Development of a novel large bandwidth front-end system for high peak power OPCPA systems.

We present the development of a laser system capable of generating bandwidths sufficient to support a sub 30 fs pulse at 910 nm. These pulses have been amplified to 500 mJ of energy at 2 Hz in two stages. The contrast measurements show that the initial seed is clean and suggests that the close in contrast is limited by the evaluation stretcher and compressor. Such a system is suitable for seeding high energy high power OPCPA systems based on KD*P.

Optical parametric chirped-pulse amplification source suitable for seeding high-energy systems.

A short-pulse source based on optical parametric chirped-pulse amplification (OPCPA) technology has been developed with properties that make it a suitable seed for a high-energy OPCPA system. This source generated a diffraction-limited pulse at 910 nm with a full bandwidth of > 165 nm and a spectrum having a transform-limited pulse duration of less than 15 fs. The technique has potential for generating bandwidths > 200 nm and pulse durations < 10 fs.

Relationship between weight, levodopa and dyskinesia: the significance of levodopa dose per kilogram body weight.

PURPOSE: Levodopa dose per kilogram body weight is reported to be a significant factor for dyskinesia in Parkinson's disease. We have investigated this hypothesis in data from the studies comparing ropinirole versus levodopa as the initial therapy. METHODS: Data from the ropinirole versus levodopa studies 056 and REAL-PET in early Parkinson's disease were pooled and manipulated to calculate levodopa dose per kilogram body weight. Logistic regression analysis was performed to investigate significant variables for the development of dyskinesia. Only the patients on levodopa monotherapy or with ropinirole were analyzed. RESULTS: Analysis of levodopa therapy patients revealed that dyskinetic patients had received significantly higher absolute levodopa dose and levodopa dose per kilogram body weight. Logistic regression revealed that the most significant factor was the higher levodopa dose per kilogram body weight, P = 0.005, odds ratio 1.078, 95% CI 1.023-1.135; younger age was the second factor -P = 0.026. Variables of gender, absolute levodopa dose, weight, disease duration and initial motor Unified Parkinson's disease rating score were not significant. CONCLUSION: Higher levodopa dose per kilogram body weight is an independently significant factor for developing dyskinesia. This relationship should be considered in treatment of Parkinson's disease patients aiming to prevent and manage dyskinesia.

35 J broadband femtosecond optical parametric chirped pulse amplification system.

We report on what is believed to be the first large-aperture and high-energy optical parametric chirped pulse amplification system. The system, based on a three-stage amplifier, shows 25% pump-to-signal conversion efficiency and amplification of the full 70 nm width of the seed spectrum. Pulse compression to 84 fs achieved after amplification indicates a potential of 300 TW pulse power for 35 J amplified pulse energy.

Efficient generation of large diffraction gratings with a grating interferometer.

The advantages of a grating interferometer for the generation of large diffraction gratings are demonstrated. In a one- and a two-stage process, high-quality gratings of 120 and 200 mm, respectively, were made with optics no larger than 50 mm together with an argon-ion laser with no line narrowing or beam stabilization and a rotating diffuser for improved beam uniformity.

Wave-front control of a large-aperture laser system by use of a static phase corrector.

In large-aperture, ultrahigh-intensity laser systems, such as Vulcan at the Rutherford Appleton Laboratory, one of the most important factors that determines the ultimate on-target focused intensity is the wave-front quality of the laser pulse. We report on a wave-front analysis carried out on Vulcan to determine the nature and contribution of the aberrations present in the laser pulse that effectively limited the available on-target intensity. We also report on a significant improvement to the wave-front quality that was achieved by static correction of the main aberration, resulting in an increase of focused intensities by a factor of 4.

Generation of terawatt pulses by use of optical parametric chirped pulse amplification.

Optical parametric chirped pulse amplifiers offer exciting prospects for generating new extremes in power, intensity, and pulse duration. An experiment is described that was used to investigate the operation of this scheme up to energies approaching a joule, as a step toward its implementation at the petawatt level. The results demonstrate an energy gain of 10(10) with an energy extraction efficiency of 20% and close to diffraction-limited performance. Some spectral narrowing during amplification was shown to be compatible with the time-varying profile of the pump beam and consistent with the measured recompressed pulse durations of 260 and 300 fs before and after amplification, respectively.

Evaluation of an ultrabroadband high-gain amplification technique for chirped pulse amplification facilities.

Recently, an amplification technique for ultrashort pulses was explored in detail in a theoretical paper by Ross et al. [Opt. Commun. 144, 125 (1997)]. The technique, based on nonlinear optics, is called optical parametric chirped pulse amplification. It has a number of features that, in principle, make it highly attractive. It primarily offers extremely large gains simultaneously with extremely large bandwidths. Additional attractions are virtually no spatial and temporal phase distortion of the amplified pulse, high efficiencies and a low thermal loading, reduced amplified spontaneous emission levels, small optical material lengths, and an inherent simplicity of implementation. We present an evaluation of the technique as a front end amplifier for the ultrashort pulse amplification chain of the Vulcan laser system. Such a device could replace some of the existing amplification in Nd:glass and additionally have a wider effect as a direct replacement of Ti:sapphire regenerative amplifiers on large-scale chirped pulse amplification scale facilities.

Long term role of pergolide as an adjunct therapy in Parkinson's disease: influence on disability, blood pressure, weight and levodopa syndrome.

Pergolide is a dopamine agonist acting on D1 and D2 receptors and has been used as an adjunct therapy with levodopa. We have retrospectively investigated its role over a duration of upto six years in Parkinson's disease (PD) patients to study: (1) its influence on the progression of disability related to PD; (2) effect on blood pressure and weight during the treatment period; (3) whether the use of pergolide has a long term levodopa sparing effect; (4) and how is it tolerated during this period? We studied 43 patients who had been on adjunct therapy with pergolide in addition to levodopa for more than six months. Mean age was 66 years, mean duration of PD prior to adding pergolide was 8 years and final assessment was done after a mean duration of adjunct therapy of 29 (6-72) months. There was no progression of disease disability as assessed on Hoehn and Yahr stage (p=0.09) and Webster score (p=0.20), while there was an improvement in symptom score (p=0.001). There was an insignificant reduction in the dose of levodopa at final assessment from 630 to 535mg (p=0.06). A significant number of patients were able to discontinue taking selegiline (p=0.002). There was no change in the number of patients with hallucinations (p=0.15) and dyskinesia (p=0.09). There was a significant fall in weight (p=0.02), systolic (p=0.023) and diastolic blood pressure (p=0.03). This fall did not correlate with age, dose of pergolide or levodopa or disease severity but was influenced by duration of treatment. Ten patients discontinued pergolide for minor reasons after a mean duration of therapy for 23 months. We conclude that pergolide is a valuable adjunct therapy with levodopa over a duration of upto six years to maintain control of motor symptoms of Parkinson's disease.

Finite size compression gratings in a large aperture chirped pulse amplification laser system.

A simple model is presented to calculate the effects of the finite size of the diffraction gratings in the compressor of a chirped pulse amplification laser system. A wavelength-dependent clipping at the second grating alters the spectral distribution of the compressed pulses, affecting their time domain as well as their spatial distribution in the focal plane. Laser parameters of paramount importance to laser/plasma interaction experiments such as peak intensity, pulse duration, and prepulse levels are affected by the compressor design. Calculations of the effect of spectral clipping on these parameters for Gaussian, sech(2), and top-hat input spectra are discussed, and the benefit of double-pass compared with single-pass compression is also investigated. As an example, with 300-mm gratings and single-pass compression, for a sech(2) spectrum the pulse length of a 400-fs pulse increases to 459 fs, the peak intensity decreases by 25%, and the focal spot size increases by 8% because of the finite size of the gratings.

Optimization of a chirped-pulse amplification Nd:glass laser.

To allow us to achieve the highest focused intensity from a chirped-pulse amplification Nd:glass laser, a number of features of the system have been considered and optimized. These include the compressor geometry, the system aberrations, and the use of mixed glasses in the amplifier chain. Calculations for the laser with a single- or double-pass pulse compressor with 450-mm gratings are presented. These indicate that, for single pass, a reduction in pulse duration from 380 to 237 fs is possible when a phosphate is changed to a mixed phosphate-silicate glass system, and there is a corresponding increase of 44% in peak intensity at beam focus.

Binary phase zone-plate arrays for laser-beam spatial-intensity distribution conversion.

We report on the theory and development of a diffractive element composed of a binary phase zone-plate array. This component conditions the intensity distribution in the focal plane of a conventional refractive lens to generate efficiently (82%) a flattop intensity envelope on target. Analysis of the design indicates that manufacturing tolerances are not critical. Experimental performances on target from x-ray emission and shock-breakout measurements are also presented.

Binary-phase zone plate arrays for the generation of uniform focal profiles.

The generation of uniform focal intensity profiles is important for a number of applications, including laser-plasma interaction experiments. We report on a focusing system that uses a novel binary-phase optic capable of producing efficient two-dimensional uniform top-hat intensity optical and x-ray profiles.

High-brightness femtosecond laser using titanium-sapphire technology and amplification in dyes.

We modify a conventional picosecond dye-amplifier system to achieve maximum brightness for 100-fs pulses derived from a titanium-sapphire oscillator. We obtain near transform-limited 4-GW pulses by using efficient chirped-pulse amplification and compression based on a prism-pair stretcher and a glass-block compressor. Good beam quality and minimum beam divergence are obtained with a Bethune cell final amplifier. The system is shown to be capable of generating beam brightness in excess of 2 × 10(7) W cm(-2) sr(-1), within a factor of 2 of that expected for a diffraction-limited beam.

Single shot measurement of pulse duration for a picosecond pulse at 249 nm.

We report the first demonstration and give experimental details of a technique for measuring the pulse temporal profile of a single picosecond pulse at a wavelength of 249 nm.

High-resolution holographic image projection at visible and ultraviolet wavelengths.

Holograms of resolution test masks have been recorded in photoresist using visible and ultraviolet lasers. Reconstructed images have been projected onto and recorded in photoresist by lithography. Speckle-free submicron resolution has been achieved using simple and inexpensive optical systems and using lasers with limited coherence. Using these techniques with excimer lasers single-shot recording with exposure time of ~20 ns and multishot reconstruction with exposure time