fabricated to efficiently collect, collimate, and focus QCL emission. A confocal system comprised of these lenses was used to measure the beam propagation figure of merit (M2) yielding 1.8 and 1.2 for the fast and slow axes, respectively. Astigmatism at the exit facet was calculated to be about 3.4 mum, or less than half a wave. To the best of our knowledge, this is the first experimental measurement of astigmatism and M^{2} reported for mid-IR QCLs.
Vibration and wave propagation characteristics of multisegmented elastic beams
NASA Technical Reports Server (NTRS)
Nayfeh, Adnan H.; Hawwa, Muhammad A.
1990-01-01
Closed form analytical solutions are derived for the vibration and wave propagation of multisegmented elastic beams. Each segment is modeled as a Timoshenko beam with possible inclusion of material viscosity, elastic foundation and axial forces. Solutions are obtained by using transfer matrix methods. According to these methods formal solutions are first constructed which relate the deflection, slope, moment and shear force of one end of the individual segment to those of the other. By satisfying appropriate continuity conditions at segment junctions, a global 4x4 matrix results which relates the deflection, slope, moment and shear force of one end of the beam to those of the other. If any boundary conditions are subsequently invoked on the ends of the beam one gets the appropriate characteristic equation for the natural frequencies. Furthermore, by invoking appropriate periodicity conditions the dispersion relation for a periodic system is obtained. A variety of numerical examples are included.
Propagation model for vector beams generated by metasurfaces.
Shu, Weixing; Liu, Yachao; Ke, Yougang; Ling, Xiaohui; Liu, Zhenxing; Huang, Bin; Luo, Hailu; Yin, Xiaobo
2016-09-01
A propagation model of vector beams generated by metasurfaces based on vector diffraction theory is established theoretically and verified experimentally. Considering the Pancharatnam-Berry phase introduced by the metasurface, analytical forms of vector beams for arbitrary incident polarization and topological charge of metasurfaces are found in the Fresnel and Fraunhofer diffraction regions, respectively. The complex amplitude of the resultant vector beam can be described in terms of a confluent hypergeometric function, with an intensity profile that manifests concentric rings in the Fresnel region and a single ring in the Fraunhofer one. Fraunhofer diffraction provides a method to create vector beams with simultaneously high purity and modal power. Further experiments verify the theoretical results.
Propagation model for vector beams generated by metasurfaces.
Shu, Weixing; Liu, Yachao; Ke, Yougang; Ling, Xiaohui; Liu, Zhenxing; Huang, Bin; Luo, Hailu; Yin, Xiaobo
2016-09-01
A propagation model of vector beams generated by metasurfaces based on vector diffraction theory is established theoretically and verified experimentally. Considering the Pancharatnam-Berry phase introduced by the metasurface, analytical forms of vector beams for arbitrary incident polarization and topological charge of metasurfaces are found in the Fresnel and Fraunhofer diffraction regions, respectively. The complex amplitude of the resultant vector beam can be described in terms of a confluent hypergeometric function, with an intensity profile that manifests concentric rings in the Fresnel region and a single ring in the Fraunhofer one. Fraunhofer diffraction provides a method to create vector beams with simultaneously high purity and modal power. Further experiments verify the theoretical results. PMID:27607720
Adaptive optics for laser power beaming
NASA Technical Reports Server (NTRS)
Leland, Robert P.
1992-01-01
It has been proposed to use a high energy pulsed laser to beam power into space for satellites or a lunar base. The effects of atmospheric transmission are critical to such a system. Thermal blooming in the atmosphere can cause the beam to spread rapidly. Atmospheric turbulence can cause beam bending or beam spreading, resulting in the loss of transmitted energy that fails to hit the target receiver.
High-power beam combining: a step to a future laser weapon system
NASA Astrophysics Data System (ADS)
Protz, Rudolf; Zoz, Jürgen; Geidek, Franz; Dietrich, Stephan; Fall, Michael
2012-11-01
Due to the enormous progress in the field of high-power fiber lasers during the last years commercial industrial fiber lasers are now available, which deliver a near-diffraction limited beam with power levels up to10kW. For the realization of a future laser weapon system, which can be used for Counter-RAM or similar air defence applications, a laser source with a beam power at the level of 100kW or more is required. At MBDA Germany the concept for a high-energy laser weapon system is investigated, which is based on such existing industrial laser sources as mentioned before. A number of individual high-power fiber laser beams are combined together, using one common beam director telescope. By this "geometric" beam coupling scheme, sufficient laser beam power for an operational laser weapon system can be achieved. The individual beams from the different lasers are steered by servo-loops, using fast tip-tilt mirrors. This principle enables the concentration of the total laser beam power at the common focal point on a distant target, also allowing fine tracking of target movements and first order compensation of turbulence effects on laser beam propagation. The proposed beam combination concept was demonstrated using several experimental set-ups. Different experiments were performed, to investigate laser beam target interaction and target fine tracking also at large distances. Content and results of these investigations are reported. An example for the lay-out of an Air Defence High Energy Laser Weapon (ADHELW ) is given. It can be concluded, that geometric high-power beam combining is an important step for the realization of a laser weapon system in the near future.
Spreading and wandering of Gaussian–Schell model laser beams in an anisotropic turbulent ocean
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Zhu, Yun; Hu, Zhengda
2016-09-01
The effect of anisotropic turbulence on the spreading and wandering of Gaussian–Schell model (GSM) laser beams propagating in an ocean is studied. The long-term spreading of a GSM beam propagating through the paraxial channel of a turbulent ocean is also developed. Expressions of random wander for such laser beams are derived in an anisotropic turbulent ocean based on the extended Huygens–Fresnel principle. We investigate the influence of parameters in a turbulent ocean on the beam wander and spreading. Our results indicate that beam spreading and random beam wandering are smaller without considering the anisotropy of turbulence in the oceanic channel. Salinity fluctuation has a greater contribution to both the beam spreading and beam wander than that of temperature fluctuations in a turbulent ocean. Our results could be helpful for designing a free-space optical wireless communication system in an oceanic environment.
Spreading and wandering of Gaussian-Schell model laser beams in an anisotropic turbulent ocean
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Zhu, Yun; Hu, Zhengda
2016-09-01
The effect of anisotropic turbulence on the spreading and wandering of Gaussian-Schell model (GSM) laser beams propagating in an ocean is studied. The long-term spreading of a GSM beam propagating through the paraxial channel of a turbulent ocean is also developed. Expressions of random wander for such laser beams are derived in an anisotropic turbulent ocean based on the extended Huygens-Fresnel principle. We investigate the influence of parameters in a turbulent ocean on the beam wander and spreading. Our results indicate that beam spreading and random beam wandering are smaller without considering the anisotropy of turbulence in the oceanic channel. Salinity fluctuation has a greater contribution to both the beam spreading and beam wander than that of temperature fluctuations in a turbulent ocean. Our results could be helpful for designing a free-space optical wireless communication system in an oceanic environment.
Space Optical Communications Using Laser Beam Amplification
NASA Technical Reports Server (NTRS)
Agrawal, Govind
2015-01-01
The Space Optical Communications Using Laser Beam Amplification (SOCLBA) project will provide a capability to amplify a laser beam that is received in a modulating retro-reflector (MRR) located in a satellite in low Earth orbit. It will also improve the pointing procedure between Earth and spacecraft terminals. The technology uses laser arrays to strengthen the reflected laser beam from the spacecraft. The results of first year's work (2014) show amplification factors of 60 times the power of the signal beam. MMRs are mirrors that reflect light beams back to the source. In space optical communications, a high-powered laser interrogator beam is directed from the ground to a satellite. Within the satellite, the beam is redirected back to ground using the MMR. In the MMR, the beam passes through modulators, which encode a data signal onto the returning beam. MMRs can be used in small spacecraft for optical communications. The SOCLBA project is significant to NASA and small spacecraft due to its application to CubeSats for optical data transmission to ground stations, as well as possible application to spacecraft for optical data transmission.
Self-Focusing/Defocusing of Chirped Gaussian Laser Beam in Collisional Plasma with Linear Absorption
NASA Astrophysics Data System (ADS)
Wani, Manzoor Ahmad; Kant, Niti
2016-09-01
This paper presents an investigation on the self-focusing/defocusing of chirped Gaussian laser beam in collisional plasma with linear absorption. We have derived the differential equation for the beam width parameter by using WKB and paraxial approximations and solved it numerically. The effect of chirp and other laser plasma parameters is seen on the behavior of beam width parameter with dimensionless distance of propagation. The results are discussed and presented graphically. Our simulation results show that the amplitude of oscillations decreases with the distance of propagation. Due to collisional frequency, the laser beam shows fast divergence which can be minimized by the introduction of chirp parameter. The chirp decreases the effect of defocusing and increases the ability of self-focusing of laser beam in collisional plasma. Supported by a financial grant from CSIR, New Delhi, India, under Project No. 03(1277)/13/EMR-II
Generic propagation of beams with sharp spatial boundaries.
Luz, Eitam; Ben Yaakov, Tamar; Leiman, Shaul; Sternklar, Shmuel; Granot, Er'el
2015-04-01
The propagation of spatial beams with initially sharp transverse boundaries is investigated theoretically and experimentally with the paraxial wave equation (PWE). The sharp boundaries generate a universal pattern, which is a consequence of the Schrödinger-like nature of the paraxial dynamics. As a consequence, an approximate analytical expression can be derived for the longitudinal propagation dynamics of the beam. Furthermore, it is shown that the validation of the derived analytical approximation is not limited to the zone in which the PWE is valid, but it is valid in the entire space. Therefore, this solution is a good approximation for the solution of the scalar wave equation (and to the Maxwell wave equation whenever the aperture is much wider than the wavelength of light) in the entire space. Good agreement between the analytical expression and experiment results is presented. PMID:26366779
Generic propagation of beams with sharp spatial boundaries.
Luz, Eitam; Ben Yaakov, Tamar; Leiman, Shaul; Sternklar, Shmuel; Granot, Er'el
2015-04-01
The propagation of spatial beams with initially sharp transverse boundaries is investigated theoretically and experimentally with the paraxial wave equation (PWE). The sharp boundaries generate a universal pattern, which is a consequence of the Schrödinger-like nature of the paraxial dynamics. As a consequence, an approximate analytical expression can be derived for the longitudinal propagation dynamics of the beam. Furthermore, it is shown that the validation of the derived analytical approximation is not limited to the zone in which the PWE is valid, but it is valid in the entire space. Therefore, this solution is a good approximation for the solution of the scalar wave equation (and to the Maxwell wave equation whenever the aperture is much wider than the wavelength of light) in the entire space. Good agreement between the analytical expression and experiment results is presented.
Producing National Ignition Facility (NIF)-quality beams on the Nova and Beamlet lasers
Widmayer, C.C.; Auerbach, J.M.; Ehrlich, R.B.
1996-08-01
The Nova and Beamlet lasers were used to simulate the beam propagation conditions that will be encountered during the National Ignition Facility operation. Perturbation theory predicts that there is a 5mm scale length propagation mode that experiences large nonlinear power growth. This mode was observed in the tests. Further tests have confirmed that this mode can be suppressed with improved spatial filtering.
Evolution of a Gaussian laser beam in warm collisional magnetoplasma
NASA Astrophysics Data System (ADS)
Jafari, M. J.; Jafari Milani, M. R.; Niknam, A. R.
2016-07-01
In this paper, the spatial evolution of an intense circularly polarized Gaussian laser beam propagated through a warm plasma is investigated, taking into account the ponderomotive force, Ohmic heating, external magnetic field, and collisional effects. Using the momentum transfer and energy equations, both modified electron temperature and electron density in plasma are obtained. By introducing the complex dielectric permittivity of warm magnetized plasma and using the complex eikonal function, coupled differential equations for beam width parameter are established and solved numerically. The effects of polarization state of laser and magnetic field on the laser spot size evolution are studied. It is observed that in case of the right-handed polarization, an increase in the value of external magnetic field causes an increase in the strength of the self-focusing, especially in the higher values, and consequently, the self-focusing occurs in shorter distance of propagation. Moreover, the results demonstrate the existence of laser intensity and electron temperature ranges where self-focusing can occur, while the beam diverges outside of these regions; meanwhile, in these intervals, there exists a turning point for each of intensity and temperature in which the self-focusing process has its strongest strength. Finally, it is found that the self-focusing effect can be enhanced by increasing the plasma frequency (plasma density).
Computation of Diffractive Beam Propagation of Monochromatic Light
1999-02-20
Computation of diffractive beam propagation of monochromatic light through a l-dimensional (slab) structure defined by a piecewise continuous complex index of refraction. Finite difference equations are fourth-order-accurate in the lateral grid size and include discontinuities of higher-order field derivatives at dielectric interfaces. Variable grid spacing is allowed, and all dielectric interfaces are assumed to coincide with grid points.
Enhanced thermal self-focusing of a Gaussian laser beam in a collisionless plasma
Gupta, Devki Nandan; Suk, Hyyong
2011-12-15
Theory given by Wang-Zhou [Phys. Plasmas 18, 043101 (2011)] for the thermal self-focusing of a Gaussian laser beam in a collisionless plasma is revisited by including the effect of a localized upward plasma-density ramp. As the equilibrium electron density is an increasing function of the distance of propagation of the laser beam, the diffraction length decreases rapidly as the beam penetrates deeper into the plasma and the diffraction effect becomes reduced; thus, the laser becomes more focused. A significant enhancement in laser thermal self-focusing in a collisionless plasma is consequently observed if a localized plasma density ramp is introduced.
Processing of diamond by laser beam irradiation
NASA Astrophysics Data System (ADS)
Yoshikawa, Masanori; Hirata, Atsushi
1998-10-01
YAG and ArF excimer laser beams, of which wavelengths are 1.06 micrometers and 193 nm respectively, have been applied to processing of a variety of diamonds. Cutting and smoothing of natural, CVD and sintered diamonds have been performed. CVD diamond films were prepared by arc discharge plasma jet CVD and microwave plasma CVD, and sintered diamonds contain metallic or ceramic binder have been used. Fundamental removal processes of diamond with YAG and ArF excimer laser have been investigated using natural single crystal and CVD diamonds in various atmospheres changing laser irradiation conditions such as average power, energy density and pulse repetition rates. Cutting of natural and CVD diamonds with YAG laser proceeds at higher peal power that occurs at lower pulse repetition rates. Smooth surfaces are obtained by excimer laser irradiation at the incident angle of 80 percent. In the cases of the processing with YAG laser, the effect of local heating by laser beam irradiation mainly assists the diamond processing, and diamond appears to be removed after graphitization and oxidization following vaporization in the atmosphere contains oxygen. The temperature measurement was carried out at backside of irradiation surface, and increase of temperature when YAG laser beam was irradiated was larger than that when excimer laser was irradiated. On the contrary, the detection of C, C2, C+, O2 and CO from the emission at the irradiation area with ArF excimer laser beam suggest that processing partly proceeds by the separation of carbon atoms from the surface of diamond after braking bonds between carbon atoms caused by laser beam. Cutting of sintered diamond with metallic binder was difficult because metallic binder remains in the groove while ceramic binder was easily removed. Processing technique using laser beams has been applied to surface planing, chip preparation and edge formation of CVD diamond and curved surface formation on sintered diamond. Surface planing was
Intense Underwater Laser Propagation and Ionization at Visible and Ultraviolet Wavelengths
NASA Astrophysics Data System (ADS)
Jones, Ted; Kaganovich, Dmitri; Helle, Mike; Ting, Tony; Palastro, John; Hafizi, Bahman; Gordon, Dan; Penano, Joe; Chen, Yu-Hsin
2015-11-01
Intense underwater laser propagation, filamentation, and ionization are under investigation at NRL for applications including remote laser acoustic generation for low-frequency sonar. Time-resolved absorption spectroscopy of fs underwater laser ionization revealed hydrated electron density of 5.4 x 1018 cm-3 and lifetime of 350 ps. In addition, high-resolution fluorescence imaging of ns underwater laser propagation using two-photon absorbing dye, independently confirmed previous measurements of 100 micron diameter filament structures [Helle et al., Appl. Phys. Lett. 103, 121101]. A patented scheme for generating an elongated, meter-scale, high energy density underwater plasma [USP 9,088,123] is under study, in which such a filament structure could serve as a target for a second energetic ``heater'' laser pulse. Early experiments suggested improved ionization efficiency using the current configuration, with a 266 nm filament pulse, and a 532 nm heater pulse. 1- and 2-D simulations using a nonlinear laser propagation code are underway to predict beam envelope propagation, filamentation, and stimulated Raman and Brillouin scattering behavior. Results from recent experiments and simulations will be presented. This work is supported by NRL Base Funds.
Propagation of a narrow plasma beam in an oblique magnetic field
Heidbrink, W.W.; Adams, D.; Drum, S.; Evans, K.; Manson, J.; Price, T.; Urayama, P.; Wessel, F.J. )
1992-10-01
The propagation of an intense neutralized ion beam ({ital v}{similar to}5{times}10{sup 8} cm/sec, {ital n}{similar to}10{sup 10} cm{sup {minus}3}) through a large insulated vacuum chamber is measured as a function of magnetic field strength and direction. When the beam propagates parallel to the applied field, beam divergence is reduced. When the beam propagates perpendicular to the applied field, the downstream beam density decreases with increasing field strength. When the beam velocity vector intersects the magnetic field at an oblique angle, beam propagation is determined primarily by the perpendicular component of the field.
Propagation of a narrow plasma beam in an oblique magnetic field
NASA Technical Reports Server (NTRS)
Heidbrink, W. W.; Adams, D.; Drum, S.; Evans, K.; Manson, J.; Price, T.; Urayama, P.; Wessel, F. J.
1992-01-01
The propagation of an intense neutralized ion beam (v is about 5 x 10 exp 8 cm/sec, n is about 10 exp 10/cu cm) through a large insulated vacuum chamber is measured as a function of magnetic field strength and direction. When the beam propagates parallel to the applied field, beam divergence is reduced. When the beam propagates perpendicular to the applied fields, the downstream beam density decreases with increasing field strength. When the beam velocity vector intersects the magnetic field at an oblique angle, beam propagation is determined primarily by the perpendicular component of the field.
NASA Astrophysics Data System (ADS)
Zheng, Yonghui; Sun, Huayan; Zhao, Yanzhong; Chen, Jianbiao
2015-10-01
Active laser detection technique has a broad application prospect in antimissile and air defense, however the aerodynamic flow field around the planes and missiles cause serious distortion effect on the detecting laser beams. There are many computational fluid dynamics(CFD) codes that can predict the air density distribution and also the density fluctuations of the flow field, it's necessary for physical optics to be used to predict the distortion properties after propagation through the complex process. Aiming at the physical process of laser propagation in "Cat-eye" lenses and aerodynamic flow field for twice, distortion propagation calculation method is researched in this paper. In the minds of dividing the whole process into two parts, and tread the aero-optical optical path difference as a phase distortion, the incidence and reflection process are calculated using Collins formula and angular spectrum diffraction theory respectively. In addition, turbulent performance of the aerodynamic flow field is estimated according to the electromagnetic propagation theory through a random medium, the rms optical path difference and Strehl ratio of the turbulent optical distortion are obtained. Finally, Computational fluid mechanics and aero-optical distortion properties of the detecting laser beams are calculated with the hemisphere-on-cylinder turret as an example, calculation results are showed and analysed.
Simulation based analysis of laser beam brazing
NASA Astrophysics Data System (ADS)
Dobler, Michael; Wiethop, Philipp; Schmid, Daniel; Schmidt, Michael
2016-03-01
Laser beam brazing is a well-established joining technology in car body manufacturing with main applications in the joining of divided tailgates and the joining of roof and side panels. A key advantage of laser brazed joints is the seam's visual quality which satisfies highest requirements. However, the laser beam brazing process is very complex and process dynamics are only partially understood. In order to gain deeper knowledge of the laser beam brazing process, to determine optimal process parameters and to test process variants, a transient three-dimensional simulation model of laser beam brazing is developed. This model takes into account energy input, heat transfer as well as fluid and wetting dynamics that lead to the formation of the brazing seam. A validation of the simulation model is performed by metallographic analysis and thermocouple measurements for different parameter sets of the brazing process. These results show that the multi-physical simulation model not only can be used to gain insight into the laser brazing process but also offers the possibility of process optimization in industrial applications. The model's capabilities in determining optimal process parameters are exemplarily shown for the laser power. Small deviations in the energy input can affect the brazing results significantly. Therefore, the simulation model is used to analyze the effect of the lateral laser beam position on the energy input and the resulting brazing seam.
Mid-IR laser source using hollow waveguide beam combining
NASA Astrophysics Data System (ADS)
Elder, Ian F.; Thorne, Daniel H.; Lamb, Robert A.; Jenkins, R. M.
2016-03-01
Hollow waveguide technology is a route to efficient beam combining of multiple laser sources in a compact footprint. It is a technology appropriate for combining free-space or fibre-coupled beams generated by semiconductor, fibre or solidstate laser sources. This paper will present results of a breadboard mid-IR system comprising four laser sources combined using a hollow waveguide optical circuit. In this approach the individual dichroic beam combiner components are held in precision alignment slots in the hollow waveguide circuit and the different input wavelengths are guided between the components to a common output port. The hollow waveguide circuit is formed in the surface of a Macor (machinable glass-ceramic) substrate using precision CNC machining techniques. The hollow waveguides have fundamentally different propagation characteristics to solid core waveguides leading to transmission characteristics close to those of the atmosphere while still providing useful light guidance properties. The transmission efficiency and power handling of the hollow waveguide circuit can be designed to be very high across a broad waveband range. Three of the sources are quantum cascade lasers (QCLs), a semiconductor laser technology providing direct generation of midwave IR output. The combined beams provide 4.2 W of near diffraction-limited output co-boresighted to better than 20 µrad. High coupling efficiency into the waveguides is demonstrated, with negligible waveguide transmission losses. The overall transmission of the hollow waveguide beam combining optical circuit, weighted by the laser power at each wavelength, is 93%. This loss is dominated by the performance of the dichroic optics used to combine the beams.
High power laser beam delivery monitoring for laser safety
NASA Astrophysics Data System (ADS)
Corder, D. A.; Evans, D. R.; Tyrer, J. R.; Freeland, C. M.; Myler, J. K.
1997-07-01
The output of high power lasers used for material processing presents extreme radiation hazards. In normal operation this hazard is removed by the use of local shielding to prevent accidental exposure and system design to ensure efficient coupling of radiation into the workpiece. Faults in laser beam delivery or utilization can give rise to hazardous levels of laser radiation. A passive hazard control strategy requires that the laser system be enclosed such that the full laser power cannot burn through the housing under fault conditions. Usually this approach is too restrictive. Instead, active control strategies can be used in which a fault condition is detected and the laser cut off. This reduces the requirements for protective housing. In this work a distinction is drawn between reactive and proactive strategies. Reactive strategies rely on detecting the effects of an errant laser beam, whereas proactive strategies can anticipate as well as detect fault conditions. This can avoid the need for a hazardous situation to exist. A proactive strategy in which the laser beam is sampled at the final turning mirror is described in this work. Two control systems have been demonstrated; the first checks that beam power is within preset limits, the second monitors incoming beam power and position, and the radiation reflected back from the cutting head. In addition to their safety functions the accurate monitoring of power provides an additional benefit to the laser user.
Propagation of intense laser pulses in strongly magnetized plasmas
Yang, X. H. Ge, Z. Y.; Xu, B. B.; Zhuo, H. B.; Ma, Y. Y.; Shao, F. Q.; Yu, W.; Xu, H.; Yu, M. Y.; Borghesi, M.
2015-06-01
Propagation of intense circularly polarized laser pulses in strongly magnetized inhomogeneous plasmas is investigated. It is shown that a left-hand circularly polarized laser pulse propagating up the density gradient of the plasma along the magnetic field is reflected at the left-cutoff density. However, a right-hand circularly polarized laser can penetrate up the density gradient deep into the plasma without cutoff or resonance and turbulently heat the electrons trapped in its wake. Results from particle-in-cell simulations are in good agreement with that from the theory.
Laser-induced shockwave propagation from ablation in a cavity
Zeng Xianzhong; Mao Xianglei; Mao, Samuel S.; Wen, S.-B.; Greif, Ralph; Russo, Richard E.
2006-02-06
The propagation of laser-induced shockwaves from ablation inside of cavities was determined from time-resolved shadowgraph images. The temperature and electron number density of the laser-induced plasma was determined from spectroscopic measurements. These properties were compared to those for laser ablation on the flat surface under the same energy and background gas condition. A theoretical model was proposed to determine the amount of energy and vaporized mass stored in the vapor plume based on these measurements.
Electron beam magnetic switch for a plurality of free electron lasers
Schlitt, Leland G.
1984-01-01
Apparatus for forming and utilizing a sequence of electron beam segments, each of the same temporal length (substantially 15 nsec), with consecutive beams being separated by a constant time interval of the order of 3 nsec. The beam sequence is used for simultaneous inputs to a plurality of wiggler magnet systems that also accept the laser beams to be amplified by interaction with the co-propagating electron beams. The electron beams are arranged substantially in a circle to allow proper distribution of and simultaneous switching out of the beam segments to their respective wiggler magnets.
Split-step non-paraxial beam propagation method
NASA Astrophysics Data System (ADS)
Sharma, Anurag; Agrawal, Arti
2004-06-01
A new method for solving the wave equation is presented, which, being non-paraxial, is applicable to wide-angle beam propagation. It shows very good stability characteristics in the sense that relatively larger step-sizes can be used. It is both faster and easier to implement. The method is based on symmetrized splitting of operators, one representing the propagation through a uniform medium and the other, the effect of the refractive index variation of the guiding structure. The method can be implemented in the FD-BPM, FFT-BPM and collocation schemes. The method is stable for a step size of 1 micron in a graded index waveguide with accuracy better than 0.001 in the field overlap integral for 1000-micron propagation. At a tilt angle of 50°, the method shows an error less than 0.001 with 0.25-micron step. In the benchmark test, the present method shows a relative power of ~0.96 in a 100 micron long waveguide with 1000 propagation steps and 800 sample points, while FD-BPM with Pade(2,2) approximation gives a relative power of 0.95 with 1000 sample points and 2048 propagation steps. Thus, the method requires fewer points, is easier to implement, faster, more accurate and highly stable.
A critical review of laser beam welding
NASA Astrophysics Data System (ADS)
Martukanitz, Richard P.
2005-03-01
The use of lasers for welding has exhibited tremendous growth over the last decade for improving efficiency and reducing costs in a broad range of industries. Much of these successes are based on the development and availability of enabling technologies, which include improvements in process understanding, enhancements in laser sources and systems, and continued development and progression in process technology for laser beam welding of macro and micro components. The development of accurate numerical simulation techniques has provided an unprecedented opportunity to view the transient nature of laser processing. Advancements in laser source technology include the introduction of higher-power Nd:YAG lasers, utilizing diode pumped rods or disks, and fiber lasers, both providing the capability for fiber optic beam delivery. Although CO2 laser systems continue to dominate thick section welding, this influence will be challenged by emerging source technologies, namely high power fiber lasers. One of the most promising advances in laser process technology is laser-arc hybrid welding, which is seeing considerable interest worldwide and is currently being evaluated for various applications within heavy industry and manufacturing. The benefit of hybrid welding is the synergistic effect of improved processing rates and joint accommodation over either of the processes viewed separately. Other processing methods are also being developed to increase the utility of laser beam welding for industry, such as the use of dual beams and beam manipulation. The continued advancement in process knowledge is seen as a key element for facilitating the development of new processes and encouraging the acceptance of new source technology.
Laser beam riding artillery missiles guidance device is designed
NASA Astrophysics Data System (ADS)
Yan, Mingliang; Huo, Zhicheng; Chen, Wei
2014-09-01
Laser driving gun missile guidance type beam of laser information field formed by any link failure or reduced stability will directly lead to ballistic or miss out of control, and based on this, this paper designed the driving beam of laser guided missile guidance beam type forming device modulation and zoom mechanism, in order to make the missile can recognize its position in the laser beam, laser beam gun missile, by means of spatial encoding of the laser beam laser beam into information after forming device, a surface to achieve the purpose of precision guidance.
Satellites Would Transmit Power By Laser Beams
NASA Technical Reports Server (NTRS)
Williams, M. D.; Walker, Gilbert H.; HUMES D. H.; Kwon, J. H.
1995-01-01
Arrays of diode lasers concentrate power into narrow beams. Baseline design of system formulated with regard to two particular missions that differ greatly in power requirements, thus showing scalability and attributes of basic system. Satellite system features large-scale array amplifier of high efficiency, injection-locked amplifiers, coherent combination of beams, and use of advanced lithographic technology to fabricate diode lasers in array. Extremely rapid development of applicable technologies make features realizable within decade.
Characterizing output beams for lasers that use high-magnification unstable resonators.
Saghafi, S; Withford, M J; Piper, J A
2001-07-01
Laser beams generated from high-magnification on-axis unstable resonators by use of hard-edged optics typically have a doughnut-shaped distribution in the near field (i.e., a flat-top profile with a hole in the middle for an axially coupled beam). We derive analytical expressions describing this distribution by using the flattened Gaussian beams concept. The superposition of two flattened Gaussian beams whose flatness and steepness of edges are controlled by defined parameters (i.e., the beam width and the order) is used to analyze the output beam intensity along the propagation axis. Finally, experimental measurements of beam propagation from a copper-vapor laser fitted with a high-magnification unstable resonator show excellent agreement with theoretical predictions. PMID:11444555
Two-photon flow cytometer with laser scanning Bessel beams
NASA Astrophysics Data System (ADS)
Wang, Yongdong; Ding, Yu; Ray, Supriyo; Paez, Aurelio; Xiao, Chuan; Li, Chunqiang
2016-03-01
Flow cytometry is an important technique in biomedical discovery for cell counting, cell sorting and biomarker detection. In vivo flow cytometers, based on one-photon or two-photon excited fluorescence, have been developed for more than a decade. One drawback of laser beam scanning two-photon flow cytometer is that the two-photon excitation volume is fairly small due to the short Rayleigh range of a focused Gaussian beam. Hence, the sampling volume is much smaller than one-photon flow cytometry, which makes it challenging to count or detect rare circulating cells in vivo. Bessel beams have narrow intensity profiles with an effective spot size (FWHM) as small as several wavelengths, making them comparable to Gaussian beams. More significantly, the theoretical depth of field (propagation distance without diffraction) can be infinite, making it an ideal solution as a light source for scanning beam flow cytometry. The trade-off of using Bessel beams rather than a Gaussian beam is the fact that Bessel beams have small concentric side rings that contribute to background noise. Two-photon excitation can reduce this noise, as the excitation efficiency is proportional to intensity squared. Therefore, we developed a two-photon flow cytometer using scanned Bessel beams to form a light sheet that intersects the micro fluidic channel.
Rippled-beam free-electron laser
Carlsten, B.E.
1997-10-01
The authors describe a new microwave generation mechanism involving a scalloping annular electron beam. The beam interacts with the axial electric field of a TM{sub 0n} mode in a smooth circular waveguide through the axial free-electron laser interaction, in which the beam ripple period is synchronous with the phase slippage of the rf mode relative to the electron beam. Due to nonlinearities in the orbit equation, the interaction can be made autoresonant, where the phase and amplitude of the gain is independent of the beam energy.
Gupta, Devki Nandan; Hur, Min Sup; Suk, Hyyong
2007-08-20
Propagation of a high power Gaussian laser beam through a plasma with a density ramp where a magnetic field is present has been investigated. The spot size of the laser beam decreases as the beam penetrates into the plasma due to the role of a plasma density ramp. The studies show that the combined effect of a plasma density ramp and a magnetic field enhances the self-focusing property of the laser beam. Both factors not only reduce the spot size of the laser beam but also maintain it with only a mild ripple over several Rayleight lengths.
Beam wander of Gaussian-Schell model beams propagating through oceanic turbulence
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Li, Ye; Hu, Zhengda
2016-07-01
For Gaussian-Schell model beams propagating in the isotropic turbulent ocean, theoretical expression of beam wander is derived based on the extended Huygens-Fresnel principle. The spatial coherence radius of spherical waves propagating in the paraxial channel of turbulent ocean including inner scale is also developed. Our results show that the beam wander decreases with the increasing rate of dissipation of kinetic energy per unit mass of fluid ɛ, but it increases as the increasing of the dissipation rate of temperature variance χt and the relative strength of temperature and salinity fluctuations ϖ. The salinity fluctuation has greater influence on the beam wander than that of temperature fluctuations. The model can be evaluated submarine-to-submarine/ship optical wireless communication performance.
NASA Astrophysics Data System (ADS)
Pope, L. E.; McDonald, T. G.
1981-11-01
A program to develop diagnostic techniques for pulsed Nd:YAG lasers for welding is described, and problems encountered when deviations from ideal optical collimation of a laser beam is defined, the diagnostic system is described, and the SNLA welding system is discussed.
Varying the Divergence of Multiple Parallel Laser Beams
NASA Technical Reports Server (NTRS)
Kovalik, Joseph M.; Wright, Malcolm W.
2008-01-01
A provision for controlled variation of the divergence of a laser beam or of multiple parallel laser beams has been incorporated into the design of a conceptual free-space optical-communication station from which the transmitted laser beam(s) would be launched via a telescope. The original purpose to be served by this provision was to enable optimization, under various atmospheric optical conditions, of the divergence of a laser beam or beams transmitted from a ground station to a spacecraft.
Laser beam welding of any metal.
Leong, K. H.
1998-10-01
The effect of a metal's thermophysical properties on its weldability are examined. The thermal conductivity, melting point, absorptivity and thermal diffusivity of the metal and the laser beam focused diameter and welding speed influence the minimum beam irradiance required for melting and welding. Beam diameter, surface tension and viscosity of the molten metal affect weld pool stability and weld quality. Lower surface tension and viscosity increases weld pool instability. With larger beam diameters causing wider welds, dropout also increases. Effects of focused beam diameter and joint fitup on weldability are also examined. Small beam diameters are sensitive to beam coupling problems in relation to fitup precision in addition to beam alignment to the seam. Welding parameters for mitigating weld pool instability and increasing weld quality are derived from the above considerations. Guidelines are presented for the tailoring of welding parameters to achieve good welds. Weldability problems can also be anticipated from the properties of a metal.
Spiral laser beams in inhomogeneous media.
Mahalov, Alex; Suazo, Erwin; Suslov, Sergei K
2013-08-01
Explicit solutions of the inhomogeneous paraxial wave equation in a linear and quadratic approximation are applied to wave fields with invariant features, such as oscillating laser beams in a parabolic waveguide and spiral light beams in varying media. A similar effect of superfocusing of particle beams in a thin monocrystal film, harmonic oscillations of cold trapped atoms, and motion in magnetic field are also mentioned. PMID:23903135
Beam wandering of femtosecond laser filament in air.
Yang, Jing; Zeng, Tao; Lin, Lie; Liu, Weiwei
2015-10-01
The spatial wandering of a femtosecond laser filament caused by the filament heating effect in air has been studied. An empirical formula has also been derived from the classical Karman turbulence model, which determines quantitatively the displacement of the beam center as a function of the propagation distance and the effective turbulence structure constant. After fitting the experimental data with this formula, the effective turbulence structure constant has been estimated for a single filament generated in laboratory environment. With this result, one may be able to estimate quantitatively the displacement of a filament over long distance propagation and interpret the practical performance of the experiments assisted by femtosecond laser filamentation, such as remote air lasing, pulse compression, high order harmonic generation (HHG), etc.
Beam wandering of femtosecond laser filament in air.
Yang, Jing; Zeng, Tao; Lin, Lie; Liu, Weiwei
2015-10-01
The spatial wandering of a femtosecond laser filament caused by the filament heating effect in air has been studied. An empirical formula has also been derived from the classical Karman turbulence model, which determines quantitatively the displacement of the beam center as a function of the propagation distance and the effective turbulence structure constant. After fitting the experimental data with this formula, the effective turbulence structure constant has been estimated for a single filament generated in laboratory environment. With this result, one may be able to estimate quantitatively the displacement of a filament over long distance propagation and interpret the practical performance of the experiments assisted by femtosecond laser filamentation, such as remote air lasing, pulse compression, high order harmonic generation (HHG), etc. PMID:26480079
Generation of low-divergence laser beams
Kronberg, James W.
1993-01-01
Apparatus for transforming a conventional beam of coherent light, having a Gaussian energy distribution and relatively high divergence, into a beam in which the energy distribution approximates a single, non-zero-order Bessel function and which therefore has much lower divergence. The apparatus comprises a zone plate having transmitting and reflecting zones defined by the pattern of light interference produced by the combination of a beam of coherent light with a Gaussian energy distribution and one having such a Bessel distribution. The interference pattern between the two beams is a concentric array of multiple annuli, and is preferably recorded as a hologram. The hologram is then used to form the transmitting and reflecting zones by photo-etching portions of a reflecting layer deposited on a plate made of a transmitting material. A Bessel beam, containing approximately 50% of the energy of the incident beam, is produced by passing a Gaussian beam through such a Bessel zone plate. The reflected beam, also containing approximately 50% of the incident beam energy and having a Bessel energy distribution, can be redirected in the same direction and parallel to the transmitted beam. Alternatively, a filter similar to the Bessel zone plate can be placed within the resonator cavity of a conventional laser system having a front mirror and a rear mirror, preferably axially aligned with the mirrors and just inside the front mirror to generate Bessel energy distribution light beams at the laser source.
Generation of low-divergence laser beams
Kronberg, J.W.
1993-09-14
Apparatus for transforming a conventional beam of coherent light, having a Gaussian energy distribution and relatively high divergence, into a beam in which the energy distribution approximates a single, non-zero-order Bessel function and which therefore has much lower divergence. The apparatus comprises a zone plate having transmitting and reflecting zones defined by the pattern of light interference produced by the combination of a beam of coherent light with a Gaussian energy distribution and one having such a Bessel distribution. The interference pattern between the two beams is a concentric array of multiple annuli, and is preferably recorded as a hologram. The hologram is then used to form the transmitting and reflecting zones by photo-etching portions of a reflecting layer deposited on a plate made of a transmitting material. A Bessel beam, containing approximately 50% of the energy of the incident beam, is produced by passing a Gaussian beam through such a Bessel zone plate. The reflected beam, also containing approximately 50% of the incident beam energy and having a Bessel energy distribution, can be redirected in the same direction and parallel to the transmitted beam. Alternatively, a filter similar to the Bessel zone plate can be placed within the resonator cavity of a conventional laser system having a front mirror and a rear mirror, preferably axially aligned with the mirrors and just inside the front mirror to generate Bessel energy distribution light beams at the laser source. 11 figures.
Apparatus and method for laser beam diagnosis
Salmon, Jr., Joseph T.
1991-01-01
An apparatus and method is disclosed for accurate, real time monitoring of the wavefront curvature of a coherent laser beam. Knowing the curvature, it can be quickly determined whether the laser beam is collimated, or focusing (converging), or de-focusing (diverging). The apparatus includes a lateral interferometer for forming an interference pattern of the laser beam to be diagnosed. The interference pattern is imaged to a spatial light modulator (SLM), whose output is a coherent laser beam having an image of the interference pattern impressed on it. The SLM output is focused to obtain the far-field diffraction pattern. A video camera, such as CCD, monitors the far-field diffraction pattern, and provides an electrical output indicative of the shape of the far-field pattern. Specifically, the far-field pattern comprises a central lobe and side lobes, whose relative positions are indicative of the radius of curvature of the beam. The video camera's electrical output may be provided to a computer which analyzes the data to determine the wavefront curvature of the laser beam.
Apparatus and method for laser beam diagnosis
Salmon, J.T. Jr.
1991-08-27
An apparatus and method are disclosed for accurate, real time monitoring of the wavefront curvature of a coherent laser beam. Knowing the curvature, it can be quickly determined whether the laser beam is collimated, or focusing (converging), or de-focusing (diverging). The apparatus includes a lateral interferometer for forming an interference pattern of the laser beam to be diagnosed. The interference pattern is imaged to a spatial light modulator (SLM), whose output is a coherent laser beam having an image of the interference pattern impressed on it. The SLM output is focused to obtain the far-field diffraction pattern. A video camera, such as CCD, monitors the far-field diffraction pattern, and provides an electrical output indicative of the shape of the far-field pattern. Specifically, the far-field pattern comprises a central lobe and side lobes, whose relative positions are indicative of the radius of curvature of the beam. The video camera's electrical output may be provided to a computer which analyzes the data to determine the wavefront curvature of the laser beam. 11 figures.
Beam uniformity of flat top lasers
NASA Astrophysics Data System (ADS)
Chang, Chao; Cramer, Larry; Danielson, Don; Norby, James
2015-03-01
Many beams that output from standard commercial lasers are multi-mode, with each mode having a different shape and width. They show an overall non-homogeneous energy distribution across the spot size. There may be satellite structures, halos and other deviations from beam uniformity. However, many scientific, industrial and medical applications require flat top spatial energy distribution, high uniformity in the plateau region, and complete absence of hot spots. Reliable standard methods for the evaluation of beam quality are of great importance. Standard methods are required for correct characterization of the laser for its intended application and for tight quality control in laser manufacturing. The International Organization for Standardization (ISO) has published standard procedures and definitions for this purpose. These procedures have not been widely adopted by commercial laser manufacturers. This is due to the fact that they are unreliable because an unrepresentative single-pixel value can seriously distort the result. We hereby propose a metric of beam uniformity, a way of beam profile visualization, procedures to automatically detect hot spots and beam structures, and application examples in our high energy laser production.
Transmission Of Power Via Combined Laser Beams
NASA Technical Reports Server (NTRS)
Kwon, Jin H.; Lee, Ja H.
1992-01-01
Laser Diode Array (LDA) appears to be most efficient means of transferring power from Earth to satellites and between satellites, in terms of mass and size, of various laser configurations. To form large-scale-array amplifier (LSAA), element LDA's must generate well-defined diffraction-limited beams. Coherent matching of phases among LDA's enables system to generate good beam pattern in far field over thousands of kilometers. By passing beam from master laser through number of LDA amplifiers simultaneously, one realizes coherence among amplified output beams. LSAA used for transmission of power with efficiency of approximately 80 percent into receiver of moderate size at 5,000 km. Also transmits data at high rates by line-of-sight rather than fiber optics.
Collimation of laser-produced proton beam
NASA Astrophysics Data System (ADS)
Takano, M.; Nagashima, T.; Izumiyama, T.; Gu, Y. J.; Barada, D.; Kong, Q.; Wang, P. X.; Ma, Y. Y.; Wang, W. M.; Kawata, S.
2016-03-01
In intense laser plasma interaction for particle acceleration several issues remain to be solved. In this paper we focus on a collimation of ion beam, which is produced by a laser plasma interaction. In this study, the ion beam is collimated by a thin film target. When an intense short pulse laser illuminates a target, target electrons are accelerated, and create an electron cloud that generates a sheath electric field at the target surface. Such the ion acceleration mechanism is called the target normal sheath acceleration (TNSA). The TNSA field would be used for the ion beam collimation by the electric field. We have successfully obtained a collimated beam in our particle-in-cell simulations.
Design Considerations for Plasma Accelerators Driven by Lasers or Particle Beams
Schroeder, C. B.; Esarey, E.; Benedetti, C.; Toth, Cs.; Geddes, C. G. R.; Leemans, W.P.
2010-06-01
Plasma accelerators may be driven by the ponderomotive force of an intense laser or the space-charge force of a charged particle beam. The implications for accelerator design and the different physical mechanisms of laser-driven and beam-driven plasma acceleration are discussed. Driver propagation is examined, as well as the effects of the excited plasma wave phase velocity. The driver coupling to subsequent plasma accelerator stages for high-energy physics applications is addressed.
Terahertz generation by two cross focused Gaussian laser beams in magnetized plasma
Singh, Ram Kishor Sharma, R. P.
2014-11-15
This paper presents a theoretical model for terahertz (THz) radiation generation by two cross-focused Gaussian laser beams in a collisionless magnetoplasma. The plasma is redistributed due to the ponderomotive nonlinearity which leads to the cross focusing of the laser beams. The focusing of the copropagating laser beams increases with increasing the externally applied static magnetic field which is perpendicular to the wave propagation direction. The nonlinear current at THz frequency arises on account of nonlinear ponderomotive force as a result of beating of the two lasers. The generated THz radiation amplitude increases significantly with increasing magnetic field. The cross focusing of two laser beams enhances the THz yield. Optimization of laser-plasma parameters gives the radiated normalized THz power of the order of 10 kW.
Electron beam, laser beam and plasma arc welding studies
NASA Technical Reports Server (NTRS)
Banas, C. M.
1974-01-01
This program was undertaken as an initial step in establishing an evaluation framework which would permit a priori selection of advanced welding processes for specific applications. To this end, a direct comparison of laser beam, electron beam and arc welding of Ti-6Al-4V alloy was undertaken. Ti-6Al-4V was selected for use in view of its established welding characteristics and its importance in aerospace applications.
Influence of propagation in digital wireless beam, microwave links
NASA Astrophysics Data System (ADS)
Bursztejn, J.
1984-10-01
Methods are presented for determining the parameters which permit the prediction of the quality of tropospheric scattering and line of sight microwave links. Wireless beam, microwave links with tropospheric scattering are considered based on experiments for determining the coherence band which is the essential parameter for digital transmission by tropospheric scattering. The effects of propagation difficulties in line of sight links are discussed with focus on depolarization and selective fading. Experimental results are given which permit calculating the sensitivity of equipment and predicting the quality of the links.
Propagation of a nonrelativistic electron beam in a plasma in a magnetic field
Okuda, H.; Horton, R.; Ono, M.; Ashour-Abdalla, M.
1986-10-01
Propagation of a nonrelativistic electron beam in a plasma in a strong magnetic field has been studied using electrostatic one-dimensional particle simulation models. Electron beams of finite pulse length and of continuous injection are followed in time to study the effects of beam-plasma interaction on the beam propagation. For the case of pulsed beam propagation, it is found that the beam distribution rapidly spreads in velocity space generating a plateaulike distribution with a high energy tail extending beyond the initial beam velocity.
ALCBEAM - Neutral beam formation and propagation code for beam-based plasma diagnostics
NASA Astrophysics Data System (ADS)
Bespamyatnov, I. O.; Rowan, W. L.; Liao, K. T.
2012-03-01
ALCBEAM is a new three-dimensional neutral beam formation and propagation code. It was developed to support the beam-based diagnostics installed on the Alcator C-Mod tokamak. The purpose of the code is to provide reliable estimates of the local beam equilibrium parameters: such as beam energy fractions, density profiles and excitation populations. The code effectively unifies the ion beam formation, extraction and neutralization processes with beam attenuation and excitation in plasma and neutral gas and beam stopping by the beam apertures. This paper describes the physical processes interpreted and utilized by the code, along with exploited computational methods. The description is concluded by an example simulation of beam penetration into plasma of Alcator C-Mod. The code is successfully being used in Alcator C-Mod tokamak and expected to be valuable in the support of beam-based diagnostics in most other tokamak environments. Program summaryProgram title: ALCBEAM Catalogue identifier: AEKU_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEKU_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 66 459 No. of bytes in distributed program, including test data, etc.: 7 841 051 Distribution format: tar.gz Programming language: IDL Computer: Workstation, PC Operating system: Linux RAM: 1 GB Classification: 19.2 Nature of problem: Neutral beams are commonly used to heat and/or diagnose high-temperature magnetically-confined laboratory plasmas. An accurate neutral beam characterization is required for beam-based measurements of plasma properties. Beam parameters such as density distribution, energy composition, and atomic excited populations of the beam atoms need to be known. Solution method: A neutral beam is initially formed as an ion beam which is extracted from
Laser power beaming for satellite applications
Friedman, H.W.
1993-09-22
A serious consideration of laser power beaming for satellite applications appears to have grown out of a NASA mission analysis for transmitting power to lunar bases during the two week dark period. System analyses showed that laser power beaming to the moon in conjunction with efficient, large area solar cell collection panels, were an attractive alternative to other schemes such as battery storage and nuclear generators, largely because of the high space transportation costs. The primary difficulty with this scheme is the need for very high average power visible lasers. One system study indicated that lasers in excess of 10 MW at a wavelength of approximately 850 nm were required. Although such lasers systems have received much attention for military applications, their realization is still a long term goal.
Beam propagation factor of partially coherent flat-topped beams in a turbulent atmosphere.
Dan, Youquan; Zhang, Bin
2008-09-29
The Wigner distribution function (WDF) has been used to study the beam propagation factor (M(2)-factor) for partially coherent flat-topped (PCFT) beams with circular symmetry in a turbulent atmosphere. Based on the extended Huygens-Fresnel principle and the definition of the WDF, an expression for the WDF of PCFT beams in turbulence has been given. By use of the second-order moments of the WDF, the analytical formulas for the root-mean-square (rms) spatial width, the rms angular width, and the M(2)-factor of PCFT beams in turbulence have been derived, which can be applied to cases of different spatial power spectra of the refractive index fluctuations. The rms angular width and the M(2)-factor of PCFT beams in turbulence have been discussed with numerical examples. It can be shown that the M(2)-factor of PCFT beams in turbulence depends on the beam order, degree of global coherence of the source, waist width, wavelength, spatial power spectrum of the refractive index fluctuations, and propagation distance.
Optical Device for Converting a Laser Beam into Two Co-aligned but Oppositely Directed Beams
NASA Technical Reports Server (NTRS)
Jennings, Donald
2013-01-01
Optical systems consisting of a series of optical elements require alignment from the input end to the output end. The optical elements can be mirrors, lenses, sources, detectors, or other devices. Complex optical systems are often difficult to align from end-to-end because the alignment beam must be inserted at one end in order for the beam to traverse the entire optical path to the other end. The ends of the optical train may not be easily accessible to the alignment beam. Typically, when a series of optical elements is to be aligned, an alignment laser beam is inserted into the optical path with a pick-off mirror at one end of the series of elements. But it may be impossible to insert the beam at an end-point. It can be difficult to locate the pick-off mirror at the desired position because there is not enough space, there is no mounting surface, or the location is occupied by a source, detector, or other component. Alternatively, the laser beam might be inserted at an intermediate location (not at an end-point) and sent, first in one direction and then the other, to the opposite ends of the optical system for alignment. However, in this case, alignment must be performed in two directions and extra effort is required to co-align the two beams to make them parallel and coincident, i.e., to follow the same path as an end-to-end beam. An optical device has been developed that accepts a laser beam as input and produces two co-aligned, but counter-propagating beams. In contrast to a conventional alignment laser placed at one end of the optical path, this invention can be placed at a convenient position within the optical train and aligned to send its two beams simultaneously along precisely opposite paths that, taken together, trace out exactly the same path as the conventional alignment laser. This invention allows the user the freedom to choose locations within the optical train for placement of the alignment beam. It is also self-aligned by design and requires
Extended Propagation of Powerful Laser Pulses in Focusing Kerr Media
NASA Astrophysics Data System (ADS)
Malkin, V. M.; Fisch, N. J.
2016-09-01
Powerful incoherent laser pulses can propagate in focusing Kerr media much longer distances than can coherent pulses, due to the fast phase mixing that prevents transverse filamentation. This distance is limited by 4-wave scattering, which accumulates waves at small transverse wave numbers, where phase mixing is too slow to retain the incoherence and thus prevent the filamentation. However, we identify how this theoretical limit can be overcome by countering this accumulation through transverse heating of the pulse by random fluctuations of the refractive index. Thus, the laser pulse propagation distances are significantly extended, making feasible, in particular, the generation of unprecedentedly intense and powerful short laser pulses in a plasma by means of backward Raman amplification in new random laser regimes.
Numerical simulation of broadband vortex terahertz beams propagation
NASA Astrophysics Data System (ADS)
Semenova, V. A.; Kulya, M. S.; Bespalov, V. G.
2016-08-01
Orbital angular momentum (OAM) represents new informational degree of freedom for data encoding and multiplexing in fiber and free-space communications. OAM-carrying beams (also called vortex beams) were successfully used to increase the capacity of optical, millimetre-wave and radio frequency communication systems. However, the investigation of the OAM potential for the new generation high-speed terahertz communications is also of interest due to the unlimited demand of higher capacity in telecommunications. Here we present a simulation-based study of the propagating in non-dispersive medium broadband terahertz vortex beams generated by a spiral phase plate (SPP). The algorithm based on scalar diffraction theory was used to obtain the spatial amplitude and phase distributions of the vortex beam in the frequency range from 0.1 to 3 THz at the distances 20-80 mm from the SPP. The simulation results show that the amplitude and phase distributions without unwanted modulation are presented in the wavelengths ranges with centres on the wavelengths which are multiple to the SPP optical thickness. This fact may allow to create the high-capacity near-field communication link which combines OAM and wavelength-division multiplexing.
Initial alignment method for free space optics laser beam
NASA Astrophysics Data System (ADS)
Shimada, Yuta; Tashiro, Yuki; Izumi, Kiyotaka; Yoshida, Koichi; Tsujimura, Takeshi
2016-08-01
The authors have newly proposed and constructed an active free space optics transmission system. It is equipped with a motor driven laser emitting mechanism and positioning photodiodes, and it transmits a collimated thin laser beam and accurately steers the laser beam direction. It is necessary to introduce the laser beam within sensible range of the receiver in advance of laser beam tracking control. This paper studies an estimation method of laser reaching point for initial laser beam alignment. Distributed photodiodes detect laser luminescence at respective position, and the optical axis of laser beam is analytically presumed based on the Gaussian beam optics. Computer simulation evaluates the accuracy of the proposed estimation methods, and results disclose that the methods help us to guide the laser beam to a distant receiver.
Laser pulse propagation in a meter scale rubidium vapor/plasma cell in AWAKE experiment
NASA Astrophysics Data System (ADS)
Joulaei, A.; Moody, J.; Berti, N.; Kasparian, J.; Mirzanejhad, S.; Muggli, P.
2016-09-01
We present the results of numerical studies of laser pulse propagating in a 3.5 cm Rb vapor cell in the linear dispersion regime by using a 1D model and a 2D code that has been modified for our special case. The 2D simulation finally aimed at finding laser beam parameters suitable to make the Rb vapor fully ionized to obtain a uniform, 10 m-long, at least 1 mm in radius plasma in the next step for the AWAKE experiment.
Digital Controller For Laser-Beam-Steering Subsystem: Part 2
NASA Technical Reports Server (NTRS)
Ansari, Homayoon; Voisinet, Leeann
1995-01-01
A report presents additional information about laser-beam-steering apparatus described in "Digital Controller for Laser-Beam-Steering Subsystem" (NPO-19193) and "More About Beam-Steering Subsystem for Laser Communication" (NPO-19381). Reiterates basic principles of operation of beam-steering subsystem, with emphasis on modes of operation, basic design concepts, and initial experiments on partial prototype of apparatus.
Laser beam shaping for biomedical microscopy techniques
NASA Astrophysics Data System (ADS)
Laskin, Alexander; Kaiser, Peter; Laskin, Vadim; Ostrun, Aleksei
2016-04-01
Uniform illumination of a working field is very important in optical systems of confocal microscopy and various implementations of fluorescence microscopy like TIR, SSIM, STORM, PALM to enhance performance of these laser-based research techniques. Widely used TEM00 laser sources are characterized by essentially non-uniform Gaussian intensity profile which leads usually to non-uniform intensity distribution in a microscope working field or in a field of microlenses array of a confocal microscope optical system, this non-uniform illumination results in instability of measuring procedure and reducing precision of quantitative measurements. Therefore transformation of typical Gaussian distribution of a TEM00 laser to flat-top (top hat) profile is an actual technical task, it is solved by applying beam shaping optics. Due to high demands to optical image quality the mentioned techniques have specific requirements to a uniform laser beam: flatness of phase front and extended depth of field, - from this point of view the microscopy techniques are similar to holography and interferometry. There are different refractive and diffractive beam shaping approaches used in laser industrial and scientific applications, but only few of them are capable to fulfil the optimum conditions for beam quality required in discussed microscopy techniques. We suggest applying refractive field mapping beam shapers πShaper, which operational principle presumes almost lossless transformation of Gaussian to flat-top beam with flatness of output wavefront, conserving of beam consistency, providing collimated low divergent output beam, high transmittance, extended depth of field, negligible wave aberration, and achromatic design provides capability to work with several lasers with different wavelengths simultaneously. The main function of a beam shaper is transformation of laser intensity profile, further beam transformation to provide optimum for a particular technique spot size and shape has to
Optimization of beam configuration in laser fusion based on the laser beam pattern
Xu, Teng; Xu, Lixin; Wang, Anting; Gu, Chun; Wang, Shengbo; Liu, Jing; Wei, Ankun
2013-12-15
A simple method based on the laser beam pattern is proposed and numerically demonstrated to optimize a beam configuration for direct drive laser fusion. In this method, both the geometrical factor G{sub l} and the single beam factor B{sub l} are considered. By diminishing the product of B{sub l}·G{sub l}, the irradiation nonuniformity can be decreased to the order of 10{sup −5}. This optimization method can be applied on the design of irradiation systems for an arbitrary number of beams and any axially symmetric beam patterns.
Method and apparatus for laser-controlled proton beam radiology
Johnstone, C.J.
1998-06-02
A proton beam radiology system provides cancer treatment and proton radiography. The system includes an accelerator for producing an H{sup {minus}} beam and a laser source for generating a laser beam. A photodetachment module is located proximate the periphery of the accelerator. The photodetachment module combines the H{sup {minus}} beam and laser beam to produce a neutral beam therefrom within a subsection of the H{sup {minus}} beam. The photodetachment module emits the neutral beam along a trajectory defined by the laser beam. The photodetachment module includes a stripping foil which forms a proton beam from the neutral beam. The proton beam is delivered to a conveyance segment which transports the proton beam to a patient treatment station. The photodetachment module further includes a laser scanner which moves the laser beam along a path transverse to the cross-section of the H{sup {minus}} beam in order to form the neutral beam in subsections of the H{sup {minus}} beam. As the scanning laser moves across the H{sup {minus}} beam, it similarly varies the trajectory of the proton beam emitted from the photodetachment module and in turn varies the target location of the proton beam upon the patient. Intensity modulation of the proton beam can also be achieved by controlling the output of the laser. 9 figs.
Method and apparatus for laser-controlled proton beam radiology
Johnstone, Carol J.
1998-01-01
A proton beam radiology system provides cancer treatment and proton radiography. The system includes an accelerator for producing an H.sup.- beam and a laser source for generating a laser beam. A photodetachment module is located proximate the periphery of the accelerator. The photodetachment module combines the H.sup.- beam and laser beam to produce a neutral beam therefrom within a subsection of the H.sup.- beam. The photodetachment module emits the neutral beam along a trajectory defined by the laser beam. The photodetachment module includes a stripping foil which forms a proton beam from the neutral beam. The proton beam is delivered to a conveyance segment which transports the proton beam to a patient treatment station. The photodetachment module further includes a laser scanner which moves the laser beam along a path transverse to the cross-section of the H.sup.- beam in order to form the neutral beam in subsections of the H.sup.- beam. As the scanning laser moves across the H.sup.- beam, it similarly varies the trajectory of the proton beam emitted from the photodetachment module and in turn varies the target location of the proton beam upon the patient. Intensity modulation of the proton beam can also be achieved by controlling the output of the laser.
Undulator radiation driven by laser-wakefield accelerator electron beams
NASA Astrophysics Data System (ADS)
Wiggins, S. M.; Anania, M. P.; Welsh, G. H.; Brunetti, E.; Cipiccia, S.; Grant, P. A.; Reboredo, D.; Manahan, G.; Grant, D. W.; Jaroszynski, D. A.
2015-05-01
The Advanced Laser-Plasma High-Energy Accelerators towards X-rays (ALPHA-X) programme is developing laserplasma accelerators for the production of ultra-short electron bunches with subsequent generation of coherent, bright, short-wavelength radiation pulses. The new Scottish Centre for the Application of Plasma-based Accelerators (SCAPA) will develop a wide range of applications utilising such light sources. Electron bunches can be propagated through a magnetic undulator with the aim of generating fully coherent free-electron laser (FEL) radiation in the ultra-violet and Xrays spectral ranges. Demonstration experiments producing spontaneous undulator radiation have been conducted at visible and extreme ultra-violet wavelengths but it is an on-going challenge to generate and maintain electron bunches of sufficient quality in order to stimulate FEL behaviour. In the ALPHA-X beam line experiments, a Ti:sapphire femtosecond laser system with peak power 20 TW has been used to generate electron bunches of energy 80-150 MeV in a 2 mm gas jet laser-plasma wakefield accelerator and these bunches have been transported through a 100 period planar undulator. High peak brilliance, narrow band spontaneous radiation pulses in the vacuum ultra-violet wavelength range have been generated. Analysis is provided with respect to the magnetic quadrupole beam transport system and subsequent effect on beam emittance and duration. Requirements for coherent spontaneous emission and FEL operation are presented.
Continuous-Wave Laser Beam Fanning in Organic Solutions: A Novel Phenomenon
NASA Technical Reports Server (NTRS)
Abdeldayem, Hossin; Witherow, William K.; Shields, Angela; Penn, Benjamin; Frazier, Donald O.; Moghbel, Mehdi; Venkateswarlu, P.; Sekhar, P. Chandra; George, M. C.
1994-01-01
If a low-power cw Ar(+) laser beam (approx. 50 mW) is sent horizontally and focused on the entrance side of a cuvette containing an absorptive solution, the beam fans into the lower half of the cuvette instead of propagating through and forming self-phase-modulation fringes. We call this phenomenon self-beam fanning, which has been observed in several organic solutions. We present here several experimental results and a descriptive model of the phenomenon.
Optical trapping with superfocused high-M2 laser diode beam
NASA Astrophysics Data System (ADS)
Sokolovskii, G. S.; Dudelev, V. V.; Melissinaki, V.; Losev, S. N.; Soboleva, K. K.; Deryagin, A. G.; Kuchinskii, V. I.; Farsari, M.; Sibbett, W.; Rafailov, E. U.
2015-03-01
Many applications of high-power laser diodes demand tight focusing. This is often not possible due to the multimode nature of semiconductor laser radiation possessing beam propagation parameter M2 values in double-digits. We propose a method of `interference' superfocusing of high-M2 diode laser beams with a technique developed for the generation of Bessel beams based on the employment of an axicon fabricated on the tip of a 100 μm diameter optical fiber with high-precision direct laser writing. Using axicons with apex angle 1400 and rounded tip area as small as ~10 μm diameter, we demonstrate 2-4 μm diameter focused laser `needle' beams with approximately 20 μm propagation length generated from multimode diode laser with beam propagation parameter M2=18 and emission wavelength of 960 nm. This is a few-fold reduction compared to the minimal focal spot size of ~11 μm that could be achieved if focused by an `ideal' lens of unity numerical aperture. The same technique using a 1600 axicon allowed us to demonstrate few-μm-wide laser `needle' beams with nearly 100 μm propagation length with which to demonstrate optical trapping of 5-6 μm rat blood red cells in a water-heparin solution. Our results indicate the good potential of superfocused diode laser beams for applications relating to optical trapping and manipulation of microscopic objects including living biological objects with aspirations towards subsequent novel lab-on-chip configurations.
High-average-power and high-beam-quality Innoslab picosecond laser amplifier.
Xu, Liu; Zhang, Hengli; Mao, Yefei; Yan, Ying; Fan, Zhongwei; Xin, Jianguo
2012-09-20
We demonstrated a laser-diode, end-pumped picosecond amplifier. With effective shaping of the seed laser, we achieved 73 W amplified laser output at the pump power of 255 W, and the optical-optical efficiency was about 28%. The beam propagation factors M(2) measured at the output power of 60 W in the horizontal direction and the vertical direction were 1.5 and 1.4, respectively.
Wu, Huiyun; Sheng, Shen; Huang, Zhisong; Zhao, Siqing; Wang, Hua; Sun, Zhenhai; Xu, Xiegu
2013-02-25
As a new attractive application of the vortex beams, power coupling of annular vortex beam propagating through a two- Cassegrain-telescope optical system in turbulent atmosphere has been investigated. A typical model of annular vortex beam propagating through a two-Cassegrain-telescope optical system is established, the general analytical expression of vortex beams with limited apertures and the analytical formulas for the average intensity distribution at the receiver plane are derived. Under the H-V 5/7 turbulence model, the average intensity distribution at the receiver plane and power coupling efficiency of the optical system are numerically calculated, and the influences of the optical topological charge, the laser wavelength, the propagation path and the receiver apertures on the power coupling efficiency are analyzed. These studies reveal that the average intensity distribution at the receiver plane presents a central dark hollow profile, which is suitable for power coupling by the Cassegrain telescope receiver. In the optical system with optimized parameters, power coupling efficiency can keep in high values with the increase of the propagation distance. Under the atmospheric turbulent conditions, great advantages of vortex beam in power coupling of the two-Cassegrain-telescope optical system are shown in comparison with beam without vortex.
Beam uniformity analysis of infrared laser illuminators
NASA Astrophysics Data System (ADS)
Allik, Toomas H.; Dixon, Roberta E.; Proffitt, R. Patrick; Fung, Susan; Ramboyong, Len; Soyka, Thomas J.
2015-02-01
Uniform near-infrared (NIR) and short-wave infrared (SWIR) illuminators are desired in low ambient light detection, recognition, and identification of military applications. Factors that contribute to laser illumination image degradation are high frequency, coherent laser speckle and low frequency nonuniformities created by the laser or external laser cavity optics. Laser speckle analysis and beam uniformity improvements have been independently studied by numerous authors, but analysis to separate these two effects from a single measurement technique has not been published. In this study, profiles of compact, diode laser NIR and SWIR illuminators were measured and evaluated. Digital 12-bit images were recorded with a flat-field calibrated InGaAs camera with measurements at F/1.4 and F/16. Separating beam uniformity components from laser speckle was approximated by filtering the original image. The goal of this paper is to identify and quantify the beam quality variation of illumination prototypes, draw awareness to its impact on range performance modeling, and develop measurement techniques and methodologies for military, industry, and vendors of active sources.
Laser beaming demonstrations to high-orbit satellites
Lipinski, R.J.; Meister, D.C.; Tucker, S.
1993-12-31
Laser power beaming to satellites and orbital transfer vehicles requires the accurate pointing of a low-divergence laser beam to its target, whether the target is in the sunlight or the earth`s shadow. The Air Force Phillips Laboratory (AFPL) has demonstrated reduction in the image size of stars by a factor of 10 or more by using laser beacons and adaptive optics for atmospheric compensation. This same technology is applicable to reducing the divergence of laser beams propagated from earth to space. A team of Phillips Laboratory, COMSAT Laboratories, and Sandia National Laboratories plans to demonstrate the state of the art in this area with laser-beaming demonstrations to high-orbit satellites. The demonstrations will utilize the 1.5-m diameter telescope with adaptive optics at the AFPL Starfire Optical Range (SOR) and a ruby laser provided by the Air Force and Sandia (1--50 kill and 6 ms at 694.3 nm). The first targets will be corner-cube retro-reflectors left on the moon by the Apollo 11, 14, and 15 landings. We will attempt to use adaptive optics for atmospheric compensation to demonstrate accurate and reliable beam projection with a series of shots over a span of time and shot angle. We will utilize the return signal from the retro-reflectors to help determine the beam diameter on the moon and the variations in pointing accuracy caused by atmospheric tilt. This will be especially challenging because the retro-reflectors will need to be in the lunar shadow to allow detection over background light. If the results from this experiment are encouraging, we will at a later date direct the beam at a COMSAT satellite in geosynchronous orbit as it goes into the shadow of the earth. We will utilize an onboard monitor to measure the current generated in the solar panels on the satellite while the beam is present. A threshold irradiance of about 4 W/m{sup 2} on orbit is needed for this demonstration.
Industrial fiber beam delivery system for ultrafast lasers: applications and recent advances
NASA Astrophysics Data System (ADS)
Eilzer, Sebastian; Funck, Max C.; Wedel, Björn
2016-03-01
Fiber based laser beam delivery is the method of choice for high power laser applications whenever great flexibility is required. For cw-lasers fiber beam delivery has long been established but has recently also become available for ultrafast lasers. Using micro-structured hollow core fibers that guide the laser beam mostly inside a hollow core, nonlinear effects and catastrophic damage that arise in conventional glass fibers can be avoided. Today, ultrafast pulses with several 100 μJ and hundreds of MW can be transmitted in quasi single mode fashion. In addition, the technology opens new possibilities for beam delivery systems as the pulse propagation inside the fiber can be altered on purpose. For example to shorten the pulse duration of picosecond lasers down into the femtosecond regime. We present a modular fiber beam delivery system for micromachining applications with industrial pico- and femtosecond lasers that is flexibly integrated into existing applications. Micro-structured hollow core fibers inside the sealed laser light cable efficiently guide high-power laser pulses over distances of several meters with excellent beam quality, while power, pulse duration and polarization are maintained. Robust and stable beam transport during dynamic operation as in robot or gantry systems will be discussed together with optional pulse compression.
Phoenix's Laser Beam in Action on Mars
NASA Technical Reports Server (NTRS)
2008-01-01
[figure removed for brevity, see original site] Click on image to view the animation
The Surface Stereo Imager camera aboard NASA's Phoenix Mars Lander acquired a series of images of the laser beam in the Martian night sky. Bright spots in the beam are reflections from ice crystals in the low level ice-fog. The brighter area at the top of the beam is due to enhanced scattering of the laser light in a cloud. The Canadian-built lidar instrument emits pulses of laser light and records what is scattered back.
The Phoenix Mission is led by the University of Arizona, Tucson, on behalf of NASA. Project management of the mission is by NASA's Jet Propulsion Laboratory, Pasadena, Calif. Spacecraft development is by Lockheed Martin Space Systems, Denver.
NASA Astrophysics Data System (ADS)
Fortin, Pierre-Yves
2008-06-01
Vectorial laser beams propagating beyond the paraxial limit exhibit an intensity profile at focus that depends upon their field structure and the width of their plane wave spectrum. Under tight focussing conditions, the longitudinal component of the lowest order transverse magnetic laser beam has a field amplitude that becomes comparable to that of the transverse components of the beam; the global intensity profile is then narrower than that produced by a Gaussian beam, thus enabling hyperresolution. With a general polarization eigenmode approach for all propagating directions in anisotropic media, we can show that privileged propagating directions exist, allowing preservation of the transverse magnetic polarization state despite birefringence. Using wave functions satisfying the non-paraxial wave equation, we can also find exact expressions for the field components. During propagation of tightly focussed beams along those privileged directions inside an appropriate anisotropic nonlinear crystal, the longitudinal electric field component may then be used to take advantage of nonlinear tensor terms otherwise ineffective with a paraxial beam. In this work, spectral conversion rate and power conversion efficiency of second-harmonic generation are characterized as a function of effective and undepleted nonlinear pumping in the case of propagation along the anisotropic axis of an uniaxial nonlinear crystal. Even if the phase matching condition is not fully satisfied for propagation along this privileged direction, we show to which extent the nonlinear properties are preserved for a restricted interaction volume.
Generation and propagation dynamics of Airy beam with the tunable tail
NASA Astrophysics Data System (ADS)
Liu, Huilong; Lü, Yanfei; Xia, Jing; Pu, Xiaoyun; Zhang, Li
2016-05-01
We introduce a new kind of Airy beam called Airy beam with the tunable tail, which can be generated from the elliptical flat-topped Gaussian beam. The analytical formula of Airy beam with the tunable tail is derived. Airy beam with the single tail can be obtained by adjusting the ration of the beam width of elliptical flat-topped Gaussian beam. The tail length of Airy beam can be controlled by the order N of incident beam. The normalized intensity distributions of Airy beam with the tunable tail propagating in free space are studied, and the propagation dynamics of Airy beam with the single tail are investigated. Compared with the Airy beam generated from the fundamental Gaussian beam or the flat-topped Gaussian beam, some interesting and useful information has been found.
NASA Astrophysics Data System (ADS)
Lund, Steven M.; Cohen, Ronald H.; Ni, Pavel A.
2013-04-01
Ion beams (including protons) with low emittance and high space-charge intensity can be propagated with normal incidence through a sequence of thin metallic foils separated by vacuum gaps of order the characteristic transverse beam extent to transport/collimate the beam or to focus it to a small transverse spot. Energetic ions have sufficient range to pass through a significant number of thin foils with little energy loss or scattering. The foils reduce the (defocusing) radial electric self-field of the beam while not altering the (focusing) azimuthal magnetic self-field of the beam, thereby allowing passive self-beam focusing if the magnetic field is sufficiently strong relative to the residual electric field. Here we present an envelope model developed to predict the strength of this passive (beam generated) focusing effect under a number of simplifying assumptions including relatively long pulse duration. The envelope model provides a simple criterion for the necessary foil spacing for net focusing and clearly illustrates system focusing properties for either beam collimation (such as injecting a laser-produced proton beam into an accelerator) or for magnetic pinch focusing to a small transverse spot (for beam driven heating of materials). An illustrative example is worked for an idealization of a recently performed laser-produced proton-beam experiment to provide guidance on possible beam focusing and collimation systems. It is found that foils spaced on the order of the characteristic transverse beam size desired can be employed and that envelope divergence of the initial beam entering the foil lens must be suppressed to limit the total number of foils required to practical values for pinch focusing. Relatively modest proton-beam current at 10 MeV kinetic energy can clearly demonstrate strong magnetic pinch focusing achieving a transverse rms extent similar to the foil spacing (20-50μm gaps) in beam propagation distances of tens of mm. This is a surprisingly
Pointing of laser-accelerated proton beams
Schreiber, J.; Ter-Avetisyan, S.; Risse, E.; Kalachnikov, M.P.; Nickles, P.V.; Sandner, W.; Schramm, U.; Habs, D.; Witte, J.; Schnuerer, M.
2006-03-15
Small fluctuations in the acceleration sheath change the pointing of a proton beam accelerated from the rear side of a laser irradiated thin aluminum foil. The proton acceleration was produced with 40 fs pulses of a Ti:sapphire laser at an intensity of approximately 10{sup 19} W/cm{sup 2}. This observation has been made with a high spatial resolution Thomson spectrometer. The proton beam pointing has appeared stable in the energy range between the high energy cutoff (3 MeV) and 50% of this value. Deviations of the beam position at lower energies changes in a range of 0-3 mrad. The recorded pictures show wiggled and continuous proton traces which imply a release of the proton beam from the acceleration zone with a velocity chirp.
Directed fast electron beams in ultraintense picosecond laser irradiated solid targets
Ge, X. L.; Lin, X. X.; Yuan, X. H. E-mail: ytli@iphy.ac.cn; Sheng, Z. M.; Carroll, D. C.; Neely, D.; Gray, R. J.; Tresca, O.; McKenna, P.; Yu, T. P.; Chen, M.; Liu, F.; Zhuo, H. B.; Zielbauer, B.; and others
2015-08-31
We report on fast electron transport and emission patterns from solid targets irradiated by s-polarized, relativistically intense, picosecond laser pulses. A beam of multi-MeV electrons is found to be transported along the target surface in the laser polarization direction. The spatial-intensity and energy distributions of this beam are compared with the beam produced along the laser propagation axis. It is shown that even for peak laser intensities an order of magnitude higher than the relativistic threshold, laser polarization still plays an important role in electron energy transport. Results from 3D particle-in-cell simulations confirm the findings. The characterization of directional beam emission is important for applications requiring efficient energy transfer, including secondary photon and ion source development.
Suwada, Tsuyoshi; Satoh, Masanori; Telada, Souichi; Minoshima, Kaoru
2013-09-01
A laser-based alignment system with a He-Ne laser has been newly developed in order to precisely align accelerator units at the KEKB injector linac. The laser beam was first implemented as a 500-m-long fiducial straight line for alignment measurements. We experimentally investigated the propagation and stability characteristics of the laser beam passing through laser pipes in vacuum. The pointing stability at the last fiducial point was successfully obtained with the transverse displacements of ±40 μm level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 μrad. This report contains a detailed description of the experimental investigation for the propagation and stability characteristics of the laser beam in the laser-based alignment system for long-distance linear accelerators.
Suwada, Tsuyoshi; Satoh, Masanori; Telada, Souichi; Minoshima, Kaoru
2013-09-15
A laser-based alignment system with a He-Ne laser has been newly developed in order to precisely align accelerator units at the KEKB injector linac. The laser beam was first implemented as a 500-m-long fiducial straight line for alignment measurements. We experimentally investigated the propagation and stability characteristics of the laser beam passing through laser pipes in vacuum. The pointing stability at the last fiducial point was successfully obtained with the transverse displacements of ±40 μm level in one standard deviation by applying a feedback control. This pointing stability corresponds to an angle of ±0.08 μrad. This report contains a detailed description of the experimental investigation for the propagation and stability characteristics of the laser beam in the laser-based alignment system for long-distance linear accelerators.
Generation and manipulation of proton beams by ultra-short laser pulses
Nickles, P. V.; Schnuerer, M.; Steinke, S.; Sokollik, T.; Sandner, W.; Ter-Avetisyan, S.; Andreev, A.
2009-07-25
Applying a 21-channel Thomson spectrometer setup has revealed further insight to the connection between spatial and spectral beam characteristic of laser accelerated protons. Analyzing the central emission cone (plus/minus 3 degree) shows an increasing beam divergency for protons with increasing kinetic energies. This holds for protons emitted from the same source area at the target surface. The whole beam is a well ordered system with a clear functional dependence of trajectories on proton energy. This is a consequence of the source dynamics which is determined by the sheath development in time. Thus laser-driven ion beams can be advantageously manipulated for further propagation to an experiment. We demonstrate this capability with a magnetic quadrupole and obtain a nearly parallel and monochromatized beam. Furthermore we set our achievements in beam production efficiency into context with other laser systems and demonstrate the potential of very-thin target foils.
Terahertz radiation from a laser bunched relativistic electron beam in a magnetic wiggler
Kumar, Manoj; Tripathi, V. K.
2012-07-15
We develop a formalism for tunable coherent terahertz radiation generation from a relativistic electron beam, modulated by two laser beams, as it passes through a magnetic wiggler of wave vector k{sub w}z-caret. The lasers exert a beat frequency ponderomotive force on beam electrons, and modulate their velocity. In the drift space, velocity modulation translates into density modulation. As the beam bunches pass through the wiggler, they acquire a transverse velocity, constituting a transverse current that acts as an antenna to produce coherent THz radiation, when {omega}{sub 1}-{omega}{sub 2}=k{sub w}c/(cos{theta}-v{sub 0b}/c), where {omega}{sub 1}, {omega}{sub 2} are the frequencies of the lasers, v{sub 0b}z-caret is the beam velocity, and {theta} is the direction of maximum radiated intensity with respect to the direction of propagation of the beam.
Dual-beam laser traps in biology and medicine: when one beam is not enough
NASA Astrophysics Data System (ADS)
Whyte, Graeme; Lautenschläger, Franziska; Kreysing, Moritz; Boyde, Lars; Ekpenyong, Andrew; Delabre, Ulysse; Chalut, Kevin; Franze, Kristian; Guck, Jochen
2010-08-01
Optical traps are nowadays quite ubiquitous in biophysical and biological studies. The term is often used synonymously with optical tweezers, one particular incarnation of optical traps. However, there is another kind of optical trap consisting of two non-focused, counter-propagating laser beams. This dual-beam trap predates optical tweezers by almost two decades and currently experiences a renaissance. The advantages of dual-beam traps include lower intensities on the trapped object, decoupling from imaging optics, and the possibility to trap cells and cell clusters up to 100 microns in diameter. When used for deforming cells this trap is referred to as an optical stretcher. I will review several applications of such traps in biology and medicine for the detection of cancer cells, sorting stem cells, testing light guiding properties of retinal cells and the controlled rotation of cells for single cell tomography.
Accurately modeling Gaussian beam propagation in the context of Monte Carlo techniques
NASA Astrophysics Data System (ADS)
Hokr, Brett H.; Winblad, Aidan; Bixler, Joel N.; Elpers, Gabriel; Zollars, Byron; Scully, Marlan O.; Yakovlev, Vladislav V.; Thomas, Robert J.
2016-03-01
Monte Carlo simulations are widely considered to be the gold standard for studying the propagation of light in turbid media. However, traditional Monte Carlo methods fail to account for diffraction because they treat light as a particle. This results in converging beams focusing to a point instead of a diffraction limited spot, greatly effecting the accuracy of Monte Carlo simulations near the focal plane. Here, we present a technique capable of simulating a focusing beam in accordance to the rules of Gaussian optics, resulting in a diffraction limited focal spot. This technique can be easily implemented into any traditional Monte Carlo simulation allowing existing models to be converted to include accurate focusing geometries with minimal effort. We will present results for a focusing beam in a layered tissue model, demonstrating that for different scenarios the region of highest intensity, thus the greatest heating, can change from the surface to the focus. The ability to simulate accurate focusing geometries will greatly enhance the usefulness of Monte Carlo for countless applications, including studying laser tissue interactions in medical applications and light propagation through turbid media.
Beam shaping for laser initiated optical primers
NASA Astrophysics Data System (ADS)
Lizotte, Todd E.
2008-08-01
Remington was one of the first firearm manufacturing companies to file a patent for laser initiated firearms, in 1969. Nearly 40 years later, the development of laser initiated firearms has not become a mainstream technology in the civilian market. Requiring a battery is definitely a short coming, so it is easy to see how such a concept would be problematic. Having a firearm operate reliably and the delivery of laser energy in an efficient manner to ignite the shock-sensitive explosive primer mixtures is a tall task indeed. There has been considerable research on optical element based methods of transferring or compressing laser energy to ignite primer charges, including windows, laser chip primers and various lens shaped windows to focus the laser energy. The focusing of laser light needs to achieve igniting temperatures upwards of >400°C. Many of the patent filings covering this type of technology discuss simple approaches where a single point of light might be sufficient to perform this task. Alternatively a multi-point method might provide better performance, especially for mission critical applications, such as precision military firearms. This paper covers initial design and performance test of the laser beam shaping optics to create simultaneous multiple point ignition locations and a circumferential intense ring for igniting primer charge compounds. A simple initial test of the ring beam shaping technique was evaluated on a standard large caliber primer to determine its effectiveness on igniting the primer material. Several tests were conducted to gauge the feasibility of laser beam shaping, including optic fabrication and mounting on a cartridge, optic durability and functional ignition performance. Initial data will be presented, including testing of optically elements and empirical primer ignition / burn analysis.
Laser synchrotron radiation and beam cooling
Esarey, E.; Sprangle, P.; Ting, A.
1995-12-31
The interaction of intense {approx_gt} 10{sup 18} W/cm{sup 2}, short pulse ({approx_lt} 1 ps) lasers with electron beams and plasmas can lead to the generation of harmonic radiation by several mechanisms. Laser synchrotron radiation may provide a practical method for generating tunable, near monochromatic, well collimated, short pulse x-rays in compact, relatively inexpensive source. The mechanism for the generation of laser synchrotron radiation is nonlinear Thomson scattering. Short wavelengths can be generated via Thomson scattering by two methods, (i) backscattering from relativistic electron beams, in which the radiation frequency is upshifted by the relativistic factor 4{gamma}{sup 2}, and (ii) harmonic scattering, in which a multitude of harmonics are generated with harmonic numbers extending out to the critical harmonic number nc{approx_equal}a{sub 0}{sup 3} {much_gt} 1, where a{sub 0} {approx_equal}10{sup -9}{lambda}I{sup 1/2}, {lambda} is the laser wavelength in {mu}m and I is the laser intensity in W/cm{sup 2}. Laser synchrotron sources are capable of generating short ({approx_lt} ps) x-ray pulses with high peak flux ({approx_gt} 10{sup 21} photons/s) and brightness ({approx_gt}{sup 19} photons/s-mm{sup 2}-mrad{sup 2} 0.1%BW. As the electron beam radiates via Thomson scattering, it can subsequently be cooled, i.e., the beam emittance and energy spread can be reduced. This cooling can occur on rapid ({approximately} ps) time scales. In addition, electron distributions with sufficiently small axial energy spreads can be used to generate coherent XUV radiation via a laser-pumped FEL mechanism.
Dynamics of high power and long pulse laser propagation and its control in underdense plasmas
NASA Astrophysics Data System (ADS)
Nakatsutsumi, M.; Fuchs, J.; Antici, P.; Audebert, P.; Bourgeois, N.; Grech, M.; Kodama, R.; Lin, T.; Marqués, J. R.; Riazuelo, G.; Romagnani, L.; Tikhonchuk, V.
2006-10-01
The study of intense laser pulse propagation through long underdense plasmas is of crucial importance for inertial confinement fusion (ICF). We have performed a systematic study of long pulse beams (τL=400ps,I=10^10˜10^12Wcm-2) propagating through the underdense plasmas (ne=10^19˜10^20cm-3), by controlling two filaments created from the pulses with variable delay and intensity ratio. These experiments have been performed at the LULI laser facility. The results show that the earlier pulse affects the propagation characteristics of the later pulse. The 2D time-resolved sampling camera provides the ability to examine the possibility of enhanced propagation, collimation, and guiding of a trailing pulse induced by an earlier pulse. These facts are of interest for ICF and other applications. In particular, this study opens perspectives, through shaping the pulses temporally, for the control of propagation of long pulses in the low density plasmas that are present within ICF hohlraums.
Phenomena in oscillating downward propagating flames induced by external laser irradiation method
Park, June Sung; Fujita, Osamu; Honko, Teruaki; Yamada, Yuichiro; Ito, Hiroyuki; Nakamura, Yuji
2010-11-15
Experiments in C{sub 2}H{sub 4}/CO{sub 2}-O{sub 2} premixed flames (Le < 1) propagating downwardly in a tube have been conducted to observe transition phenomena from laminar flame front to turbulent flame propagation triggered by external laser irradiation method. To investigate the exact motions of flame tip fluctuation at the initial moment of irradiating CO{sub 2} laser, the completely flat flame front is selected as a default flame, which is corresponding to the primary acoustic instability as reported by Searby (1992). According to the time-resolved observation, the flame front exposed to CO{sub 2} laser beam shows extremely unstable flame motions in which highly curved flame front towards unburned mixture is subject to diffusive-thermal instability. Then, the sudden enhanced burning state (increased flame surface) caused by flame instability induces the secondary acoustic instability which is akin to the observation in Ref. In the present study, we report the detailed descriptions of flame fronts on the transient behaviors leading the primary acoustic instability to turbulent motions actively induced by the absorption of externally irradiated CO{sub 2} laser beam. (author)
More About Beam-Steering Subsystem For Laser Communication
NASA Technical Reports Server (NTRS)
Page, Norman A.; Chen, Chien-Chu; Hemmati, Hamid; Lesh, James R.
1995-01-01
Two reports present additional information about developmental beam-steering subsystem of laser-communication system. Aspects of this subsystem described previously in "Beam-Steering Subsystem for Laser Communication" (NPO-19069) and "Digital Controller for Laser-Beam-Steering Subsystem" (NPO-19193). Reports reiterate basic principles of operation of beam-steering subsystem and of laser-communication system as whole. Also presents some of details of optical and mechanical design of prototype of subsystem, called Optical Communication Demonstrator.
The analysis of optical wave beams propagation in lens systems
NASA Astrophysics Data System (ADS)
Kazakov, I.; Mosentsov, S.; Moskaletz, O.
2016-08-01
In this paper some aspects of the formation and propagation of optical wave beams in lens systems were considered. As an example, the two-lens optical information processing system was considered. Analysis of the two-lens optical circuit has been made with a systems approach perspective. As part of the radio-optical analogies had been applied certain provisions of the theory of dynamical systems to the spatial optical system. The lens system is represented as a simple series-connected optical elements with known spatial impulse response. General impulse response of such a system has been received, as well as consider some special cases of the impulse response. The question of the relationship between the parameters and the size of the input aperture lenses for undistorted transmission of the optical signal has been considered. Analysis of the energy loss resulting from the finite aperture of the lens. It's based on an assessment of the fraction of radiation that propagates beyond the lens. Analysis showed that the energy losses depend explicitly on the following parameters: radiation wavelength, distance between input aperture and lens, and ratio of the input aperture and lens aperture. With the computer help simulation the dependence of losses was shown on the above parameters
Systems analysis on laser beamed power
NASA Technical Reports Server (NTRS)
Zeiders, Glenn W., Jr.
1993-01-01
The NASA SELENE power beaming program is intended to supply cost-effective power to space assets via Earth-based lasers and active optics systems. Key elements of the program are analyzed, the overall effort is reviewed, and recommendations are presented.
Coherent beam combiner for a high power laser
Dane, C. Brent; Hackel, Lloyd A.
2002-01-01
A phase conjugate laser mirror employing Brillouin-enhanced four wave mixing allows multiple independent laser apertures to be phase locked producing an array of diffraction-limited beams with no piston phase errors. The beam combiner has application in laser and optical systems requiring high average power, high pulse energy, and low beam divergence. A broad range of applications exist in laser systems for industrial processing, especially in the field of metal surface treatment and laser shot peening.
Propagation properties of quantized Laguerre-Gaussian beams in atmospheric turbulence
NASA Astrophysics Data System (ADS)
Saito, Aya; Tanabe, Ayano; Kurihara, Makoto; Hashimoto, Nobuyuki; Ogawa, Kayo
2016-03-01
Effect of scintillations is serious problems in optical systems which require the atmospheric propagation, the optimization of optical system to minimize the effects of scintillation have been examined using the simulation of propagation in atmospheric turbulence. The analytic studies of scintillation index of LG beams show that LG beams have less scintillation than Gaussian beams. However, in these researches, the diameter of receiving aperture was set as point receiver without considering the effects of aperture averaging, which is phenomenon that reduced scintillations over finite aperture. In this paper, considering size of a receiving aperture, the propagation losses and the scintillation index of LG beams are simulated. Also, for practical applications, propagation properties of "quantized" LG(5,1) beams simulated. As a result of the examination, the propagation losses and the scintillation index of LG beams is smaller than those of Gaussian beams. By applying LG beams for optical wireless communications, it is expected to improve better the effect of scintillations than using Gaussian beams. The result is that the scintillation index of quantized LG beams is equal to those of LG beams, and it suggested that quantized LG beams can be treat the quantized LG beams the same as LG beams.
Phasing surface emitting diode laser outputs into a coherent laser beam
Holzrichter, John F.
2006-10-10
A system for generating a powerful laser beam includes a first laser element and at least one additional laser element having a rear laser mirror, an output mirror that is 100% reflective at normal incidence and <5% reflective at an input beam angle, and laser material between the rear laser mirror and the output mirror. The system includes an injector, a reference laser beam source, an amplifier and phase conjugater, and a combiner.
Ultra-Intense Laser Pulse Propagation in Gas and Plasma
Antonsen, T. M.
2004-10-26
It is proposed here to continue their program in the development of theories and models capable of describing the varied phenomena expected to influence the propagation of ultra-intense, ultra-short laser pulses with particular emphasis on guided propagation. This program builds upon expertise already developed over the years through collaborations with the NSF funded experimental effort lead by Professor Howard Milchberg here at Maryland, and in addition the research group at the Ecole Polytechnique in France. As in the past, close coupling between theory and experiment will continue. The main effort of the proposed research will center on the development of computational models and analytic theories of intense laser pulse propagation and guiding structures. In particular, they will use their simulation code WAKE to study propagation in plasma channels, in dielectric capillaries and in gases where self focusing is important. At present this code simulates the two-dimensional propagation (radial coordinate, axial coordinate and time) of short pulses in gas/plasma media. The plasma is treated either as an ensemble of particles which respond to the ponderomotive force of the laser and the self consistent electric and magnetic fields created in the wake of pulse or as a fluid. the plasma particle motion is treated kinetically and relativistically allowing for study of intense pulses that result in complete cavitation of the plasma. The gas is treated as a nonlinear medium with rate equations describing the various stages of ionization. A number of important physics issues will be addressed during the program. These include (1) studies of propagation in plasma channels, (2) investigation of plasma channel nonuniformities caused by parametric excitation of channel modes, (3) propagation in dielectric capillaries including harmonic generation and ionization scattering, (4) self guided propagation in gas, (5) studies of the ionization scattering instability recently
NASA Astrophysics Data System (ADS)
Mitri, F. G.
2016-08-01
In this work, counterintuitive effects such as the generation of an axial (i.e., long the direction of wave motion) zero-energy flux density (i.e., axial Poynting singularity) and reverse (i.e., negative) propagation of nonparaxial quasi-Gaussian electromagnetic (EM) beams are examined. Generalized analytical expressions for the EM field's components of a coherent superposition of two high-order quasi-Gaussian vortex beams of opposite handedness and different amplitudes are derived based on the complex-source-point method, stemming from Maxwell's vector equations and the Lorenz gauge condition. The general solutions exhibiting unusual effects satisfy the Helmholtz and Maxwell's equations. The EM beam components are characterized by nonzero integer degree and order (n ,m ) , respectively, an arbitrary waist w0, a diffraction convergence length known as the Rayleigh range zR, and a weighting (real) factor 0 ≤α ≤1 that describes the transition of the beam from a purely vortex (α =0 ) to a nonvortex (α =1 ) type. An attractive feature for this superposition is the description of strongly focused (or strongly divergent) wave fields. Computations of the EM power density as well as the linear and angular momentum density fluxes illustrate the analysis with particular emphasis on the polarization states of the vector potentials forming the beams and the weight of the coherent beam superposition causing the transition from the vortex to the nonvortex type. Should some conditions determined by the polarization state of the vector potentials and the beam parameters be met, an axial zero-energy flux density is predicted in addition to a negative retrograde propagation effect. Moreover, rotation reversal of the angular momentum flux density with respect to the beam handedness is anticipated, suggesting the possible generation of negative (left-handed) torques. The results are particularly useful in applications involving the design of strongly focused optical laser
Schiffer, J.P.; Hangst, J.S.; Nielsen, J.S.
1995-08-01
In collaboration with the Arhus group, the laser cooling of a beam bunched by an rf electrode was investigated at the ASTRID storage ring. A single laser is used for unidirectional cooling, since the longitudinal velocity of the beam will undergo {open_quotes}synchrotron oscillations{close_quotes} and the ions are trapped in velocity space. As the cooling proceeds the velocity spread of the beam, as well as the bunch length is measured. The bunch length decreases to the point where it is limited only by the Coulomb repulsion between ions. The measured length is slightly (20-30%) smaller than the calculated limit for a cold beam. This may be the accuracy of the measurement, or may indicate that the beam still has a large transverse temperature so that the longitudinal repulsion is less than would be expected from an absolutely cold beam. Simulations suggest that the coupling between transverse and longitudinal degrees of freedom is strong -- but this issue will have to be resolved by further measurements.
Higher--order CO/sub 2/ laser beam spot size and depth of focus determined
Luxon, J.T.; Parker, D.E.
1981-06-01
Measurements of higher-order CO/sub 2/ laser beam spot size have been made and found in good agreement with a Hermite-Gaussian rectangular beam propagation model. A modified working definition of spot size is introduced, and a useful depth of focus relationship is presented. It is shown that a single measurement of spot size for any higher-order mode is all that is required to reasonably predict spot size for the same laser operating in different modes. Alternatively, beam size can be predicted theoretically on the basis of the optical cavity parameters.
Nonlinear interaction of intense hypergeometric Gaussian subfamily laser beams in plasma
NASA Astrophysics Data System (ADS)
Sobhani, H.; Vaziri (Khamedi), M.; Rooholamininejad, H.; Bahrampour, A. R.
2016-07-01
Propagation of Hypergeometric-Gaussian laser beam in a nonlinear plasma medium is investigated by considering the Source Dependent Expansion method. A subfamily of Hypergeometric-Gaussian beams with a non-negative, even and integer radial index, can be expressed as the linear superposition of finite number of Laguerre-Gaussian functions. Propagation of Hypergeometric-Gaussian beams in a nonlinear plasma medium depends on the value of radial index. The bright rings' number of these beams is changed during the propagation in plasma medium. The effect of beam vortex charge number l and initial (input) beam intensity on the self-focusing of Hypergeometric-Gaussian beams is explored. Also, by choosing the suitable initial conditions, Hypergeometric-Gaussian subfamily beams can be converted to one or more mode components that a typical of mode conversion may be occurred. The self-focusing of these winding beams can be used to control the focusing force and improve the electron bunch quality in laser plasma accelerators.
Adaptive slit beam shaping for direct laser written waveguides.
Salter, P S; Jesacher, A; Spring, J B; Metcalf, B J; Thomas-Peter, N; Simmonds, R D; Langford, N K; Walmsley, I A; Booth, M J
2012-02-15
We demonstrate an improved method for fabricating optical waveguides in bulk materials by means of femtosecond laser writing. We use an LC spatial light modulator (SLM) to shape the beam focus by generating adaptive slit illumination in the pupil of the objective lens. A diffraction grating is applied in a strip across the SLM to simulate a slit, with the first diffracted order mapped onto the pupil plane of the objective lens while the zeroth order is blocked. This technique enables real-time control of the beam-shaping parameters during writing, facilitating the fabrication of more complicated structures than is possible using nonadaptive methods. Waveguides are demonstrated in fused silica with a coupling loss to single-mode fibers in the range of 0.2 to 0.5 dB and propagation loss <0.4 dB/cm.
NASA Astrophysics Data System (ADS)
Arlantsev, S. V.; Grigor'yants, E. A.; Vadkovskii, A. D.; Zvorykin, V. D.; Metreveli, G. E.
1994-03-01
The transport of high-current electron beams from vacuum diodes to the laser chamber of the GARPUN wide-aperture excimer laser was investigated experimentally and theoretically. The processes involving the transport of fast electrons in argon and krypton in a longitudinal magnetic field were also studied. Pumping by counter-propagating electron beams resulted in the deposition of up to 2.1 kJ of energy into the active medium of the laser, which corresponded to a specific excitation power of ~0.8 MW cm-3 with an inhomogeneity of less than 20% over a 12 cm × 18 cm aperture. The efficiency of the energy deposition by electron beams was ~60% and the overall efficiency of the laser pumping system was ~16%.
Laser-driven ion acceleration with hollow laser beams
Brabetz, C. Kester, O.; Busold, S.; Bagnoud, V.; Cowan, T.; Deppert, O.; Jahn, D.; Roth, M.; Schumacher, D.
2015-01-15
The laser-driven acceleration of protons from thin foils irradiated by hollow high-intensity laser beams in the regime of target normal sheath acceleration (TNSA) is reported for the first time. The use of hollow beams aims at reducing the initial emission solid angle of the TNSA source, due to a flattening of the electron sheath at the target rear side. The experiments were conducted at the PHELIX laser facility at the GSI Helmholtzzentrum für Schwerionenforschung GmbH with laser intensities in the range from 10{sup 18} W cm{sup −2} to 10{sup 20} W cm{sup −2}. We observed an average reduction of the half opening angle by (3.07±0.42)° or (13.2±2.0)% when the targets have a thickness between 12 μm and 14 μm. In addition, the highest proton energies were achieved with the hollow laser beam in comparison to the typical Gaussian focal spot.
Coherent beam combination of fiber lasers with a strongly confined waveguide: numerical model.
Tao, Rumao; Si, Lei; Ma, Yanxing; Zhou, Pu; Liu, Zejin
2012-08-20
Self-imaging properties of fiber lasers in a strongly confined waveguide (SCW) and their application in coherent beam combination (CBC) are studied theoretically. Analytical formulas are derived for the positions, amplitudes, and phases of the N images at the end of an SCW, which is important for quantitative analysis of waveguide CBC. The formulas are verified with experimental results and numerical simulation of a finite difference beam propagation method (BPM). The error of our analytical formulas is less than 6%, which can be reduced to less than 1.5% with Goos-Hahnchen penetration depth considered. Based on the theoretical model and BPM, we studied the combination of two laser beams based on an SCW. The effects of the waveguide refractive index and Gaussian beam waist are studied. We also simulated the CBC of nine and 16 fiber lasers, and a single beam without side lobes was achieved.
Beam loading in a laser-plasma accelerator using a near-hollow plasma channel
Schroeder, C. B.; Benedetti, C.; Esarey, E.; Leemans, W. P.
2013-12-15
Beam loading in laser-plasma accelerators using a near-hollow plasma channel is examined in the linear wake regime. It is shown that, by properly shaping and phasing the witness particle beam, high-gradient acceleration can be achieved with high-efficiency, and without induced energy spread or emittance growth. Both electron and positron beams can be accelerated in this plasma channel geometry. Matched propagation of electron beams can be achieved by the focusing force provided by the channel density. For positron beams, matched propagation can be achieved in a hollow plasma channel with external focusing. The efficiency of energy transfer from the wake to a witness beam is calculated for single ultra-short bunches and bunch trains.
Laser-cooled continuous ion beams
Schiffer, J.P.; Hangst, J.S.; Nielsen, J.S.
1995-08-01
A collaboration with a group in Arhus, Denmark, using their storage ring ASTRID, brought about better understanding of ion beams cooled to very low temperatures. The longitudinal Schottky fluctuation noise signals from a cooled beam were studied. The fluctuation signals are distorted by the effects of space charge as was observed in earlier measurements at other facilities. However, the signal also exhibits previously unobserved coherent components. The ions` velocity distribution, measured by a laser fluorescence technique suggests that the coherence is due to suppression of Landau damping. The observed behavior has important implications for the eventual attainment of a crystalline ion beam in a storage ring. A significant issue is the transverse temperature of the beam -- where no direct diagnostics are available and where molecular dynamics simulations raise interesting questions about equilibrium.
Hybrid laser-beam-shaping system for rotatable dual beams with long depth of focus
NASA Astrophysics Data System (ADS)
Chou, Fu-Lung; Chen, Cheng-Huan; Lin, Yu-Chung; Lin, Mao-Chi
2016-10-01
A laser processing system consisting of two diffractive elements and one refractive element is proposed enabling a Gaussian laser beam to be transformed into two beams with a depth of focus of up to 150 µm and focal spot smaller than 5 µm. For specific laser processing, the two beams are rotatable when the beam-splitting diffractive element is rotated. The overall system is versatile for laser cutting and drilling.
Hybrid laser-beam-shaping system for rotatable dual beams with long depth of focus
NASA Astrophysics Data System (ADS)
Chou, Fu-Lung; Chen, Cheng-Huan; Lin, Yu-Chung; Lin, Mao-Chi
2016-08-01
A laser processing system consisting of two diffractive elements and one refractive element is proposed enabling a Gaussian laser beam to be transformed into two beams with a depth of focus of up to 150 µm and focal spot smaller than 5 µm. For specific laser processing, the two beams are rotatable when the beam-splitting diffractive element is rotated. The overall system is versatile for laser cutting and drilling.
Semiconductor laser asymmetry cutting glass with laser induced thermal-crack propagation
NASA Astrophysics Data System (ADS)
Zhao, Chunyang; Zhang, Hongzhi; Wang, Yang
2014-12-01
Laser induced thermal-crack propagation (LITP) makes the material to produce an uneven temperature field, maximum temperature can't soften or melt the material, induces the thermal stress, then the crack separates along the cutting path. One of the problems in laser asymmetry cutting glass with LITP is the cutting deviation along scanning trajectory. This study lays great emphasis on considering the dynamic extension of crack to explain the reason of the cutting deviation in laser asymmetry cutting glass, includes asymmetric linear cutting and a quarter of a circular curve cutting. This paper indicates the experiments of semiconductor laser asymmetry cutting glass with LITP. Optical microscope photographs of the glass sheet are obtained to examine the cutting deviation. The extended finite element method (XFEM) is used to simulate the dynamic propagation of crack; the crack path does not have to be specified a priori. The cutting deviation mechanism and the crack propagation process are studied by the stress fields using finite element software ABAQUS. This work provides a theoretical basis to investigate the cutting deviation in laser asymmetry cutting glass. In semiconductor laser asymmetry cutting glass, the tensile stress is the basis of crack propagation, then the compressive stress not only makes the crack to extend stably, but also controls the direction of crack propagation.
Nonparaxial optical vortices and Kummer laser beams
NASA Astrophysics Data System (ADS)
Kovalev, Alexey A.; Kotlyar, Victor V.; Nalimov, Anton G.
2013-09-01
Two approaches to describe nonparaxial optical vortices were considered. One approach is to use a revised Kirchhoff integral, which does not neglect the relief of an optical element. Using this integral and the finite-difference time-domain method it is shown that an optical vortex generated by a refractive spiral plate with a relief step has an asymmetric profile. The annular diffraction pattern in the vortex beam cross-section is found to be disturbed not only for the near-field diffraction but also for the middle-field diffraction, at a distance of several Fresnel lengths. Another approach is to solve the Helmholtz equation without any approximations. An analytical solution to describe propagation of a light beam in the positive direction of the optical axis was found. The complex amplitude of such a beam is found to be in direct proportion to the product of two linearly independent solutions of Kummer's differential equation. Relationships for a particular case of such beams-namely, the Hankel-Bessel (HB) beams-are deduced. The autofocusing of the HB beams is studied.
Ipser, J.R.
1986-08-01
The propagation of laser beams through the atmosphere is discussed. Processes which are pertinent are Raman scattering, self-focusing of beams, and two-photon absorption. Comments on the subroutine PRAMAN are given in the appendix. This subroutine calculates the effect of stimulated Raman scattering in the atmosphere. (WRF)
Guiding of Laser Beams in Plasmas by Radiation Cascade Compression
NASA Astrophysics Data System (ADS)
Kalmykov, Serguei; Shvets, Gennady
2006-11-01
The near-resonant heatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few-fs electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the beat frequency. Consequently, the cascade of sidebands red- and blue-shifted from the fundamental by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion [S. Kalmykov and G. Shvets, Phys. Rev. E 73, 046403 (2006)]. In the 3D cylindrical geometry, the frequency-downshifted EPW not only modulates the laser frequency, but also causes the pulse to self-focus [P. Gibbon, Phys. Fluids B 2, 2196 (1990)]. After self-focusing, the multi-frequency laser beam inevitably diverges. Remarkably, the longitudinal beatnote compression can compensate the intensity drop due to diffraction. A train of high-intensity radiation spikes with continually evolving longitudinal profile can be self-guided over several Rayleigh lengths in homogeneous plasmas. High amplitude of the EPW is maintained over the entire propagation length. Numerical experiments on the electron acceleration in the cascade-driven (cascade-guided) EPW [using the code WAKE by P. Mora and T. M. Antonsen Jr., Phys. Plasmas 4, 217 (1997)] show that achieving GeV electron energy is possible under realistic experimental parameters.
Guiding of Laser Beams in Plasmas by Radiation Cascade Compression
Kalmykov, Serguei; Shvets, Gennady
2006-11-27
The near-resonant heatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few-fs electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the beat frequency. Consequently, the cascade of sidebands red- and blue-shifted from the fundamental by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion [S. Kalmykov and G. Shvets, Phys. Rev. E 73, 046403 (2006)]. In the 3D cylindrical geometry, the frequency-downshifted EPW not only modulates the laser frequency, but also causes the pulse to self-focus [P. Gibbon, Phys. Fluids B 2, 2196 (1990)]. After self-focusing, the multi-frequency laser beam inevitably diverges. Remarkably, the longitudinal beatnote compression can compensate the intensity drop due to diffraction. A train of high-intensity radiation spikes with continually evolving longitudinal profile can be self-guided over several Rayleigh lengths in homogeneous plasmas. High amplitude of the EPW is maintained over the entire propagation length. Numerical experiments on the electron acceleration in the cascade-driven (cascade-guided) EPW [using the code WAKE by P. Mora and T. M. Antonsen Jr., Phys. Plasmas 4, 217 (1997)] show that achieving GeV electron energy is possible under realistic experimental parameters.
Guiding of laser beams in plasmas by electromagnetic cascade compression
NASA Astrophysics Data System (ADS)
Kalmykov, S.; Shvets, G.
2006-10-01
The near-resonant beatwave excitation of an electron plasma wave (EPW) can be employed for generating trains of few- femtosecond electromagnetic pulses in rarefied plasmas. The EPW produces a co-moving index grating that induces a laser phase modulation at the difference frequency. As a result, the cascade of sidebands red- and blue-shifted by integer multiples of the beat frequency is generated in the laser spectrum. When the beat frequency is lower than the electron plasma frequency, the phase chirp enables laser beatnote compression by the group velocity dispersion. In the 3D cylindrical geometry, the frequency-downshifted EPW not only modulates the laser phase, but also causes the pulse to self-focus [P. Gibbon, Phys. Fluids B 2, 2196 (1990)]. After self-focusing, the laser beam inevitably diverges. Remarkably, the longitudinal beatnote compression can compensate the intensity drop due to diffraction. Thus, a train of high intensity radiation spikes with continually evolving longitudinal profile can be self- guided over several Rayleigh lengths in homogeneous plasma. High amplitude of the EPW is maintained over the entire propagation length. Numerical experiments on the electron acceleration in the cascade-driven (cascade-guided) EPW show that achieving GeV energy is possible under realistic experimental conditions.
Underlying conservation and stability laws in nonlinear propagation of axicon-generated Bessel beams
NASA Astrophysics Data System (ADS)
Porras, Miguel A.; Ruiz-Jiménez, Carlos; Losada, Juan Carlos
2015-12-01
In light filamentation induced by axicon-generated, powerful Bessel beams, the spatial propagation dynamics in the nonlinear medium determines the geometry of the filament channel and hence its potential applications. We show that the observed steady and unsteady Bessel beam propagation regimes can be understood in a unified way from the existence of an attractor and its stability properties. The attractor is identified as the nonlinear unbalanced Bessel beam (NLUBB) whose inward Hänkel beam amplitude equals the amplitude of the linear Bessel beam that the axicon would generate in linear propagation. A simple analytical formula that determines the NLUBB attractor is given. Steady or unsteady propagation depends on whether the attracting NLUBB has a small, exponentially growing, unstable mode. In the case of unsteady propagation, periodic, quasiperiodic, or chaotic dynamics after the axicon reproduces similar dynamics after the development of the small unstable mode into the large perturbation regime.
SRμCT study of crack propagation within laser-welded aluminum-alloy T-joints
NASA Astrophysics Data System (ADS)
Herzen, J.; Beckmann, F.; Riekehr, S.; Bayraktar, F. S.; Haibel, A.; Staron, P.; Donath, T.; Utcke, S.; Kocak, M.; Schreyer, A.
2008-08-01
Using laser welding in fabrication of metallic airframes reduces the weight and hence fuel consumption. Currently only limited parts of the airframes are welded. To increase laser beam welded parts, there is the need for a better understanding of crack propagation and crack-pore interaction within the welds. Laser beam welded Al-alloys may contain isolated small process pores and their role and interaction with growing crack need to be investigated. The present paper presents the first results of a crack propagation study in laser beam welded (LBW) Al-alloy T-joints using synchrotron radiation based micro computed tomography (SRμCT). A region-of-interest technique was used, since the specimens exceeded the field of view of the X-ray detector. As imaging with high density resolution at high photon energies is very challenging, a feasibility measurement on a small laser weld, cut cylindrically from the welded region of a T-joint, was done before starting the crack-propagation study. This measurement was performed at the beamline HARWI-II at DESY to demonstrate the potential of the SRμCT as non-destructive testing method. The result has shown a high density resolution, hence, the different Al alloys used in the T-joint and the weld itself were clearly separated. The quantitative image analysis of the 3D data sets allows visualizing non-destructively and calculating the pore size distribution.
Skupsky, Stanley; Craxton, R. Stephen; Soures, John
1990-01-01
In order to control the intensity of a laser beam so that its intensity varies uniformly and provides uniform illumination of a target, such as a laser fusion target, a broad bandwidth laser pulse is spectrally dispersed spatially so that the frequency components thereof are spread apart. A disperser (grating) provides an output beam which varies spatially in wavelength in at least one direction transverse to the direction of propagation of the beam. Temporal spread (time delay) across the beam is corrected by using a phase delay device (a time delay compensation echelon). The dispersed beam may be amplified with laser amplifiers and frequency converted (doubled, tripled or quadrupled in frequency) with nonlinear optical elements (birefringent crystals). The spectral variation across the beam is compensated by varying the angle of incidence on one of the crystals with respect to the crystal optical axis utilizing a lens which diverges the beam. Another lens after the frequency converter may be used to recollimate the beam. The frequency converted beam is recombined so that portions of different frequency interfere and, unlike interference between waves of the same wavelength, there results an intensity pattern with rapid temoral oscillations which average out rapidly in time thereby producing uniform illumination on target. A distributed phase plate (also known as a random phase mask), through which the spectrally dispersed beam is passed and then focused on a target, is used to provide the interference pattern which becomes nearly modulation free and uniform in intensity in the direction of the spectral variation.
Skupsky, S.; Craxton, R.S.; Soures, J.
1990-10-02
In order to control the intensity of a laser beam so that its intensity varies uniformly and provides uniform illumination of a target, such as a laser fusion target, a broad bandwidth laser pulse is spectrally dispersed spatially so that the frequency components thereof are spread apart. A disperser (grating) provides an output beam which varies spatially in wavelength in at least one direction transverse to the direction of propagation of the beam. Temporal spread (time delay) across the beam is corrected by using a phase delay device (a time delay compensation echelon). The dispersed beam may be amplified with laser amplifiers and frequency converted (doubled, tripled or quadrupled in frequency) with nonlinear optical elements (birefringent crystals). The spectral variation across the beam is compensated by varying the angle of incidence on one of the crystals with respect to the crystal optical axis utilizing a lens which diverges the beam. Another lens after the frequency converter may be used to recollimate the beam. The frequency converted beam is recombined so that portions of different frequency interfere and, unlike interference between waves of the same wavelength, there results an intensity pattern with rapid temporal oscillations which average out rapidly in time thereby producing uniform illumination on target. A distributed phase plate (also known as a random phase mask), through which the spectrally dispersed beam is passed and then focused on a target, is used to provide the interference pattern which becomes nearly modulation free and uniform in intensity in the direction of the spectral variation. 16 figs.
Propagation and absorption of high-intensity femtosecond laser radiation in diamond
Kononenko, V V; Konov, V I; Gololobov, V M; Zavedeev, E V
2014-12-31
Femtosecond interferometry has been used to experimentally study the photoexcitation of the electron subsystem of diamond exposed to femtosecond laser pulses of intensity 10{sup 11} to 10{sup 14} W cm{sup -2}. The carrier concentration has been determined as a function of incident intensity for three harmonics of a Ti : sapphire laser (800, 400 and 266 nm). The results demonstrate that, in a wide range of laser fluences (up to those resulting in surface and bulk graphitisation), a well-defined multiphoton absorption prevails. We have estimated nonlinear absorption coefficients for pulsed radiation at λ = 800 nm (four-photon transition) and at 400 and 266 nm (indirect and direct two-photon transitions, respectively). It has also been shown that, at any considerable path length of a femtosecond pulse in diamond (tens of microns or longer), the laser beam experiences a severe nonlinear transformation, determining the amount of energy absorbed by the lattice, which is important for the development of technology for diamond photostructuring by ultrashort pulses. The competition between wave packet self-focusing and the plasma defocusing effect is examined as a major mechanism governing the propagation of intense laser pulses in diamond. (interaction of laser radiation with matter. laser plasma)
The laser propagation demonstration: a STEM-based outreach project
NASA Astrophysics Data System (ADS)
Spencer, Mark F.; Steinbock, Michael J.; Hyde, Milo W.; Marciniak, Michael A.
2014-09-01
Investment in laser technology has led to significant advances in remote sensing, astronomy, industrial processing, and medical technology. To celebrate this rich heritage and promote public awareness in optics and photonics, the SPIE Student Chapter at the Air Force Institute of Technology (AFIT) developed the Laser Propagation Demonstration (LPD). This interactive demonstration serves as one of AFIT's legacy outreach projects for events involving education in science, technology, engineering, and mathematics (STEM). Initially developed with funding from a LaserFest grant awarded by SPIE in 2010, the goal was to develop a simple hands-on demonstration to highlight the optical effects of diffraction, refraction, and attenuation on laser propagation. Since then, the LPD has undergone several upgrades (thanks to the continued support from a 2012 SPIE Education Outreach Grant) to better highlight these optical phenomena and make it more engaging for a wider range of audiences. This paper celebrates the continued success of the LPD and shares the knowledge gained with an overview of its design and use in STEM-based outreach events.
Microdrilling in steel using ultrashort pulsed laser beams with radial and azimuthal polarization.
Kraus, Martin; Ahmed, Marwan Abdou; Michalowski, Andreas; Voss, Andreas; Weber, Rudolf; Graf, Thomas
2010-10-11
A linear to radial and/or azimuthal polarization converter (LRAC) has been inserted into the beam delivery of a micromachining station equipped with a picosecond laser system. Percussion drilling and helical drilling in steel have been performed using radially as well as azimuthally polarized infrared radiation at 1030 nm. The presented machining results are discussed on the basis of numerical simulations of the polarization-dependent beam propagation inside the fabricated capillaries.
The influence of the energy reservoir on the plasma channel in focused femtosecond laser beams
NASA Astrophysics Data System (ADS)
Dergachev, A. A.; Ionin, A. A.; Kandidov, V. P.; Mokrousova, D. V.; Seleznev, L. V.; Sinitsyn, D. V.; Sunchugasheva, E. S.; Shlenov, S. A.
2015-06-01
The influence of the energy reservoir on plasma channel formation during the filamentation of tightly focused femtosecond laser beams was studied both experimentally and numerically. It was found that for the reservoir localized near the propagation axis, its diameter is much smaller than in the case of a collimated beam and decreases in the vicinity of the focus. A small diaphragm placed in the focal area does not eliminate the plasma channel behind the focal point.
Filamentation and Forward Brillouin Scatter of Entire Smoothed and Aberrated Laser Beams
Still, C.H.; Berger, R.L.; Langdon, A.B.; Hinkel, D.E.; Williams, E.A.
1999-10-29
Laser-plasma interactions are sensitive to both the fine-scale speckle and the larger scale envelope intensity of the beam. For some time, simulations have been done on volumes taken from part of the laser beam cross-section, and the results from multiple simulations extrapolated to predict the behavior of the entire beam. However, extrapolation could very well miss effects of the larger scale structure on the fine-scale. The only definitive method is to simulate the entire beam. These very large calculations have been infeasible until recently, but they are now possible on massively parallel computers. Whole beam simulations show the dramatic difference in the propagation and break up of smoothed and aberrated beams.
Beam-energy and laser beam-profile monitor at the BNL LINAC
Connolly, R.; Briscoe, B.; Degen, C.; DeSanto, L.; Meng, W.; Minty, M.; Nayak, S.; Raparia, D.; Russo, T.
2010-05-02
We are developing a non-interceptive beam profile and energy monitor for H{sup -} beams in the high energy beam transport (HEBT) line at the Brookhaven National Lab linac. Electrons that are removed from the beam ions either by laser photodetachment or stripping by background gas are deflected into a Faraday cup. The beam profile is measured by stepping a narrow laser beam across the ion beam and measuring the electron charge vs. transverse laser position. There is a grid in front of the collector that can be biased up to 125kV. The beam energy spectrum is determined by measuring the electron charge vs. grid voltage. Beam electrons have the same velocity as the beam and so have an energy of 1/1836 of the beam protons. A 200MeV H{sup -} beam yields 109keV electrons. Energy measurements can be made with either laser-stripped or gas-stripped electrons.
Propagation properties of Gaussian Schell-model array beams in non-Kolmogorov turbulence
NASA Astrophysics Data System (ADS)
Song, Zhenzhen; Liu, Zhengjun; Zhou, Keya; Sun, Qiongge; Liu, Shutian
2016-10-01
A stochastic beam generated by a recently introduced Gaussian Schell-model array (GSMA) source (2015 Opt. Lett. 40 5662) is investigated. We derive the analytical propagation formulae for the spectral density and the propagation factor in non-Kolmogorov turbulence by utilizing the extended Huygens-Fresnel principle and second-order moments of the Wigner distribution function. Numerical results show that the lattice patterns of GSMA beams, which keep propagation-invariant in free space, are destroyed by the turbulence at sufficiently large distances. The GSMA beams have significant advantage over the Gaussian Schell-model beam in the robustness of the destructive effect of non-Kolmogorov turbulence, especially for the GSMA beam with more lattice elements and bigger relative separation distance of each lattice element. The effects of beam parameters and non-Kolmogorov turbulence on the propagation factor are analyzed in detail.
Freeform beam shaping for high-power multimode lasers
NASA Astrophysics Data System (ADS)
Laskin, Alexander; Laskin, Vadim
2014-03-01
Widening of using high power multimode lasers in industrial laser material processing is accompanied by special requirements to irradiance profiles in such technologies like metal or plastics welding, cladding, hardening, brazing, annealing, laser pumping and amplification in MOPA lasers. Typical irradiance distribution of high power multimode lasers: free space solid state, fiber-coupled solid state and diodes lasers, fiber lasers, is similar to Gaussian. Laser technologies can be essentially improved when irradiance distribution on a workpiece is uniform (flattop) or inverse-Gauss; when building high-power pulsed lasers it is possible to enhance efficiency of pumping and amplification by applying super-Gauss irradiance distribution with controlled convexity. Therefore, "freeform" beam shaping of multimode laser beams is an important task. A proved solution is refractive field mapping beam shaper like Shaper capable to control resulting irradiance profile - with the same unit it is possible to get various beam profiles and choose optimum one for a particular application. Operational principle of these devices implies transformation of laser irradiance distribution by conserving beam consistency, high transmittance, providing collimated low divergent output beam. Using additional optics makes it possible to create resulting laser spots of necessary size and round, elliptical or linear shape. Operation out of focal plane and, hence, in field of lower wavefront curvature, allows extending depth of field. The refractive beam shapers are implemented as telescopes and collimating systems, which can be connected directly to fiber-coupled lasers or fiber lasers, thus combining functions of beam collimation and irradiance transformation.
Compact prisms for polarisation splitting of fibre laser beams
Davydov, B L; Yagodkin, D I
2005-11-30
Simple compact monoprisms for spatial splitting of polarised laser beams with relatively small diameters (no more than 1 mm) are considered. Prisms can be made of optically inactive CaCO{sub 3}, {alpha}-BaB{sub 2}O{sub 4} ({alpha}-BBO), LiIO{sub 3}, LiNbO{sub 3}, YVO{sub 4}, and TiO{sub 2} crystals known in polarisation optics. The exact solution of the Snell equation for the extraordinary wave reflected from a surface arbitrarily tilted to its wave vector is obtained. The analysis of variants of the solution allows the fabrication of prisms with any deviation angles of the extraordinary wave by preserving the propagation direction of the ordinary wave. Three variants of prisms are considered: with minimised dimensions, with the Brewster output of the extraordinary beam, and with the deviation of the extraordinary wave by 90{sup 0}. Calcite prisms with the deviation angles for the extraordinary beam {approx}19{sup 0} and 90{sup 0} are tested experimentally. (control of laser radiation parameters)
Laser-driven relativistic electron beam interaction with solid dielectric
NASA Astrophysics Data System (ADS)
Sarkisov, G. S.; Ivanov, V. V.; Leblanc, P.; Sentoku, Y.; Yates, K.; Wiewior, P.; Chalyy, O.; Astanovitskiy, A.; Bychenkov, V. Yu.; Jobe, D.; Spielman, R. B.
2012-07-01
The multi-frames shadowgraphy, interferometry and polarimetry diagnostics with sub-ps time resolution were used for an investigation of ionization wave dynamics inside a glass target induced by laser-driven relativistic electron beam. Experiments were done using the 50 TW Leopard laser at the UNR. For a laser flux of ˜2×1018W/cm2 a hemispherical ionization wave propagates at c/3. The maximum of the electron density inside the glass target is ˜2×1019cm-3. Magnetic and electric fields are less than ˜15 kG and ˜1 MV/cm, respectively. The electron temperature has a maximum of ˜0.5 eV. 2D interference phase shift shows the "fountain effect" of electron beam. The very low ionization inside glass target ˜0.1% suggests a fast recombination at the sub-ps time scale. 2D PIC-simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields.
Laser-driven relativistic electron beam interaction with solid dielectric
Sarkisov, G. S.; Ivanov, V. V.; Leblanc, P.; Sentoku, Y.; Yates, K.; Wiewior, P.; Chalyy, O.; Astanovitskiy, A.; Bychenkov, V. Yu.; Jobe, D.; Spielman, R. B.
2012-07-30
The multi-frames shadowgraphy, interferometry and polarimetry diagnostics with sub-ps time resolution were used for an investigation of ionization wave dynamics inside a glass target induced by laser-driven relativistic electron beam. Experiments were done using the 50 TW Leopard laser at the UNR. For a laser flux of {approx}2 Multiplication-Sign 10{sup 18}W/cm{sup 2} a hemispherical ionization wave propagates at c/3. The maximum of the electron density inside the glass target is {approx}2 Multiplication-Sign 10{sup 19}cm{sup -3}. Magnetic and electric fields are less than {approx}15 kG and {approx}1 MV/cm, respectively. The electron temperature has a maximum of {approx}0.5 eV. 2D interference phase shift shows the 'fountain effect' of electron beam. The very low ionization inside glass target {approx}0.1% suggests a fast recombination at the sub-ps time scale. 2D PIC-simulations demonstrate radial spreading of fast electrons by self-consistent electrostatic fields.
Attraction and repulsion of multi-color laser beams in plasmas: a computational study
Yi, S. A.; Kalmykov, S.; Shvets, G.
2009-01-22
The nonlinear interaction of high-power multi-color laser beams in plasmas is investigated numerically. Both the relativistic mass increase and the driven plasma wave contribute to the mutual beam-beam interaction and to the development of the electromagnetic cascade. The propagation of the individual cascade sidebands is modelled in the paraxial approximation. The resulting set of coupled nonlinear envelope equations is solved numerically using a newly developed pseudospectral method. We predict that two beams intersecting in the plasma can either attract or deflect each other depending on whether their frequency detuning is slightly below or above the electron Langmuir frequency.
Optical remote diagnostics of atmospheric propagating beams of ionizing radiation
Karl JR., Robert R.
1990-03-06
Data is obtained for use in diagnosing the characteristics of a beam of ionizing radiation, such as charged particle beams, neutral particle beams, and gamma ray beams. In one embodiment the beam is emitted through the atmosphere and produces nitrogen fluorescence during passage through air. The nitrogen fluorescence is detected along the beam path to provide an intensity from which various beam characteristics can be calculated from known tabulations. Optical detecting equipment is preferably located orthogonal to the beam path at a distance effective to include the entire beam path in the equipment field of view.
NASA Astrophysics Data System (ADS)
Furumoto, Tatsuaki; Kasai, Atsushi; Tachiya, Hiroshi; Hosokawa, Akira; Ueda, Takashi
2010-09-01
In dental treatment, many types of laser beams have been used for various surgical treatments, and the influences of laser beam irradiation on bactericidal effect have been investigated. However, most of the work has been performed by irradiating to an agar plate with the colony of bacteria, and very few studies have been reported on the physical mechanism of bactericidal effects induced by laser beam irradiation. This paper deals with the measurement of dynamic stress induced in extracted human enamel by irradiation with Nd:YAG laser beams. Laser beams can be delivered to the enamel surface through a quartz optical fiber. Dynamic stress induced in the specimen using elastic wave propagation in a cylindrical long bar made of aluminum alloy is measured. Laser induced stress intensity is evaluated from dynamic strain measured by small semiconductor strain gauges. Carbon powder and titanium dioxide powder were applied to the human enamel surface as absorbents. Additionally, the phenomenon of laser beam irradiation to the human enamel surface was observed with an ultrahigh speed video camera. Results showed that a plasma was generated on the enamel surface during laser beam irradiation, and the melted tissues were scattered in the vertical direction against the enamel surface with a mushroom-like wave. Averaged scattering velocity of the melted tissues was 25.2 m/s. Induced dynamic stress on the enamel surface increased with increasing laser energy in each absorbent. Induced dynamic stresses with titanium dioxide powder were superior to those with carbon powder. Induced dynamic stress was related to volume of prepared cavity, and induced stress for the removal of unit volume of human enamel was 0.03 Pa/mm 3.
Effects of laser beam shapes on depths of penetration in dermatology
NASA Astrophysics Data System (ADS)
Saghafi, S.; Withford, M.; Farhadi, M.; Ghaderi, R.; Granmayeh, A.; Ghoranneviss, Z.; Moravej, F.
2006-04-01
For many medical laser applications, a particular beam shape is required. The output beam of a laser can be approximated by a Gaussian, higher-order Gaussian, annular or a flat-top (uniform) distribution. Here, we investigate, analytically and experimentally, the effects of laser beam shapes on the depths of penetration in treatments of any types of vascular malformation. In order to do this, the physical and optical parameters of the skin must be known and measured correctly. Using the Monte-Carlo method for seven layers of skin, a software predicting the beam propagation and intensity distribution inside of tissue has been developed in our centre. In this paper, a 15 watts copper vapour laser producing (511nm and 578 nm) for treatments of patients having PWS (Port Wine Stains) of different sizes is employed. The output beam of this laser was Gaussian. We have designed a beam homogenizer converting a Gaussian beam into flat-top distribution. Therefore, the effects of the laser irradiance beam shape (before and after beam shaping) on the depth of penetration have been investigated before people's treatments. Initially, two laser beams having Gaussian output distribution of the same power are considered. The diameter of one beam is 5mm and the other one is 10 mm. The intensity distribution of these beam inside of similar tissues are predicted and it is concluded that for deep but small size PWS the Gaussian beam having smaller beam diameter is more suitable than the larger spot size. Then, the beam intensity distribution inside of the same tissue (similar parameters) for two flat-top beams of the same power but different diameters (one is 5mm and the other is 10 mm) is calculated. It can be seen that the flat top beam of bigger spot-size has smaller penetration depth but it illuminates a larger area uniformly (suitable for large but not deep area). The depth of penetration of flat-top beam with smaller spot size is deeper but it illuminates a smaller area uniformly
Propagation of a finite optical beam in an inhomogeneous medium.
Lutomirski, R F; Yura, H T
1971-07-01
The first part of this paper is devoted to extending the Huygens-Fresnel principle to a medium that exhibits a spatial (but not temporal) variation in index of refraction. Utilizing a reciprocity theorem for a monochromatic disturbance in a weakly inhomogeneous medium, it is shown that the secondary wave-front will be determined by the envelope of spherical wavelets from the primary wavefront, as in the vacuum problem, but that each wavelet is now determined by the propagation of a spherical wave in the refractive medium. In the second part, the above development is applied to the case in which the index of refraction is a random variable; a further application of the reciprocity theorem results in a formula for the mean intensity distribution from a finite aperture in terms of the complex disturbance in the aperture and the modulation transfer function (MTF) for a spherical wave in the medium. The results are applicable for an arbitrary complex disturbance in the transmitting aperture in both the Fresnel and Fraunhofer regions of the aperture. Using a Kolmogorov spectrum for the index of refraction fluctuations and a second-order expression for the MTF, the formula is used to calculate the mean intensity distribution for a plane wave diffracting from a circular aperture and to give approximate expressions for the beam spreading at various ranges. PMID:20111181
Truncated Thermal Equilibrium Distribution for Intense Beam Propagation
Ronald C. Davidson; Hong Qin; Steven M. Lund
2003-02-26
An intense charged-particle beam with directed kinetic energy ({lambda}{sub b}-1)m{sub b}c{sup 2} propagates in the z-direction through an applied focusing field with transverse focusing force modeled by F{sub foc} = -{lambda}{sub b}m{sub b}{omega}{sub beta}{sup 2} {perpendicular} x {perpendicular} in the smooth focusing approximation. This paper examines properties of the axisymmetric, truncated thermal equilibrium distribution F(sub)b(r,p perpendicular) = A exp (-H Perpendicular/T perpendicular (sub)b) = (H perpendicular-E(sub)b), where A, T perpendicular (sub)b, and E (sub)b are positive constants, and H perpendicular is the Hamiltonian for transverse particle motion. The equilibrium profiles for beam number density, n(sub)b(r) = * d{sup 2}pF(sub)b(r,p perpendicular), and transverse temperature, T perpendicular (sub)b(r) = * d{sup 2}p(p{sup 2} perpendicular/2 lambda (sbu)bm (sub)b)F(sub)b(r,p perpendicular), are calculated self-consistently including space-charge effects. Several properties of the equilibrium profiles are noteworthy. For example, the beam has a sharp outer edge radius r(sub)b with n(sub)b(r greater than or equal to rb) = 0, where r(sub)b depends on the value of E(sub)b/T (sub)perpendicular(sub)b. In addition, unlike the choice of a semi-Gaussian distribution, F{sup SG}(sub)b = A exp (-p{sup 2}(sub)perpendicular/2lambda(sub)bm(sub)bTperpendicular(sub)b) = (r-r(sub)b), the truncated thermal equilibrium distribution F(sub)b(r,p) depends on (r,p) only through the single-particle constant of the motion Hperpendiuclar and is therefore a true steady-state solution (*/*t = 0) of the nonlinear Vlasov-Maxwell equations.
Beam control and laser characterization for NIF
Boege, S. J., LLNL
1998-06-10
The demanding energy, power, pulse shape, focusability, pointing, and availability requirements placed on the 192 National Ignition Facility (NIF) beams lead to the need for an automatic operation capability that is well beyond that of previous inertial confinement fusion (ICF) lasers. Alignment, diagnostic, and wavefront correction subsystems are integrated in an approach that, by permitting maximal sharing of instrumentation between subsystems, meets performance requirements at a reasonable cost.
Laser beamed power: Satellite demonstration applications
NASA Technical Reports Server (NTRS)
Landis, Geoffrey A.; Westerlund, Larry H.
1992-01-01
It is possible to use a ground-based laser to beam light to the solar arrays of orbiting satellites, to a level sufficient to provide all or some of the operating power required. Near-term applications of this technology for providing supplemental power to existing satellites are discussed. Two missions with significant commercial pay-off are supplementing solar power for radiation-degraded arrays and providing satellite power during eclipse for satellites with failed batteries.
Smith-Purcell terahertz radiation from laser modulated electron beam over a metallic grating
NASA Astrophysics Data System (ADS)
Kumar, Pawan; Bhasin, Lalita; Tripathi, V. K.; Kumar, Ashok; Kumar, Manoj
2016-09-01
We propose a novel scheme of terahertz (THz) radiation generation from the beat frequency modulation of an electron beam by two co-propagating lasers and the generation of terahertz radiation by the modulated beam passing over a periodic metallic grating. The lasers cause velocity modulation of the beam by exerting a longitudinal ponderomotive force on it. In the drift space between the modulator and metallic grating, the velocity modulation translates into density and current modulation. The modulated beam, propagating over the grating of specific wave number, induces space periodic image current in the conductor that emits beat frequency Smith-Purcell radiation. With 1 μm, 4 × 1016 W/cm2 lasers, beam current modulation of the order of 50% can be achieved at optimum lengths of the modulator and drift space. Employing 10 mA, 0.5 MeV short-period electron beam, propagating at a height of 50 μ m above the grating of period 150 μm, one may obtain THz radiated power of the order of 6 mW at 10 THz.
Propagation properties of Airy-Gaussian vortex beams through the gradient-index medium.
Zhao, Ruihuang; Deng, Fu; Yu, Weihao; Huang, Jiayao; Deng, Dongmei
2016-06-01
Propagation of Airy-Gaussian vortex (AiGV) beams through the gradient-index medium is investigated analytically and numerically with the transfer matrix method. Deriving the analytic expression of the AiGV beams based on the Huygens diffraction integral formula, we obtain the propagate path, intensity and phase distributions, and the Poynting vector of the first- and second-order AiGV beams, which propagate through the paraxial ABCD system. The ballistic trajectory is no longer conventional parabolic but trigonometric shapes in the gradient-index medium. Especially, the AiGV beams represent the singular behavior at the propagation path and the light intensity distribution. The phase distribution and the Poynting vector exhibit in reverse when the AiGV beams through the singularity. As the order increases, the main lobe of the AiGV beams is gradually overlapped by the vortex core. Further, the sidelobe weakens when the AiGV beams propagate nearly to the singularity. Additionally, the figure of the Poynting vector of the AiGV beams proves the direction of energy flow corresponding to the intensity distribution. The vortex of the second-order AiGV beams is larger, and the propagation velocity is faster than that of the first order. PMID:27409428
NASA Astrophysics Data System (ADS)
Mira, J.; Solana, P.; Bolado, R.
2003-03-01
In many physical processes, there is uncertainty in the parameters which define the process and this input uncertainty is propagated through the equations of the process to its output. Experimental design is essential to quantify the uncertainty of the input parameters. If the process is simulated by a computer code, propagation of uncertainties is carried out through the Monte Carlo method by sampling in the input parameter distribution and running the code for each sample. It is then important to obtain information about the way in which the parameters are influential on the output of the process. This is useful in order to decide how to sample in the input space when propagating uncertainties and on which parameters experimental effort should be more concentrated. Here, we use dimensional and similarity analyses to reduce the dimension of the input variable space with no loss of information and profit from this reduction when propagating uncertainties by Monte Carlo. Using dimensional analysis, the output is expressed in terms of the inputs through a series of dimensionless numbers, a dimension reduction is achieved since there are less dimensionless numbers than original parameters. In order to minimize the uncertainty of the estimation of the output, propagation of uncertainties should be carried out by sampling on the space of the dimensionless numbers and not on the space of the original parameters. The purpose of this paper is an application of propagation of uncertainties to a code which simulates the interaction of metal drilling with a laser beam, where there exists uncertainty in the absorbed intensity of the beam and the density of the medium. By sampling in the reduced input space, a substantial variance reduction is achieved for the estimators of the mean, variance and distribution function of the output. Moreover, the output is found to depend on the intensity and the density through their quotient.
Laser beam collimation using Talbot interferometry
NASA Technical Reports Server (NTRS)
Ganesan, A. R.; Venkateswarlu, Putcha
1993-01-01
A modified method of checking laser beam collimation using a single grating and a right-angled prism is presented. The self-images (Talbot images) of a grating illuminated by a collimated beam are formed at some distance from the grating. The use of a right-angled prism makes it possible to carry out the folding of the self-image with respect to the original grating and to ensure that the grating lines in the self-image and the actual grating are inclined at equal angles with respect to horizontal direction. It is concluded that the proposed collimation test method has an in-built reference and does not require precise orientation of the grating as in the two-grating method. Large beams can be tested with a small-size assembly.
Active annular-beam laser autocollimator system.
Yoder, P R; Schlesinger, E R; Chickvary, J L
1975-08-01
An autocollimator using an axicon and a beam expander telescope to generate a 12.5-cm. o.d. annular beam of helium-neon laser light with high (25:1) diameter-to-width ratio has been developed. It is used with a two-axis, electromagnetically actuated mirror assembly to acquire automatically and maintain dynamically autocollimation from a nearby but separately mounted annular mirror. The servo system controls beam alignment even though angular vibratory motions of the annular mirror make it appear to tilt relative to the autocollimator as much as 7 mrad at frequencies below 300 Hz. This paper describes the optical system and the alignment sensing and control system.
Hydrodynamics simulations of 2 (omega) laser propagation in underdense gasbag plasmas
Meezan, N B; Divol, L; Marinak, M M; Kerbel, G D; Suter, L J; Stevenson, R M; Slark, G E; Oades, K
2004-04-05
Recent 2{omega} laser propagation and stimulated Raman backscatter (SRS) experiments performed on the Helen laser have been analyzed using the radiation-hydrodynamics code hydra. These experiments utilized two diagnostics sensitive to the hydrodynamics of gasbag targets: a fast x-ray framing camera (FXI) and an SRS streak spectrometer. With a newly implemented nonlocal thermal transport model, hydra is able to reproduce many features seen in the FXI images and the SRS streak spectra. Experimental and simulated side-on FXI images suggest that propagation can be explained by classical laser absorption and the resulting hydrodynamics. Synthetic SRS spectra generated from the hydra results reproduce the details of the experimental SRS streak spectra. Most features in the synthetic spectra can be explained solely by axial density and temperature gradients. The total SRS backscatter increases with initial gasbag fill density up to {approx} 0.08 times the critical density, then decreases. Images from a near-backscatter camera (NBI) show that severe beam spray is not responsible for the trend in total backscatter. Filamentation does not appear to be a significant factor in gasbag hydrodynamics. The simulation and analysis techniques established here can be used in upcoming experimental campaigns on the Omega laser facility and the National Ignition Facility.
Hydrodynamics simulations of 2{omega} laser propagation in underdense gasbag plasmas
Meezan, N.B.; Divol, L.; Marinak, M.M.; Kerbel, G.D.; Suter, L.J.; Stevenson, R.M.; Slark, G.E.; Oades, K.
2004-12-01
Recent 2{omega} laser propagation and stimulated Raman backscatter (SRS) experiments performed on the Helen laser have been analyzed using the radiation-hydrodynamics code HYDRA [M. M. Marinak, G. D. Kerbel, N. A. Gentile, O. Jones, D. Munro, S. Pollaine, T. R. Dittrich, and S. W. Haan, Phys. Plasmas 8, 2275 (2001)]. These experiments utilized two diagnostics sensitive to the hydrodynamics of gasbag targets: a fast x-ray framing camera (FXI) and a SRS streak spectrometer. With a newly implemented nonlocal thermal transport model, HYDRA is able to reproduce many features seen in the FXI images and the SRS streak spectra. Experimental and simulated side-on FXI images suggest that propagation can be explained by classical laser absorption and the resulting hydrodynamics. Synthetic SRS spectra generated from the HYDRA results reproduce the details of the experimental SRS streak spectra. Most features in the synthetic spectra can be explained solely by axial density and temperature gradients. The total SRS backscatter increases with initial gasbag fill density up to {approx_equal}0.08 times the critical density, then decreases. Data from a near-backscatter imaging camera show that severe beam spray is not responsible for the trend in total backscatter. Filamentation does not appear to be a significant factor in gasbag hydrodynamics. The simulation and analysis techniques established here can be used in ongoing experimental campaigns on the Omega laser facility and the National Ignition Facility.
Propagation features of beams with axially symmetric polarization
NASA Astrophysics Data System (ADS)
Nesterov, A. V.; Niziev, V. G.
2001-04-01
The general solution of the wave equation for axially symmetric polarized (ASP) beams consists of two independent solutions: an azimuthally polarized beam and a beam with longitudinal and radial field components. The maximum of the longitudinal field is at the beam axis where the transverse component is equal to zero. While the longitudinal component is maximum in the waist it does not contribute to beam divergence here, and therefore the wavefront of ASP-beams is flat in the focal plane. The ASP-beams are free from polarization aberrations, which are inherent for linearly polarized beams passing through a lens with large annular apertures, and these beams are prospective for experiments on obtaining `diffraction-free' beams. The formulae and their electromagnetic field analysis in the case of sharp focusing of ASP-beams in the Debye approximation are presented.
Beam Emittance Measurement with Laser Wire Scanners in the ILC Beam Delivery System
Agapov, I.; Blair, G.A.; Woodley, M.; /SLAC
2008-02-01
Accurate measurement of the beam phase-space is essential for the next generation of electron accelerators. A scheme for beam optics optimization and beam matrix reconstruction algorithms for the diagnostics section of the beam delivery system of the International Linear Collider based on laser-wire beam profile monitors are discussed. Possible modes of operation of the laser-wire system together with their corresponding performance are presented. Based on these results, prospects for reconstructing the ILC beam emittance from representative laser-wire beam size measurements are evaluated.
Laser-Beam-Absorption Chemical-Species Monitor
NASA Technical Reports Server (NTRS)
Gersh, Michael; Goldstein, Neil; Lee, Jamine; Bien, Fritz; Richtsmeier, Steven
1996-01-01
Apparatus measures concentration of chemical species in fluid medium (e.g., gaseous industrial process stream). Directs laser beam through medium, and measures intensity of beam after passage through medium. Relative amount of beam power absorbed in medium indicative of concentration of chemical species; laser wavelength chosen to be one at which species of interest absorbs.
NASA Astrophysics Data System (ADS)
Li, Ya-Qing; Wu, Zhen-Sen
2012-05-01
On the basis of the extended Huygens—Fresnel principle and the model of the refractive-index structure constant in the atmospheric turbulence proposed by the International Telecommunication Union-Radio Communication Sector, the characteristics of the partially coherent Gaussian Schell-model (GSM) beams propagating in slanted atmospheric turbulence are studied. Using the cross- spectral density function (CSDF), we derive the expressions for the effective beam radius, the spreading angle, and the average intensity. The variance of the angle-of-arrival fluctuation and the wander effect of the GSM beam in the turbulence are calculated numerically. The influences of the coherence degree, the propagation distance, the propagation height, and the waist radius on the propagation characteristics of the partially coherent beams are discussed and compared with those of the fully coherent Gaussian beams.
NASA Astrophysics Data System (ADS)
Yan, H.; Lü, B.
2010-06-01
The propagation of spectral Stokes singularities (vortices) of stochastic electromagnetic vortex beams through atmospheric turbulence is studied, where the electromagnetic Gaussian Schell-model (GSM) vortex beam is taken as an illustrative example. It is shown that the spectral Stokes vortices S 12 ( C-points), S 23 and S 31 introduced to describe the polarization singularities of stochastic electromagnetic beams appear in turbulence. The motion, creation, annihilation and polarization changes of S 12, S 23 and S 31 vortices, as well as the handedness inversion of S 12 vortices may appear as the propagation distance or one beam parameter varies. In the process the topological relationship holds true. In comparison with the free-space propagation, the variation of the refractive index structure constant Cn2 in atmospheric turbulence results in similar effects as above. The dependence of S 12, S 23 and S 31 vortices on the propagation distance and beam and turbulence parameters are illustrated by numerical examples.
T-3 electron-beam-excited laser system
Klein, R A
1981-02-01
A laser system specifically designed to study the kinetics of electron-beam driven systems is described. Details of the system are given along with measurements of the electron-beam uniformity and deposition in the laser medium. Some HF laser results obtained with this system are also given.
NASA Astrophysics Data System (ADS)
Charnotskii, Mikhail; Baker, Gary J.
2011-06-01
Asymptotic theory of the finite beam scintillations (Charnotskii, WRM, 1994, JOSA A, 2010) provides an exhaustive description of the dependence of the beam scintillation index on the propagation conditions, beam size and focusing. However the complexity of the asymptotic configuration makes it difficult to apply these results for the practical calculations of the scintillation index (SI). We propose an estimation technique and demonstrate some examples of the calculations of the scintillation index dependence on the propagation path length, initial beam size, wavelength and turbulence strength for the beam geometries and propagation scenarios that are typical for applications. We suggest simple analytic bridging approximations that connect the specific asymptotes with the accuracy sufficient for the engineering estimates. Proposed technique covers propagation of the wide, narrow, collimated and focused beams under the weak and strong scintillation conditions. Direct numeric simulation of the beam waves propagation through turbulence expediently complements the asymptotic theory being most efficient when the governing scales difference is not very large. We performed numerical simulations of the beam wave propagation through turbulence for conditions that partially overlap with the major parameter space domains of the asymptotic theory. The results of the numeric simulation are used to confirm the asymptotic theory and estimate the accuracy of the bridging approximations.
Propagation and self-healing ability of a Bessel-Gaussian beam modulated by Bessel gratings
NASA Astrophysics Data System (ADS)
Qiao, Chunhong; Feng, Xiaoxing; Chu, Xiuxiang
2016-04-01
A new type of Bessel-like beam which can be generated by using Bessel gratings to modulate the amplitude and phase of a Bessel beam is proposed. In analogy to study a Bessel beam in free space, the intensity evolution and self-healing property of the Bessel-like beam have been studied. Meanwhile, based on the Fresnel diffraction integral, the propagation of the Bessel-like beam in free space has also been investigated. Results show that the Bessel-like beam and the Bessel-Gaussian-like beams have some special and interesting properties.
Zhou, Yuan; Yuan, Yangsheng; Qu, Jun; Huang, Wei
2016-05-16
Analytical formulas are derived for the average intensity, the root-mean-square (rms) angular width, and the M^{2}-factor of Laguerre-Gaussian correlated Schell-model (LGCSM) beam propagating in non-Kolmogorov turbulence. The influence of the beam and turbulence parameters on the LGCSM beam is numerically calculated. It is shown that the quality of the LGCSM beam can be improved by choosing appropriate beam or turbulence parameter values. It is also found that the LGCSM beam has advantage over the Gaussian Schell-model (GSM) beam for reducing the turbulence-induced degradation. Our results will have some theoretical reference value for optical communications.
NASA Astrophysics Data System (ADS)
Land, Phillip; Majumdar, Arun K.
2016-05-01
This paper describes a new concept of mitigating signal distortions caused by random air-water interface using an adaptive optics (AO) system. This is the first time the concept of using an AO for mitigating the effects of distortions caused mainly by a random air-water interface is presented. We have demonstrated the feasibility of correcting the distortions using AO in a laboratory water tank for investigating the propagation effects of a laser beam through an airwater interface. The AO system consisting of a fast steering mirror, deformable mirror, and a Shack-Hartmann Wavefront Sensor for mitigating surface water distortions has a unique way of stabilizing and aiming a laser onto an object underneath the water. Essentially the AO system mathematically takes the complex conjugate of the random phase caused by air-water interface allowing the laser beam to penetrate through the water by cancelling with the complex conjugates. The results show the improvement of a number of metrics including Strehl ratio, a measure of the quality of optical image formation for diffraction limited optical system. These are the first results demonstrating the feasibility of developing a new sensor system such as Laser Doppler Vibrometer (LDV) utilizing AO for mitigating surface water distortions.
Collaborative Research: Instability and transport of laser beam in plasma
Rose, Harvey Arnold; Lushnikov, Pavel
2014-11-18
Our goal was to determine the onset of laser light scattering due to plasma wave instabilities. Such scatter is usually regarded as deleterious since laser beam strength is thereby diminished. While this kind of laser-plasma-instability (LPI) has long been understood for the case of coherent laser light, the theory of LPI onset for a laser beam with degraded coherence is recent. Such a laser beam fills plasma with a mottled intensity distribution, which has large fluctuations. The key question is: do the exceptionally large fluctuations control LPI onset or is it controlled by the relatively quiescent background laser intensity? We have answered this question. This is significant because LPI onset power in the former case is typically small compared to that of the latter. In addition, if large laser intensity fluctuations control LPI onset, then nonlinear effects become significant for less powerful laser beams than otherwise estimated.
Quantum well, beam deflecting surface emitting lasers
NASA Technical Reports Server (NTRS)
Kim, Jae H. (Inventor)
1992-01-01
This invention relates to surface emitting semiconductor lasers (SELs), with integrated 45 deg. beam deflectors. A SEL is formed on a wafer including vertical mirrors and 45 deg. beam deflectors formed in grooves by tilted ion beam etching. A SEL is a lattice matched, or unstrained, AlGaAs/GaAs GRINSCH SQW SEL. An alternate embodiment is shown, in which a SEL is lattice mismatched, strained or pseudomorphic, or InGaAs/AlGaAs GRINSCH SQW SEL which emits radiation at a wavelength to which its substrate is transparent. Both SELs exhibit high output power, low threshold current density, and relatively high efficiency, and each are processing compatible with conventional large scale integration technology. Such SELs may be fabricated in large numbers from single wafers. The novel features of this invention include the use of tilted ion beam etching to form a pair of grooves each including vertical mirrors and 45 deg. beam deflectors. The embodiment provides substantial circuit design flexibility because radiation may be coupled both up and/or down through the substrate.
Quantum well, beam deflecting surface emitting lasers
NASA Astrophysics Data System (ADS)
Kim, Jae H.
1992-10-01
This invention relates to surface emitting semiconductor lasers (SELs), with integrated 45 deg. beam deflectors. A SEL is formed on a wafer including vertical mirrors and 45 deg. beam deflectors formed in grooves by tilted ion beam etching. A SEL is a lattice matched, or unstrained, AlGaAs/GaAs GRINSCH SQW SEL. An alternate embodiment is shown, in which a SEL is lattice mismatched, strained or pseudomorphic, or InGaAs/AlGaAs GRINSCH SQW SEL which emits radiation at a wavelength to which its substrate is transparent. Both SELs exhibit high output power, low threshold current density, and relatively high efficiency, and each are processing compatible with conventional large scale integration technology. Such SELs may be fabricated in large numbers from single wafers. The novel features of this invention include the use of tilted ion beam etching to form a pair of grooves each including vertical mirrors and 45 deg. beam deflectors. The embodiment provides substantial circuit design flexibility because radiation may be coupled both up and/or down through the substrate.
Quantum well, beam deflecting surface emitting lasers
NASA Astrophysics Data System (ADS)
Kim, Jae H.
1991-06-01
This invention relates to surface emitting semiconductor lasers (SELs), with integrated 45 deg. beam deflectors. A SEL is formed on a wafer including vertical mirrors and 45 deg. beam deflectors formed in grooves by tilted ion beam etching. A SEL is a lattice matched, or unstrained, AlGaAs/GaAs GRINSCH SQW SEL. An alternate embodiment is shown, in which a SEL is lattice mismatched, strained or pseudomorphic, or InGaAs/AlGaAs GRINSCH SQW SEL which emits radiation at a wavelength to which its substrate is transparent. Both SELs exhibit high output power, low threshold current density, and relatively high efficiency, and each are processing compatible with conventional large scale integration technology. Such SELs may be fabricated in large numbers from single wafers. The novel features of this invention include the use of tilted ion beam etching to form a pair of grooves each including vertical mirrors and 45 deg. beam deflectors. The embodiment provides substantial circuit design flexibility because radiation may be coupled both up and/or down through the substrate.
Defocusing of an ion beam propagating in background plasma due to two-stream instability
Tokluoglu, Erinc; Kaganovich, Igor D.
2015-04-15
The current and charge neutralization of charged particle beams by background plasma enable ballistic beam propagation and have a wide range of applications in inertial fusion and high energy density physics. However, the beam-plasma interaction can result in the development of collective instabilities that may have deleterious effects on ballistic propagation of an ion beam. In the case of fast, light-ion beams, non-linear fields created by instabilities can lead to significant defocusing of the beam. We study an ion beam pulse propagating in a background plasma, which is subjected to two-stream instability between the beam ions and plasma electrons, using PIC code LSP. The defocusing effects of the instability on the beam can be much more pronounced in small radius beams. We show through simulations that a beamlet produced from an ion beam passed through an aperture can be used as a diagnostic tool to identify the presence of the two-stream instability and quantify its defocusing effects. The effect can be observed on the Neutralized Drift Compression Experiment-II facility by measuring the spot size of the extracted beamlet propagating through several meters of plasma.
NASA Astrophysics Data System (ADS)
Li, Jinhong; Lü, Baida
2009-04-01
Taking the Gaussian Schell-model (GSM) vortex beam as a typical example of partially coherent vortex beams, the analytical expressions for the cross-spectral density, average intensity and root mean square (rms) width of a GSM vortex beam with topological charge m = ± 1 propagating through atmospheric turbulence are derived, which enable us to study the propagation properties of GSM vortex beams through atmospheric turbulence and evolution behavior of their coherent vortices. The propagation of GSM vortex beams undergoes several stages of evolution of the intensity profile in both free space and turbulence, and is different from that of GSM non-vortex beams. An increase of the refraction index structure constant Cn2 and a decrease of the spatial correlation length σ0 speed up the evolution process. The beam-width spreading of GSM vortex beams is less than that of GSM non-vortex beams. The smaller the correlation length σ0 is, the less the beam-width spreading of GSM vortex beams is affected by turbulence. The position and number of coherent vortices depend on the structure constant Cn2, correlation length σ0 and topological charge m. The smaller Cn2 and larger σ0 result in a larger propagation distance for the conservation of the topological charge in turbulence.
Efficient laser production of energetic neutral beams
NASA Astrophysics Data System (ADS)
Mollica, F.; Antonelli, L.; Flacco, A.; Braenzel, J.; Vauzour, B.; Folpini, G.; Birindelli, G.; Schnuerer, M.; Batani, D.; Malka, V.
2016-03-01
Laser-driven ion acceleration by intense, ultra-short, laser pulse has received increasing attention in recent years, and the availability of much compact and versatile ions sources motivates the study of laser-driven sources of energetic neutral atoms. We demonstrate the production of a neutral and directional beam of hydrogen and carbon atoms up to 200 keV per nucleon, with a peak flow of 2.7× {{10}13} atom s-1. Laser accelerated ions are neutralized in a pulsed, supersonic argon jet with tunable density between 1.5× {{10}17} cm-3and 6× {{10}18} cm-3. The neutralization efficiency has been measured by a time-of-flight detector for different argon densities. An optimum is found, for which complete neutralization occurs. The neutralization rate can be explained only at high areal densities (>1× {{10}17} cm-2) by single electron charge transfer processes. These results suggest a new perspective for the study of neutral production by laser and open discussion of neutralization at a lower density.
Laser beam riding guided system principle and design research
NASA Astrophysics Data System (ADS)
Qu, Zhou; Jin, Yi; Xu, Zhou; Xing, Hao
2016-01-01
With the development of science and technology, precision-strike weapons has been considered to be important for winning victory in military field. Laser guidance is a major method to execute precision-strike in modern warfare. At present, the problems of primary stage of Laser guidance has been solved with endeavors of countries. Several technical aspects of laser-beam riding guided system have been mature, such as atmosphere penetration of laser beam, clutter inhibition on ground, laser irradiator, encoding and decoding of laser beam. Further, laser beam quality, equal output power and atmospheric transmission properties are qualified for warfare situation. Riding guidance instrument is a crucial element of Laser-beam riding guided system, and is also a vital element of airborne, vehicle-mounted and individual weapon. The optical system mainly consist of sighting module and laser-beam guided module. Photoelectric detector is the most important sensing device of seeker, and also the key to acquire the coordinate information of target space. Currently, in consideration of the 1.06 u m of wavelength applied in all the semi-active laser guided weapons systems, lithium drifting silicon photodiode which is sensitive to 1.06 u m of wavelength is used in photoelectric detector. Compared to Solid and gas laser, diode laser has many merits such as small volume, simple construction, light weight, long life, low lost and easy modulation. This article introduced the composition and operating principle of Laser-beam riding guided system based on 980 nm diode laser, and made a analysis of key technology; for instance, laser irradiator, modulating disk of component, laser zooming system. Through the use of laser diode, Laser-beam riding guided system is likely to have smaller shape and very light.
16 W output power by high-efficient spectral beam combining of DBR-tapered diode lasers.
Müller, André; Vijayakumar, Deepak; Jensen, Ole Bjarlin; Hasler, Karl-Heinz; Sumpf, Bernd; Erbert, Götz; Andersen, Peter E; Petersen, Paul Michael
2011-01-17
Up to 16 W output power has been obtained using spectral beam combining of two 1063 nm DBR-tapered diode lasers. Using a reflecting volume Bragg grating, a combining efficiency as high as 93.7% is achieved, resulting in a single beam with high spatial coherence. The result represents the highest output power achieved by spectral beam combining of two single element tapered diode lasers. Since spectral beam combining does not affect beam propagation parameters, M2-values of 1.8 (fast axis) and 3.3 (slow axis) match the M2-values of the laser with lowest spatial coherence. The principle of spectral beam combining used in our experiments can be expanded to combine more than two tapered diode lasers and hence it is expected that the output power may be increased even further in the future.
Application of reactor-pumped lasers to power beaming
Repetti, T.E.
1991-10-01
Power beaming is the concept of centralized power generation and distribution to remote users via energy beams such as microwaves or laser beams. The power beaming community is presently performing technical evaluations of available lasers as part of the design process for developing terrestrial and space-based power beaming systems. This report describes the suitability of employing a nuclear reactor-pumped laser in a power beaming system. Although there are several technical issues to be resolved, the power beaming community currently believes that the AlGaAs solid-state laser is the primary candidate for power beaming because that laser meets the many design criteria for such a system and integrates well with the GaAs photodiode receiver array. After reviewing the history and physics of reactor-pumped lasers, the advantages of these lasers for power beaming are discussed, along with several technical issues which are currently facing reactor-pumped laser research. The overriding conclusion is that reactor-pumped laser technology is not presently developed to the point of being technially or economically competitive with more mature solid-state technologies for application to power beaming. 58 refs.
Zhang, Yiqi; Liu, Xing; Belić, Milivoj R; Zhong, Weiping; Wen, Feng; Zhang, Yanpeng
2015-08-15
We analytically and numerically investigate an anharmonic propagation of two-dimensional beams in a harmonic potential. We pick noncentrosymmetric beams of common interest that carry orbital angular momentum. The examples studied include superposed Bessel-Gauss (BG), Laguerre-Gauss (LG), and circular Airy (CA) beams. For the BG beams, periodic inversion, phase transition, and rotation with periodic angular velocity are demonstrated during propagation. For the LG and CA beams, periodic inversion and variable rotation are still there but not the phase transition. On the whole, the "center of mass" and the orbital angular momentum of a beam exhibit harmonic motion, but the motion of the beam intensity distribution in detail is subject to external and internal torques and forces, causing it to be anharmonic. Our results are applicable to other superpositions of finite circularly asymmetric beams.
Wu, Yuqian; Zhang, Yixin; Zhu, Yun
2016-08-01
We studied Gaussian beams with three different partially coherent models, including the Gaussian-Schell model (GSM), Laguerre-Gaussian Schell model (LGSM), and Bessel-Gaussian Schell model (BGSM), propagating through oceanic turbulence. The expressions of average intensity, beam spreading, and beam wander for GSM, LGSM, and BGSM beams in the paraxial channel are derived. We make a contrast for the three models in numerical simulations and find that the GSM beam has smaller spreading than the others, and the LGSM beam needs longer propagation distance to transform into a well-like profile of average intensity than the BGSM beam in the same conditions. The salinity fluctuation has a greater contribution to the wander of LGSM and BGSM beams than that of the temperature fluctuation. Our results can be helpful in the design of an optical wireless communication link operating in oceanic environment. PMID:27505642
Wu, Yuqian; Zhang, Yixin; Zhu, Yun
2016-08-01
We studied Gaussian beams with three different partially coherent models, including the Gaussian-Schell model (GSM), Laguerre-Gaussian Schell model (LGSM), and Bessel-Gaussian Schell model (BGSM), propagating through oceanic turbulence. The expressions of average intensity, beam spreading, and beam wander for GSM, LGSM, and BGSM beams in the paraxial channel are derived. We make a contrast for the three models in numerical simulations and find that the GSM beam has smaller spreading than the others, and the LGSM beam needs longer propagation distance to transform into a well-like profile of average intensity than the BGSM beam in the same conditions. The salinity fluctuation has a greater contribution to the wander of LGSM and BGSM beams than that of the temperature fluctuation. Our results can be helpful in the design of an optical wireless communication link operating in oceanic environment.
Laser characterization of ultrasonic wave propagation in random media.
Scales, John A; Malcolm, Alison E
2003-04-01
Lasers can be used to excite and detect ultrasonic waves in a wide variety of materials. This allows the measurement of absolute particle motion without the mechanical disturbances of contacting transducers. In an ultrasound transmission experiment, the wave field is usually accessible only on the boundaries of a sample. Using optical methods, one can measure the surface wave field, in effect, within the scattering region. Here, we describe noncontacting (laser source and detector) measurements of ultrasonic wave propagation in randomly heterogeneous rock samples. By scanning the surface of the sample, we can directly visualize the complex dynamics of diffraction, multiple scattering, mode conversion, and whispering gallery modes. We will show measurements on rock samples that have similar elastic moduli and intrinsic attenuation, but different grain sizes, and hence, different scattering strengths. The intensity data are well fit by a radiative transfer model, and we use this fact to infer the scattering mean free path. PMID:12786520
Ultraviolet laser beam monitor using radiation responsive crystals
McCann, Michael P.; Chen, Chung H.
1988-01-01
An apparatus and method for monitoring an ultraviolet laser beam includes disposing in the path of an ultraviolet laser beam a substantially transparent crystal that will produce a color pattern in response to ultraviolet radiation. The crystal is exposed to the ultraviolet laser beam and a color pattern is produced within the crystal corresponding to the laser beam intensity distribution therein. The crystal is then exposed to visible light, and the color pattern is observed by means of the visible light to determine the characteristics of the laser beam that passed through crystal. In this manner, a perpendicular cross sectional intensity profile and a longitudinal intensity profile of the ultraviolet laser beam may be determined. The observation of the color pattern may be made with forward or back scattered light and may be made with the naked eye or with optical systems such as microscopes and television cameras.
Laser systems configured to output a spectrally-consolidated laser beam and related methods
Koplow, Jeffrey P.
2012-01-10
A laser apparatus includes a plurality of pumps each of which is configured to emit a corresponding pump laser beam having a unique peak wavelength. The laser apparatus includes a spectral beam combiner configured to combine the corresponding pump laser beams into a substantially spatially-coherent pump laser beam having a pump spectrum that includes the unique peak wavelengths, and first and second selectively reflective elements spaced from each other to define a lasing cavity including a lasing medium therein. The lasing medium generates a plurality of gain spectra responsive to absorbing the pump laser beam. Each gain spectrum corresponds to a respective one of the unique peak wavelengths of the substantially spatially-coherent pump laser beam and partially overlaps with all other ones of the gain spectra. The reflective elements are configured to promote emission of a laser beam from the lasing medium with a peak wavelength common to each gain spectrum.
NASA Astrophysics Data System (ADS)
Liu, Dajun; Wang, Yaochuan; Yin, Hongming
2016-04-01
The partially coherent four-petal Gaussian vortex beam is introduced and described by analytical expressions. The analytical propagation equation for partially coherent four-petal Gaussian vortex beam in turbulent atmosphere is derived by using the extended Huygens-Fresnel diffraction integral formula. The influences of refraction index structure, beam order n, topological charge M and the coherence length on the average intensity distributions of beam are investigated by numerical examples.
NASA Astrophysics Data System (ADS)
Ando, Takahiro; Sato, Shunichi; Terakawa, Mitsuhiro; Ashida, Hiroshi; Obara, Minoru
2010-02-01
Laser-based gene delivery is attractive as a new method for topical gene therapy because of the high spatial controllability of laser energy. Previously, we demonstrated that an exogenous gene can be transferred to cells both in vitro and in vivo by applying nanosecond pulsed laser-induced stress waves (LISWs) or photomechanical waves (PMWs). In this study, we investigated effects of laser parameters on the propagation characteristics of LISWs in soft tissue phantoms and depth-dependent properties of gene transfection. Temporal pressure profiles of LISWs were measured with a hydrophone, showing that with a larger laser spot diameter, LISWs can be propagated more efficiently in phantoms with keeping flat wavefront. Phantoms with various thicknesses were placed on the rat dorsal skin that had been injected with plasmid DNA coding for reporter gene, and LISWs were applied from the top of the phantom. Efficient gene expression was observed in the rat skin that had interacted with LISWs propagating through a 15-mm-thick phantom. These results would be useful to determine appropriate laser parameters for gene delivery to deep-located tissue by transcutaneous application of LISWs.
Further remarks on electron beam pumping of laser materials.
Klein, C A
1966-12-01
This article demonstrates that recently completed studies on the energy dissipation of kilovolt electron beams in solids provide readily applicable methods for assessing the situation in electron beam pumped lasers. PMID:20057662
Growth of the current modulation in an electron beam propagating through background plasma
Uhm, Han S.
2007-11-26
Amplitude oscillation of the current modulation in an electron beam propagating through background plasma is investigated. An analytical calculation of the beam current modulation indicates amplitude oscillation at the beginning of propagation due to the perturbed space-charge fluctuation of the beam. It was also found that the mode strength of the beam current modulation further downstream grows exponentially from half, a{sub 0}/2, of the initial perturbation instead of its value of a{sub 0}, in contrast with the conventional understanding of two-stream instability. The analytical results are in good agreement with earlier simulation data.
Evolution of phase singularities of vortex beams propagating in atmospheric turbulence.
Ge, Xiao-Lu; Wang, Ben-Yi; Guo, Cheng-Shan
2015-05-01
Optical vortex beams propagating through atmospheric turbulence are studied by numerical modeling, and the phase singularities of the vortices existing in the turbulence-distorted beams are calculated. It is found that the algebraic sum of topological charges (TCs) of all the phase singularities existing in test aperture is approximately equal to the TC of the input vortex beam. This property provides us a possible approach for determining the TC of the vortex beam propagating through the atmospheric turbulence, which could have potential application in optical communication using optical vortices.
Beam shaping in high-power laser systems with using refractive beam shapers
NASA Astrophysics Data System (ADS)
Laskin, Alexander; Laskin, Vadim
2012-06-01
Beam Shaping of the spatial (transverse) profile of laser beams is highly desirable by building optical systems of high-power lasers as well in various applications with these lasers. Pumping of the crystals of Ti:Sapphire lasers by the laser radiation with uniform (flattop) intensity profile improves performance of these ultrashort pulse high-power lasers in terms of achievable efficiency, peak-power and stability, output beam profile. Specifications of the solid-state lasers built according to MOPA configuration can be also improved when radiation of the master oscillator is homogenized and then is amplified by the power amplifier. Features of building these high power lasers require that a beam shaping solution should be capable to work with single mode and multimode beams, provide flattop and super-Gauss intensity distributions, the consistency and divergence of a beam after the intensity re-distribution should be conserved and low absorption provided. These specific conditions are perfectly fulfilled by the refractive field mapping beam shapers due to their unique features: almost lossless intensity profile transformation, low output divergence, high transmittance and flatness of output beam profile, extended depth of field, adaptability to real intensity profiles of TEM00 and multimode laser sources. Combining of the refractive field mapping beam shapers with other optical components, like beam-expanders, relay imaging lenses, anamorphic optics makes it possible to generate the laser spots of necessary shape, size and intensity distribution. There are plenty of applications of high-power lasers where beam shaping bring benefits: irradiating photocathode of Free Electron Lasers (FEL), material ablation, micromachining, annealing in display making techniques, cladding, heat treating and others. This paper will describe some design basics of refractive beam shapers of the field mapping type, with emphasis on the features important for building and applications
Conceptual development of the Laser Beam Manifold (LBM)
NASA Technical Reports Server (NTRS)
Campbell, W.; Owen, R. B.
1979-01-01
The laser beam manifold, a device for transforming a single, narrow, collimated beam of light into several beams of desired intensity ratios is described. The device consists of a single optical substrate with a metallic coating on both optical surfaces. By changing the entry point, the number of outgoing beams can be varied.
Preparation of Fiber Optics for the Delivery of High-Energy High-Beam-Quality Nd:YAG Laser Pulses.
Kuhn, A; French, P; Hand, D P; Blewett, I J; Richmond, M; Jones, J D
2000-11-20
Recent improvements in design have made it possible to build Nd:YAG lasers with both high pulse energy and high beam quality. These lasers are particularly suited for percussion drilling of holes of as much as 1-mm diameter thick (a few millimeters) metal parts. An example application is the production of cooling holes in aeroengine components for which 1-ms duration, 30-J energy laser pulses produce holes of sufficient quality much more efficiently than with a laser trepanning process. Fiber optic delivery of the laser beam would be advantageous, particularly when one is processing complex three-dimensional structures. However, lasers for percussion drilling are available only with conventional bulk-optic beam delivery because of laser-induced damage problems with the small-diameter (approximately 200-400-mum) fibers that would be required for preserving necessary beam quality. We report measurements of beam degradation in step-index optical fibers with an input beam quality corresponding to an M(2) of 22. We then show that the laser-induced damage threshold of 400-mum core-diameter optical fibers can be increased significantly by a CO(2) laser treatment step following the mechanical polishing routine. This increase in laser-induced damage threshold is sufficient to propagate 25-J, 1-ms laser pulses with a 400-mum core-diameter optical fiber and an output M(2) of 31.
Beam-path conditioning for high-power laser systems
Stephens, T.; Johnson, D.; Languirand, M.
1990-01-01
Heating of mirrors and windows by high-power radiation from a laser transmitter produces turbulent density gradients in the gas near the optical surfaces. If the gradients are left uncontrolled, the resulting phase errors reduce the intensity on the target and degrade the signal returned to a receiver. Beam path conditioning maximizes the efficiency of the optical system by alleviating thermal turbulence within the beam path. Keywords: High power radiation, Beam path, Optical surface, Laser beams, Reprints. (JHD)
The beam properties of high-power InGaAs/AlGaAs quantum well lasers
NASA Astrophysics Data System (ADS)
Wu, Xiang; Lu, Zukang; Wang, You; Takiguchi, Yoshihiro; Kan, Hirofumi
2003-11-01
The vertical beam quality factor of the fundamental TE propagating mode for InGaAs/AlGaAs SCH DQW lasers emitting at 940 nm is investigated by using the transfer matrix method and the non-paraxial vectorial moment theory for non-paraxial beams. An experimental approach is given for the measurement of the equivalent vertical beam quality factor of an InGaAs/AlGaAs SCH DQW laser. It has been shown that the vertical beam quality factor Mx2 is always larger than unity, whether the thickness of the active region of LDs is much smaller than the emission wavelength or not.
NASA Astrophysics Data System (ADS)
Zhao, Yuqiong; Feng, Qibo; Zhang, Bin; Cui, Cunxing
2016-08-01
The laser beam drift is a main factor that influences laser collimation measurement accuracies. In such measurements, the common-path compensation method is an efficient way to eliminate errors which are normally produced by the laser beam drift. Based on our current common-path compensation system, compensations for the laser beam drift were studied by different laser beam radii and detectors. The measurements have shown that the compensation effect for 3 mm beam radius is better than the ones of 1.5 mm and 4.0 mm beam radii. Based on this, the ratio between the 3 mm beam radius and the total area of the quadrant detector, which is 36%, has indicated the best compensation effect.
Wandering of laser beams: a useful tool for local atmospheric investigations
NASA Astrophysics Data System (ADS)
Consortini, A.; Innocenti, C.
2010-05-01
Wandering of a laser beam in the atmosphere is due to fluctuations of the refractive index of the atmosphere and, having a strong dependence on the path length, is very useful to investigate random or continuous changes of the refractive index during time. First, we describe methods we developed and applied to locally investigate the parameters of turbulence (inner scale, outer scale and structure constant) based on our previous theory of propagation of "thin" beams. Then we describe use of thin beams to investigate the evolution of the refractive index gradient and show experimental results including non stationary and non isotropic conditions.
Wandering of laser beams: a useful tool for local atmospheric investigations
NASA Astrophysics Data System (ADS)
Consortini, A.; Innocenti, C.
2009-09-01
Wandering of a laser beam in the atmosphere is due to fluctuations of the refractive index of the atmosphere and, having a strong dependence on the path length, is very useful to investigate random or continuous changes of the refractive index during time. First, we describe methods we developed and applied to locally investigate the parameters of turbulence (inner scale, outer scale and structure constant) based on our previous theory of propagation of "thin" beams. Then we describe use of thin beams to investigate the evolution of the refractive index gradient and show experimental results including non stationary and non isotropic conditions.
A miracle happening to a laser beam in a soap film
Startsev, Aleksandr V; Stoilov, Yurii Yu
2003-05-31
When a 10 {mu}W - 3 W laser beam (for example, at 632.8 nm) is focused into a usual soap film of thickness between 10 nm and 10 {mu}m from the side or through a defect on the film surface, the self-channeling of the beam propagating in the film is observed. The beam also exhibits self-branching into submicron filaments, the so-called whiskers of length several tens of centimetres. The results of experiments on the dynamics of behaviour of these whiskers in a soap film, their polariton nature, and possible applications are discussed. (letters)
Staging Laser Plasma Accelerators for Increased Beam Energy
Panasenko, D.; Shu, A. J.; Schroeder, C. B.; Gonsalves, A. J.; Nakamura, K.; Matlis, N. H.; Cormier-Michel, E.; Plateau, G.; Lin, C.; Toth, C.; Geddes, C. G. R.; Esarey, E.; Leemans, W. P.
2009-01-22
Staging laser plasma accelerators is an efficient way of mitigating laser pump depletion in laser driven accelerators and necessary for reaching high energies with compact laser systems. The concept of staging includes coupling of additional laser energy and transporting the electron beam from one accelerating module to another. Due to laser damage threshold constraints, in-coupling laser energy with conventional optics requires distances between the accelerating modules of the order of 10 m, resulting in decreased average accelerating gradient and complicated e-beam transport. In this paper we use basic scaling laws to show that the total length of future laser plasma accelerators will be determined by staging technology. We also propose using a liquid jet plasma mirror for in-coupling the laser beam and show that it has the potential to reduce distance between stages to the cm-scale.
Staging laser plasma accelerators for increased beam energy
Panasenko, Dmitriy; Shu, Anthony; Schroeder, Carl; Gonsalves, Anthony; Nakamura, Kei; Matlis, Nicholas; Cormier-Michel, Estelle; Plateau, Guillaume; Lin, Chen; Toth, Csaba; Geddes, Cameron; Esarey, Eric; Leemans, Wim
2008-09-29
Staging laser plasma accelerators is an efficient way of mitigating laser pump depletion in laser driven accelerators and necessary for reaching high energies with compact laser systems. The concept of staging includes coupling of additional laser energy and transporting the electron beam from one accelerating module to another. Due to laser damage threshold constraints, in-coupling laser energy with conventional optics requires distances between the accelerating modules of the order of 10m, resulting in decreased average accelerating gradient and complicated e-beam transport. In this paper we use basic scaling laws to show that the total length of future laser plasma accelerators will be determined by staging technology. We also propose using a liquid jet plasma mirror for in-coupling the laser beam and show that it has the potential to reduce distance between stages to the cm-scale.
NASA Astrophysics Data System (ADS)
Aden, Mirko
2016-06-01
Radiation propagation and temperature development are simulated for laser-transmission welding of polycarbonate and polybutylene terephthalate parts. The simulations are carried out for a Gaussian- and an M-shape laser beam. For polycarbonate the shape of the laser beam is preserved, while for polybutylene terephthalate it is altered due to scattering processes. The resulting intensity and integrated intensity distribution in the joining zone are calculated for both polymers. They give rise to different temperature fields. The dimensions of the model seam are approximated by the dimensions of the melt isotherm. For polycarbonate the seam generated by a Gaussian beam has a non-homogeneous thickness and a width that is smaller than the beam diameter. For an M-shape beam it has a homogeneous thickness and its width scales with the width of the integrated intensity. For polybutylene terephthalate volumetric scattering destroys the original beam shape in the joining zone. The distributions of the integrated intensities and the dimensions of the seam are similar for both types of beams.
Propagation factors of cosine-Gaussian-correlated Schell-model beams in non-Kolmogorov turbulence.
Xu, Hua-Feng; Zhang, Zhou; Qu, Jun; Huang, Wei
2014-09-22
Based on the extended Huygens-Fresnel principle and second-order moments of the Wigner distribution function (WDF), we have studied the relative root-mean-square (rms) angular width and the propagation factor of cosine-Gaussian-correlated Schell-model (CGSM) beams propagating in non-Kolmogorov turbulence. It has been found that the CGSM beam has advantage over the Gaussian Schell-model (GSM) beam for reducing the turbulence-induced degradation, and this advantage will be more obvious for the beams with larger parameter n and spatial coherence δ or under the condition of stronger fluctuation of turbulence. The CGSM beam with larger parameter n or smaller spatial coherence δ will be less affected by the turbulence. In addition, the effects of the slope-parameter α, inner and outer scale and the refractive-index structure constant of the non-Kolmogorov's power spectrum on the propagation factor are also analyzed in detailed.
Comparison between Bessel and Gaussian beam propagation for in-depth optogenetic stimulation
NASA Astrophysics Data System (ADS)
Tejeda, Hector; Li, Ting; Mohanty, Samarendra
2013-03-01
Optogenetics technology has opened new landscapes for neuroscience research. Due to its non-diffracting and selfhealing nature, Bessel beam has potential to improve in-depth optogenetic stimulation. A detailed understanding of Bessel beam propagation, as well as its superiority over commonly used Gaussian beam, is essential for delivery and control of light irradiation for optogenetics and other light stimulation approaches. We developed an algorithm for modeling Bessel beam propagation and then compared both beam propagations in two-layered mice brain under variance of multiple variables (i.e., wavelength, numerical aperture, and beam size). These simulations show that Bessel beam is significantly advantageous over Gaussian beam for in-depth optogenetic stimulation, leading to development of lessinvasive probes. While experimental measurements using single-photon Bessel-Gauss beam generated by axicon-tip fiber did not show improved stimulation-depth, near-infrared Bessel beam generated using free-space optics and an axicon led to better penetration than near-infrared Gaussian beam.
NASA Astrophysics Data System (ADS)
Saedjalil, N.; Mehrangiz, M.; Jafari, S.; Ghasemizad, A.
2016-06-01
In this paper, the interaction of a self-focused laser beam with a DT fusion target in a plasma-loaded cone-guided ICF scheme has been presented. We propose here to merge a plasma-loaded cone with the precompressed DT target in order to strongly focus the incident laser beam on the core to improve the fusion gain. The WKB approximation is used to derive a differential equation that governs the evolution of beamwidth of the incident laser beam with the distance of propagation in the plasma medium. The effects of initial plasma and laser parameters, such as initial plasma electron temperature, initial radius of the laser beam, initial laser beam intensity and plasma density, on self-focusing and defocusing of the Gaussian laser beam have been studied. Numerical results indicate that with increasing the plasma frequency (or plasma density) in the cone, the laser beam will be self-focused noticeably, while for a thinner laser beam (with small radius), it will diverge as propagate in the cone. By evaluating the energy deposition of the relativistic electron ignitors in the fuel, the importance of electron transportation in the cone-attached shell was demonstrated. Moreover, by lessening the least energy needed for ignition, the electrons coupling with the pellet enhances. Therefore, it increases the fusion efficiency. In this scheme, with employing a plasma-loaded cone, the fusion process improves without needing an ultrahigh-intensity laser beam in a conventional ICF.
Nonlinear modes of an intense laser beam interacting with a periodic lattice of nanoparticle
Sepehri Javan, N. Homami, S. H. H.
2015-08-15
Self-guided nonlinear propagation of an intense laser beam through a periodic lattice of nanoparticle is studied. Using a perturbative method, a cubic nonlinear wave equation describing the laser-nanoparticle interaction in the weakly relativistic regime is derived. Transverse Eigen modes of the laser, nonlinear dispersion relation and its related group velocity are obtained. It is shown that the best fitted function to the transverse profile is Gaussian. Effect of the laser amplitude and also the ratio of nanoparticles radius to their separation on the nonlinear dispersion and amplitude profiles are investigated. It is found that the increase in the just mentioned parameters leads to the localization of transverse profile around the propagation axis.
Beam optimization of a TEA-CO2 laser
NASA Astrophysics Data System (ADS)
Gross, Tobias; Ristau, Detlev; Wallas, Gordon; Dumitru, Gabriel; Sporea, Dan G.; Timus, Clementina A.
1998-07-01
The paper describes the methods used to adapt an industrial TEA- CO2 laser to the requirements of the ISO standard 11 254-2 for a laser induced damage threshold experimental facility. The goals were to improve the pulse energy stability and the laser beam spatial profile and the methods were: (1) finding the best discharge voltage; (2) adapting the laser cavity, (3) using suitable apertures. There is also presented the experimental set- up for beam characterization, which included a laser beam profiler (a line of 60 pyroelectric detectors), an energy-meter to monitor the pulse energies and KCl optical components for beam splitting and beam guiding. Every beam distribution was regarded as a linear combination of normalized Gauss-Hermite functions and the fitting algorithm allows the calculation of the coefficients of this combination.
Propagation of intense short laser pulses in a gas of atomic clusters.
Gupta, Ayush; Antonsen, T M; Milchberg, H M
2004-10-01
We present a model and numerical simulations for the propagation of intense short laser pulses in gases of atomic clusters. As the pulse propagates through the clusters, they absorb energy, expand and explode. The clustered gas thus acts as a medium with time dependent effective dielectric constant. A self-consistent model for the cluster expansion and the laser pulse propagation is developed. Self-focusing of the laser pulse, coupling of laser energy to clusters and the evolution of the pulse spectrum are studied for a laser-cluster system with typical laboratory parameters.
High-power Er:YAG laser with quasi-top-hat output beam.
Kim, J W; Mackenzie, J I; Hayes, J R; Clarkson, W A
2012-05-01
A simple method for simultaneously exciting the fundamental (TEM00) transverse mode and first order Laguerre-Gaussian (LG01) donut mode in an end-pumped solid-state laser to yield a quasi-top-hat output beam is reported. This approach has been applied to an Er:YAG laser, in-band pumped by an Er,Yb fiber laser, yielding 9.6 W of continuous-wave output at 1645 nm in a top-hat-like beam with beam propagation factor (M2)<2.1 for 24 W of incident pump power at 1532 nm. The corresponding slope efficiency with respect to incident pump power was 49%. The prospects of further scaling of output power and improved overall efficiency are considered.
Plume dynamics of cross-beam pulsed-laser ablation of graphite
Sanchez Ake, C.; Sangines de Castro, R.; Sobral, H.; Villagran-Muniz, M.
2006-09-01
The dynamics of the interaction between two plasmas induced by cross-beam pulsed-laser ablation was analyzed by time resolved optical emission spectroscopy and fast photography. The plasmas were created in vacuum by irradiating two perpendicular graphite targets with an excimer (248 nm) and a Nd:yttrium-aluminum-garnet (1064 nm) laser. In this configuration, a laser is focused onto a target generating a highly directed plume; subsequently, an additional laser produces a second plasma from the perpendicular target which expands through the first plume. Collisional processes cause a reduction of the kinetic energy of the second plume species as compared to the single pulse experiment. For a fixed delay between lasers of 2 {mu}s, the second plume was divided in two perpendicular directions. The dynamics of this plasma has been compared with laser-induced plume propagation through a background gas in terms of the drag model.
NASA Astrophysics Data System (ADS)
Wu, Yuqian; Zhang, Yixin; Wang, Qiu; Hu, Zhengda
2016-11-01
For Gaussian beams with three different partially coherent models, including Gaussian-Schell model (GSM), Laguerre-Gaussian Schell-model (LGSM) and Bessel-Gaussian Schell-model (BGSM) beams propagating through a biological turbulent tissue, the expression of the spatial coherence radius of a spherical wave propagating in a turbulent biological tissue, and the average intensity and beam spreading for GSM, LGSM and BGSM beams are derived based on the fractal model of power spectrum of refractive-index variations in biological tissue. Effects of partially coherent model and parameters of biological turbulence on such beams are studied in numerical simulations. Our results reveal that the spreading of GSM beams is smaller than LGSM and BGSM beams on the same conditions, and the beam with larger source coherence width has smaller beam spreading than that with smaller coherence width. The results are useful for any applications involved light beam propagation through tissues, especially the cases where the average intensity and spreading properties of the light should be taken into account to evaluate the system performance and investigations in the structures of biological tissue.
Time-resolved Visualization of Laser Beam Melting of Silica Glass Powder
NASA Astrophysics Data System (ADS)
Zhirnov, I.; Khmyrov, R. S.; Protasov, C. E.; Gusarov, A. V.
Silica glass is an inorganic dielectric material that can be used for laser beam melting without cracking. However, the extremely high viscosity makes consolidation of powder very slow. To study the dynamics of consolidation, a 10.6 μm laser beam was directed on the powder layer deposited on the solid substrate of the same material. The laser-interaction zone was lighted with green laser and filmed with a high-speed camera at 6000 fps. The process develops steadily. Neither fluctuation nor droplets are observed. An expanding consolidation zone is observed. Viscous merging of softened powder particles is supposed to be the principal mechanism of consolidation. Mathematical model based on this mechanism confirms formation of the consolidated zone in the center. Both the experiment and the model indicate that consolidation looks like propagation of a sharp front. Comparison of the experiments and the calculations estimates the consolidation front temperature of about 1800-1900 K.
RADLAC II high current electron beam propagation experiment
Frost, C.A.; Shope, S.L.; Mazarakis, M.G.; Poukey, J.W.; Wagner, J.S.; Turman, B.N.; Crist, C.E.; Welch, D.R.; Struve, K.W.
1992-08-01
This resistive hose instability of an electron beam was observed to be convective in recent RADLAC II experiments for higher current shots. The effects of air scattering for these shots were minimal. These experiments and theory suggest low-frequency hose motion which does not appear convective may be due to rapid expansion and subsequent drifting of the beam nose.
Zhang, P; Saleh, N; Chen, S; Sheng, Z M; Umstadter, D
2003-11-28
The effects of interference due to crossed laser beams were studied experimentally in the high-intensity regime. Two ultrashort (400 fs), high-intensity (4 x 10(17) and 1.6 x 10(18) W/cm(2)) and 1 microm wavelength laser pulses were crossed in a plasma of density 4 x 10(19) cm(3). Energy was observed to be transferred from the higher-power to the lower-power pulse, increasing the amplitude of the plasma wave propagating in the direction of the latter. This results in increased electron self-trapping and plasma-wave acceleration gradient, which led to an increased number of hot electrons (by 300%) and hot-electron temperature (by 70%) and a decreased electron-beam divergence angle (by 45%), as compared with single-pulse illumination. Simulations reveal that increased stochastic heating of electrons may have also contributed to the electron-beam enhancement.
Propagation of an Airy-Gaussian vortex beam in linear and nonlinear media
NASA Astrophysics Data System (ADS)
Chen, Chidao; Peng, Xi; Chen, Bo; Peng, Yulian; Zhou, Meiling; Yang, Xiangbo; Deng, Dongmei
2016-05-01
We investigate the propagation of an Airy-Gaussian vortex (AiGV) beam in free space and Kerr media. It is interesting to see that the beam will perform self-healing and main lobe focusing both in free space and Kerr media when the vortex locates at the center of the plane. By controlling the number of the topological charge, the beam distribution factor χ 0 and the position of the vortex, we can control the intensity distribution of the AiGV beam in the out plane both in free space and Kerr media. It is found that when the vortex is close to the center of the plane, it has a strong effect on the intensity distribution of the beam. When the beam propagates in the number of the topological charge, the partial collapse will take place even with low initial input power. We find that the main lobe focusing contributes to this partial collapse.
Generation and propagation of a sine-azimuthal wavefront modulated Gaussian beam
Lao, Guanming; Zhang, Zhaohui; Luo, Meilan; Zhao, Daomu
2016-01-01
We introduce a method for modulating the Gaussian beam by means of sine-azimuthal wavefront and carry out the experimental generation. The analytical propagation formula of such a beam passing through a paraxial ABCD optical system is derived, by which the intensity properties of the sine-azimuthal wavefront modulated Gaussian (SWMG) beam are examined both theoretically and experimentally. Both of the experimental and theoretical results show that the SWMG beam goes through the process from beam splitting to a Gaussian-like profile, which is closely determined by the phase factor and the propagation distance. Appropriate phase factor and short distance are helpful for the splitting of beam. However, in the cases of large phase factor and focal plane, the intensity distributions tend to take a Gaussian form. Such unique features may be of importance in particle trapping and medical applications. PMID:27443798
Injection and propagation of a nonrelativistic electron beam and spacecraft charging
Okuda, H.; Berchem, J.
1987-05-01
Two-dimensional numerical simulations have been carried out in order to study the injection and propagation of a nonrelativistic electron beam from a spacecraft into a fully ionized plasma in a magnetic field. Contrary to the earlier results in one-dimension, a high density electron beam whose density is comparable to the ambient density can propagate into a plasma. A strong radial electric field resulting from the net charges in the beam causes the beam electrons to spread radially reducing the beam density. When the injection current exceeds the return current, significant charging of the spacecraft is observed along with the reflection of the injected electrons back to the spacecraft. Recent data on the electron beam injection from the Spacelab 1 (SEPAC) are discussed.
Propagation evolution of an off-axis high-order cylindrical vector beam.
Li, Yang; Zhu, Zhuqing; Wang, Xiaolei; Gong, Liping; Wang, Ming; Nie, Shouping
2014-11-01
The propagation characteristics of an off-axis high-order cylindrical vector beam (OHCVB) are studied in this paper. The analytic expressions for the electric field and intensity distribution of the OHCVB propagating in free space are presented, to our knowledge for the first time. The transverse intensity of the OHCVB, different from that of the input Gaussian beam, does not have an axially symmetric distribution, owing to a slight dislocation between the polarization singularity located in the vector field generator and the center point of the Gaussian beam. Numerical results show that the intensity distribution during propagation strongly depends on the propagation distance, dislocation displacement, and topological charge. Accompanied by beam expansion, the intensity distribution of the OHCVB tends to eventually become steady, and the dark core of the vector beam will disappear gradually during the process of propagation. Moreover, with the increase of the topological charge, more energy will be transferred from the x axis to the y axis, and the annular intensity is split into two parts along the y-axis direction. The results help us to investigate the dynamic propagation behaviors of the HCVB under the off-axis condition and also guide the calibration of the off-axis high-order cylindrical vector field in practice. PMID:25401345
NASA Astrophysics Data System (ADS)
Zhu, Fan; Tan, Jiubin; Cui, Jiwen
2013-06-01
Beam splitting target reflector based compensation for the angular drift of laser beam in laser autocollimation is proposed in this article to improve the measurement accuracy and stability of small angle deviations. A beam splitting target reflector is used to replace the plane mirror in laser autocollimation to generate a reference beam when returning the measurement beam. The reference beam and measurement beam have the same angular drift, but have different sensitivities to the rotation angle of the reflector due to the unique characteristics of the reflector. Thus, the angular drift of laser beam in laser autocollimation can be compensated in real time by using the drift of reference beam. Experimental results indicate that an output stability of 0.085 arc sec in 2 h can be achieved after compensation. And a measurement accuracy of ±0.032 arc sec can be obtained over the range of ±1190 arc sec with an effective resolution of 0.006 arc sec. It is confirmed that the compensation method for the angular drift of laser beam is necessary for improving the measurement accuracy and stability in laser autocollimation.
Zhu Fan; Tan Jiubin; Cui Jiwen
2013-06-15
Beam splitting target reflector based compensation for the angular drift of laser beam in laser autocollimation is proposed in this article to improve the measurement accuracy and stability of small angle deviations. A beam splitting target reflector is used to replace the plane mirror in laser autocollimation to generate a reference beam when returning the measurement beam. The reference beam and measurement beam have the same angular drift, but have different sensitivities to the rotation angle of the reflector due to the unique characteristics of the reflector. Thus, the angular drift of laser beam in laser autocollimation can be compensated in real time by using the drift of reference beam. Experimental results indicate that an output stability of 0.085 arc sec in 2 h can be achieved after compensation. And a measurement accuracy of {+-}0.032 arc sec can be obtained over the range of {+-}1190 arc sec with an effective resolution of 0.006 arc sec. It is confirmed that the compensation method for the angular drift of laser beam is necessary for improving the measurement accuracy and stability in laser autocollimation.
Characterisation of electron beams from laser-driven particle accelerators
Brunetti, E.; Manahan, G. G.; Shanks, R. P.; Islam, M. R.; Ersfeld, B.; Anania, M. P.; Cipiccia, S.; Issac, R. C.; Vieux, G.; Welsh, G. H.; Wiggins, S. M.; Jaroszynski, D. A.
2012-12-21
The development, understanding and application of laser-driven particle accelerators require accurate measurements of the beam properties, in particular emittance, energy spread and bunch length. Here we report measurements and simulations showing that laser wakefield accelerators can produce beams of quality comparable to conventional linear accelerators.
NASA Astrophysics Data System (ADS)
Chen, Xudong; Zhao, Daomu
2016-08-01
A model of electromagnetic rectangular multi-Gaussian Schell-model (ERMGSM) beams is introduced. Its analytic expression for the elements of the cross-spectral density matrix of such beams passing through oceanic turbulence is derived. It is shown that the rectangular shape of the ERMGSM beams holds a small distance on propagation in oceanic turbulence. The spectral density, the degree of coherence and the degree of polarization of ERMGSM beams are also studied in detail. The results will be helpful for underwater communication by using ERMGSM beams.
Beam propagation through uniaxial anisotropic media: global changes in the spatial profile.
Martínez-Herrero, R; Movilla, J M; Mejías, P M
2001-08-01
The propagation of electromagnetic beams through uniaxial anisotropic media is investigated. The Maxwell equations are solved in the paraxial limit in terms of the plane-wave spectrum associated with each Cartesian field component. Attention is focused on the global changes in the spatial structure of the beam, which are described by means of the second-order intensity moment formalism. In particular, the propagation law for the intensity moments through this kind of media is obtained. As a consequence it is inferred that it is possible to improve the beam-quality parameter by using these media.