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Laser Interactions for the Synthesis and In Situ Diagnostics of Nanomaterials

Description: Laser interactions have traditionall been at thec center of nanomaterials science, providing highly nonequilibrium growth conditions to enable the syn- thesis of novel new nanoparticles, nanotubes, and nanowires with metastable phases. Simultaneously, lasers provide unique opportunities for the remote char- acterization of nanomaterial size, structure, and composition through tunable laser spectroscopy, scattering, and imaging. Pulsed lasers offer the opportunity, there- fore, to supply the required energy and excitation to both control and understand the growth processes of nanomaterials, providing valuable views of the typically nonequilibrium growth kinetics and intermediates involved. Here we illustrate the key challenges and progress in laser interactions for the synthesis and in situ diagnostics of nanomaterials through recent examples involving primarily carbon nanomaterials, including the pulsed growth of carbon nanotubes and graphene.
Date: January 1, 2014
Creator: Geohegan, David B.; Puretzky, Alexander A.; Yoon, Mina; Eres, Gyula; Rouleau, Christopher; Xiao, Kai et al.
Partner: UNT Libraries Government Documents Department

Field Evaluation of the U.S. Army Engineer Topographic Laboratories' Laser Dam Alignment Instrument

Description: Summary: Several series of laser instrument alignment surveys were made at the exterior roadway deck level and within the interior inspection gallery of Keystone Dam, Oklahoma, and compared with theodolite surveys over the same lines and under similar conditions.
Date: April 1973
Creator: Davis, Carl D.
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

Free-Electron Lasers: Present Status and Future Prospects

Description: Free-electron lasers as scientific instruments are reviewed. The present status and future prospects are delineated with attention drawn to the size, complexity, availability, and performance capability of this new tool. The Free-Electron Laser (FEL) was proposed by John Madey in 1970 (1), although earlier work, relevant to the concept, had been performed by Motz (2) and by Phillips (3). Experimental demonstration was achieved by Madey, et. al. in 1975 and 1976 (4). Since that time, FELs of diverse configurations have been operated at several laboratories around the world. At present, FEL development is focused in two directions: in constructing reliable FELs for scientific research and in extending FEL capability to vacuum ultra-violet (VUV) and even shorter wavelengths. In this article we shall only very briefly review the principles of an FEL, putting emphasis on those aspects that limit performance, after which we shall discuss the applications, present status and future prospects of FELs. Much material that we wish to present is in the form of Tables, and they are an essential part of this article.
Date: May 1, 1990
Creator: Kim, K.-J. & Sessler, Andrew M.
Partner: UNT Libraries Government Documents Department

Limits to Electron Beam Emittance from Stochastic Coulomb Interactions

Description: Dense electron beams can now be generated on an ultrafast timescale using laser driven photo-cathodes and these are used for a range of applications from ultrafast electron defraction to free electron lasers. Here we determine a lower bound to the emittance of an electron beam limited by fundamental stochastic Coulomb interactions.
Date: August 22, 2008
Creator: Coleman-Smith, Christopher; Padmore, Howard A. & Wan, Weishi
Partner: UNT Libraries Government Documents Department

Fundamental mechanisms of optical damage in short-wavelength high-power lasers

Description: Evidence has been accumulating for many years that the physical mechanisms responsible for damage to optical materials in and from high-power, short-wave-length lasers (SWLs) differ in fundamental ways from the thermal processes identified in infrared and visible-wavelength laser damage problems. We propose that this difference stems primarily from the electronic nature of the absorption and excitation processes which occur when SWL photons strike an optical surface, and that electrons, ions and uv photons generated in the laser excitation cycle also contribute to optical damage. In this paper, we present recent experimental results which have pinpointed specific electronic excitation mechanisms which can operate in the high-power laser environment. In many optical materials of interest for SWLs, the deposition of electronic energy creates self-trapped excitons which decay through the energetic expulsion of atoms and molecules from the surface of the material. This erosion process is accompanied by the creation of permanent electronic defects which become nucleation sites for further damage. The relationship between these microscopic mechanisms and observed macroscopic damage phenomenology is discussed, along with evidence for the existence of a surface overlayer which may point the way to radically new techniques for protecting SWL optical elements from laser damage.
Date: October 1, 1985
Creator: Haglund, R.F. Jr.; Tolk, N.H. & York, G.W.
Partner: UNT Libraries Government Documents Department


Description: Two independently-driven laser accelerators were operated together in series for the first time in a proof-of-principle experiment to demonstrate staging. The ability to stage together these devices is important for eventually building practical laser-driven accelerators. The laser accelerators consisted of two identical inverse free electron lasers (IFEL), where the first IFEL served as a prebuncher, which created {approx}3-fs long microbunches that were accelerated by the second IFEL. Precise and stable control of the phasing between the microbunches and laser wave inside the second IFEL was demonstrated. The effects of over-modulation of the prebuncher were also investigated. In all cases there was good agreement with the model. Additional details of the microbunch characteristics could be inferred by using the model. Plans for demonstrating monoenergetic laser acceleration are also presented.
Date: June 18, 2001
Creator: Kimura, W. D.; Campbell, L. P.; DILLEY,C.E.; Gottschalk, S. C.; Quimby, D. C.; BABZIEN,M. BEN-ZVI,I. et al.
Partner: UNT Libraries Government Documents Department

Time Resolved Shadowgraph Images of Silicon during Laser Ablation:Shockwaves and Particle Generation

Description: Time resolved shadowgraph images were recorded of shockwaves and particle ejection from silicon during laser ablation. Particle ejection and expansion were correlated to an internal shockwave resonating between the shockwave front and the target surface. The number of particles ablated increased with laser energy and was related to the crater volume.
Date: May 6, 2006
Creator: Liu, C.Y.; Mao, X.L.; Greif, R. & Russo, R.E.
Partner: UNT Libraries Government Documents Department

Short-pulse Laser Capability on the Mercury Laser System

Description: Applications using high energy ''petawatt-class'' laser drivers operating at repetition rates beyond 0.01 Hz are only now being envisioned. The Mercury laser system is designed to operate at 100 J/pulse at 10 Hz. We investigate the potential of configuring the Mercury laser to produce a rep-rated, ''petawatt-class'' source. The Mercury laser is a prototype of a high energy, high repetition rate source (100 J, 10 Hz). The design of the Mercury laser is based on the ability to scale in energy through scaling in aperture. Mercury is one of several 100 J, high repetition rate (10 Hz) lasers sources currently under development (HALNA, LUCIA, POLARIS). We examine the possibility of using Mercury as a pump source for a high irradiance ''petawatt-class'' source: either as a pump laser for an average power Ti:Sapphire laser, or as a pump laser for OPCPA based on YCa{sub 4}O(BO{sub 3}){sub 3} (YCOB), ideally producing a source approaching 30 J /30 fs /10 Hz--a high repetition rate petawatt. A comparison of the two systems with nominal configurations and efficiencies is shown in Table 1.
Date: June 22, 2006
Creator: Ebbers, C; Armstrong, P; Bayramian, A; Barty, C J; Bibeau, C; Britten, J et al.
Partner: UNT Libraries Government Documents Department

The effect of temporal pulse shape on optical damage

Description: The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. We present here data from a simple single-parameter model and a supporting experiment which predicts that a Flat-In-Time-pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same FWHM duration.
Date: August 15, 2006
Creator: Carr, C W; Trenholme, J B & Spaeth, M L
Partner: UNT Libraries Government Documents Department

Multimode-diode-pumped gas (alkali-vapor) laser

Description: We report the first demonstration of a multimode-diode-pumped gas laser--Rb vapor operating on the 795 nm resonance transition. Peak output of {approx}1 Watt was obtained using a volume-Bragg-grating stabilized pump diode array. The laser's output radiance exceeded the pump radiance by a factor greater than 2000. Power scaling (by pumping with larger diode arrays) is therefore possible.
Date: August 22, 2005
Creator: Page, R H; Beach, R J & Kanz, V K
Partner: UNT Libraries Government Documents Department

The effect of multiple wavelengths on Laser-induced damage in DKDP crystals

Description: Laser-induced damage is a key factor that constrains how optical materials are used in high-power laser systems. In this work the size and density of bulk laser-induced damage sites formed during frequency tripling in a DKDP crystal are studied. The characteristics of the damage sites formed during tripling, where 1053-nm, 526-nm, and 351-nm light is simultaneously present, are compared to damage sites formed by 351-nm light alone. The fluence of each wavelength is calculated as a function of depth with a full 4D(x,y,z,t) frequency conversion code and compared to measured damage density and size distributions. The density of damage is found be predominantly governed by 351-nm light with some lesser, though non-negligible contribution from 526-nm light. The morphology of the damage sites, however, is seen to be relatively insensitive to wavelength and depend only on total fluence of all wavelengths present.
Date: July 11, 2005
Creator: Carr, C W & Auerbach, J M
Partner: UNT Libraries Government Documents Department

Narrow band tuning with small long pulse excimer lasers

Description: We discuss frequency narrowing and tuning with simple dispersion elements with small long-pulse excimer lasers. The improved performance over short-pulse lasers is discussed and attributed to the increased number of round trips. A physical model of the dynamics of line narrowing is presented.
Date: December 1, 1985
Creator: Sze, R.C.; Kurnit, N.; Watkins, D. & Bigio, I.
Partner: UNT Libraries Government Documents Department

Long-pulse excimer lasers for materials processing and medical applications

Description: Present day commercial excimer lasers with the exception of the Helionetics device are inherently short pulse ultraviolet sources. The pulses are short due to the inherent instability of the avalanche discharge with electronegative elements in the gas mix. The utilization of an initial fast voltage risetime allows one to overcome this difficulty and a number of long-pulse lasers are built using this technique. While the initial lasers of this form used a series rail-gap to achieve the fast voltage risetime, subsequent schemes using magnetic pulse compression and a fast prepulse have greatly improved the viability of the technique as a commercial device. Presently, however, these devices are generally rather bulky. This report discusses a passive stabilization technique that not only allows long pulse laser operation, but allows for a much slower charging circuit as well as a factor of 10 gain in pulse repetition rate per given gas flow compared with more conventional excimer laser systems. The slower charging circuit greatly eases the stress on the pulse power components such as thyratrons and capacitors and should be an important factor contributing to dependable industrial excimer laser systems. The gain of a factor of 10 in pulse repetition rate per unit gas flow results in extremely high pulse repetition rate laser systems in a very compact package; such lasers should find a place in a number of industrial and medical applications. 10 figs.
Date: January 1, 1986
Creator: Sze, R.C.
Partner: UNT Libraries Government Documents Department

Laser-based instrumentation for detection of chemical-warfare agents

Description: Several laser-based techniques are being developed for remote, point, and surface contamination detection of chemical warfare agents. These techniques include optoacoustic spectroscopy, laser-induced breakdown spectroscopy, and synchronous detection of laser-induced fluorescence. Detection limits in the part-per-million to part-per-billion regime have been demonstrated.
Date: January 1, 1981
Creator: Quigley, G.P.; Radziemski, L.J.; Sander, R.K. & Hartford, A. Jr.
Partner: UNT Libraries Government Documents Department