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Extreme prepulse contrast utilizing cascaded-optical parametric amplification

Description: It has been shown recently that an optical parametric chirped-pulse amplifier can be easily reconfigured into a cascaded-optical parametric amplifier (COPA), enabling complete prepulse removal and optical switching with a window defined by the pump pulse duration. We have demonstrated instrument-limited measurement of the COPA prepulse contrast >1.4 x 10{sup 11} using 30-mJ pulses. The COPA technique is applicable to all energy ranges and pulse durations. A convenient millijoule-scale implementation of this technique is presented using a single, large-aspect-ratio quasi-phase-matched nonlinear crystal.
Date: June 15, 2006
Creator: Jovanovic, I; Haefner, C; Wattellier, B & Barty, C J
Partner: UNT Libraries Government Documents Department

Optical switching and contrast enhancement in intense laser systems by cascaded optical parametric amplification

Description: Optical parametric chirped-pulse amplification (OPCPA) can be used to improve the prepulse contrast in chirped-pulse amplification systems by amplifying the main pulse with a total saturated OPCPA gain, while not affecting the preceding prepulses of the seed oscillator mode-locked pulse train. We show that a simple modification of a multistage OPCPA system into a cascaded optical parametric amplifier (COPA) results in an optical switch and extreme contrast enhancement which can completely eliminate the preceding and trailing oscillator pulses. Instrument-limited measurement of prepulse contrast ratio of 1.4 x 10{sup 11} is demonstrated from COPA at a 30-mJ level.
Date: September 6, 2005
Creator: Jovanovic, I; Haefner, C; Wattellier, B & Barty, C J
Partner: UNT Libraries Government Documents Department

Parametric Techniques for Extreme-Contracts, High-Energy Petawatt Pulses

Description: Prepulses are of great concern in high-power lasers: if their intensity is sufficiently high, they can heat and/or destroy a target before the arrival of the main pulse. For ultrahigh peak power lasers, for which focused intensity can exceed 10{sup 21} W/cm{sup 2}, a contrast of at least 10{sup 8} is the minimum requirement to avoid preionization of solid targets. Conventional preamplification stages do not meet this requirement, primarily due to prepulse originating from regenerative amplification. Optical parametric amplification (OPA) is well-known to generate pulses with a prepulse contrast equal to the gain of the amplifier, but it does not remove pre-existing prepulses. In this paper we describe a novel technique for contrast enhancement in cascaded optical parametric amplifiers (COPA). Based on cascaded idler utilization, COPA represents a versatile technique with a potentially infinite prepulse contrast enhancement. We have experimentally demonstrated COPA, producing a prepulse contrast of 10{sup 8}, limited by the sensitivity of measurement. A simple modification of the front end of a petawatt-type laser that utilizes optical parametric chirped pulse amplification (OPCPA) can yield unprecedented levels of prepulse contrast.
Date: September 5, 2003
Creator: Jovanovic, I; Wattellier, B & Barty, C P J
Partner: UNT Libraries Government Documents Department

Advanced Compressor Designs for High Energy Petawatt Pulse Generation

Description: We discuss compressor designs for a proposed multikilojoule, sub-picosecond beamline at the National Ignition Facility. A novel grating configuration reduces the size of the compressor chamber. Optimization of the design leads to a 4.7 x 1.4 x 0.4 m{sup 3} minimum compressor volume.
Date: September 9, 2003
Creator: Fittinghoff, D N; Wattellier, B & Barty, C P J
Partner: UNT Libraries Government Documents Department

Diffraction Limited Focal Spots for Off-Thermal Equilibrium 100-TW Nd: Glass Laser Chain using a Dielectric Coated Deformable Mirror

Description: We demonstrate the use of a dielectric-coated deformable mirror to correct LULI 100-TW Nd:Glass facility spatial aberrations. Almost diffraction limited foci have been obtained even when the laser chain amplifiers were highly off thermal equilibrium.
Date: November 18, 2002
Creator: Wattellier, B; Fuchs, J; Zou, J P; Abdeli, K; Chanteloup, J C & Haefner, K
Partner: UNT Libraries Government Documents Department

Fiber Optic Solutions for Short Pulse Lasers

Description: For applications requiring high beam quality radiation from efficient, compact and rugged sources, diffraction limited fiber lasers are ideal, and to date have been demonstrated at average CW power levels exceeding 100 W with near diffraction limited: output. For conventional single-core step-index single-mode fibers, this power level represents the sealing limit because of nonlinear and laser damage considerations. Higher average powers would exceed nonlinear process thresholds such as the Raman and stimulated Brillouin scattering limit, or else damage the fiber due to the high intensity level in the fiber's core. The obvious way to increase the average power capability of fibers is to increase the area of their core. Simply expanding the core dimensions of the fiber allows a straightforward power sealing due to enhanced nonlinear and power handling characteristics that scale directly with the core area. Femtosecond, chirped-pulse, fiber lasers with pulse energies greater than 1mJ have been demonstrated in the literature [2] using this technique. This output energy was still limited by the onset of stimulated Raman scattering. We have pursued an alternative and complimentary approach which is to reduce the intensity of light propagating in the core by distributing it more evenly across the core area via careful design of the refractive index profile [3]. We have also sought to address the primary issue that results from scaling the core. The enhanced power handling capability comes at the expense of beam quality, as increasing the core diameter in standard step index fibers permits multiple transverse modes to lase simultaneously. Although this problem of multimode operation can be mitigated to some extent by appropriately designing the fiber's waveguide structure, limitations such as bend radius loss, sensitivity to thermally induced perturbations of the waveguide structure, and refractive index control, all become more stringent as the core diameter grows, limiting ...
Date: January 29, 2003
Creator: Beach, R; Dawson, J; Liao, Z; Jovanovic, I; Wattellier, B; Payne, S et al.
Partner: UNT Libraries Government Documents Department

Feasibility of Thin Fresnel Lens Use in Multi-kj, Short Pulse Laser Systems

Description: Recently-developed, thin-Fresnel-lens technology offers the potential for transmissive focusing of high-peak-power, ultrashort-duration laser pulses. Calculations of the transverse and longitudinal spectral blurring effects of thin Fresnel lenses when used to focus ultrashort, high-energy laser pulses are presented.
Date: November 18, 2002
Creator: Jovanovic, I; Dixit, S N; Wattellier, B; Hermann, M R & Barty, C P J
Partner: UNT Libraries Government Documents Department

Precision damage tests of multilayer dielectric gratings for high-energy petawatt lasers

Description: The next generation of high-energy petawatt (HEPW)-class lasers will utilize multilayer dielectric diffraction gratings for pulse compression due to their high efficiency and high damage threshold for picosecond pulses. We have developed a short-pulse damage test station for accurate determination of the damage threshold of the optics used on future HEPW lasers. The design and performance of the damage test laser source, based on a highly stable, high-beam-quality optical parametric chirped-pulse amplifier, is presented. Our short-pulse damage measurement methodology and results are discussed. The damage initiation is attributed to multiphoton-induced avalanche ionization, strongly dependent on the electric field enhancement in the grating groove structure and surface defects. Measurement results of the dependence of damage threshold on the pulse width, angular dependence of damage threshold of diffraction gratings, and an investigation of short-pulse conditioning effects are presented. We report record >4 J/cm{sup 2} right section surface damage thresholds obtained on multilayer dielectric diffraction gratings at 76.5 incidence angles for 10-ps pulses.
Date: November 8, 2004
Creator: Jovanovic, I; Brown, C G; Stuart, B C; Molander, W; Nielsen, N; Wattellier, B et al.
Partner: UNT Libraries Government Documents Department

Precision short-pulse damage test station utilizing optical parametric chirped-pulse amplification

Description: The next generation of high-energy petawatt (HEPW)-class lasers will utilize multilayer dielectric diffraction gratings for pulse compression, due to their high efficiency and high damage threshold for picosecond pulses. The peak power of HEPW lasers will be determined by the aperture and damage threshold of the final dielectric grating in the pulse compressor and final focusing optics. We have developed a short-pulse damage test station for accurate determination of the damage threshold of the optics used on future HEPW lasers. Our damage test station is based on a highly stable, high-beam-quality optical parametric chirped-pulse amplifier (OPCPA) operating at 1053 nm at a repetition rate of 10 Hz. We present the design of our OPCPA system pumped by a commercial Q-switched pump laser and the results of the full system characterization. Initial short-pulse damage experiments in the far field using our system have been performed.
Date: March 22, 2004
Creator: Jovanovic, I; Brown, C; Wattellier, B; Nielsen, N; Molander, W; Stuart, B et al.
Partner: UNT Libraries Government Documents Department

Design and Test of Advanced Multi-Layer Dielectric Gratings for High Energy Petawatt

Description: In this paper we discuss recent work on the development of high damage threshold, high efficiency MLD (multilayer dielectric) diffraction gratings for use in high energy, petawatt laser systems. This effort involves a close integration between modeling, fabrication, and testing. The modeling work is used to identify grating designs that satisfy the constraints of high efficiency (>94%) and low field enhancement which is a necessary condition for high damage threshold. Subscale MLD gratings for test are being fabricated in an advanced ion-etch machine we have recently built. The testing effort is being conducted in a dedicated laboratory. The laser beam used to test the samples is based on an OPCPA (optical parametric chirped-pulse amplifier) and a compressor that can provide pulse energies up to 50mJ with pulse lengths variable from 0.3-20 ps. This test station is equipped with diagnostics to fully characterize both the spatial and temporal characteristics of the test beam at the plane of the sample. Initial results have demonstrated a dependence of damage threshold on incident angle that is in good agreement with the field enhancement calculations. We have demonstrated a grating design with a damage threshold of 3J/cm{sup 2} and are investigating manufacturability and reproducibility issues as well.
Date: September 5, 2003
Creator: Molander, W; Komashko, A; Britten, J; Jones, L; Brown, C; Caird, J et al.
Partner: UNT Libraries Government Documents Department

All Fiber Technology for High-Energy Petawatt Front End Laser Systems

Description: We are developing an all fiber front end for the next generation high-energy petawatt (HEPW) laser at Lawrence Livermore National Laboratory (LLNL). The ultimate goal of the LLNL HEPW effort is to generate 5-kJ pulses capable of compression to 5ps at 1053nm, enabling advanced x-ray backlighters and possible demonstration of fast ignition. We discuss the front-end of the laser design from the fiber master oscillator, which generates the mode-locked 20nm bandwidth initial pulses through the 10mJ output of the large flattened mode (LFM) fiber amplifier. Development of an all fiber front end requires technological breakthroughs in the key areas of the master oscillator and fiber amplification. Chirped pulse amplification in optical fibers has been demonstrated to 1mJ. Further increase is limited by the onset of stimulated Raman scattering (SRS). We have recently demonstrated a new flattened mode fiber technology, which reduces peak power for a given energy and thus the onset of SRS. Controlled experiments with 1st generation fibers yielded 0.5mJ of energy while significantly increasing the point at which nonlinear optical effects degrade the amplified pulse. In this paper we will discuss our efforts to extend this work to greater than 20mJ using our large flattened mode fiber amplifier.
Date: September 5, 2003
Creator: Dawson, J W; Liao, Z M; Jovanovic, I; Wattellier, B; Beach, R; Payne, S A et al.
Partner: UNT Libraries Government Documents Department

An Overview of High Energy Short Pulse Technology for Advanced Radiography of Laser Fusion Experiments

Description: The technical challenges and motivations for high-energy, short-pulse generation with NIF-class, Nd:glass laser systems are reviewed. High energy short pulse generation (multi-kilojoule, picosecond pulses) will be possible via the adaptation of chirped pulse amplification laser techniques on the NIF. Development of meter-scale, high efficiency, high-damage-threshold final optics is a key technical challenge. In addition, deployment of HEPW pulses on NIF is constrained by existing laser infrastructure and requires new, compact compressor designs and short-pulse, fiber-based, seed-laser systems. The key motivations for high energy petawatt pulses on NIF is briefly outlined and includes high-energy, x-ray radiography, proton beam radiography, proton isochoric heating and tests of the fast ignitor concept for inertial confinement fusion.
Date: June 18, 2004
Creator: Barty, C J; Key, M; Britten, J; Beach, R; Beer, G; Brown, C et al.
Partner: UNT Libraries Government Documents Department