Ultra-high Power Laser Research Articles

Production of multiply charged ion beams with an energy of tens of MeV/nucleon by ultrahigh-power laser radiation for nuclear physics problems

We report a comprehensive analysis of an earlier proposed method which employs ultrahigh-power (petawatt) circularly polarised laser radiation to generate multiply charged ion beams in its interaction with a nanostructured two-component target; the ion beams are intended for application in nuclear physics. The problems of heavy atom ionisation in a superstrong laser field and laser-induced acceleration of the resultant ions to energies of ∼20–30 MeV/nucleon are considered.

Note: A large aperture four-mirror reflective wave-plate for high-intensity short-pulse laser experiments

We report on a four-mirror reflective wave-plate system based on a phase-shifting mirror (PSM) for a continuous variation of elliptical polarization without changing the beam position and direction. The system presented and characterized here can replace a conventional retardation plate providing all advantages of a PSM, such as high damage-threshold, large scalability, and low dispersion. This makes reflective wave-plates an ideal tool for ultra-high power laser applications.

Multistep redirection by cross-beam power transfer of ultrahigh-power lasers in a plasma

A demonstration of the ability to control the flow of laser energy in a dense plasma by tuning the colour of multiple laser beams injected into it could be useful in the development of laser-driven fusion.

Laboratory planetary physics using intense heavy ion beams at the Facility for Antiprotons and Ion Research at Darmstadt: the HEDgeHOB collaboration

Development of ultra-high power lasers has lead to the very interesting and important field of Laboratory Astrophysics. Recent progress and expected near future developments in the technology of strongly bunched intense particle beams has opened up the possibility of studying planetary interiors in the laboratory which hopefully will eventually converge in the new field of Laboratory Planetary Physics. GSI Helmholzzentrum fur Schwerionenforschung, Darmstadt is a well known laboratory worldwide due to its unique particle accelerator facilities. Construction of the new huge accelerator complex, the Facility for Antiprotons and Ion Research (FAIR), will substantially improve the existing capabilities of the GSI. A dedicated program named, HEDgeHOB, that aims to study different problems in High Energy Density (HED) Physics at the FAIR facility, has been proposed. One of these proposed experiments LAPLAS (LAboratory PLAnetary Science), aim to study materials at extreme conditions as relevant for the interiors of giant planets. In this paper we present simulation results that show that various regions of the high-pressure phase diagram of water can be probed within the LAPLAS experiments. For instance, the plasma and the superionic phase are predicted to occur in the interior of water-rich planets such as Uranus and Neptune as well as in extrasolar planets such as GJ 436b.

Development of Ultrahigh-power Laser System for Relativistic Laser-Matter Interactions

물리학과 첨단기술 April 2010 19 저자약력 정태문 박사는 한국과학기술원 이학박사(1999)로서 한국원자력연구소(1998 -2000), 삼성전자(2000-2002), 로체스터 대학교(2002-2005)를 거쳐 2005 년부터 광주과학기술원 고등광기술연구소에서 재직 중이며 레이저 연구실장 으로 펨토초 페타와트 레이저 개발에 참여하고 있다. (jeongtm@gist.ac.kr) 성재희 박사는 한국과학기술원 이학박사(2005)로서 2005년부터 광주과학 기술원 고등광기술연구소에서 재직 중으로 극초단 페타와트 레이저 개발 에 참여하고 있다. (sungjh@gist.ac.kr) 이성구 박사는 한국과학기술원 이학박사(2005)로서 2005년부터 광주과학 기술원 고등광기술연구소에서 재직 중으로 펨토초 페타와트 레이저 개발 에 참여하고 있다. (lsk@gist.ac.kr) 유태준 박사 약력은 2쪽 참조. 이종민 교수 약력은 2쪽 참조. 상대론적 레이저-물질 상호작용 연구를 위한 초고출력 레이저

アジアの先端レーザー研究施設

Ultrashort and ultrahigh peak power lasers opened new front of ultrafast and high fi eld optical physics.

Fusion energy without radioactivity: laser ignition of solid hydrogen–boron (11) fuel

The advent of ultra-high power lasers allows laser power levels that are about 1000 times the power of all the power stations in the USA. This opens the way to new approaches for inertial confinement fusions (ICF) that in turn can drastically reduce the laser input energy needed to achieve practical ICF power. The specific approach discussed here involves inducing a fusion burn wave by laser-driven impact of a relatively large block of plasma on the outside of a solid density fusion target. This new method is specifically selected to enable the extremely attractive, but demanding, neutron-free proton–B-11 fusion that potentially can lead to the long sought goal of an ultra “clean” fusion power plant.

Progress in the growth of large scale Ti:sapphire crystals by the heat exchanger method (HEM) for petawatt class lasers

In modelocked laser systems, the shortest possible pulse width is determined by the Fourier transform of the spectral bandwidth of the pulse; the wider the spectral bandwidth, the shorter the pulse. Titanium-doped sapphire (Ti:sapphire) offers the widest gain bandwidth of any currently available laser gain material, enabling systems to deliver pulse widths shorter than 10 fs (10 −14 s). Because of the short pulse durations, the peak power can be extremely high, and therefore Ti:sapphire lasers have been at the forefront of research into ultrafast, ultrahigh power lasers. These intense ultrashort laser pulses are the light source for fundamental studies of light–matter interactions. Interesting scientific results have been achieved with these lasers in the fields of high order harmonic and short pulse X-ray generations, high density plasmas, relativistic acceleration, relativistic nonlinear optics, time resolved X-ray diffraction with unprecedented time resolution and others. Researchers have recently achieved near petawatt (10 15 W) peak power laser operation using large diameter Ti:sapphire amplifiers, and are developing higher power lasers for research into high energy physics. However, the saturation fluence of the Ti:sapphire gain medium is limited to about 1 J/cm 2. Thus, continued scale up in peak laser energy requires the scale up of high-quality Ti:sapphire crystals for laser amplifiers. Current demand is for 100 mm diameter crystals, and this requirement is projected to grow up to 250 mm diameter crystals in a few years. To address this technological bottleneck, Crystal Systems has upgraded its heat exchanger method (HEM) furnaces and fabrication and metrology to scale up the production of Ti:sapphire crystals. Currently, 175 mm diameter Ti:sapphire amplifier crystals are being fabricated from high-quality 208 mm boules.

Direct acceleration of electrons by radially polarized laser pulse

Direct electron acceleration by highly focused ultrahigh-power laser pulses of radial polarization in the ultrarelativistic mode was studied. The mode at which the focusing spot size appears of the same order as the laser radiation wavelength was considered. Electromagnetic fields were calculated using exact Stratton-Chu diffraction integrals. Calculations showed that, as for the case of linear polarization, too sharp focusing (in the diffraction limit) is not optimum for electron acceleration, despite the strong axial field namely in the case of a submicrometer laser spot. At the same time, the case of moderate focusing is more attractive for electron acceleration.

Nonparaxial theory of cross-focusing of two laser beams and its effects on plasma wave excitation and particle acceleration: Relativistic case

Cross-focusing of two propagating ultrahigh power laser beams in homogeneous plasma (laser intensity IL>016W∕cm2) has been studied in the nonparaxial region. By expanding the eikonal and other relevant quantities up to the fourth power of r (radial distance), we observed that the focusing of the laser beams becomes fast in the nonparaxial region. The difference in focusing/defocusing of the axial and off-axial rays leads to the formation of a splitted profile of laser beams in the plasma. A remarkable change is also observed in the amplitude of plasma wave excitation and particle acceleration in the nonparaxial region in comparison to the paraxial region.

Laser beam filamentation and stochastic electron heating at upper hybrid layer

This paper presents an investigation of the filamentation (single hot spot) of an ultrahigh-power laser beam in homogeneous plasma. Upper hybrid wave (UHW) coupling in these filaments has been studied. We have discussed two extreme scenarios: (1) The laser beam has ultrahigh power so that relativistic and ponderomotive nonlinearities are operative; and (2) the laser beam power is moderate, therefore only ponderomotive nonlinearity dominates. At ultrahigh laser powers, relativistic and ponderomotive nonlinearities lead to filamentation of the laser beam. In these filamentary regions, the UHW gets coupled to the laser beam, and a large fraction of the pump (laser beam) energy gets transferred to UHW and this excited UHW can accelerate the electrons. In the second case, nonlinear coupling between the laser beam and the upper hybrid wave leads to the localization of the UHW. Electrons interacting with the localized fields of the UHW demonstrate chaotic motion. The simulation result confirms the presence of chaotic fields, and interaction of these fields with electrons leads to velocity space diffusion, which is accompanied by particle heating. Using the Fokker–Planck equation, the heating of electrons has been estimated. The effect of the change of background magnetic field strength on heating has also been discussed.

32 TW atmospheric white-light laser

Ultrahigh power laser pulses delivered by the Alisé beamline (26J, 32TW pulses) have been sent vertically into the atmosphere. The highly nonlinear propagation of the beam in the air gives rise to more than 400 self-guided filaments. This extremely powerful bundle of laser filaments generates a supercontinuum propagating up to the stratosphere, beyond 20km. This constitutes the highest power “atmospheric white-light laser” to date.

Analysis of evolution and life-time of the plasma channel produced by ultra-stort ultra-high power laser pulse

Using the perturbed theory, the plasma channel produced by ultra-short ultra-high power laser pulses is considered. Under the actions of recombination, attachment and detachment, the perturbed asymptotic expressions of the density of each kind of charged particles in the course of evolution of the plasma channel are obtained. The influence of each action on the evolution and life_time of the channel is discussed.

Non-uniform carrier accumulation in optical confinement layer as ultimate power limitation in ultra-high-power broad-waveguide pulsed InGaAs/GaAs/AlGaAs laser diodes

The effect of spatially non-uniform accumulation of carriers in the optical confinement layer of broad-waveguide InGaAs/GaAs/AlGaAs-based ultra-high power lasers operating at 1.06 µm under very high pulsed pumping has been analysed and shown to be an important limitation for the output power. A calculation using a semi-analytical theory is in good agreement with the recently published experimental data. A narrow asymmetric waveguide laser construction is predicted to alleviate the problem.

The plasma mirror—A subpicosecond optical switch for ultrahigh power lasers

Plasma mirrors are devices capable of switching very high laser powers on subpicosecond time scales with a dynamic range of 20–30 dB. A detailed study of their performance in the near-field of the laser beam is presented, a setup relevant to improving the pulse contrast of modern ultrahigh power lasers (TW–PW). The conditions under which high reflectivity can be achieved and focusability of the reflected beam retained are identified. At higher intensities a region of high specular reflectivity with rapidly decreasing focusability was observed, suggesting that specular reflectivity alone is not an adequate guide to the ideal range of plasma mirror operation. It was found that to achieve high reflectivity with negligible phasefront distortion of the reflected beam the inequality csΔt<λLaser must be met (cs: sound speed, Δt: time from plasma formation to the peak of the pulse). The achievable contrast enhancement is given by the ratio of plasma mirror reflectivity to cold reflectivity.

Lifetime of the plasma channel produced by ultra-short and ultra-high power laser pulse in the air

The time evolution of plasma channel produced by ultrashort and ultra high power laser pulses in the air has been investigated. The theoretical model considers the recombinati on of free electrons, positive and negative ions, as well as the attachment and detachment of electrons on neutral molecules in the air under the interaction with the successive coming laser's pulses. The analytical solution of rate equations of the charged particles in the plasma channel has been found when the detachment laser intensity is constant. Calculations show that the lifetime of the plasma channel with an electron density higher than 1012—1013cm-3 can be extended to microseconds by using a detachment laser to suppress the attachment between el ectrons and neutral moleculars. In the case of same wavelength and average power, the detachment efficiency of a short pulse sequence with a high repetiti on rate is higher than that of a continuous detachment laser.

Ti:sapphire crystal used in ultrafast lasers and amplifiers

The improvement of peak power of femeto-laser depends on the compression of pulse width. The titanium-doped sapphire crystal is the excellent laser crystal with the shortest pulse width. Its theoretical pulse width limit is 3 fs. At present 50-TW tabletop Ti:sapphire lasers have been commercialized. In this paper, comparison of Ti:sapphire crystals grown by temperature gradient technology (TGT) and heat exchange method (HEM) is presented, and results show that the laser quality of Ti:sapphire crystals grown by TGT is similar to or higher than those grown by HEM. ∅ 10–30 mm high optical homogeneity Ti:sapphire amplifiers were fabricated successfully and 5–40 TW high power were obtained. We believe that up to ∅ 100 Ti:sapphire amplifiers (grown by TGT) can be obtained for ultrahigh power laser systems using all Ti:sapphire crystals in near future.

Measurement of Thermal Diffusivity of Multilayer Optical Thin Film Systems Using Photoacoustic Effect

In other to develop ultrahigh-power laser systems, laser mirrors must be highly resistant to thermal shock and effectively cooled; therefore, the study of optical multilayer systems which have high thermal diffusivity has become important. In this study, we designed and developed two-layer antireflection (AR) optical coating samples and five-layer high-reflection (HR) optical coating samples on glass substrate under different evaporation conditions of coating speed (10, 20 Å/s) and substrate temperature (50, 100, 150, 200°C), using two dielectric materials MgF2 and ZnS which have different refractive indices, and the through-plane thermal diffusivity was measured using the photoacoustic effect. The thermal diffusivities of the samples were obtained from the measured photoacoustic signals by changing the modulation frequency of the Ar+ laser beam. The results indicated that the thermal diffusivity is maximum when the coating speed is 10 Å/s and substrate temperature is 150°C, and is closely related to the morphology of the films.

Recent studies of laser produced plasmas

Recent work on laser produced plasmas is presented focusing on the theoretical studies of four topics which have been carried out at the Institute of Laser Engineering (ILE), Osaka University, after a brief explanation of the six physics issues to be studied for plasma physics related to the laser fusion. The importance of integrated code development is emphasized and it is shown that the growth of the Rayleigh-Taylor instability at the ablation front is reduced partly due to non-local electron transport. Non-uniformity of implosion dynamics is studied by comparing a two-dimensional simulation with a spectroscopic post-processing package. It is concluded that all the available experimental data are consistently explained. The fast-ignition with ultra-high power laser is studied. The ignition criteria are clarified with a two-dimensional burning wave simulation. The possibility to study astrophysics by designing model experiments with intense lasers is introduced. The computational design of models of the ejecta-ring collision of SN1987A is shown by comparing with the event in the space.

Development of a compact high brightness X-ray source

Based on the concept of interacting electron with intense light stored in a supercavity, a compact and high brightness soft X-ray source has been proposed for lithography at ILT/ILE. For the purpose of enhancing the collision frequency of electron-photon beams, the idea of a combination of a supercavity pumped by a cw diode laser with an electrostatic dc accelerator has been put forward, for which a high average spectral brightness of 1.79×10 17 with a wavelength of 9.8 Å, and a bandwidth of 0.17% can be expected. Two other upgraded systems for the production of high peak brightness X-ray radiation and high brightness γ-ray radiation have also been proposed, which are based on an ultrahigh power laser (2 TW, 5 ps) and a compact electron storage ring (300 MeV/89.3 mA). Meanwhile, the prototype laser undulator system and the current experiments on photon storage in a Fabry-Perot cavity pumped by a high power mode-locked Nd:YAG laser (25 MW, 89.25 MHz) are introduced.