Japanese Scientists Fire the Most Powerful Laser On the Planet

Sepa Blackforesta writes: Scientist from University of Osaka claim have fired the world's most powerful laser. The beam was intact for 2-petawatt, pulse lasted just one picosecond. While it produced a huge amount of power, the energy required for the beam itself is equivalent to that needed to power a microwave for two seconds. An associate professor of electrical engineering at Osaka University Junji Kawanaka says “With heated competition in the world to improve the performance of lasers, our goal now is to increase our output to 10 petawatts.”

Comments

Re:disappointing

[Anonymous Coward]

It only lasted for a picosecond...

Longer than I usually do.

Re:disappointing

[ShanghaiBill]

It only lasted for a picosecond...

A petawatt for a picosecond is one kilojoule. That is enough energy to warm a liter of water by 0.24C.

Why does anyone care?

[quenda]

Why should anyone care about the power level, as opposed to the pulse energy?
ie why does it matter if the kilojoule is spread over one or ten picoseconds? Without this vital piece of information, it is hard to get excited (pardon the pun).

Re:Why does anyone care?

[Noah Haders]

Why should anyone care about the power level, as opposed to the pulse energy?

people who have tattoos should care, for one. the ideal tattoo removal laser has really high instantaneous power but really short pulses. this way you get high power but low energy per pulse.

the tattoo ink breaks down better with higher power lasers because it breaks the bonds holding the ink molecules together. but by keeping the energy per pulse low, you're minimizing the tissue damage since tissue damage grows with the amount of energy absorbed by the skin. when you break up the ink molecules into smaller pieces then the immune system can flush away the bits into your lymph nodes. tattoo is gone!

Re:Why does anyone care?

[Michael Woodhams]

You can use high powered lasers in short pulses to compress and heat a fuel pellet to achieve fusion. A particular approach called fast ignition requires a petawatt pulse. Given that the laser is named LFEX for "Laser for Fast Ignition Experiments", it is a good bet this is what it is for.

(My expertise in this is limited to having had an inkling which Wikipedia article to look in for the answer. Further input from real experts is welcome.)

Re:Why does anyone care?

[Anonymous Coward]

Timewise, atomic/molecular physics spans many orders of magnitude (from metastable states with lifetimes measured in hours, to inner-shell Auger processes with lifetimes measured in femtoseconds).

However making short pulses isn't the true goal of lasers like this (A Q-switched laser that fits on a coffee table can make femtosecond pulses). The true thing of interest is the *number density of photons*. Since it's a laser, the photons have the same energy. Then the total number of photons is proportional to the energy in the pulse, but the *number density* - N/V - scales as the inverse of the spot size and the inverse of the duration (since duration = length / c).

Therefore, the smaller the spot size and the shorter the pulse, the higher the number density of photons that is acheived in a given energy.

When you have a high enough number density, nonlinear things (whose rate of occurrence is the number density of photons raised to the order of the nonlinearity) happen and nonlinear things are Generally Interesting. For example, a sufficiently high laser power is capable of literally blowing protons/neutrons out of an atomic nucleus - IF you can dump roughly a nucleon binding energy into an area the size of a nucleus, in less than the time it will try to radiate it away.

Re:Why does anyone care?

[whoever57]

You can use high powered lasers in short pulses to compress and heat a fuel pellet to achieve fusion. A particular approach called fast ignition requires a petawatt pulse

I think that should be "a very short pulse" -- but pulses used for ignition are much higher energy -- from 70kJ to 2MJ, according to your link.

I would not believe anything in the article, though, since the writer seems to have a very poor grasp of basic physics:

Two quadrillion wattsit self is a massive amount of output. The burst only lasted about one picosecond (1/1,000,000,000,000 of a second), so while the energy output was incredibly large, the actual amount of power (energy divided by time) the LFEX used wasnâ(TM)t all that big. When it was all said and done, the laser only produced enough power to run a microwave for about two seconds.

Re:Why does anyone care?

[umafuckit]

I don't know about those times scales, but femto-second pulsed lasers are damn useful for imaging. Briefly, say the experimenter images green fluorescence. Normally, to get green fluorescence you need to excite with blue light of, say, 450 nm. However, if you can pack enough photons into a short packet then you can also get green fluorescence at about double the wavelength. It's called "two photon absorption" and won a Nobel prize. So you pump in 900 nm light and get back green. The advantage is that longer wavelengths are scattered less by biological tissue and, crucially, the depth of field is much better so there is very little out of focus emitted green light (see image in link). Because the laser scans over the specimen relatively slowly (e.g. a few times a second), you can collect scattered green photons and still assign them back to where they came from. So it's very efficient. Maybe this new laser will all for the process to work efficiently with 3 or even 4 photons.

Analogies?

[marciot]

Help me understand. Is a two petawatt laser being fired for a picosecond more like being sneezed on by a rhino with a cold or more like being shat on by an elephant with a bad case of explosive diarrhea?

If I only worked for 1 picosecond...

[SlithyMagister]

I'd get fired too

The next step...

[turbinicarpus]

"We are currently working on mounting this laser on a giant robot," added Professor Kawanaka.

Make Popcorn?

[Xistenz99]

But can it fill a house with popcorn from that short burst?

Re:disappointing

[arglebargle_xiv]

It only lasted for a picosecond...

They couldn't risk cooking the shark it was attached to.