Laser Technology Advancements (at least from my easily impressed perspective)

[paul1598419]

Then there was this:



We don't know how the EM drive works, or even if it really does work. The thrust that has been observed can still be attributed to unknown errors in the experiment. Even if it does work (Hope it does), to say that it's a warp drive before we even have any idea of how it works is just silly. There's no evidence of any warp bubble - at least not yet.[/QUOTE]

This is the one I was talking about. I've read a lot of these and don't remember seeing this at all. Where did it come from?

 

[diachi]

Then there was this:



We don't know how the EM drive works, or even if it really does work. The thrust that has been observed can still be attributed to unknown errors in the experiment. Even if it does work (Hope it does), to say that it's a warp drive before we even have any idea of how it works is just silly. There's no evidence of any warp bubble - at least not yet.

This is the one I was talking about. I've read a lot of these and don't remember seeing this at all. Where did it come from? [/QUOTE]

Oh haha, I see what you're getting at! It was on the article that was linked.

Last year, NASA scientists developed the ability to create a warp drive engine like the one that powers the Enterprise. The EmDrive project was able to create a small warp bubble that suspended spacetime for objects inside the bubble. The technology could theoretically be used to allow a ship to travel faster than light without the negative effects; the front of the bubble pushed space time away from the object which then reformed around the back.
Read more at 'Beam Me Up Scotty', Breakthrough In Star Trek Style Transporter Technology

 

[madmacmo]

ScienceAndTechnologyResearchNews.com | January 24, 2016
Petawatt Laser System Passes A Key Milestone

HAPLS team members (from left) Constantin Haefner, Jiri Thoma, James Nissen (sitting), Pavel Bakule and Bedrich Rus review the results of pump laser commissioning tests in the HAPLS control room. Photo by Jason Laurea/LLNL

The High-Repetition-Rate Advanced Petawatt Laser System (HAPLS) under construction at LLNL recently achieved a key average power milestone more than two months ahead of schedule, and is now moving into the next phase in its development.

The HAPLS high-energy diode-pumped solid-state pump laser, firing at a repetition rate of 3.3 Hz (3.3 shots per second), achieved 70 joules of infrared (1,053-nanometer) energy and 39 joules of green (527-nm) energy. Completion of this average-power milestone marks another major step in the HAPLS commissioning plan: the beginning of the integration of the pump laser with the HAPLS high-energy short-pulse beamline

This computer-aided design shows HAPLS’ two interconnected Livermore-developed laser systems. The diode-pumped, solid-state laser will deliver up to 200 joules of energy at a repetition rate of 10 Hz. At the pump laser output, a frequency converter doubles the laser frequency from infrared to green. The solid-state, short-pulse laser converts the energy from the pump laser to 30-joule, 30-femtosecond pulses for a peak power exceeding one petawatt. The laser system measures 4.6 meters wide and 17 meters long.

HAPLS is designed to reach a peak power exceeding one petawatt at a repetition rate of 10 times per second to deliver intensities on target up to 1023 watts per square centimeter. Achieving this intensity would open up entirely new areas of laser–matter investigation, enable new applications of laser-driven X rays and particles, and for the first time allow researchers to study laser interactions with the sea of virtual particles that comprise a vacuum.

Ramping of the laser to its full performance has been organized in several phases. The first phase, completed last October, brought the pump laser to an intermediate performance level in a “single shot” regime, as opposed to an average power regime in which the amplifiers are thermally loaded. “In the second phase,” Haefner said, “we brought it up to average power, and that was an intermediate performance level. And now we’re integrating the pump laser and the short-pulse system. Together with ELI Beamlines we will integrate the short-pulse performance diagnostics, and then we will ramp the short-pulse laser system, similar to what we did for the pump laser system, first to energy and then to average power.”

Representatives from the European Union’s Extreme Light Infrastructure Beamlines(link is external) (ELI-Beamlines) facility in the Czech Republic, where HAPLS will be installed, attended the demonstration. “We are delighted to see the HAPLS pump laser work with a performance exceeding the project expectations for this phase, and achieve this important milestone on budget and ahead of schedule,” said ELI Beamlines Chief Laser Scientist Bedrich Rus.

 

[madmacmo]

Berkley Lab | February 1, 2016 | -Written by Paul Preuss | News Release Glenn Roberts Jr. 510-486-5582
Coupling 2 ‘Tabletop’ Laser-Plasma Accelerators, a Decisive First Step Toward Tomorrow’s Ultrapowerful Compact Machines

Berkeley Lab Scientists Create the First-ever, 2-stage Laser-plasma Accelerator Powered by Independent Laser Pulses

Laser-plasma accelerators (LPAs) got the nickname “tabletop” because, as shown by the unique BELLA accelerator at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), they can boost electron beams to multibillion electron-volt energies (GeVs) in a few centimeters—a distance thousands of times shorter than conventional accelerators.

Past those few centimeters, however, the laser pulse weakens and energy gain stalls. LPAs will have to get off the tabletop if they are to rival proposed conventional colliders, such as 30-kilometer-long electron-positron linear colliders or circular proton colliders 100 kilometers in circumference, with electron-volt energies in the trillions (TeVs), not billions. Only by coupling a hundred LPAs in series, each powered by a BELLA-class laser in series, and accelerating a well-shaped beam from one stage to the next, will such high energies be achieved.

“Long before planning began for BELLA, we’d set our sights on staging as the way to achieve energies needed for compact particle colliders, free-electron lasers, and other tools of future science,” says Wim Leemans, Director of Berkeley Lab’s Accelerator Technology and Applied Physics Division (ATAP)and Director of the BELLA Center. But because of the daunting technical challenges, including maintaining electron beams with dimensions measured in millionths of a meter and laser pulses measured in quadrillionths of a second (femtoseconds), Leemans says, “Lots of people told us we’d never be able to do it.”

In an experiment packed with scientific firsts, Leemans and his BELLA Center colleagues have now demonstrated that a laser pulse can accelerate an electron beam and couple it to a second laser plasma accelerator, where another laser pulse accelerates the beam to higher energy—a fundamental breakthrough in advanced accelerator science. The results are reported in the Feb. 1 issue of Nature

Schematic of the first experiment to achieve staging of laser plasma accelerators (LPAs) with independent laser pulses: a pulse from laser 1 (at left) creates a plasma wakefield in the stage 1 LPA, a gas jet. The resulting electron beam is focused by a capillary-discharge plasma lens and then penetrates a moving tape. Almost simultaneously, an incoming pulse from laser 2 strikes the tape and creates a plasma mirror, which combines the laser beam and electron beam. Entering stage 2, a capillary-discharge LPA, the second laser pulse creates a wakefield in the plasma which further accelerates the electron beam; downstream diagnostics (at right) measure the beam.


Stable Beams, Disposable Mirrors

Sven Steinke, lead author of the Nature paper, says that to achieve staging wasn’t about huge energy gains; the challenge was handing off a useful beam. “A billion electron-volts wouldn’t matter,” he says. “What mattered was stability,” an experiment that would work reliably for days at a time and many thousands of laser shots. “You don’t want to spend three-quarters of your day tuning your beam injector, with no time left to do an experiment.”

The solution was to use two different kinds of LPA. The more advanced but more finicky type is a discharge capillary, a block of sapphire with a thin horizontal tube through it. Hydrogen gas fills the tube; a potent electrical discharge ionizes it, separating electrons from their nuclei and forming a plasma. Almost instantly this discharge arc heats the plasma and forms a laser waveguide, a cylindrical channel of thinner plasma in the center; the incoming laser pulse drives through it like a speedboat on water, picking up free electrons in its wake and hurling them forward like a surfer on a following wave.

A critical challenge was how to introduce the second laser pulse, using a mirror, within the few-millimeter space between the two stages. The electron beam would have to pass through a hole in the mirror. The reflected laser pulse would come close behind. Unfortunately, to focus enough power to accelerate the electron beam, the laser focus would have to be so close to the mirror it would blow it to pieces.

“We decided from the beginning of the project that instead of worrying about blowing up the mirror, we’d blow it up with every shot,” says Leemans. They first developed a prototype mirror of water film, he says, “but settled for much more robust VHS tape.”

Video cassette players may be out of fashion, but VHS tape is thin, stretch-resistant, and capable of running for hours at a time. The electron beam pierces the tape virtually untouched. On the opposite side, in the merest fraction of a second before the laser pulse can penetrate the tape, it ionizes the surface to form a dense, perfectly flat plasma: a highly efficient mirror.
Steinke, whose dissertation involved plasma mirrors and who was a postdoc at the Max Born Institute in Berlin before joining the BELLA Center, characterized the mirror system for the staging experiment. Previous plasma mirrors were based on expensive solid optics made for completely different purposes. Steinke and Leemans agree: “This was the first use of a continuous, high-repetition-rate, disposable plasma mirror.”


A Serendipitous Plasma Lens

The staging system was ready for its first test. In the gas-jet LPA, the first laser pulse created an electron beam that passed through the tape, while the plasma mirror reflected the second laser pulse. Electron beam and laser pulse both entered the stage 2 capillary.

No beam came out.

“We were stunned,” says Jeroen van Tilborg, a long-time member of the BELLA Center and its predecessor, the LOASIS Program, where he earned his PhD from Eindhoven Technical University. “Suddenly there were four or five of us sitting around scribbling on the backs of envelopes.”

ATAP scientists had used discharge capillaries to inject and accelerate electrons for over 10 years, but this was the first time anyone had shot an external electron beam into one. They’d never dealt with the full effects of the powerful discharge current: it ionizes the gas and forms an optical waveguide through the plasma, but also creates a strong magnetic field that can blow apart a pre-existing electron beam.

Or, more optimistically, can shape and focus it. Van Tilborg called dibs on studying the problem and soon realized the pulsed magnetic field would make an excellent plasma lens. Such a fast-acting lens could find many uses, for example by conditioning beams of existing free-electron lasers. Its immediate application was to tightly focus the staging experiment’s injector beam.
The final configuration—gas-jet injector, plasma lens, plasma mirror, discharge capillary second stage, and diagnostics—showed energy gains, for significant portions of the electron beam, of around a hundred million electron-volts.

The success of the experiment resulted from on-the-job discoveries plus continuous feedback between experimental observations and computer modeling. Running on a Cray supercomputer at DOE’s National Energy Research Scientific Computing Center (NERSC) at Berkeley Lab, the highly efficient INF&RNO code for modeling laser and plasma interactions could turn a day’s experimental data into a simulation almost overnight, like “dailies” on a movie set. Among many other questions, intricacies of laser timing could be explored; focusing the energetic but ragged beam from the gas jet could be simulated even as the serendipitous discovery of how to actually do it was becoming a reality.

“We’re ready for staging BELLA,” says Leemans, using two charge-capillary LPAs. “We’ll split the BELLA laser beam,” capable of a quadrillion watts (a petawatt) per 40-femtosecond pulse every second. “The first stage should bring up the beam to about 5 GeV. We will do the bunch transport with our capillary lens and play around with the timing of the second pulse. We should come out of the second stage with 10 GeV. And, while in the staging experiment we’re only trapping about three or four percent of the electrons available, in BELLA we’ll be able to trap 100 percent of the charge.”
Even better, says Steinke, “BELLA is much simpler. The effects of the tape on beam quality should be much less, and the beam is much ‘stiffer,’ easier to handle.”

Van Tilborg concurs: “At 5 GeV per stage there may be no problem. The higher energy saves you.”

 

[madmacmo]

LiveScience.com | By Megan Gannon | February 11, 2016 06:28am ET
'Lost' Roads of Ancient Rome Discovered with 3D Laser Scanners

The U.K.'s Environmental Agency released this image of Vindolanda, a Roman fort in northern England, just south of Hadrian's Wall.

Over the past 18 years, the U.K.'s Environment Agency has used a technology called lidar to collect data for more than 72 percent of England's surface. This remote sensing technique bounces laser light beams off the ground to make 3D terrain maps that can peer below vegetation and reveal the contours of every ditch and boulder below. The U.K.'s lidar maps were used primarily for environmental purposes, such as for planning flood defenses or tracking eroding coastlines. But last summer, the agency dumped all 11TB of its data sets onto the Survey Open Data website. Roman Fort: See Images of the Long-Lost Discoveries

The maps grabbed the attention of archaeologists and history buffs —among them, David Ratledge, a 70-year-old retired road engineer who has spent nearly five decades searching for ancient Roman roads. One mystery for Ratledge was, how did the Romans get from Ribchester to Lancaster? With access to the new maps, Ratledge thinks he has solved the puzzle. He traced an 11-mile (17 kilometers) road from Ribchester to the main north-south road at Catterall that then led to Lancaster.

Ratledge said a prominent stretch of a Roman rampart is even visible in Google Street View. "How nobody —me included —spotted it is a mystery," he wrote

Archaeologists Hugh Toller and Bryn Gethin have also used the lidar data to find four other roads, including a missing part of a Roman road called the Maiden Way

 

[madmacmo]

MarketBusinessNews.com | March 9, 2016| Written by Christian Nordqvist
Laser On A Silicon Chip Holy Grail Of Incredibly Fast Communications

The Holy Grail of incredibly fast communications – a laser on a silicon chip – has been achieved in an incredible breakthrough by a team of British scientists. The researchers say their first practical silicon laser has the potential to completely transform energy, healthcare and communications systems.

The research, led by scientists from Cardiff University, who worked alongside academics from University College London (UCL) and the University of Sheffield, claim they have demonstrated the first practical laser that has been grown directly on a silicon substrate (underlying substance).


Breakthrough Could Transform Several Sectors

They say their breakthrough could lead to mega-fast communication between computer chips and electronic systems, which would completely transform a vast range of sectors

(A) Schematic of the layer structure of an InAs/GaAs QD laser on a silicon substrate. (B) A cross-sectional SEM image of the fabricated laser with as-cleaved facets, showing very good facet quality. (C) SEM overview of the complete III–V laser on silicon.


Silicon Photonics

Scientists say keeping up with this ever-growing demand using conventional electrical interconnects between computer chips and systems is a race we will eventually lose. That is why they have turned to light as a potential super-fast connector.

Silicon photonics is a futuristic technology in which data is transferred among computer chips by optical rays (light). Optical rays can carry considerably more data in less time than electrical conductors.

The main obstacle has been combining a semiconductor laser – the ideal light source – with silicon. In fact, scientists wondered whether it might be impossible, that is, until this latest breakthrough. The British team have now overcome these obstacles and managed to successfully integrate a laser directly grown onto a silicon substrate for the first time.


Silicon Photonics is the Future

Professor Peter Smowton, Deputy Head of Cardiff University’s School of Physics and Astronomy and Director of Research, said: “Realising electrically-pumped lasers based on Si substrates is a fundamental step towards silicon photonics. The precise outcomes of such a step are impossible to predict in their entirety, but it will clearly transform computing and the digital economy, revolutionise healthcare through patient monitoring, and provide a step-change in energy efficiency.”

“Our breakthrough is perfectly timed as it forms the basis of one of the major strands of activity in Cardiff University’s Institute for Compound Semiconductors and the University’s joint venture with compound semiconductor specialists IQE.”

Dr. Huiyun Liu (pictured above) and his research team have created a laser that can grow on one single silicon chip. What they have done is provided a method to generate the light actually on the chip itself. That is the Holy Grail of silicon photonics. (Image: From YouTube video below)

Head of the Photonics Group at University College London, Professor Alwyn Seeds said: “The techniques that we have developed permit us to realise the Holy Grail of silicon photonics – an efficient and reliable electrically driven semiconductor laser directly integrated on a silicon substrate.” “Our future work will be aimed at integrating these lasers with waveguides and drive electronics leading to a comprehensive technology for the integration of photonics with silicon electronics.”

As silicon chips get progressively faster, the copper connections used to transmit electrical signals between them are struggling to keep up. The obvious next step must be optical signals. However, integrating them with silicon systems is difficult.

Video – Why lasers are the future for silicon

 

[madmacmo]

TechCentral.co.za |15 March 2016
SA Researchers In Laser Breakthrough

South African and Italian researchers have demonstrated a new type of laser that paves the way for novel new lasers for use in optical communication, laser machining and medicine.

Artist’s impression of spiral light created at the source
South African and Italian researchers published a research paper on Tuesday demonstrating a new type of laser that is able to produce laser beams “with a twist” as its output, opening the way for novel new lasers for use in optical communication, laser machining and medicine.

The South African-Italian research team, which has published its findings in Nature Photonics, has shown the outputs and “superpositions” of the new type of laser form a set of beams, called “vector vortex beams”.

The idea was conceived by Andrew Forbes of Wits University, who also led the collaboration, while all the key experiments were performed by Darryl Naidoo of the CSIR. The team members of Stef Roux (Wits and the CSIR), Angela Dudley (Wits and the CSIR) and Igor Litvin (CSIR) all contributed significantly to the work, Wits University said in a statement. The custom geometric phase optics, without which the realisation of the idea would not be possible, were produced by the Italian team from the University of Naples, Lorenzo Marrucci and Bruno Piccirillo.

“We are all familiar with angular momentum in our everyday lives: the spinning Earth carries spin angular momentum, while the orbiting Earth carries orbital angular momentum (OAM). Light can also carry angular momentum: through its polarisation (spin), and through its pattern and phase OAM,” explained Forbes in the statement.

The researchers said that producing light with a controlled spin in a laser has been known for decades, but producing OAM beams inside a laser is not so simple. “Light carrying OAM is created by twisting the phase of light into a helical shape, forming a spiral. Because the twisting of the pattern gets tighter and tighter as you move towards the centre of the beam, the light disappears and such beams are often called donut beams or vortex beams.

“The problem is that usually lasers cannot tell the difference between light that is twisted clockwise and light that is twisted anti-clockwise, and so the laser simply gives a combination of both in an uncontrolled manner. “Moreover, combining spin and orbital components to produce general beams from a single laser that are mixtures of the two momenta, have not been demonstrated before,” they said.

Forbes explained that the team’s novelty was “realise that by using custom-geometric phase optics to map polarisation to OAM, the laser could be designed to tell the difference between the clockwise and anticlockwise light”. “The control is achieved by simply rotating a single optical element inside the laser, without any need for realignment. Such beams have been used in optical communication, optical trapping of micro particles and metrology — and now a single laser can create them on demand,” he said. In its statement, Wits University said the geometric phase of light is a very abstract concept, first appearing in quantum theory, but the researchers have used it to create particular types of twisted light.

The custom optic, called a q-plate, changes the handedness of the OAM twist according to the handedness of the polarisation twist, mapping one to the other. We like to call this a spiral laser because both the polarisation and OAM of the beam give rise to light that spins or twists in complicated ways,” said Forbes. Importantly, the same laser can produce any combination of these OAM beams and various polarisations of light, Wits said. The team was able to show that the outcome was the generation of arbitrary vector vortex beams, known as higher-order Poincaré sphere beams.

“For example, in addition to the special cases of OAM beams, the same laser also produces radially and azimuthally polarised light, where the polarisation (direction of the electric field) changes in space. For example, radially polarised light has the field always pointing away from the centre of the circle, which is very useful for cutting and drilling metals. Such beams are often called ‘vector’ beams because the polarisation changes across the beam. When the polarisation pattern stays constant across the beam, it is called a ‘scalar’ beam. In the reported work, the researchers have shown that either can be created from the same laser.”

Said Naidoo, who performed the experiments as part of his doctoral studies and who is the lead author of the paper: “You have to understand that vector vortex laser beams have proven immensely useful in machining metals and other materials with lasers, for example, in the automotive industry. But until now we have not been able to produce all of them in one laser.”

Wits said the laser concept is likely to attract interest from both the academic and industrial communities. “Vector and scalar vortex beams that exist on the higher-order Poincaré sphere have many applications, such as microscopy, imaging, laser machining, and communication in free space and in fibres. Often one has to decide beforehand which beam is the most desirable and then design a laser for it. Now it is possible to have such beams available on demand from a single laser.”

 

[madmacmo]

IBTimes.com | April 7, 2016 18:18 BST | By Mary-Ann Russon
Quantum Cryptography Breakthrough: 'Unbreakable Security' Possible Using Pulse Laser Seeding

Researchers have figured out how to transmit information using lasers at up to 1Mbps, which means that unbreakable quantum cryptography could now be possible

Computer scientists and engineers from Cambridge University and Toshiba have devised a new laser-based system that speeds up the rate at which data is securely transmitted to 1Mbps, paving the way for impossible-to-break quantum cryptography. Although quantum computers are still only a concept, many computer scientists believe that the super-powerful computers will be available within the next 50 years, and that they will be able to solve extremely large numbers quickly, using quantum computing algorithms, such as Shor's factoring algorithm. While solving large prime numbers quickly would mean computers could perform tasks much faster, it also means that quantum computers would find it easy to break current encryption methods, which rely on complex mathematical problems.

The National Security Agency (NSA) in the US is deeply afraid that current security cryptography used to protect almost all electronic data over the past 50 years will easily be unravelled by hackers once quantum computers become a reality, and to that end, has been advising US businesses to start investing in quantum-resistant algorithms since August 2015. Computer scientists and engineers from Cambridge University and Toshiba have devised a new laser-based system that speeds up the rate at which data is securely transmitted to 1Mbps, paving the way for impossible-to-break quantum cryptography.

 

[madmacmo]

Phys.org | April 18, 2016
Technology For Growth Of Single Crystals Leads To An Eye-Safe Laser

A team of scientists at Lomonosov Moscow State University and the Belarusian National Technical University has created a unique laser. It's a compact light source with wavelengths harmless to the human eye. The device can be used in medicine, communications systems and also in research. The works are published in Journal of Crystal Growth and Optics Letters.

In collaboration with our colleagues of the Center for Optical Materials and Technologies, Belarusian National Technical University, we have developed a highly efficient, diode-pumped, eye-safe laser, which can be used in ophthalmology, communication systems and ranging,' says co-author Nikolay Leonyuk. The development of this laser followed the team's development of laboratory growth technology for single crystals with desired properties.

The emission with wavelengths of 1500 to 1600 nm is safe for the eyes and offers practical applications in medicine, ranging systems, communication systems and optical location. The light-refracting system of the eye, consisting of the cornea and crystalline lens, has a sufficiently high absorption coefficient in this part of the spectrum, so only a small fraction of the energy reaches the sensitive retina. And the radiation in the 1500 to 1600 nm spectral range suffers low losses passing through the atmosphere, making the device advantageous for applications in telecoms.

To date, among the sources of radiation in this spectral range, the most widely used are the solid-state lasers based on phosphate glasses co-doped with Er (erbium), and Yb (ytterbium) ions. Such lasers are also relatively simple, compact and capable of operating in adjusted Q-mode required for producing short impulses. In the meantime, the main disadvantage restricting the usage of erbium phosphate glasses in continuous diode systems is the low thermal conductivity of the matrix. To avoid this limitation, Er and Yb containing a crystalline matrix can be used.

In the published research, GdAl3 (BO3)4 single crystals co-doped with Er and Yb were used to improve the efficiency of generation pulse energy and repetition rate, and hence to increase the maximal measurement range, reducing errors and time. These single crystals are characterized by a record value of thermal conductivity and high thermochemical stability (decomposition at temperatures of 1280° C, resistant to corrosive environments) as well as mechanical strength.

'The solid-state laser based on yttrium gadolinium borate crystals is a unique compact source of emission with varying eye-safe wavelengths,' says Nikolay Leonyuk. 'Reliable laser design, along with high performance, makes applicable in laser ranging systems, metrology and laser-induced breakdown spectroscopy.'

The use of laser diodes as a pump source increases the lifetime of the laser up to 100,000 hours. The laser system is easy to use, does not require water cooling, and does not generate any vibration during operations. Compared with the widely used CW erbium fiber lasers, the (Er,Yb):GdAl3 (BO3)4-based laser is characterized by linear laser radiation and lower price.

 

[madmacmo]

Phys.org | April 27, 2016
First light for the Four Laser Guide Star Facility on ESO's Very Large Telescope

On April 26, 2016, an event at ESO's Paranal Observatory in Chile marked the brilliant first light for the four powerful lasers that form a crucial part of the adaptive optics systems on ESO's Very Large Telescope. Attendees were treated to a spectacular display of cutting-edge laser technology against the majestic skies of Paranal. These are the most powerful laser guide stars ever used for astronomy and mark the first use of multiple laser guide stars at ESO.

This spectacular image shows the four beams emerging from the new laser system on Unit Telescope 4 of the VLT. Credit: ESO/F. Kamphues

The Four Laser Guide Star Facility (4LGSF) shines four 22-watt laser beams into the sky to create artificial guide stars by making sodium atoms in the upper atmosphere glow so that they look just like real stars. The artificial stars allow the adaptive optics systems to compensate for the blurring caused by the Earth's atmosphere and so that the telescope can create sharp images. Using more than one laser allows the turbulence in the atmosphere to be mapped in far greater detail to significantly improve the image quality over a larger field of view.

 

[madmacmo]

AIP Journal of Laser Applications - Volume 28, Issue 2, May 2016
Yujie Xu1, Zhenying Du1, Liang Ruan1 and Wenwu Zhang1,a)
Research status and development of laser shock peening

Laser shock peening (LSP) is a surface strengthening technology. Compared with the traditional surface treatment technologies (for instance, shot peening), it has many advantages such as noncontact, no heat-affected zone, good controllability, and significant strengthening effect. As an advanced manufacturing method, LSP has been widely used in military industry, petrochemicals, marine vessels, and aerospace fields. The mechanism of LSP is shown in Fig. 1 below.

In this process, a short-pulse (tens of nanoseconds) and high power (in the magnitude of 109 W) laser spot passes through the transparent confinement layer and acts on the surface of the coated absorption layer. After absorbing the laser energy, the absorption layer evaporates rapidly, and the dense plasma under high temperature and high pressure is formed. The plasma explodes as it continues to absorb the laser energy, and then a shock wave generates. The shock pressure can reach several gigapascal, far beyond the yield strength of the workpiece. The shock wave impacts the surface of workpiece and spreads to the interior, which leads to plastic deformation in the surface layer of the workpiece. As a result of this process, the density of dislocation increases, the crystalline grain is refined, and a considerable residual compressive stress presents in the surface layer of the workpiece. The significant improvements of the fatigue resistance, antiwear and corrosion resistance of the material greatly extend the service life of the material.1,2

LSP has made considerable progress during the past four decades, but some technical issues affecting their applications remain to be resolved, for instance, the utilization rate of laser shock energy is only about 50%, the processing adaptability of rigid confinement layer is poor, and the thickness of the flexible confinement layer represented by a water layer is difficult to control.

In response to these deficiencies, a patented new LSP method with a cavity used to confine the water layer is presented in this paper, and its working principle is shown in Fig. 2. The laser focus on the absorbing layer after passing through the transparent water in the cavity, and then a plasma shock wave is formed. The shock wave transforms to a composite shock wave when reflecting back and forth in the cavity (shown as Fig. 3), which repeatedly acts on the surface of the workpiece. It is realized that multiple shock pulses are obtained with one laser pulse, and the energy efficiency is significantly improved. Furthermore, since the fluid is confined in the cavity with fixed shape, the issue in the present process such as poor adaptability, lack of rigidity, and thickness uncontrollability can be resolved effectively.

 

[madmacmo]

Physics | May 6, 2016 | Physics 9, 50
Focus: How to Make an Intense Gamma-Ray Beam


Computer simulations show that blasting plastic with strong laser pulses could produce gamma rays with unprecedented intensity, good for fundamental physics experiments and possibly cancer treatments.

Intense beams of gamma rays would find a host of uses in fundamental physics research, nuclear fusion, and medicine, but they are hard to produce. A team has now used computer simulations to show that a powerful laser hitting a plastic surface can generate intense gamma-ray emission. In the simulations, the laser light creates a plasma in the plastic and accelerates electrons enough to produce large numbers of gamma-ray photons. The researchers say that the system might work with current technology.

In extreme astrophysical environments, such as near a supermassive black hole, matter and antimatter (electrons and positrons) regularly annihilate, producing gamma rays. Researchers would like to study the reverse process by colliding beams of gamma rays, which should create electrons and positrons, a transformation of light into matter [1]. Gamma-ray beams could also enable a wide range of other fundamental experiments and might have a role in radiation therapy and radiosurgery [2]. Previous attempts to make these beams involved the interaction of a laser beam with an electron beam [3]. But to produce copious gamma-ray photons with energies in the MeV range, the laser beam would need to be more intense than any current device.

Alexey Arefiev at the University of Texas at Austin and his co-workers now propose a different method that requires somewhat less laser power. It involves shining pulses of a petawatt W
(1015W)
infrared laser onto a carbon-rich, plastic target. The power density of such a pulsed laser can reach around W/cm 5×1022W/cm2, which is about 500 times greater than would be produced by focusing all of the sunlight reaching the Earth onto a pencil tip.

In the team’s scenario, the laser pulse heats the target, creating a plasma of electrons and ions. The electrons in the plasma are high-energy, and according to special relativity, they acquire a large effective mass, making them too sluggish to follow the oscillations of the laser’s electromagnetic field. This effect renders the plasma transparent to the light, so the laser beam can penetrate tens of micrometers into the target, filling it with a dense plasma.

In the team’s simulations, the laser pulse pushes the electrons in this plasma forward, like a leaf blower propelling leaves, and this motion of charge sets up a strong magnetic field that curls around the axis of the laser beam. This field accelerates the electrons forward even more but along zigzag trajectories as they move through the plastic. This electron motion generates so-called synchrotron radiation of very high energy (gamma-ray photons) that is emitted from the rear of the plastic target in the direction of the laser beam.

The simulations that Arefiev and colleagues conducted using the Stampede supercomputer at the University of Texas showed that the method works in principle

Donald Umstadter of the University of Nebraska at Lincoln, who works on new laser technologies, says that the gamma-ray beam could be used to study nuclear weapons materials that are relevant for managing the large stockpile of obsolete warheads. However, he also foresees many potential engineering difficulties in putting the idea into practice.The expected magnetic field would be 10 times stronger than that of any previous laser plasma, says Tony Bell of the University of Oxford, UK. But “the simulations are credible,” he says. “If it is successful, the beam of gamma rays thus generated would be extraordinarily intense.”

 

[RedCowboy]

:drool: :drool: :drool: :drool: The pump diodes must be hundreds of watts each.

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Indeed, good info man! :thanks: Super cool pic. ^

 

[paul1598419]

Jees, Mac. I'm still trying to get through all the information you posted last night. I'm half way through and have to take a break, but want to thank you for bringing all this to us on the forum. I'd rep you, but it won't let me yet.