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A microsphere-based short-wavelength recombination x-ray laser

Description: We describe a scheme for obtaining very short wavelengths ({lambda} {similar to} 10{Angstrom}) in recombination lasers. The rapid cooling rates necessary to achieve population inversion during recombination are attained by adiabatic expansion of sub micron spheres. The lasing region is made up of many such spheres. The spheres are heated impulsively by a powerful picosecond laser. First, they ionize, then as they expand, they cool and recombine. We have calculated the optimum sphere size and initial temperature for maximum gain in the n = 3 to n = 2 transition of hydrogen-like ions of elements with atomic numbers, Z, between 10 and 30. Gain of about 10{sup 3}cm{sup {minus}1} is calculated in aluminum at 38.8{Angstrom}. Gain rapidly decreases with Z so that gain in titanium at 13.6{Angstrom} is about 40 cm{minus}1. We have calculated the required pump laser intensity and found it to be attainable with current lasers. The propagation of the pump through the gas'' of spheres is considered and the problems arising from pump scattering by the spheres are discussed.
Date: April 1, 1992
Creator: Valeo, E.J. & Cowley, S.C.
Partner: UNT Libraries Government Documents Department

Resonator modes in high gain free electron lasers

Description: When the gain in a free electron laser is high enough to produce optical guiding, the resonator mode distorts and loses its forward-backward symmetry. We show that the resonator mode in a high gain FEL can be easily constructed using the mode expansion technique taken separately in the interaction and the free-space regions. We propose design strategies to achieve maximal gain and optimal mode quality, and discuss the stability of the optimized mode. 11 refs., 4 figs.
Date: October 1, 1989
Creator: Xie, Ming (Lawrence Berkeley Lab., CA (USA)); Deacon, D.A.G. (Deacon Research, Palo Alto, CA (USA)) & Madey, J.M.J. (Duke Univ., Durham, NC (USA). Dept. of Physics)
Partner: UNT Libraries Government Documents Department

High efficiency surface-emitting semiconductor laser resonators

Description: We have synthesized a new tool, a lasing phase diagram, for designing high efficiency surface-emitting laser resonators and have demonstrated its usefulness by fabricating and operating many different laser resonators. 4 refs., 4 figs.
Date: January 1, 1990
Creator: Gourley, P.L.; Warren, M.E.; Vawter, G.A.; Hadley, G.R.; Brennan, T.M.; Hammons, B.E. et al.
Partner: UNT Libraries Government Documents Department

All-optical pulse switching and shaping by a nonlinear sandwich

Description: We demonstrate a simple model system comprised of a thin nonlinear layer sandwiched between two glass plates. This double Nonlinear Interface allows the investigation of both the transmitted and reflected beams for all-optical switching. Various potential applications of this Nonlinear Sandwich based on its intensity-dependent reflectivity and transmissivity are discussed. Focus is given to energy limiting, prepulse suppression, pulse shortening, and shaping. Experimental results show feasibility of these applications. 7 refs., 6 figs.
Date: January 1, 1991
Creator: Strobl, K. & Golub, I.
Partner: UNT Libraries Government Documents Department

The Brookhaven Accelerator Test Facility laser linac beam line

Description: We report here the low emittance beam transport line for laser acceleration experiments at the Brookhaven Accelerator Test Facility (ATF). In order to preserve the low emittance ({approximately} 10{sup -10} m-rad) 50 MeV electron beam, great care has to be paid to the higher-order effects. The low-emittance transport line consists of two parts; the first part performs and emittance selection, and the other part provides the possibility of energy selection and beam transport to the experimental area. 7 refs., 5 figs., 7 tabs.
Date: September 26, 1989
Creator: Wang, Xijie (Brookhaven National Lab., Upton, NY (USA) California Univ., Los Angeles, CA (USA). Center for Advanced Accelerators Physics) & Kirk, H.G. (Brookhaven National Lab., Upton, NY (USA))
Partner: UNT Libraries Government Documents Department

Polymeric-host sulforhodamine-B lasers: Doubled Nd:YAG pumped

Description: Solid-state dye lasers, pumped by a doubled Nd:YAG laser, were evaluated as a function of concentration, output coupler reflectivity and oscillator dimensions. A slope efficiency of up to 62% was achieved. A maximum irradiance of 59 MW/cm{sup 2} to the dye laser cavity was achieved. 7 refs., 2 figs., 4 tabs.
Date: January 1, 1991
Creator: Gettemy, D.J.; Hermes, R.E. (Los Alamos National Lab., NM (USA)) & Barnes, N.P. (National Aeronautics and Space Administration, Hampton, VA (USA). Langley Research Center)
Partner: UNT Libraries Government Documents Department

LLE Review

Description: This volume of the LLE Review, covering the period January--March 1992, contains articles on the use of diffraction gratings in laser applications, and the fabrication of gratings for use in these applications. there are two articles on the use of lasers to explore fundamental physics issues and an article on the use of a solid-state diode array for x-ray imaging. Finally, the activities of the National Laser Users Facility and the GDL and OMEGA laser systems are summarized.
Date: January 1, 1992
Creator: Keck, R.L. (ed.)
Partner: UNT Libraries Government Documents Department

The mutual coherence of simultaneously injection-locked laser diode arrays

Description: The modulus of the mutual coherence function, {vert bar}g{sub 12}({tau}){vert bar}, has been measured for two physically separated laser diode arrays that were simultaneously injection locked to the same master laser. The measured value {vert bar}g{sub 12}({tau}){vert bar} = 0.96 {plus minus} 0.06, is close to ideal. 2 figs.
Date: April 22, 1990
Creator: Brewer, L.R.
Partner: UNT Libraries Government Documents Department

Nonlinear dynamics of broad-band lasers

Description: Significant progress has been made in several areas. The source of mode-intensity fluctuations in a three-mirror, multimode dye laser has been identified in the typical operating regime well above threshold. It was found experimentally that deterministic four-wave mixing interactions are the underlying cause. We have also made new theoretical studies concerning the regime just above threshold and predicted that the mode fluctuations will be dominated by quantum noise in this regime. We have constructed a preliminary-design short-cavity dye laser in an attempt to enhance this quantum effect, and are now beginning to characterize its output. We have also constructed a Ti:Sapphire laser, and are beginning its study.
Date: February 1, 1990
Creator: Raymer, M.G.
Partner: UNT Libraries Government Documents Department

Beam dynamics and rf evolution in a multistage klystron-like free- electron laser

Description: Current understandings of beam dynamics and RF evolution in a klystron-like free-electron laser are present. Phase sensitiveness to injection jitters estimated by existing two theories is discussed. BBU suppression due to linear detuning is proposed as an alternative of ever proposed techniques. 13 refs., 2 figs., 1 tab.
Date: January 1, 1991
Creator: Ohnuma, S. (Houston Univ., TX (United States). Inst. for Beam Particle Dynamics) & Takayama, K. (Houston Univ., TX (United States). Inst. for Beam Particle Dynamics Texas Accelerator Center, The Woodlands, TX (United States))
Partner: UNT Libraries Government Documents Department

Three-dimensional simulation of a hole-coupled FEL oscillator

Description: The performance of a two-mirror resonator with holes for out-coupling has been examined in a previous study in which the FEL gain was neglected, but the geometrical effect of the wiggler aperture was included in the optical calculation. The phenomenon of mode degeneracy was found to occur, that has serious implications for the stability of performance when the FEL gain is included. We have developed a FEL oscillator code based on TDA'', a three-dimensional FEL amplifier code, to study the mode characteristics in the presence of an FEL. We find that the interaction of the radiation and the FEL has an important, and positive, impact on the mode-profile and related cavity performance parameters. In particular, mode degeneracy is not expected to be a serious problem for reasonable FEL oscillator designs. 8 refs., 4 figs., 1 tab.
Date: August 1, 1991
Creator: Krishnagopal, S.; Xie, M.; Kim, K.J. & Sessler, A.
Partner: UNT Libraries Government Documents Department

INEX (integrated numerical experiment) simulations of the Boeing FEL system

Description: The INEX (integrated numerical experiment) numerical model is applied to the 0.6 {mu}m FEL oscillator at Boeing Aerospace and Electronics Company in Seattle, WA. This system consists of a 110 MeV L-band rf linac, a beam transport line from the accelerator to the entrance of the wiggler, the 5.0 meter THUNDER variable taper wiggler, and a near concentric two mirror optical oscillator. Many aspects of the model for the electron beam accelerator and transport line agree with experimental measurements. Predictions for lasing performance are compared with data obtained in May and June 1989 using a mild tapered wiggler. We obtain good agreement with the achieved extraction efficiency, while 1D pulse simulations reproduce the observed sideband instability. 15 refs., 11 figs.
Date: January 1, 1989
Creator: Tokar, R.L.; Young, L.M.; Lumpkin, A.H.; McVey, B.D.; Thode, L.E.; Bender, S.C. et al.
Partner: UNT Libraries Government Documents Department

Free-electron laser sources of extreme-ultraviolet radiation and their vacuum requirements

Description: Recent development of free-electron laser (FEL) component technologies should enable these devices to operate in the extreme-ultraviolet, well below 100 nm. When fully developed, FELs represent the next generation of coherent-radiation sources with peak- and average-power outputs surpassing those of any existing, continuously tunable photon source by many orders of magnitude. An rf-linac-based, multiple-FEL facility, spanning the spectral range from 1 nm to 100 {mu}m, is proposed. To enable such a facility to operate without significant degradation over long periods, contamination of certain of the FEL components must be prevented. Requirements for ultra-high vacuum and restricted contamination from outgassing from chamber walls are discussed. 73 refs., 11 figs., 4 tabs.
Date: January 1, 1990
Creator: Newnam, B.E.
Partner: UNT Libraries Government Documents Department

Overview of the program on soft x-ray lasers and their applications at Princeton

Description: In the last several years, rapid progress in the development of soft x-ray lasers (SXL) has been observed at a number of laboratories worldwide. Although SXLs are very young'' devices they have already been used for microscopy and holography, and new ideas emerging for broader application of SXLs to microscopy, holography and lithography. This paper describes the work at Princeton University on the development of a soft x-ray imaging transmission microscopy using a SXL as a radiation source and work on the development of a novel soft x-ray reflection microscope and its application to biological cell studies and lithography. Progress in the development of a photopumped VUV laser (60 nm), and programs for the development of a small scale SXL and for the application of a powerful subpicosecond KrF laser system are also discussed. 35 refs., 9 figs., 1 tab.
Date: May 1, 1991
Creator: Suckewer, S. & Ilcisin, K. (Princeton Univ., NJ (USA). Plasma Physics Lab. Princeton Univ., NJ (USA). Dept. of Mechanical and Aerospace Engineering)
Partner: UNT Libraries Government Documents Department

Review of soft x-ray lasers and their applications

Description: The emerging technology of soft x-ray lasers is in a transition phase between the first laboratory demonstrations of gain and the acceptance of soft x-ray lasers as practical tools for novel applications. Current research is focused on several fronts. The operational wavelength range has been extended to the water window'', important for applications in the life sciences. Gain has also been generated with substantially simpler technology (such as a 6J laser) and this augurs well for the commercially availability in the near future of soft x-ray lasers for a variety of applications. Advanced soft x-ray laser concepts are being developed from investigations into ultra-high intensity laser/matter interactions. The first paper a brief historical perspective of x-ray microscopy and holography have begun. In this paper a brief historical perspective of x-ray laser development will be followed by a review of recent advances in recombination, collisional and photo-pumped systems and applications. A summary of current gain-length performance achieved in laboratories worldwide is presented. Near term prospects for applications to novel fields are discussed. 81 refs., 9 figs., 1 tab.
Date: March 1, 1991
Creator: Skinner, C.H.
Partner: UNT Libraries Government Documents Department

Spontaneous emission from free electron lasers

Description: Characteristics of the fundamental and harmonic emission from free-electron lasers (FELs) is examined in the spontaneous emission regime. The radiation at both odd and even harmonic frequencies is treated for electron beams with finite emittance and energy spread. For wigglers with many wiggle periods, calculation of the SE by integrating an ensemble of electrons along their exact trajectories becomes exceedingly cumbersome. Therefore, a different technique is used in which the far-field radiation pattern of a single electron is manipulated in transform space to include the effects if emittance. The effects of energy spread can be included by weighted sum over the energy distribution. The program execution time for wigglers of arbitrary length is negligible. The transverse radiation patterns including the transverse frequency dependences, are given. How this radiation is modeled in FEL simulation codes is discussed. 8 refs., 5 figs.
Date: January 1, 1991
Creator: Schmitt, M.J.
Partner: UNT Libraries Government Documents Department

X rays generated in the interaction of subpicosecond laser pulses with solid targets

Description: We are investigating the generation of short pulse short wavelength x-rays for pumping inner-shell x-ray lasers by photo-ionization. In contrast with previous proposals, we are looking at the use of a single line as an efficient means of pumping these lasers. As a first step we are optimizing the flashlamp x-ray conversion efficiency and characterizing the x-ray pulse length. 18 refs., 5 figs., 2 tabs.
Date: January 1, 1991
Creator: Kyrala, G.A.; Wahlin, E.K.; Fulton, R.D.; Schappert, G.T.; Jones, L.A.; Taylor, A.J. et al.
Partner: UNT Libraries Government Documents Department

Spatial intensity profiling of an industrial laser welding system

Description: A investigation was conducted to devise a method to sense the laser beam intensity profile of an industrial laser welding system. The research focuses on monitoring methods and assessing locations within the system where data can be taken which reveal the relationship between the laser beam intensity profile and the input system parameters of the laser beam welding process. Emphasis has been placed on the configuration of a distributed computing environment to acquire, analyze and display the results of the sensed beam profile. Conventional image processing techniques are demonstrated. It was found that a distributed computing environment was useful for processing the large volumes of data generated by this process characterization method, and the distributed computing environment provided the computing power required for computationally intensive analysis and display techniques. The mathematical techniques used to discriminate one data set from another and relate the results to processing conditions are discussed.
Date: January 1, 1991
Creator: Milewski, J.O.
Partner: UNT Libraries Government Documents Department

The Los Alamos high-brightness photoinjector

Description: For a number of years Los Alamos National Laboratory has been developing photocathode RF guns for high-brightness electron beam applications such as free-electron lasers (FELs). Previously thermionic high-voltage guns have been the source of choice for the electron accelerators used to drive FELs. The performance of such FELs is severely limited by the emittance growth produced by the subharmonic bunching process and also by the low peak current of the source. In a photoinjector, a laser driven photocathode is placed directly in a high-gradient RF accelerating cavity. A photocathode allows unsurpassed control over the current, and the spatial and temporal profile of the beam. In addition the electrodeless emission'' avoids many of the difficulties associated with multi-electrode guns, i.e. the electrons are accelerated very rapidly to relativistic energies, and there are no electrodes to distort the accelerating fields. For the past two years we have been integrating a photocathode into our existing FEL facility by replacing our thermionic gun and subharmonic bunchers with a high-gradient 1.3 GHz photoinjector. The photoinjector, which is approximately 0.6 m in length, produces 6 MeV, 300 A, 15 ps linac, and accelerated to a final energy of 40 MeV. We have recently begun lasing at wavelengths near 3 {mu}m. 16 refs., 2 figs., 5 tabs.
Date: January 1, 1991
Creator: O'Shea, P.G.
Partner: UNT Libraries Government Documents Department

Progress with the slotted-tube pulsed microwiggler

Description: A pulsed microwiggler can produce a wiggler field of unusually short period and high strength. A period of a few millimeters and a field of 5 appear possible. A satisfactory design is hard to realize, however, for many reasons: the high current, the current nonuniformities caused by the skin effect, thermal stresses in the parts, the high precision, etc. In addition, measuring the field with adequate resolution in the time domain, as well as in all three spatial coordinates, is challenging, particularly inside the small bore of a microwiggler. This paper presents recent design modifications that illustrate new solutions to these problems, and details of the construction, testing, and performance of wigglers already built. 6 refs., 5 figs.
Date: January 1, 1991
Creator: Warren, R.W.
Partner: UNT Libraries Government Documents Department

Physics design of the high brightness linac for the advanced free-electron laser initiative at Los Alamos

Description: Free electron lasers and high energy physics accelerators have increased the demand for very high brightness electron beam sources. This paper describes the design of an accelerator which can produce beams of greater than 7 {times} 10{sup 11} A/m{sup 2} (brightness = 2*1/{var epsilon}{sup 2}, with {var epsilon} = 90% normalized emittance = 4* rms emittance). The beam emittance growth in the accelerator is minimized by the following: producing a short electron bunch in a high gradient rf cavity, using a focusing solenoid to correct the emittance growth due to space charge, and designing the coupling slots between accelerator cavities to minimize quadruple effects. The simulation code PARMELA was modified for this design effort. This modified version uses SUPERFISH output files for the accelerator cavity field, MAFIA output files for the 3-D perturbation fields due to the coupling slots in the accelerator cells, and POISSON output files for the solenoid field in the gun region. The results from simulations are, at 2.3 nC, a peak current of 180 A and a 90% emittance of 9.4 {pi} mm-mmrad. The exit energy from the linac is 20 MeV for both cases. A magnetic pulse compressor can be used to further increase the peak current. 8 refs., 10 figs.
Date: January 1, 1991
Creator: Sheffield, R.L.; Browman, M.J.; Carlsten, B.E. & Young, L.M.
Partner: UNT Libraries Government Documents Department

Photocathode transfer and storage techniques using alkali vapor feedback control

Description: Photocathodes of quantum efficiency above 1% at the doubled YAG frequency of 532 nM are very sensitive to the local vacuum environment. These cathodes must have a band gap of less than 2.3 eV, and a work function that is also on the order of {approximately}2 volts or less. As such, these surfaces are very reactive as they provide many surface states for the residual gases that have positive electron affinities such as oxygen and omnipotent water. Attendant to this problem is that the optimal operating point for some of these cesium based cathodes is unstable. Three of the cesium series were tried, the Cs-Ag-Bi-O, the Cs{sub 3}Sb and the K{sub 2}CsSb. The most stable material found is the K{sub 2}CsSb. The vacuum conditions can be met by a variety of pumping schemes. The vacuum is achieved by using sputter ion diode pumps, and baking at 250{degrees}C or less for whatever time is required to reduce the pump currents to below 1 uA at room temperature. To obtain the required partial pressure of cesium, a simple very sensitive diagnostic gauge has been developed that can discriminate between free alkali and other gases present. This Pressure Alkali Monitor (PAM) can be used cesium sources to provide a low partial pressure using standard feedback techniques. Photocathodes of arbitrary composition have been transferred to a separate vacuum system and preserved for over 10 days with less than a 25% loss to the QE at 543.5 nM.
Date: December 20, 1991
Creator: Springer, R.W. & Cameron, B.J.
Partner: UNT Libraries Government Documents Department

Rapid development of a measurement and control system for the Advanced Free-Electron Laser

Description: The Experimental Physics and Industrial Control System (EPICS) is being used to develop a measurement and control system for the Advanced Free-Electron laser (AFEL) at the Los Alamos National Laboratory. EPICS is an integrated system of applications development tools and a distributed run time environment that supports an input-output database, a graphical operator interface, sequential control through state'' definition, data archiving, data analysis, and fault management. It is very advantageous in terms of both time and system integrity to be able to perform much of the control system development before the actual hardware for the AFEL is in place. Using the EPICS applications tools, we are developing prototype measurements and controls that can be directly transferred to the AFEL during installation and commissioning. This is possible due primarily to three aspects of EPICS. First we can easily model physical systems with the state notation language. Second, we can simulate input and output channels with soft'' database channels, which are created using the database configuration tool. Third, we can easily build and modify operator interface screens with the display editor. 8 refs., 3 figs.
Date: January 1, 1991
Creator: Wilson, W.L. Jr.; May, M.W. & Kozubal, A.J.
Partner: UNT Libraries Government Documents Department