Can Two Intersecting Laser Pulses Create a Visible 'Flash' in Midair?

[trini]

Hey guys, I've been wondering what would happen if you had two lasers pointed at the same spot emitting pulses of visible light such that the pulses would meet the spot at the same time(lets assume the spot is in midair, no screen). the lasers could either be directly opposite each other or they could be at angles, but would it be possible to get them to intersect and make a 'flash' in midair?

 

[sophiecentaur]

Are you suggesting that this "flash" would be due to the Electric Field Strength being high enough to cause ionisation? The answer to that question is yes because the two fields could add up at some point in space so that the total field was twice that of one beam on its own.

 

[trini]

actually i was thinking more along the lines of a suspended dot as it were (in midair) that would be the same colour as the lasers being used. perhaps more specifically, if a tried to make a standing wave out of red light using laser pulses, would it appear as though i had a 'string' of stationary red pulses in midair?

 

[sophiecentaur]

You can't expect to produce a single dot using interference because the wavelength is wrong and you would need a very complicated light source arrangement.
Also, of course, the only way you will get a visible dot would be to have a cloud of dust or droplets to scatter the light where the 'dot' should appear. Light of any intensity will not be visible from the 'side' of a beam without some scattering. (You don't see the sunlight streaming past the Earth on a dark night, do you?)

A large diameter reflector could be used to focus light into a small region but you would see a cone rather than a spot in the scattering particles.

 

[cjameshuff]

actually i was thinking more along the lines of a suspended dot as it were (in midair) that would be the same colour as the lasers being used. perhaps more specifically, if a tried to make a standing wave out of red light using laser pulses, would it appear as though i had a 'string' of stationary red pulses in midair?

You can't see an optical standing wave...you see light that propagates into your eye, and the notable quality of standing waves is that they stay put. You need a way to scatter light passing through the area of the "spot" into your eye, another laser pulse will not do this in empty space.

Something produced by another laser in a medium might, however. For example, you might be able to engineer some material that becomes temporarily cloudy when hit by infrared, or by the intersection of two beams. Maybe produce an "antifog" of tiny bubbles that condense quickly when the medium cools or when they travel outside the area heated by the laser. Or some sort of crystalline phase transition.

 

[sophiecentaur]

Cjameshuff's comments show how your basic idea is 'not on'.

If you could find the right nonlinear medium, it could be possible to 'generate' light (em with a visible frequency) by beating two high intensity em waves of a higher frequency than that of light (ultraviolet) and forming an intermodulation produce with a frequency equal to the difference between the two input frequencies. The visible light would only be produced in the region where the beams overlap.

 

[cjameshuff]

If you could find the right nonlinear medium, it could be possible to 'generate' light (em with a visible frequency) by beating two high intensity em waves of a higher frequency than that of light (ultraviolet) and forming an intermodulation produce with a frequency equal to the difference between the two input frequencies. The visible light would only be produced in the region where the beams overlap.

A rather different mechanism, but I recall reading some time ago about a 3D display using two-photon fluorescence in a special glass that glowed in visible light when illuminated by near-infrared lasers of two specific wavelengths, but was transparent to each alone (at least, at the intensities used). Ah, here:

http://www.3dtl.com/page9.php
http://www.felix3d.com/web/download/paper_pw_03.pdf

 

[sophiecentaur]

A rather different mechanism, but I recall reading some time ago about a 3D display using two-photon fluorescence in a special glass that glowed in visible light when illuminated by near-infrared lasers of two specific wavelengths, but was transparent to each alone (at least, at the intensities used). Ah, here:

http://www.3dtl.com/page9.php
http://www.felix3d.com/web/download/paper_pw_03.pdf

Well there you go. Just what you want, using double photon upconversion. Is sounds just like a radio superhet system with three tuned circuits and a non-linearity. How interesting.