There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Recent years have witnessed many breakthroughs in research on graphene (the first two-dimensional atomic crystal) as well as a significant advance in the mass production of this material. This one-atom-thick fabric of carbon uniquely combines extreme mechanical strength, exceptionally high electronic and thermal conductivities, impermeability to gases, as well as many other supreme properties, all of which make it highly attractive for numerous applications. Here we review recent progress in graphene research and in the development of production methods, and critically analyse the feasibility of various graphene applications.

/pdf/a-roadmap-for-graphene-1nstzmbk5x.pdf

A roadmap for graphene

QUANTUM gravitational effects are usually ignored in calculations of the formation and evolution of black holes. The justification for this is that the radius of curvature of space-time outside the event horizon is very large compared to the Planck length (Għ/c3)1/2 ≈ 10−33 cm, the length scale on which quantum fluctuations of the metric are expected to be of order unity. This means that the energy density of particles created by the gravitational field is small compared to the space-time curvature. Even though quantum effects may be small locally, they may still, however, add up to produce a significant effect over the lifetime of the Universe ≈ 1017 s which is very long compared to the Planck time ≈ 10−43 s. The purpose of this letter is to show that this indeed may be the case: it seems that any black hole will create and emit particles such as neutrinos or photons at just the rate that one would expect if the black hole was a body with a temperature of (κ/2π) (ħ/2k) ≈ 10−6 (M/M)K where κ is the surface gravity of the black hole1. As a black hole emits this thermal radiation one would expect it to lose mass. This in turn would increase the surface gravity and so increase the rate of emission. The black hole would therefore have a finite life of the order of 1071 (M/M)−3 s. For a black hole of solar mass this is much longer than the age of the Universe. There might, however, be much smaller black holes which were formed by fluctuations in the early Universe2. Any such black hole of mass less than 1015 g would have evaporated by now. Near the end of its life the rate of emission would be very high and about 1030 erg would be released in the last 0.1 s. This is a fairly small explosion by astronomical standards but it is equivalent to about 1 million 1 Mton hydrogen bombs. It is often said that nothing can escape from a black hole. But in 1974, Stephen Hawking realized that, owing to quantum effects, black holes should emit particles with a thermal distribution of energies — as if the black hole had a temperature inversely proportional to its mass. In addition to putting black-hole thermodynamics on a firmer footing, this discovery led Hawking to postulate 'black hole explosions', as primordial black holes end their lives in an accelerating release of energy.

Black Hole Explosions

Terahertz spectroscopy systems use far-infrared radiation to extract molecular spectral information in an otherwise inaccessible portion of the electromagnetic spectrum. Materials research is an essential component of modern terahertz systems: novel, higher-power terahertz sources rely heavily on new materials such as quantum cascade structures. At the same time, terahertz spectroscopy and imaging provide a powerful tool for the characterization of a broad range of materials, including semiconductors and biomolecules.

Materials for terahertz science and technology

Space aberration effects which arise in high energy or in high average power laser chains are important parameters to control in order to emit a beam quality close to the diffraction limit. For that purpose we present recent experiments using an original adaptive and programmable module allowing the spatial control of the beam amplitude and the correction of the phase distortions due to the optical components and the gain media of the laser chain. Beam shaping is achieved by an optically addressed photoconductor-liquid crystal light valve. The light valve is addressed in the blue-green spectral range by incoherent projection of a VGA liquid crystal display. This adaptive optics module controls either the amplitude or the phase of near infrared laser beams depending on the liquid crystal operating mode. The other specific characteristics of the module will be detailed: no spurious diffraction effects, up to 10(pi) phase excursion and tri-lateral wavefront sensor. Experimental results of compensation of aberrations introduced on different laser beams will also be presented.

Optically addressed liquid crystal light valves for adaptive control of amplitude and phase of laser beam

This summary describes a novel GaAs electro-optic modulator that utilizes a resonant free, broadband, and velocity matching in order to achieve a reduced half-wave voltage and improved optical confinements. We have developed a technique to deposit, at room temperature, an amorphous hydrogenated silicon cover on the coplanar electrical waveguide of the electro-optic modulator.

https://ieeexplore.ieee.org/iel3/4988/14076/00645443.pdf

Traveling-wave electro-optic modulator with a novel broadband velocity-matching structure

Purpose: The authors present a microsurgery experimental system using Nd: Glass femtosecond laser. It is coupled to a confocal microscopy observation system to investigate intrastromal effects of the femtosecond laser. Methods: The femtosecond laser is a CPA system with a regenerative amplifier delivering pulses at a wavelength of 1.065 µm, with a pulse duration of 500 fs, an energy of 60 µJ for a repetition rate of 10 KHz. The amplified pulses power fluctuations are lower than 1%. Pulses repetition rate is adjustable up to 10kHz and can even be reduced to single shot. The laser beam has a Gaussian distribution shape TEM00. The obtainable peak power density is on the order of 10^15W/cm^2. The laser beam travels to the samples guided by one six–lens set and one magnifier. The last lens can be changed to adjust the focal distance from 2 to 5 cm and the focal spot from 1 to 4 µm. The samples are fixed to an anterior chamber system, which is driven by a micrometric precision motor system. The 3 dimensional movements are computer controlled. The laser energy is continuously monitor for measurements consistency. The experimental set up is also composed of a confocal microscope, which permits corneal sample analysis without removing them from the artificial chamber system. Results: The experimental set up permits complex geometry to be done. Penetrating and lamellar cuts could be performed in silicon dioxide and human corneal samples. The confocal microscopy observation system permits precise parameter control of the cutting system (cut shape, shot scanning and treatment depth). Conclusions: Applications for femtosecond laser are the refractive surgery and corneal keratoplasty. The development of concepts as sutureless keratoplasty needs an experimental system with large flexibility in order to work out useful cut parameters.

Setup for femtosecond laser corneal surgery

An ultrafast laser irradiation method for the removal of corrosion from Daguerreotypes without detrimentally affecting image quality has been developed. Corrosion products such as silver oxide and silver sulfide may be removed by chemical cleaning but these reactions are hard to control and are often damaging to the underlying silver, ruining the image. The Ti:Sapphire 150 fs laser pulses used in this study are focused to a beam diameter of 60 μm and are normally incident to the Daguerreotype. It was found that the corrosion layer has a lower material removal threshold than silver allowing for removal of corrosion with minimal removal of vital information contained in the silver substrate.

Ultrafast Laser Cleaning of Daguerreotypes

Recently there has been significant progress in the development of high-repetition-rate, highpeak-power Tisapphire systems.' Recent experiments in high harmonic generation (HHG) have demonstrated that with sufficiently short laser pulses (-20 fs), laser energies of 2-10 mJ can be used to generate very high-order harmonics, with photon energy up to 240 eV.2,3 However, to date, the lasers used to generate very high-order harmonics have typically been low-repetition-rate (10 Hz) systems. A kHz repetition-rate laser with sufficient peak power for high-harmonic generation would result in a 100 times increase in x-ray flux, with vastly improved signal-tonoise ratios. In addition, other processes such as low-order harmonic generation in gases4 become even more efficient with millijoules of laser energy. Thermal lensing is the main obstacle to scaling ultrafast Tisapphire systems to high average power, because the thermal time constant for sapphire is tens of milliseconds. If the focal length of the thermal lens is longer than the Rayleigh range in a focused beam, as it is in oscillators and low average power amplifiers ( < O S mJ compressed), the lensing effect is not ~ t r o n g . ~ However, with the larger beam sizes found in power amplifiers, thermal lensing compensation is critical. We have developed a Tisapphire amplifier system that generates a peak power of 0.125 TW, at 1-kHz repetition rate, with 2.5 mJ of energy, in a 20-fs pulse duration. The first stage is a ring multipass amplifier, which has been demonstrated previously.' It is pumped by 9 mJ from an intracavity doubled Nd:YLF laser (Quantronix 527). The second stage has a similar design to the first stage, and is pumped

Gerard Mourou

Papers

Optically addressed liquid crystal light valves for adaptive control of amplitude and phase of laser beam

Traveling-wave electro-optic modulator with a novel broadband velocity-matching structure

Setup for femtosecond laser corneal surgery

Ultrafast Laser Cleaning of Daguerreotypes

High-dynamic-range Measurement Of Laser Pulse Contrast By Use Of A Plasmashuttered Jitter-free Streak Camera