Interesting laser ideas.. / General Science and Electronics / Forums

Forums

4hv.org :: Forums :: General Science and Electronics

« Previous topic | Next topic »

Interesting laser ideas..

1 2 next

Move Thread

LAN_403

Conundrum

Sat Jun 26 2010, 04:57PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4062

Hi all.

#include "bigscarylaseryadayada.h"

Seems that some of the newer diode lasers (the 445nm 1W ones come to mind) just might be powerful enough that several combined beams could *possibly* generate an air breakdown.

the main reasoning being that the beam from a shortwave laser can be focussed to a far finer spot than an infrared diode so a relatively simple system consisting of two cooled pulsed diodes with their own galvos and focus servos could generate a 3-D plasma effect.

obviously to be able to see this would need a glass sphere with the appropriate wavelength blocking filters, however by alternating the coatings it would be trivial to generate colour.

this all depends how good the optics are, at this sort of power level even dust can cause a runaway breakdown which destroys the lens or potentially the output window (a common problem with bluray setups, see laserpointerforums)

an alternate idea could be to generate "bubbles" in water directly, as the breakdown energy is slightly lower for a liquid medium than for air.

comments?
-A

#include "ClassIV_lasers_DANGER_EYE_SKIN_HAZARD.h"

Proud Mary

Sat Jun 26 2010, 05:41PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

I've been thinking of focusing a laser beam with a microscope objective to see what I could do with it that might be interesting and useful - such as gap ionisation - but will need to do some serious study before starting, as it's something I don't know much about.

Pinky's Brain

Sat Jun 26 2010, 06:31PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Can you really get near the diffraction limit for long (more than a couple of cm) focal lengths?

Proud Mary

Sat Jun 26 2010, 06:54PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Pinky's Brain wrote ...

Can you really get near the diffraction limit for long (more than a couple of cm) focal lengths?

If you mean 'long working distance', here are the figures for Nikon's specialist Super Long Working Distance (SLWD) objectives:

SLWD 20x NA 0.35 20.5 mm
SLWD 50x NA 0.45 13.8 mm
SLWD 100x NA0.73 4.7 mm

If you have to ask the price, it means you can't afford it.

I expect there are lens systems specifically made for micro laser focusing, but don't know anything about them.

Pinky's Brain

Sat Jun 26 2010, 07:15PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

I know about long working distance objectives ... but as I said, more than a couple of cm. I don't think a microscope objective will give you much room to work with for a 3D plasma display.

PS. I looked a while back, and you can occasionally find some cheap on ebay (especially old non-achromats). Also this one (no idea about the quality).

Sun Jun 27 2010, 07:38AM

Registered Member #2372 Joined:
Location:
Posts: 62

The intensity needed for air breakdown is basically not possible unless you use a pulsed laser, the intensity that people typically use is something on the order of 10^12 W/cm^2. As far as diffraction limited spot size, I know some people that do that, they have a 1.2 micron spot size for a 800 nm laser and they use a f/1 off axis parabola to focus the beam which is phase front corrected with a deformable mirror, not exactly something you can do at home.

IntraWinding

Sun Jun 27 2010, 08:51AM

Registered Member #2261 Joined: Mon Aug 03 2009, 01:19AM
Location: London, UK
Posts: 581

The beam from a high power laser diode is has a much lower 'optical quality' than from, say, a HeNe laser and that makes really tight focusing a problem.
On the other hand, doesn't UV light eject electrons from metal surfaces? Perhaps one of those Blu-ray diodes at 405nm would still be useful on that basis? I think a better bet would be a Xenon flash lamp with a non Ozone free envelope. Vacuum UV is very good at generating Ozone, so I imagine it would trigger an air spark gap.

lpfthings

Sun Jun 27 2010, 03:04PM

Registered Member #1361 Joined: Thu Feb 28 2008, 10:57AM
Location: Cairns, Australia
Posts: 305

You will have problems getting air breakdown from these 1W 445nm diodes. For starters, they are multimode, meaning it's not just 1 laser die, so you actually end up with multiple beams stacked *very* closely together. This means you won't be able to focus it down very far.

Also, the lasers used for air breakdown are run pulsed, as mentioned before. This means that can deliver kW laser pulses in very small amounts of times, these diodes won't even come close to 10W pulsed before they explode!

Dr. Slack

Mon Jun 28 2010, 07:50PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

On the other hand, doesn't UV light eject electrons from metal surfaces? Perhaps one of those Blu-ray diodes at 405nm would still be useful on that basis?

Nah! Did the sums for that a while ago. You need much harder UV than you get from UV leds to eject electrons from a useful material (steel, copper etc) with a high work function. The only electrode materials you could use with a low enough work function for UV leds are the alkali metals. A sodium spark gap in air anyone?

Proud Mary

Mon Jun 28 2010, 09:09PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Dr. Slack wrote ...

On the other hand, doesn't UV light eject electrons from metal surfaces? Perhaps one of those Blu-ray diodes at 405nm would still be useful on that basis?

The Roithner's catalogue has deep UV LEDs down to 245nm, - i.e. 5.07eV - which exceeds the work function of a good many metals, including Fe, Ag, Ti, Zn, Mo, Nb, Th, U, V, many Cu and W surface presentations, and important metalloids such as As and Si.

1 2 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob