Lasers, so yesterday, meet the Saser!

[0iD]

http://www.theengineer.co.uk/Article...ops&dte=220609

A SASER operates on principles remarkably similar to those of a laser. A stack of thin semiconductor wafers are placed in a lattice within an acoustically reflective chamber. Upon the addition of electrons, short-wavelength (in the terahertz range) phonons are produced. Since the electrons are confined to the quantum wells existing within the lattice, the transmission of their energy depends upon the phonons they generate. As these phonons strike other layers in the lattice, they excite electrons, which produce further phonons, which go on to excite more electrons, and so on. Eventually, a very narrow beam of high-frequency ultrasound exits the device

[capt_cornflake]

Nice.
Can't see many obvious applications atm, but then most of the applications of the laser weren't really envisaged 50 years ago either

[Fraz]

Interesting. Shame it doesn't really explain how the phonons get turned into a narrow band of high-frequency ultrasound. As I understand things, a phonon is a quantization of a lattice vibration. I don't understand how the ultrasound beam comes about.

[samcross]

Interesting. Shame it doesn't really explain how the phonons get turned into a narrow band of high-frequency ultrasound. As I understand things, a phonon is a quantization of a lattice vibration. I don't understand how the ultrasound beam comes about.

Show off

[Peter Parker]

Like it, because it got me thinking. I wouldn't normally associate THz with sound waves - they're closer to microwaves and infra-red - but I guess it might be possible for these to travel through a solid?

In air, once the wavelength shrinks down to something similar to the mean free path (distance that a molecule travels before hitting another), the wave doesn't really propagate. I think the theoretical max frequency in air at sea level is 'speed of sound' / 'mean free path', which after some google work is 340 / 68E-9 = 5GHz. Realistically much less.

No idea what happens in solids/liquids.

[Whiternoise]

Interesting. Shame it doesn't really explain how the phonons get turned into a narrow band of high-frequency ultrasound. As I understand things, a phonon is a quantization of a lattice vibration. I don't understand how the ultrasound beam comes about.

Sound = vibration?

[Fraz]

Sound = vibration?

Well, obviously. Maybe I'm just overcomplicating things. I'm just saying that a load of coherent lattice vibration quanta in a crystalline solid turning into a narrow beam of rarefaction/compression in air is a leap that my poor brain doesn't understand. I guess it's the narrow beam bit I don't get. Isn't it pretty hard to get a narrow beam of sound in air?

[Georgy291]

so let me get this straght?

atm i got a green pointer that goes 2km away, i can annoy people 2km away by pointing at them (i know its silly but its fun at those distances with binocs)

now i can do that with sound? by

[Whiternoise]

No, sadly not - it's far too high frequency for you to hear or even feel

[GoNz0]

No, sadly not - it's far too high frequency for you to hear or even feel

unless your a chav

[Lanky123]

No, sadly not - it's far too high frequency for you to hear or even feel

Hmm, I was trying to work out how fast in the opposite direction you would have to travel to get the freqency down to the hearable range and it turns out it's faster than the speed of light. I'm clearly stretching the standard Doppler equation a bit too far.

[Georgy291]

yeah but i guess i can still spill their drink if its ultrasonic