On 13/04/2022 16:45, jlarkin@highlandsniptechnology.com wrote:
> On Wed, 13 Apr 2022 13:19:14 +0100, Martin Brown
> <'''newspam'''@nonad.co.uk> wrote:
>
>> On 13/04/2022 01:09, jlarkin@highlandsniptechnology.com wrote:
>
>> Red is fairly unusual fluorescence with 400nm excitation.
>
>The other direction is even more unusual, but is barely possible with
> 2-photon excitation.
We used to use NdYAG 266nm UV for sampling laser ablation quadrupled
from the fundamental NdYAG 1064 line which still had more than a trace
of the 532nm green line in it. Small spot size is everything in laser
ablation sampling methods solid direct to plasma at the focus.
People with more money than sense had Xenon fluoride 351nm laser kit
before the high power quadrupled laser source was perfected.
>>> That nearly-UV laser always gives me a mild headache.
>>
>> 400nm is a wavelength capable of harming human eyes at high levels.
>
> The laser has a safety diffuser that scatters the light into a neat
> speckle pattern. Even looking at that reflected off a surface gives me
> a headache.
Seriously if you can see it as bright then it is capable inflicting eye
damage. It really isn't a very friendly wavelength. The eye isn't very
sensitive to it so you get no warning and the photons are energetic.
Nowhere near as bad as the hard UV of EPROM erasers though.
--
Regards,
Martin Brown
>On Wed, 13 Apr 2022 05:00:39 -0000 (UTC), John Doe wrote:
>
>> BTW... At the same time, they can remove "floaters" too.
>
>I will definitely look into that, I have a lot of floaters.
>
>I noticed another interesting optical effect of cataracts during my last
>refraction - I could read the 20/20 line clearly twice in one eye. The
>two equally sharp images were completely separated with space in between,
>although the second image was lower contrast. Apparently cataracts are
>birefringent, with random orientation, the other eye has a smaller offset
>to the second image in a different direction. Very common according to
>my Ophthalmologist.
I've always had a double image in one eye, before and after the
cataract surgery. Some fold in the optics somewhere. I can map the
boundary by scanning through a pinhole.
--
I yam what I yam - Popeye
Reply by ●April 13, 20222022-04-13
On Wed, 13 Apr 2022 13:19:14 +0100, Martin Brown
<'''newspam'''@nonad.co.uk> wrote:
>On 13/04/2022 01:09, jlarkin@highlandsniptechnology.com wrote:
>> I had cataract surgery in one eye and will do the other one soon.
>>
>> I have a pretty high power 400 nm laser. If I shoot it at the wall,
>> the dot is bright with the repaired plastic-lens eye and invisible
>> with the one that has the cataract. My doctor explained that a
>> cataract absorbs blue light, and that's why some old ladies color
>> their hair bluish-white, because then it looks right to them.
>>
>> If I scan the laser around the room, some objects do show with the bad
>> eye and some don't. That's because many "white" objects fluoresce to
>> make them look whiter. Most things fluoresce greenish or purplish, but
>> the giant old Radiotron Designers Handbook fluoresces red.
>
>Red is fairly unusual fluorescence with 400nm excitation.
The other direction is even more unusual, but is barely possible with
2-photon excitation.
>
>The colours you get tend to vary with rare earth impurities or various
>aromatic dyes. Washing powders contain a fairly potent blue fluorescer.
>
>Bank notes and secure paper contain interesting flecks that show under
>the right wavelength of near UV light.
>
>> I have a 4FP7 CRT (DuMont, square-face, long-persistance, PDA) on a
>> bookshelf and I can paint fun patterns on it.
>>
>> That nearly-UV laser always gives me a mild headache.
>
>400nm is a wavelength capable of harming human eyes at high levels.
The laser has a safety diffuser that scatters the light into a neat
speckle pattern. Even looking at that reflected off a surface gives me
a headache.
--
I yam what I yam - Popeye
Reply by Glen Walpert●April 13, 20222022-04-13
On Wed, 13 Apr 2022 05:00:39 -0000 (UTC), John Doe wrote:
> BTW... At the same time, they can remove "floaters" too.
I will definitely look into that, I have a lot of floaters.
I noticed another interesting optical effect of cataracts during my last
refraction - I could read the 20/20 line clearly twice in one eye. The
two equally sharp images were completely separated with space in between,
although the second image was lower contrast. Apparently cataracts are
birefringent, with random orientation, the other eye has a smaller offset
to the second image in a different direction. Very common according to
my Ophthalmologist.
Reply by Clive Arthur●April 13, 20222022-04-13
On 13/04/2022 13:19, Martin Brown wrote:
<snip>
> Red is fairly unusual fluorescence with 400nm excitation.
I've noticed the same with old paperback data books, the red text on the
cover often fluoresces orangey-red. Not new data books, probably
because I don't have any.
--
Cheers
Clive
Reply by ●April 13, 20222022-04-13
On Wed, 13 Apr 2022 05:46:56 GMT, Jan Panteltje
<pNaonStpealmtje@yahoo.com> wrote:
>PS
>it is actually fun stuff, UV,
> https://www.thoughtco.com/what-glows-under-a-black-light-607615
>
>I tried it among other things on London Tonic.. the quinine in it lights up.
>Also my old EPROM eraser lightbulb works the same way, but is better more powerful UV I think,
>do not look into it.
>
>
>
Our liquid laundry detergent fluoresces bright white, to make your
clothes look clean and bright. I understand that they can be a laser
medium.
My next choice will be the focal length of my left eye. My right one,
with the plastic lens, focusses at 17". If I make the other one
closer, I should have a pretty wide range of close vision, ideal for
reading and computing and soldering. Brains are very good at stitching
images.
--
I yam what I yam - Popeye
Reply by Martin Brown●April 13, 20222022-04-13
On 13/04/2022 01:09, jlarkin@highlandsniptechnology.com wrote:
> I had cataract surgery in one eye and will do the other one soon.
>
> I have a pretty high power 400 nm laser. If I shoot it at the wall,
> the dot is bright with the repaired plastic-lens eye and invisible
> with the one that has the cataract. My doctor explained that a
> cataract absorbs blue light, and that's why some old ladies color
> their hair bluish-white, because then it looks right to them.
>
> If I scan the laser around the room, some objects do show with the bad
> eye and some don't. That's because many "white" objects fluoresce to
> make them look whiter. Most things fluoresce greenish or purplish, but
> the giant old Radiotron Designers Handbook fluoresces red.
Red is fairly unusual fluorescence with 400nm excitation.
The colours you get tend to vary with rare earth impurities or various
aromatic dyes. Washing powders contain a fairly potent blue fluorescer.
Bank notes and secure paper contain interesting flecks that show under
the right wavelength of near UV light.
> I have a 4FP7 CRT (DuMont, square-face, long-persistance, PDA) on a
> bookshelf and I can paint fun patterns on it.
>
> That nearly-UV laser always gives me a mild headache.
In article <t35q24$qlfe$1@solani.org>, dk4xp@arcor.de says...
>
> Reminds me at a guy in France some 200 years ago who discovered
> color blindness from the fact that he and his brother classified
> the color of flowers differently than other people, depending
> on sunlight or candles.
>
> Gerhard
What a co-incidence. Because as Wikipedia relates
(<https://en.wikipedia.org/wiki/Color_blindness>), John Dalton and his
brother in Manchester, England, also noticed the same thing. And colour-
blindness is known as Daltonism after him... Dalton is known for lots of
other topics and admittedly, Wikipedia says: "In 1822 he paid a short
visit to Paris."
Reply by John Walliker●April 13, 20222022-04-13
On Wednesday, 13 April 2022 at 07:19:56 UTC+1, Gerhard Hoffmann wrote:
> Am 13.04.22 um 02:09 schrieb jla...@highlandsniptechnology.com:
> > I had cataract surgery in one eye and will do the other one soon.
> >
> > I have a pretty high power 400 nm laser. If I shoot it at the wall,
> > the dot is bright with the repaired plastic-lens eye and invisible
> > with the one that has the cataract. My doctor explained that a
> > cataract absorbs blue light, and that's why some old ladies color
> > their hair bluish-white, because then it looks right to them.
> >
> > If I scan the laser around the room, some objects do show with the bad
> > eye and some don't. That's because many "white" objects fluoresce to
> > make them look whiter. Most things fluoresce greenish or purplish, but
> > the giant old Radiotron Designers Handbook fluoresces red.
> >
> > I have a 4FP7 CRT (DuMont, square-face, long-persistance, PDA) on a
> > bookshelf and I can paint fun patterns on it.
> >
> > That nearly-UV laser always gives me a mild headache.
> Reminds me at a guy in France some 200 years ago who discovered
> color blindness from the fact that he and his brother classified
> the color of flowers differently than other people, depending
> on sunlight or candles.
>
> Gerhard
We had a workman in the house once who mentioned that he was
colour blind and could not see red at all. The sun was shining on
a cut glass ornament projecting a spectrum on the wall. He pointed
out the regions of the spectrum that he could see. The red end really
was completely missing.
John
Reply by Gerhard Hoffmann●April 13, 20222022-04-13
Am 13.04.22 um 02:09 schrieb jlarkin@highlandsniptechnology.com:
> I had cataract surgery in one eye and will do the other one soon.
>
> I have a pretty high power 400 nm laser. If I shoot it at the wall,
> the dot is bright with the repaired plastic-lens eye and invisible
> with the one that has the cataract. My doctor explained that a
> cataract absorbs blue light, and that's why some old ladies color
> their hair bluish-white, because then it looks right to them.
>
> If I scan the laser around the room, some objects do show with the bad
> eye and some don't. That's because many "white" objects fluoresce to
> make them look whiter. Most things fluoresce greenish or purplish, but
> the giant old Radiotron Designers Handbook fluoresces red.
>
> I have a 4FP7 CRT (DuMont, square-face, long-persistance, PDA) on a
> bookshelf and I can paint fun patterns on it.
>
> That nearly-UV laser always gives me a mild headache.
Reminds me at a guy in France some 200 years ago who discovered
color blindness from the fact that he and his brother classified
the color of flowers differently than other people, depending
on sunlight or candles.
Gerhard