h a l f b a k e r yPoint of hors d'oevre
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TIRF, or total internal reflection microscopy <link> is a
technique
that allows a microscopist, like me, to illuminate a sample in a
very specialized way. By carefully controlling the angle of
light,
usually a laser, hitting the back of an objective lens. When you
get the angle right, the
lens surface emits an "Evanescent
wave".
The cool thing is, that beyond a few hundred nanometers, this
wave stops existing. You get VERY localized illumination. You
can
control X,Y and Z of the laser.
Laser cutters are all very much fun. <link> but they're a bit of a
one trick pony. They're great at cutting holes in sheets of
material, but because they rely on a beam emitting from the
objective to effectively infinity, you either cut all the way
through or nothing. If you want to cut half way through
something, you're back to good old drills/milling machines.
Although I appreciate things can be done with focal points and
lensing...
This is where the TIRF laser drill comes in. Your great big CO2
laser is now powering an evanescent wave that propagates only
say 100-200nm from the lens or so. So now you can remove
material
nanometers at a time in successive passes. There are also
benefits
for safety, you're not going to have anyone's eye out with this,
at
least without considerable set up, and.... clamping.. probably
better just to use a pointy stick if eye damage is your game.
The TIRF lens will have to be quite temperature-stable, what
with
it being within almost no distance from laser-ablated steel for
example, but quartz should handle it. Anyhow, "precision"
engineers often cite 0.005" tolerances as a standard and 0.001"
as
a "ooooh, that's gonna cost you" tolerance. Laser cutters only
normally get to 0.002". TIRF gets you to 0.000008", which
means
your company gets to add the extra zeros to the bill.
TIRF
https://www.microsc...nce-tirf-microscopy
[bs0u0155, Feb 27 2017]
LASER Cutting
https://en.wikipedi.../wiki/Laser_cutting
[bs0u0155, Feb 27 2017]
EDM
https://i.imgur.com/EohVuL0.gifv
Electrical discharge machining allows for a perfect fit between metal pieces [xaviergisz, Jan 25 2019]
US20150351841A1
https://patents.goo.../US20150351841A1/en
Guided wave ablation and sensing. For medical uses rather than machining, but tangentially relevant. [xaviergisz, Jan 25 2019]
[link]
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[bs], this is a bloody brilliant idea which probably would have made billions for somebody if it weren't posted here. |
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The lens would not only have to withstand the heat, it would also have to not get gunked up by the vaporized material. But presumably any material deposited on the lens would just get re-vaporized. You might have problems getting the vapour out of the way. (This would be easier in the US, because they have 'vapor', which is one letter smaller and therefore more diffusive.) |
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//made billions for somebody if it weren't posted
here// |
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on some level, ruining someone else's day is a little like
having a good one yourself. All relative. |
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//gunked up by the vaporized material. But presumably
any material deposited on the lens would just get re-
vaporized.// |
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That's the idea, even if it works it might need tuning. A
cutting blast might leave a lens deposition which would
attenuate the next blast. You can play with angles
however, so you could have 100nm range 20nm range
100nm range, to kind of cut-clean-cut. I also thought it
might be possible to charge the lens, most metals would
be prone to losing electrons so a +ve charge might do
the trick, although it's vapor not plasma. Wait... 100nm
gap in argon is only 0.1V breakdown voltage, that's not
robust even at those scales. |
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Is it strictly true that lasers can't cut to a given depth? If each pulse removed only a small amount of material, and if the depth were monitored, it ought to be possible to fix the depth of cut. |
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it's like microscopy. You have a focal point with the
most effect but also a progressive out of focus
contribution. While the focal point might be effective
as hell, the out of focus light might be enough to affect
the material at a greater than desired depth, with
fancy materials you can damage them thermally. Many
alloys lose their desirable properties when heated even
modestly. You could go confocal I suppose. Multi
photon would also be super clever, and work at longer
range. There is a type of laser cutting that uses a low
pressure water jet, the laser is contained within that by
TIR so that it behaves as a parallel beam it also uses the
water as coolant and to remove debris. That's so neat it
made my day. I want the opposite though, v.small
defined Z resolution, not infinite. Although you can see
the utility of such a system. |
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I like this idea. I may have read that microwaves passing through a wax prism, generate an evanescent wave at the prism next it, which then detected. That gap might have been like 1/2 millimeter, although I do not remember. the half millimeter gives lots of room to blow air through the gap removing vapors, or even vapours. |
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//That gap might have been like 1/2 millimeter// |
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I'm familiar with 1/2 millimeter precision. That's in the
range of my hammering skills... :-) |
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One problem might be that only a small fraction of the laser power ends up in the target material. |
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Another problem is that you only get TIR against a drop in refractive index. Most materials you would want to etch are probably denser or equal in density to the lens. |
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For etching metals you don't need this, anyway. The skin depth for metals at IR frequencies is measured in nanometers. I assume that ordinary laser cutting of metal just relies on heat conduction to penetrate beyond the surface. |
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My contribution will be of little value, and the tech referenced is no doubt out of date, but just before the turn of the century I provided visual inspection support to some guys who wanted to drill holes .003 of an inch in diameter with lasers. The material in question was some kind of low cost circuit board composite. |
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They were dismayed by the irregular diameter profiles developed. Kind of on the jagged side. |
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//Another problem is that you only get TIR against a drop in
refractive index. Most materials you would want to etch are
probably denser or equal in density to the lens.// |
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Aluminum is 1.33, so almost any lens material is OK, but
diamond or cubic zirconia will be nice and tough. For iron,
you need >3.1. But there are materials for that, silicon is
probably the best candidate. For anything extreme, you'll
need to play around with germanium mixes. |
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Also, the width of the lens and housing will make it difficult
to machine pockets, grooves, etc. |
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Since when does microscopy start with an F? |
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//Since when does microscopy start with an F?// |
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Well, it's normally "TIRF microscopy" But since it is not
operating on the micro scale and not scoping, I thought I'd
leave it out. It's also not fluorescent either so more like TIR-
laser face milling. |
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"ReFlection"? But "frustrated total internal reflection" is
abbreviated as FTIR, not FTIRF. |
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No, the "F" in TIRF is for "fluorescence", because the
evanescent wave excites fluorophores near the glass. |
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Ah. It reminds me of when I saw image sensors marketed as
being for "fluorescence lifetime imaging" applications,
abbreviated as "FLIM". I wondered why it wasn't "FLI" or
"FLTI". Turns out there's another word there, that they
hadn't included: "microscopy". |
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Sounds like this idea needs to explain how the fluorescence
is used in the milling application. Can it help with the
refractive index or millable shape limitations? |
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