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Measurement of subpicosecond electron pulse length

Description: A new frequency-resolved bunch-length measuring system has been developed at the Stanford SUNSHINE facility to characterize subpicosecond electron pulses. Using a far-infrared Michelson interferometer, this method measures the spectrum of coherent transition radiation emitted from electron bunches through optical autocorrelation. The electron bunch length is obtained from the measurement with a simple and systematic analysis which includes interference effects caused by the beam splitter. This method demonstrates subpicosecond resolving power that cannot be achieved by existing time-resolved methods. The principle of this method and experimental results are discussed.
Date: April 1, 1996
Creator: Lihn, Hung chi
Partner: UNT Libraries Government Documents Department

Measurement of sub-picosecond bunch profiles using coherent transition radiation

Description: A technique for measuring the longitudinal profile of sub-picosecond electron bunches based on autocorrelation of coherent transition radiation is reviewed. The technique uses sub-millimeter/far-infrared Michelson interferometry to obtain the autocorrelation of transition radiation emitted from a thin conducting foil placed in the beam path. The theory of coherent radiation from a charged particle beam passing through a thin conducting foil is presented for normal and oblique incidence. Michelson interferometric analysis of this radiation is shown to provide the autocorrelation of longitudinal bunch profile. The details of a noninvasive technique for measuring longitudinal bunch profile using coherent diffraction radiation are discussed.
Date: May 1, 1996
Creator: Barry, W.
Partner: UNT Libraries Government Documents Department

Imaging white light VISAR

Description: An imaging white light velocimeter consisting of two imagine superimposing Michelson interferometers in series with the target interposed is demonstrated. Interferometrically measured 2-D velocity maps can be made of moving surfaces using unlimited bandwidth incoherent and extended area sources. Short pulse and broadband chirped pulse lasers can be used to provide temporal resolution not possible with monochromatic illumination. A 20 m/s per fringe imaging velociemter is demonstrated using an ordinary camera flash for illumination.
Date: October 1, 1996
Creator: Erskine, D.J. & Holmes, N.C.
Partner: UNT Libraries Government Documents Department

An imaging white light velocimeter

Description: An imaging white light velocimeter consisting of 2 image superimposing Michelson interferometers in series with the target interposed is demonstrated. Interferometrically measured 2-D velocity maps can be made of moving surfaces using unlimited bandwith incoherent and extended source-area lamps. Short pulse and broadband chirped pulse lasers can be used to provide temporal resolution not previouslypossible with monochromatic illumination. A 20 m/x per fringe imaging velocimeter is demonstrated using an ordinary camera flash for illumination.
Date: October 1, 1996
Creator: Erskine, D.J. & Holmes, N.C.
Partner: UNT Libraries Government Documents Department

Performance of a Rapid-Scan Vacuum Michelson Interferometer at the NSLS

Description: A commercial Nicolet Magna series rapid-scan Michelson Fourier Transform Infrared (FTIR) was installed in a vacuum housing and integrated into the U4IR beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. The frequency reference laser was mounted outside vacuum, but the moving mirror mechanism and the dynamic alignment system for the fixed mirror were in vacuum. The performance of the instrument was measured in the usual way by measuring the repeatability of data collected under specific conditions of aperture, resolution and mirror scanning velocity. We briefly discuss the beamline design, to put the interferometer in context, then present signal to noise data which we discuss in terms of both instrument performance and also storage ring stability. Under optimal conditions, the instrument has a reproducibility of 0.01% in 1 minute of measuring time at a resolution of 2 cmss,{sup -1}, over a range from 100-3000 cm{sup -1}.
Date: September 1, 2001
Creator: Brierly, P.; Dumas, P.; Smith, M. & Williams, G.P.
Partner: UNT Libraries Government Documents Department

Externally Dispersed Interferometry for Precision Radial Velocimetry

Description: Externally Dispersed Interferometry (EDI) is the series combination of a fixed-delay field-widened Michelson interferometer with a dispersive spectrograph. This combination boosts the spectrograph performance for both Doppler velocimetry and high resolution spectroscopy. The interferometer creates a periodic spectral comb that multiplies against the input spectrum to create moire fringes, which are recorded in combination with the regular spectrum. The moire pattern shifts in phase in response to a Doppler shift. Moire patterns are broader than the underlying spectral features and more easily survive spectrograph blurring and common distortions. Thus, the EDI technique allows lower resolution spectrographs having relaxed optical tolerances (and therefore higher throughput) to return high precision velocity measurements, which otherwise would be imprecise for the spectrograph alone.
Date: March 27, 2007
Creator: Erskine, D J; Muterspaugh, M W; Edelstein, J; Lloyd, J; Herter, T; Feuerstein, W M et al.
Partner: UNT Libraries Government Documents Department

An Autocorrelation Technique for Measuring Sub-Picosecond Bunch Length Using Coherent Transition Radiation

Description: A new technique for determining sub-picosecond bunch length using infrared transition radiation and interferometry is proposed. The technique makes use of an infrared Michelson interferometer for measuring the autocorrelation of transition radiation emitted from a thin conducting foil placed in the beam path. The theory of coherent radiation from a charged particle beam passing through a thin conducting foil is presented. Subsequently, the analysis of this radiation through Michelson interferometry is shown to provide the autocorrelation of the longitudinal bunch profile. An example relevant to the CEBAF front end test is discussed.
Date: April 1, 1991
Creator: Barry, Walter
Partner: UNT Libraries Government Documents Department

Measurement of subpicosecond electron bunch lengths

Description: A new frequency-resolved bunch-length measuring system has been developed at the Stanford SUNSHINE facility suitable for subpicosecond electron bunches. This method utilizes a far-infrared Michelson interferometer to measure coherent transition radiation emitted from electron bunches through optical auto-correlation. A simple and systematic way has also been developed to include interference effects caused by the beam splitter, so the electron bunch length can be easily obtained from the measurement. This autocorrelation method demonstrates subpicosecond resolving power that cannot be achieved by existing time-resolved methods.
Date: November 1, 1995
Creator: Lihn, Hung-chi; Bocek, D.; Kung, P.; Settakorn, C. & Wiedemann, H.
Partner: UNT Libraries Government Documents Department

Improved operation of the Michelson interferometer ECE diagnostic on DIII-D

Description: The measurement of accurate temperature profiles is critical for transport analysis and equilibrium reconstruction in the DIII-D tokamak. Recent refinements in the Michelson interferometer diagnostic have produced more precise electron temperature measurements from electron cyclotron emission and made them available for a wider range of discharge conditions. Replacement of a lens-relay with a low-loss corrugated waveguide transmission system resulted in an increase in throughput of 6 dB and reduction of calibration error to around 5%. The waveguide exhibits a small polarization scrambling fraction of 0.05 at the quarter wavelength frequency and very stable transmission characteristics over time. Further reduction in error has been realized through special signal processing of the calibration and plasma interferograms.
Date: May 1, 1996
Creator: Austin, M.E.; Ellis, R.F.; Doane, J.L. & James, R.A.
Partner: UNT Libraries Government Documents Department

Observation of coherent undulator radiation from sub-picosecond electron pulses

Description: The generation and observation of high power, coherent, far-infrared undulator radiation from sub-picosecond electron bunches at the SUNSHINE facility is reported. Coherent undulator radiation tunable from 50 to 200 microns wavelength is demonstrated. Measurements of the energy (up to 1.7 mJ per 1 microsecs macropulse), frequency spectrum, and spatial distribution of the radiation are reported. Apparent exponential growth of the radiated energy as a function of undulator length is observed.
Date: September 1, 1995
Creator: Bocek, D.; Hernandez, M.; Kung, P.; Lihn, Hung-chi; Settakorn, C. & Wiedemann, H.
Partner: UNT Libraries Government Documents Department

Material characterization using a hyperspectral infrared imaging spectrometer

Description: Fourier transform spectroscopy has found application in many areas including chemometrics, biomedical and biochemical studies, and atmospheric chemistry. This paper describes an investigation into the application of the LLNL Hyperspectral Infrared Imaging Spectrometer (HIRIS) to the non-destructive evaluation of man-made and natural materials. We begin by describing the HIRIS system and the objects studied in the investigation. Next, we describe the technique used to collect the hyperspec- tral imagery, and discuss the processing required to transform the data into usable form. We then describe a technique to analyze the data, and provide some preliminary results.
Date: October 30, 1998
Creator: Aimonetti, W D; Bixler, J V & Roberts, R S
Partner: UNT Libraries Government Documents Department

Electron Power Deposition Measurements During Ion Cyclotron Range of Frequency Heating on C-Mod

Description: A 19-channel electron cyclotron emission (ECE) grating polychromator has been added to the existing ECE diagnostics on C-Mod, which include a 9-channel polychromator, heterodyne radiometer and Michelson interferometer. The new instrument can significantly improve the radial resolution of electron power deposition measurements in ICRF experiments on C-Mod. The improved resolution is important for resolving electron power deposition in off-axis mode conversion heating regimes where the mode conversion region can be narrow. The first data from this new instrument were acquired last year during 80 MHz hydrogen minority D-H mode conversion experiments where the H/(H+D) ratio was varied from 0.02 to 0.30 and the toroidal field was varied from 5.1 to 5.7 T. Although complicated by the presence of large sawteeth, some electron power deposition results were obtained from a break-in-slope method. These results, together with results from data acquired during the current C-Mod experimental campaign, will be presented and compared to predicted radial deposition profiles from the TORIC, 2-D full wave RF code, and the METS95, 1-D integral wave RF code.
Date: May 1, 1999
Creator: LeBlanc, B.; Phillips, C.K.; Schilling, G.; Taylor, G.; Wilson, J.R. & al, et
Partner: UNT Libraries Government Documents Department

Novel interferometer spectrometer for sensitive stellar radial velocimetry

Description: We describe a new kind of stellar radial velocimeter based on the series combination of a wide angle Michelson interferometer and a disperser, and which we call a fringing spectrometer. The simplest instrument response of the interferometer produces smaller instrumental noise, and the low resolution requirements of the disperser allows high efficiency and creates an etendue capability which is two orders of magnitude larger than current radial velocimeters. The instrument is compact, inexpensive and portable. Benchtop tests of an open-air prototype shows the short term instrumental noise to be less than 0.76 m/s. A preliminary zero point drift of 4 m/s is already competitive with traditional instruments, in spite of the lack of obvious environmental controls and a known interferometer cavity length drift. We are currently installing cavity stabilization and other improvements that will lead to testing on starlight.
Date: May 20, 1999
Creator: Erskine, D & Ge, J
Partner: UNT Libraries Government Documents Department

Laser Micromachining and Information Discovery Using a Dual Beam Interferometry

Description: Lasers have proven to be among the most promising tools for micromachining because they can process features down to the size of the laser wavelength (smaller than 1 micrometer) and they provide a non-contact technology for machining. The demand for incorporating in-situ diagnostics technology into the micromachining environment is driven by the increasing need for producing micro-parts of high quality and accuracy. Laser interferometry can be used as an on-line monitoring tool and it is the aim of this work to enhance the understanding and application of Michelson interferometry principle for the in-situ diagnostics of the machining depth on the sub-micron and micron scales. micromachining is done on two different materials and a comprehensive investigation is done to control the width and depth of the machined feature. To control the width of the feature, laser micromachining is done on copper and a detailed analysis is performed. The objective of this experiment is to make a precision mask for sputtering with an array of holes on it using an Nd:YAG laser of 532 nm wavelength. The diameter of the hole is 50 {micro}m and the spacing between holes (the distance between the centers) is 100 {micro}m. Michelson interferometer is integrated with a laser machining system to control the depth of machining. An excimer laser of 308 nm wavelength is used for micromachining. A He-Ne laser of 632.8 nm wavelength is used as the light source for the interferometer. Interference patterns are created due to the change in the path length between the two interferometer arms. The machined depth information is obtained from the interference patterns on an oscilloscope detected by a photodiode. To compare the predicted depth by the interferometer with the true machining depth, a surface profilometer is used to measure the actual machining depth on the silicon. It is ...
Date: December 31, 2001
Creator: Theppakuttaikomaraswamy, Senthil P.
Partner: UNT Libraries Government Documents Department

Bunch Length Measurements using Coherent Radiation

Description: The accelerating field that can be obtained in a beam-driven plasma wakefield accelerator depends on the current of the electron beam that excites the wake. In the E-167 experiment, a peak current above 10 kA will be delivered at a particle energy of 28 GeV. The bunch has a length of a few ten micrometers and several methods are used to measure its longitudinal profile. Among these, autocorrelation of coherent transition radiation (CTR) is employed. The beam passes a thin metallic foil, where it emits transition radiation. For wavelengths greater than the bunch length, this transition radiation is emitted coherently. This amplifies the long-wavelength part of the spectrum. A scanning Michelson interferometer is used to autocorrelate the CTR. However, this method requires the contribution of many bunches to build an autocorrelation trace. The measurement is influenced by the transmission characteristics of the vacuum window and beam splitter. We present here an analysis of materials, as well as possible layouts for a single shot CTR autocorrelator.
Date: June 24, 2005
Creator: Ischebeck, Rasmus; Barnes, Christopher; Blumenfeld, Ian; Decker, Franz-Josef; Hogan, Mark; Iverson, Richard H. et al.
Partner: UNT Libraries Government Documents Department

Material Effects and Detector Response Corrections for Bunch Length Measurements

Description: A typical diagnostic used to determine the bunch length of ultra-short electron bunches is the auto-correlation of coherent transition radiation. This technique can produce artificially short bunch length results due to the attenuation of low frequency radiation if corrections for the material properties of the Michelson interferometer and detector response are not made. Measurements were taken using FTIR spectroscopy to determine the absorption spectrum of various materials and the response of a Molectron P1-45 pyroelectric detector. The material absorption data will be presented and limitations on the detector calibration discussed.
Date: June 28, 2007
Creator: Zacherl, W.; Blumenfeld, I.; Berry, M.; Decker, F.-J.; Hogan, M.J.; Ischebeck, R. et al.
Partner: UNT Libraries Government Documents Department

Generation of Femtosecond Electron Pulses

Description: At the Fast Neutron Research Facility (FNRF), Chiang Mai University (Thailand), the SURIYA project has been established aiming to produce femtosecond electron pulses utilizing a combination of an S-band thermionic rf gun and a magnetic bunch compressor ({alpha}-magnet). A specially designed rf-gun has been constructed to obtain optimum beam characteristics for the best bunch compression. Simulation results show that bunch lengths as short as about 50 fs rms can be expected at the experimental station. The electron bunch lengths will be determined using autocorrelation of coherent transition radiation (TR) through a Michelson interferometer. The paper discusses beam dynamics studies, design, fabrication and cold tests of the rf-gun as well as presents the project current status and forth-coming experiments.
Date: May 9, 2005
Creator: Jinamoon, V.; Kusoljariyakul, K.; Rimjaem, S.; Saisut, J.; Thongbai, C.; Vilaithong, T. et al.
Partner: UNT Libraries Government Documents Department

Fiber optic calorimetry

Description: A twin-bridge calorimeter using optical fiber as the sensor element was constructed and tested. This system demonstrates the principle and capability of using optical fibers for heat-flow measurements of special nuclear material. This calorimeter uses piezoelectric-generated phase-carrier modulation with subsequent electronic signal processing to allow phase shifts as small as 1 {micro}rad to be measured. The sensing element consists of 21-m lengths of single-mode optical fiber wrapped around sample and reference chambers. The sensitivity of the calorimeter was determined to be 74 rad of phase shift per mW of thermal power. One milliwatt of thermal power is equivalent to 400 mg of plutonium (6% {sup 240}Pu). The system noise base was about 0.2 rad, equivalent to about 1 mg of plutonium.
Date: December 31, 1998
Creator: Rudy, C.R.; Bayliss, S.C.; Bracken, D.S.; Bush, I.J. & Davis, P.G.
Partner: UNT Libraries Government Documents Department

Model-based signal processing for laser ultrasonic signal enhancement

Description: The use of laser-based electronics in the testing of materials and structures offers various advantages over more traditional ultrasonic methods, but is often less sensitive when applied to real materials. Although high energy laser pulses can generate large ultrasonic displacements, nondestructive evaluation requires that the ablation regime be avoided, thus limiting the amount of optical energy which may be used. For this reason, signal processing of laser generated ultrasonic waveforms detected using laser interferometers may be required to extract the desired information from a nondestructive laser ultrasonic test. A model-based signal processing technique offers a way to enhance the signal-to-noise ratios significantly for ultrasonic waveforms obtained using laser-based systems with the generation of the ultrasound occurring in the nondestructive thermoelastic regime. Under ideal conditions, good signal-to-noise ratios can be achieved using laser-based ultrasonics. However, many materials which need to be tested have less than ideal surface finishes for optical detectors. The application of signal processing to laser-based ultrasonics may provide the necessary improvement in sensitivity. Aussel and Monchalin used cross-correlation methods to extract acoustic velocities and elastic constants from noisy measurements. Once the constraints are made available through experimentation of calculation, it is possible to enhance the noisy interferometer measurements even further by generating a predicted or reference response using a propagation model that captures the essence of the displace signal to be estimated. Using estimates of the required constants, a reasonable reference response can be generated that enables significant enhancement of the measured displacement. This work uses a model-reference approach to increase the signal-to-noise ratio in noisy laser-based ultrasonic waveforms.
Date: July 1, 1996
Creator: Huber, R.D.; Chinn, D.J.; Thomas, G.H.; Candy, J.V. & Spicer, J.B.
Partner: UNT Libraries Government Documents Department

Microwave Michelson Interferometer system report of first use on a railgun, Green Farm, San Diego, CA

Description: This report summarizes the successful first attempt to use a Michelson microwave interferometer to measure the position of a projectile throughout its acceleration by a railgun. The test was performed at the DNA Green Farm facility operated by Maxwell Labs Inc. The test was performed using the ARDEC-ACB gun to accelerate a 1.1 kg polycarbonate projectile-to about 2.5 km/s. The projectile had an initial injection velocity of about 490 m/s.
Date: October 20, 1993
Creator: Hawke, R. S.; Greenwood, D.; Morrison, J. & Schildmeyer, F.
Partner: UNT Libraries Government Documents Department

Noise Studies of Externally Dispersed Interferometry for Doppler Velocimetry

Description: Externally Dispersed Interferometry (EDI) is the series combination of a fixed-delay field-widened Michelson interferometer with a dispersive spectrograph. This combination boosts the spectrograph performance for both Doppler velocimetry and high resolution spectroscopy. The interferometer creates a periodic comb that multiplies against the input spectrum to create moire fringes, which are recorded in combination with the regular spectrum. Both regular and high-frequency spectral components can be recovered from the data--the moire component carries additional information that increases the signal to noise for velocimetry and spectroscopy. Here we present simulations and theoretical studies of the photon limited Doppler velocity noise in an EDI. We used a model spectrum of a 1600K temperature star. For several rotational blurring velocities 0, 7.5, 15 and 25 km/s we calculated the dimensionless Doppler quality index (Q) versus wavenumber v. This is the normalized RMS of the derivative of the spectrum and is proportional to the photon-limited Doppler signal to noise ratio.
Date: May 4, 2006
Creator: Erskine, D J; Edelstein, J; Lloyd, J & Muirhead, P
Partner: UNT Libraries Government Documents Department

Terahertz Light Source and User Area at FACET

Description: FACET at SLAC provides high charge, high peak current, low emittance electron beam that is bunched at THz wavelength scale during its normal operation. A THz light source based coherent transition radiation (CTR) from this beam would potentially be the brightest short-pulse THz source ever constructed. Efforts have been put into building this photon source together with a user area, to provide a platform to utilize this unique THz radiation for novel nonlinear and ultrafast phenomena researches and experiments. Being a long-time underutilized portion of the electromagnetic spectrum, terahertz (100 GHz {approx} 10 THz) spectral range is experiencing a renaissance in recent years, with broad interests from chemical and biological imaging, material science, telecommunication, semiconductor and superconductor research, etc. Nevertheless, the paucity of THz sources especially strong THz radiation hinders both its commercial applications and nonlinear processes research. FACET - Facilities for Accelerator science and Experimental Test beams at SLAC - provides 23 GeV electron beam with peak currents of {approx} 20 kA that can be focused down to 100 {mu}m{sup 2} transversely. Such an intense electron beam, when compressed to sub-picosecond longitudinal bunch length, coherently radiates high intensity EM fields well within THz frequency range that are orders of magnitude stronger than those available from laboratory tabletop THz sources, which will enable a wide variety of THz related research opportunities. Together with a description of the FACET beamline and electron beam parameters, this paper will report FACET THz radiation generation via coherent transition radiation and calculated photon yield and power spectrum. A user table is being set up along the THz radiation extraction sites, and equipped with various signal diagnostics including THz power detector, Michelson interferometer, sample stages, and sets of motorized optical components. This setup will also be presented. Potential THz research areas including studies of magnetism, ferroelectric ...
Date: November 8, 2011
Creator: Wu, Z.; Li, S.Z.; Litos, M.; Fisher, A.D.; Hogan, M.J. & /SLAC
Partner: UNT Libraries Government Documents Department

Sub-picosecond streak camera measurements at LLNL: From IR to x-rays

Description: An ultra fast, sub-picosecond resolution streak camera has been recently developed at the LLNL. The camera is a versatile instrument with a wide operating wavelength range. The temporal resolution of up to 300 fs can be achieved, with routine operation at 500 fs. The streak camera has been operated in a wide wavelength range from IR to x-rays up to 2 keV. In this paper we briefly review the main design features that result in the unique properties of the streak camera and present its several scientific applications: (1) Streak camera characterization using a Michelson interferometer in visible range, (2) temporally resolved study of a transient x-ray laser at 14.7 nm, which enabled us to vary the x-ray laser pulse duration from {approx}2-6 ps by changing the pump laser parameters, and (3) an example of a time-resolved spectroscopy experiment with the streak camera.
Date: December 21, 2003
Creator: Kuba, J; Shepherd, R; Booth, R; Steward, R; Lee, E W; Cross, R R et al.
Partner: UNT Libraries Government Documents Department

Coherent transition radiation from a laser wakefield accelerator as an electron bunch diagnostic

Description: The observation and modeling of coherent transition radiation from femtosecond laser accelerated electron bunches is discussed. The coherent transition radiation, scaling quadratically with bunch charge, is generated as the electrons transit the plasma-vacuum boundary. Due to the limited transverse radius of the plasma boundary, diffraction effects will strongly modify the angular distribution and the total energy radiated is reduced compared to an infinite transverse boundary. The multi-nC electron bunches, concentrated in a length of a few plasma periods (several tens of microns), experience partial charge neutralization while propagating inside the plasma towards the boundary. This reduces the space-charge blowout of the beam, allowing for coherent radiation at relatively high frequencies (several THz). The charge distribution of the electron bunch at the plasma-vacuum boundary can be derived from Fourier analysis of the coherent part of the transition radiation spectrum. A Michelson interferometer was used to measure the coherent spectrum, and electron bunches with duration on the order of 50 fs (rms) were observed.
Date: October 22, 2004
Creator: van Tilborg, J.; Geddes, C.G.R.; Toth, C.; Esarey, E.; Schroeder, C.B.; Martin, M.C. et al.
Partner: UNT Libraries Government Documents Department