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

Imagine being able to instantaneously run an optical cable or fiber to any point on earth, or even into space. That's what Howard Milchberg, professor of physics and electrical and computer engineering at the University of Maryland, wants to do.

In a paper published today in the July 2014 issue of the journal Optica, Milchberg and his lab report using an "air waveguide" to enhance light signals collected from distant sources. These air waveguides could have many applications, including long-range laser communications, detecting pollution in the atmosphere, making high-resolution topographic maps and laser weapons.

Milchberg's air waveguides consist of a "wall" of low-density air surrounding a core of higher density air. The wall has a lower refractive index than the core—just like an optical fiber. In the Optica paper, Milchberg, physics graduate students Eric Rosenthal and Nihal Jhajj, and associate research scientist Jared Wahlstrand, broke down the air with a laser to create a spark. An air waveguide conducted light from the spark to a detector about a meter away. The researchers collected a strong enough signal to analyze the chemical composition of the air that produced the spark.

The signal was 1.5 times stronger than a signal obtained without the waveguide. That may not seem like much, but over distances that are 100 times longer, where an unguided signal would be severely weakened, the signal enhancement could be much greater.

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Milchberg creates his air waveguides using very short, very powerful laser pulses. A sufficiently powerful laser pulse in the air collapses into a narrow beam, called a filament. This happens because the laser light increases the refractive index of the air in the center of the beam, as if the pulse is carrying its own lens with it.

Milchberg showed previously that these filaments heat up the air as they pass through, causing the air to expand and leaving behind a "hole" of low-density air in their wake. This hole has a lower refractive index than the air around it. While the filament itself is very short lived (less than one-trillionth of a second), it takes a billion times longer for the hole to appear.

Importantly, the "pipe" produced by the filaments lasted for a few milliseconds, a million times longer than the laser pulse itself. For many laser applications, Milchberg says, "milliseconds is infinity."

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The researchers’ report in Nature Photonics describes how a laser beam dressed with a second beam prevents the dissipation of energy necessary to excite charged particles in a cloud.

While high-intensity lasers can travel millions of miles, “when a laser beam becomes intense enough, it behaves differently than usual – it collapses inward on itself,” said study author Matthew Mills, a graduate student in the university’s Center for Research and Education in Optics and Lasers (CREOL).

“The collapse becomes so intense that electrons in the air’s oxygen and nitrogen are ripped off creating plasma – basically a soup of electrons,” Mills added.

When this happens, the laser beam pushes back outward – creating a battle between the spreading and collapsing of an ultra-short laser pulse. Known as filamentation, the tension helps to create a filament or “light string” that only develops temporarily until the properties of air make the beam disperse.

Currently, the Florida researchers have only been able to extend their ‘dressed’ beam about 7 feet, but said they are planning to stretch the filament even farther.

“This work could ultimately lead to ultra-long optically induced filaments or plasma channels that are otherwise impossible to establish under normal conditions,” said study Demetrios Christodoulides, a professor of optics who is overseeing work on the project.

“In principle such dressed filaments could propagate for more than 50 meters or so, thus enabling a number of applications,” Christodoulides said. “This family of optical filaments may one day be used to selectively guide microwave signals along very long plasma channels, perhaps for hundreds of meters.”

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No, not that ray gun you see above -- that was the U.S. Air Force Airborne Laser. And no, we're not talking about Boeing's Advanced Tactical Laser or its Laser Avenger projects, either. Respectively, those weapons systems require anything from the size of a Boeing 747 to a small tank to lug them around.

Boeing's newest laser weapon system, in contrast, is small enough to be transported by hand.

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. . . the company's new Compact Laser Weapon System (LWS) breaks down into four parts, each transportable by one or two Marines. Boeing says these components include:

• a battery
• a water-cooled chiller
• a commercially available fiber laser
• an upgraded beam director, weighing 40% less than a previous model

In total, the system weighs about 650 pounds and would probably be operated by a squad of eight to 12 soldiers or Marines.

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Setting up a compact laser weapon system at the Marine Aviation Weapons and Tactics Squadron One exercise in Yuma, Arizona. Image source: USMC.

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Able to be assembled in just 15 minutes, LWS is capable of generating an energy beam of up to 10 kilowatts that can, depending on the power level, be used to acquire, track, and identify a target -- or even destroy it -- at ranges of at least 22 miles. The weapon is designed specifically to track and attack moving aerial targets such as incoming artillery rounds, and low-flying aircraft and unmanned aerial vehicles.

U.S. Special Operations forces are currently testing LWS, with "multiple" branches of the U.S. military expressing interest -- and no wonder.

According to Boeing, a laser gun such as LWS offers the military a "low cost per shot and an infinite magazine" -- both very attractive attributes. Indeed, in a press release, Boeing observed that "with a steady power supply, the Compact LWS can fire continuously." Such a weapon, once operational, might be used to sweep a battlefield, destroying everything it contacts, making it a significant force multiplier for dismounted infantry units.

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Most of the lasers utilized in research laboratories are based on titanium:sapphire (Ti:Sa) crystals, and this type of instrument has been the dominant tool in the production of ultrashort light pulses for over 20 years. But this situation is likely to change very soon. All the indications are that thin-disc laser systems will soon displace their older rivals, which employ rod- or slab-like crystals. The team at the LAP has now introduced the Ytterbium:Yttrium-Aluminium-Garnet (Yb:YAG) disk laser. The instrument emits pulses lasting 7.7 femtoseconds (10-15 sec, a millionth of a billionth of a second), which corresponds to 2.2 wave periods. The average pulse power is 6 Watts and each pulse carries 0.15 microjoules of energy, 1.5 orders of magnitude greater than that attainable with commercial titanium:sapphire lasers.

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Previous experiments carried out by the team at the LAP had shown that it is indeed possible to switch electric currents on and off using specially shaped electromagnetic wave packets, i.e. phase-controlled laser pulses (Schiffrin, Nature 2012; Paasch-Colberg, Nature Photonics 2014, Krausz & Stockman, Nature Photonics 2014). However, the maximum switching rates achieved in these experiments were on the order of a few thousands per sec.
This limit has now been spectacularly breached. The new laser is capable of producing tens of millions of high-power pulses per second, and it ushers in a new era in the investigation of ultrafast physical processes. This field focuses on phenomena such as electron motions in molecules and atoms, which can take place on attosecond timescales (an attosecond lasts for a billionth of a billionth of a second, 10-18 sec). The ability to generate attosecond laser pulses effectively permits electron motions to be "photographed". With the advent of the new laser, atomic photography moves into a new phase.

The new tool will soon be able to generate pulses of high-energy light, with a wavelength of 60 nanometers, in the extreme ultraviolet segment of the spectrum.

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Previous experiments carried out by the team at the LAP had shown that it is indeed possible to switch electric currents on and off using specially shaped electromagnetic wave packets, i.e. phase-controlled laser pulses (Schiffrin, Nature 2012; Paasch-Colberg, Nature Photonics 2014, Krausz & Stockman, Nature Photonics 2014). However, the maximum switching rates achieved in these experiments were on the order of a few thousands per sec.
This limit has now been spectacularly breached.

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The eyes of a self-driving car are called LIDAR sensors.
LIDAR is a portmanteau of “light” and “radar.” In essence, these sensors monitor their surroundings by shining a light on an object and measuring the time needed for it to bounce back. They work well enough, but they aren’t without their drawbacks. Today’s self-driving cars typically use LIDARs that are quite large and expensive. Google, for instance, used $80,000 LIDARs with its early designs. “Most vehicles in the DARPA urban challenge put half-a-million-dollars worth of sensors on the car,” says Daniela Rus, the director of MIT’s Computer Science and Artificial Intelligence Laboratory, referring to the government-backed competition that helped spawn Google’s autonomous vehicles.

But researchers at the University of California, Berkeley say they’ve developed a new breed of laser technology that could significantly reduce the size, weight, cost, and power consumption of LIDARs, potentially leading to a much broader range of autonomous vehicles. “This is important for unmanned vehicles on land and in the sky,” says Weijian Yang, one of the researchers behind the project.

Yang’s work is part of a wider effort to refine LIDARs and build a cheaper breed of autonomous cars and other vehicles. A German company called SICK already offers a LIDAR that sells for less than $10,000, and researchers from MIT and the National Research Foundation of Singapore, including Rus, recently built a self-driving golf cart using no more than four of these units (see video below). As LIDAR technology improves—and as we improve the algorithms that process the data gathered from these sensors—we’ll bring autonomy not just to cars but smaller contraptions, including golf carts, robots, and flying drones.

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A More Accurate Picture
According to Yang, this same technology could improve optical coherence tomography, or OCT, which is used in medical imaging equipment. But the most intriguing possibilities lie in the world of robotics. Among other things, Yang explains, Berkeley’s method allows lasers to change wavelengths more frequently—one microsecond versus 10 or so milliseconds—and that means a LIDAR could potentially take more readings, more quickly. In other words, it could provide a more accurate picture of its surroundings.

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In 2011, Sandia National Laboratory produced white light by combining four large lasers into a single beam, but this was only a proof of concept demonstration and not a practical system.

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The breakthrough came from ASU's Ira A. Fulton Schools of Engineering, where scientists came up with a semiconductor laser that can operate across the entire visible color spectrum. Normally, semiconductors only produce a single wavelength of light, but the ASU team developed a sheet of nanoscale semiconductor based on a quaternary alloy of ZnCdSSe, which is formed into three segments. These generate red, green, and blue lasers that combine to create a pure white light.

The team achieved this by adjusting the lattice pattern of the material, so the “lattice constant” or distance between the atoms in the pattern is set to produced the desired area. According to team member Zhicheng Liu, the tricky bit was to make sure the semiconductor crystals were of high enough quality and the lattices uniform across a given area. Getting the material to shine blue was the most difficult challenge, which was overcome by using nanotechnology to create the desired lattice first, then prompting it into the right alloy composition. The result was a single material with three different lattices and compositions.

The ASU team sees several applications for the white laser once it becomes practical. The most obvious is in lighting. The new laser can not only generate white light, but is also completely tunable across the entire spectrum – allowing it to radiate any desired color – and is brighter and more efficient than LEDs.

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The white laser is currently in proof of concept form and several hurdles need to be overcome before the technology is practical. According to the team, the biggest of these is making it run off a battery. In its present form, the material runs off a separate laser, which pumps electrons into the semiconductor.

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Comments:

While a white laser beam from combining beams of the primary colors, seems hardly breakthrough news. (Hobbyists have been able to accomplish, though bulky, working prototypes going back a few years now.) The idea of being able to use one laser module to put on all the color beams to be combined to form white seems like a step ahead in terms related to the reduced size, weight, and complexity involved in manufacturing such as laser.

tense0celot03

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What I don't understand is how they can get three different wavelengths of light to resonate in the same cavity! It is the photons of light bouncing back and forth between two highly reflective surfaces and knocking electrons out of their pumped up (population inversion) state back down to ground state and creating even MORE photons that creates amplification, and if that cavity length is not tuned to the resonant frequency of that part of the EM spectrum, how can there be any gain in the medium? What am I missing here?? If the gain medium itself is not serving as the resonant cavity, then there have to be exterior mirrors set to a multiple of the wavelength and in parallel to about 1/3 wavelength, in order to get to that resonance point and thus lasing occurring. This comes straight out of some of my books about lasers and how they work. Are they trying to tell us that now somehow red, green and blue light are actually all of the same frequency and wave length??

Randy

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I never heard of a diamond laser before. It kinda reminds me of those early Reese’s peanut butter cup commercials (Two great tastes that taste great together).

So how did these two crazy kids get together? Could they really have a future together?

The diamonds used for these lasers are not dug out of the ground. They are grown synthetically in a lab using a process called chemical vapor deposition (CVD). This lays down the carbon atoms in the proper arrangement layer by layer on top of a diamond substrate. This process is critical to the superior optical quality of these diamonds compared to the previous ones, grown or dug up, and used in weaker earlier versions of these types of lasers.

The super high quality of these diamonds though, just add to the advantageous properties that already make diamonds a potentially useful lasing medium. For one, they are among the most transparent objects known, if not THE most transparent. This is because the electron orbitals around the carbon atoms are filled to capacity, meaning that it’s extra difficult for them to absorb photons which would decrease transparency. This means that diamonds are capable of producing laser light in a wide range of wavelengths, opening a broad range of applications that other lasers are less suited for. For example, solid state lasers can produce impressively powerful laser beams, well into the kilowatt range. Yet they can only do this in a far more restricted range of wavelengths.
Not only can diamond lasers produce more wavelengths of light, they can produce a certain wavelength that is immensely useful in and of itself. I’m referring to light in the 1240 nano-meter range. This wavelength interferes with our atmosphere much less than other wavelengths. It is also not as easily absorbed by the human retina. You certainly wouldn’t want to stare at such light for more than a moment but at least it wouldn’t immediately bore a hole straight through your eyeball.

Solid state lasers are also limited by the relatively small thermal load they can handle. When things get too hot, they get very cranky. Diamonds however are incredibly adept at dissipating the heat that ever-increasing power demands.

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University of Oxford

Researchers from the Department of Physics at Oxford University (with colleagues at the Rutherford Appleton Laboratory and the University of Strathclyde) have demonstrated, for the first time, that it is possible to generate ultra-short x-ray pulses using existing technology - and it could open up a huge range of scientific applications.

A new paper, published in the journal Scientific Reports, outlines how computer simulations of a technique called Raman amplification show that current short-duration x-ray flashes - lasting just a thousandth of a billionth of a second - could be compressed even further, down to a fraction of a femtosecond (one millionth of a billionth of a second).

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James Sadler, a second-year DPhil student and lead author of the paper, says: 'X-ray pulses from free electron lasers are being used in a whole host of ways, from biomedical technology and work on superconductors to research into proteins and states of matter in dense planets.

'We have shown, through our simulations, that it is possible to shorten the pulse length of x-rays by a factor of a hundred or a thousand - flashes of light shorter than the time it takes for a chemical reaction to take place. This could have exciting implications across a range of scientific disciplines.'

Those processes include some of the shortest events in physics, such as electrons moving in atoms. The key now, say the researchers, is to demonstrate the technique under laboratory conditions.

The paper, titled 'Compression of X-ray Free Electron Laser Pulses to Attosecond Duration', is published in Scientific Reports and will be available to view online at Compression of X-ray Free Electron Laser Pulses to Attosecond Duration : Scientific Reports from 1000 GMT on Monday 16 November 2015.

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Berkeley Lab Researchers Demonstrate Atomically Thin Excitonic Laser

An important step towards next-generation ultra-compact photonic and optoelectronic devices has been taken with the realization of a two-dimensional excitonic laser. Scientists with the U.S. Department of Energy (DOE)’s Lawrence Berkeley National Laboratory (Berkeley Lab) embedded a monolayer of tungsten disulfide into a special microdisk resonator to achieve bright excitonic lasing at visible light wavelengths.

“Our observation of high-quality excitonic lasing from a single molecular layer of tungsten disulfide marks a major step towards two-dimensional on-chip optoelectronics for high-performance optical communication and computing applications,” says Xiang Zhang, director of Berkeley Lab’s Materials Sciences Division and the leader of this study.

Zhang, who also holds the Ernest S. Kuh Endowed Chair at the University of California (UC) Berkeley and is a member of the Kavli Energy NanoSciences Institute at Berkeley (Kavli ENSI), is the corresponding author of a paper describing this research in the journal Nature Photonics. The paper is titled “Monolayer excitonic laser.” The lead authors are Yu Ye and Zi Jing Wong, members of Zhang’s research group, plus Xiufang Lu, Xingjie Ni, Hanyu Zhu, Xianhui Chen and Yuan Wang.

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In a previous study, Zhang and his research group had developed a “whispering gallery microcavity” for plasmons, electromagnetic waves that roll across the surfaces of metals. Based on the principle behind whispering galleries – where words spoken softly beneath a domed ceiling can be clearly heard on the opposite side of the chamber – this micro-sized metallic cavity for plasmons strengthened and greatly enhanced the Q factor of light emissions. In this new study, Zhang and his group were able to adapt this microcavity technology from plasmons to excitons – photoexcited electrons/hole pairs within a single layer of molecules.

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In addition to its photonic and optoelectronic applications, this 2D excitonic laser technology also has potential for valleytronic applications, in which digital information is encoded in the spin and momentum of an electron moving through a crystal lattice as a wave with energy peaks and valleys. Valleytronics is seen as an alternative to spintronics for quantum computing.

“TMDCs such as tungsten disulfide provide unique access to spin and valley degrees of freedom,” says co-lead author Wong. “Selective excitation of the carrier population in one set of two distinct valleys can further lead to lasing in the confined valley, paving the way for easily-tunable circularly polarized lasers. The demand for circularly polarized coherent light sources is high, ranging from three-dimensional displays to effective spin sources in spintronics, and information carriers in quantum computation.”

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When people find out you write about science, they almost always start asking questions. One of the most common questions of all: Why can’t science give me a reverse microwave? Or, why is it so much easier to heat things than to cool them? The answer is that inputing energy to a system can be very simple — just blast the thing with energy so that its atoms start moving around — while removing energy requires the much more complex process of specifically dampening whatever atomic movement already exists. On the surface, it seems like we might never get that reverse microwave, but this week researchers announced a major breakthrough for biology and perhaps far more, in the form of a laser that can efficiently cool liquids.

Well, some liquids. This can’t be used to cool a six-pack of beer (yet), since in order to be cooled by this new laser, the University of Washington team had to lace the liquid with specially engineered nanocrystals. When excited with a specific sort of infra-red light, these nanocrystals emit a glow with slightly more energy than the crystals originally absorbed — and that difference is soaked back up from the surrounding liquid, cooling it. By illuminating their crystal-laced liquid, the team can cause it to radiate its heat energy out as light. A similar approach has been tried before in a vacuum, but this is the first time under real-world conditions.

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Their approach was able to specifically cool the sample by about 36 degrees Fahrenheit. That might not sound like a lot (it isn’t) but what sets this method apart is how physically localized its effects can be. The team also designed a “laser trap” which can keep a particular cell or particle of interest trapped in one spot, so the liquid within that spot can be cooled with their new refriger-laser. By cooling just one point within a larger system, the team hopes to grant hugely important new abilities to researchers.

First among them is the ability to quickly and accurately stop a single cell in place, or even to cold-slow minute sub-sections within that cell. It could be used to cool single neurons within functional groups so the team can look at how information gets routed around the problem, but still leave that neuron undamaged so it can eventually come back online. They could adjust the kinetics of just one reaction to determine that step’s role in the chain, or slow it down so the mechanics are easier to observe.

Pointed cooling could also be applied much more widely, perhaps to cooling small, high-heat areas in computer systems. Laser cooling probably wouldn’t be terribly energy efficient, but it would also negate the need for complex circulatory systems inside liquid-cooled rigs; with laser cooling, you could just park a sample of crystal-liquid on your processor die (or whatever) and keep it cooling through the input of IR light. It wouldn’t need any fans, nor would it create any noise.

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The much-anticipated video game Fallout 4 was released earlier this week, and German cyber-weapons builder Patrick Priebe hasn't missed a beat. He's already created an AER 9 pulse laser rifle, based on the gun from the game. It's not just a prop, either – he tells us that it "will blast the paint off your car, and tiny holes into metal."

The 8-kg (17.6-lb) aluminum-bodied weapon utilizes a voltage converter to boost the 12.6-volt output of a 3-cell lithium-polymer battery up to 400 volts. That current is dumped into two onboard capacitors, which then discharge it in a single short blast into a flashlamp which is located in a mirrored chamber.

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The result is a 4-nanosecond pulse of 100,000-watt infrared laser light, which is emitted in a beam that passes through two lenses on the front of the rifle. Although Priebe claims it's "not enough to kill a man," it will certainly mark up carbon steel or even tungsten.

Some of its other features include LEDs that transition from red to green as the capacitors are charging, a grey paint job to match the gun in the game, and a wooden front grip that's purposely been chipped to give it the well-used look.

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Steampunk LaserBlaster (for Theo )

• Laser Guns
  
• Laser Rifles
  
• SteamPunk Guns
  
• Iron Man Laser Glove
  
• Cowboys & Aliens Laser

A nanotechnology breakthrough from DTU revolutionizes laser printing technology, allowing you to print high-resolution data and colour images of unprecedented quality and microscopic dimensions (Nature Nanotechnology, "Plasmonic colour laser printing").

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Researchers from DTU Nanotech and DTU Fotonik have succeeded in printing a microscopic Mona Lisa. She is 50 micrometres long or about 10,000 times smaller than the real Mona Lisa in the Louvre in Paris.
Using this new technology, DTU researchers from DTU Nanotech and DTU Fotonik have reproduced a colour image of Mona Lisa which is less than one pixel on an iPhone Retina display. The laser technology allows printing in a mind-blowing resolution of 127,000 DPI. In comparison, weekly or monthly magazines are normally printed in a resolution equivalent to 300 DPI.

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