405nm vs scotopic vision?

[Shakenawake]

I scored an 11. I thought I had them pretty good too, though I guess I am happy with 11

 

[zyxwv99]

What wizardry did you do to get a 490nm dot out of 980? Some type of frequency doubling I assume, but how?

My $15 5mW 980nm from Laserlands on eBay seems to be generating a weak second harmonic at 490nm. It's brighter than the primary since I can see the 490 dot but not the 980 dot. On the other hand, the human eye is 245 million times as sensitive to 490 as to 980. I'm guessing the 490 output on this thing is 4-20 picowatts. It seems to be coming from the lens. Even though lasers like flat mirrors, every curved survace is locally flat. It's probably bouncing off the tip of the lens and bouncing back and forth inside the lens. Maybe flattening and polishing the tip of the lens would make it work better, but I don't have the precision equipment to do that.

 

[zyxwv99]

I've started a company that makes color vision testing products. One of our first tests it for engineers who work with Blu-ray DVD and need to be able to see the color of 405 nm. I believe this diagnostic self-test may be helpful.

 

[trencheel303]

My $15 5mW 980nm from Laserlands on eBay seems to be generating a weak second harmonic at 490nm. It's brighter than the primary since I can see the 490 dot but not the 980 dot. On the other hand, the human eye is 245 million times as sensitive to 490 as to 980. I'm guessing the 490 output on this thing is 4-20 picowatts. It seems to be coming from the lens. Even though lasers like flat mirrors, every curved survace is locally flat. It's probably bouncing off the tip of the lens and bouncing back and forth inside the lens. Maybe flattening and polishing the tip of the lens would make it work better, but I don't have the precision equipment to do that.

That's really cool. Would you mind linking me to the product you bought? I might research it and/or buy one myself. It might be a common thing. I like anything to do with harmonics so this is right up my street.

I've started a company that makes color vision testing products. One of our first tests it for engineers who work with Blu-ray DVD and need to be able to see the color of 405 nm. I believe this diagnostic self-test may be helpful.

could you tell us how we use it please? Is it something to do with the grey X?

 

[zyxwv99]

Here's the link to the laser pointer.

980nm IR Infrared 5mW Laser Pointer Pen Currency Detector Anti Fake | eBay

The cyan is clearly visible (along with the red) only by shining it directly into your eye. I think some people would be willing to take such a risk for a fraction of a second with no assurance that it would be safe.

I've actually looked up case histories of 5mW laser pointers being shined in people's eyes for various periods of time, including studies on people who are about to have an eyeball removed because of cancer. I think the risks are comparable to looking directly at the sun. At sunset, the sun is probably safer than this laser, at noon the sun is probably more damaging, but it's something like that.

This kind of laser pointer is actually intended for use with currencies that have reverse-fluorescent security features that glow under 980 (technically known as reverse Stokes uptake).

As for the vision test, it was intended as a subtle form of humor. Computer monitors can't display wavelengths in the low 400s. Some people know that, some don't. Supposedly this will tell you if you can see the beam on a 405. Wherever you can see an X, that's what wavelength you can see. I just drew the Xs so that they get fainter and fainter, until the last one (at 406) is just barely visible. Nobody can see the X at 405 because I didn't put one there.

 

[Teej]

When your eyes are night adapted, you are mostly seeing in black and white...so your color vision is about off.

Most of your color reception is in the fovea, about a 2º cone of vision from the central part of your vision. Its the sharpest part of your vision, the part you squint to narrow the field of view to, when trying to resolve the finest details or most distant objects, etc.

The cones that are crowded into your fovea are great at color, and, terrible in low light. This is one of the reasons you can actually see something in near darkness by looking to the side of it (With peripheral vision), but not be able to see it at all looking directly at it.

The rods have no color reception, but, they are much much better in low light - and, when night adapted, you are mostly seeing with your rods, and not your cones.

MOST people don't realize they are seeing in B&W when night adapted, as their mind's eye fills in colors.

So, I would say to someone reporting that they are having trouble resolving colors when night adapted, that it is normal.

 

[Atomicrox]

Up! I received my 5mW 980nm pen today.

It shows up strongly on a detector card (as opposed to 808nm, which shows weakly). My phone camera picks it well, as a sort of whitish red, which is sort of different from the whitish "purple" from 808nm.

Now for the coolest part... it does project a dot which is visible in a totally dark room, but the dot isn't IR (I verified with an IR filter). I can't quite make out the color of the dot (looks like indistinct grey "scotopic color" to me), but I'm willing to bet it's the second harmonic at 490nm. It's very unstable and I can't even make sure it's a coherent line.

I'll meter the pen with the IR filter later, if it's safe (<1mW) I might attempt "the experiment".

 

[Cyparagon]

Spontaneous emission throughout the visible spectrum (in horrendously small amounts) is pretty common in laser diodes. I'll bet that's what you're seeing.

 

[Marco Polo]

When my vision is fully photopic (e.g. decently lit room) the beam appears to be a deep, black-lite violet. It's a very vivid, rich color. Smoke or fog in the air greatly enhances the visibility. It's a very "sharp", well-defined beam.

Transitioning into scotopic, the beam takes on a "lavendar" color, the same as lavendar flowers. It is still violet, but it's no longer a rich hue. The color appears washed-out, and the beam appears to be less sharply focused.

Once my vision is entirely scotopic, the beam appears indistinct and grey. It doesn't look violet at all at this point, it is just a washed-out, watery grey, and it also appears very unfocused and blurry, due to the way rod cells work.

I've been noticing for quite some time that the beam of my 405nm 200mW laser doesn't look the same color as the dot.. The dot is the usual violet and the beam is more of a greyish tone. At first I thought that could be something on the air fluorescing but rules that out because the beam can't be seen with 405nm goggles.

The only other explanation I can think of is that a weak beam of 405nm isn't strong enough to trigger photopic vision, which would explain why it looks considerably brighter than a similar 650nm beam (our scotopic vision is better on the blue end) and the greyish color.

Does everyone see the beams greyish? Can anyone confirm my hypothesis or explain this?

 

[zyxwv99]

Up! I received my 5mW 980nm pen today.

It shows up strongly on a detector card (as opposed to 808nm, which shows weakly). My phone camera picks it well, as a sort of whitish red, which is sort of different from the whitish "purple" from 808nm.

Now for the coolest part... it does project a dot which is visible in a totally dark room, but the dot isn't IR (I verified with an IR filter). I can't quite make out the color of the dot (looks like indistinct grey "scotopic color" to me), but I'm willing to bet it's the second harmonic at 490nm. It's very unstable and I can't even make sure it's a coherent line.

I'll meter the pen with the IR filter later, if it's safe (<1mW) I might attempt "the experiment".

If you shine it on brushed metal (not totally safe since it's still specular reflection, but maybe somewhat safer) you can see the cyan. At these wavelengths, the red and green cones are more sensitive than the rods, so the 490 is being seen scotopically. It is apparently a second harmonic generated between the front and back of the lens, small areas of which would be locally flat and parallel to each other. The eye is 300 million times as sensitive to 490 as to 980, so if they look equally bright (to an order of magnitude) that tells you something about the efficiency of the harmonic generation.

http://webvision.med.utah.edu/imageswv/ERGFig18.jpg

 

[Photonz]

Scored a 7. Maybe I'm just good at recognizing gradient flow:yh:

 

[Atomicrox]

Today I metered my 980nm "5mW" pen... a whopping 81mW. So if you are thinking about viewing one directly or even shining on brushed metal - DON'T!

OTOH I metered it with an IR filter and the Ophir doesn't even pick it up. Some IR does escape (the camera can see it) but it's cerainly far less than 1mW. My meter can detect a 1mW laser just fine.

After I made absolutely sure it was <1mW I tried to look into it... and there it was. A shiny blueish green light. Not quite cyan to my eyes, more like what I expected from 500nm or so. Bright like when you look straight into a high-power LED. I can't be sure it's monochromatic, but it doesn't spread much on a grating and is surely narrow-band enough not to be LED emission.

DON'T TRY THIS AT HOME UNLESS YOU'VE METERED THE LASER WITH THE EXACT SAME IR FILTER YOU'RE USING, AND YOU KNOW FOR SURE YOUR METER PICKS <1mW!!!!!

 

[Sigurthr]

Today I metered my 980nm "5mW" pen... a whopping 81mW. So if you are thinking about viewing one directly or even shining on brushed metal - DON'T!

Yep, figured as much when you said you could see the dot across the room. I've got a true 5mW 780nm and I can see the spot across the room on a white wall only when the room is dark/dim. I've tested <1mW 848nm and I could just barely see it when looking head on into the aperture.

 

[zyxwv99]

Today I metered my 980nm "5mW" pen... a whopping 81mW. So if you are thinking about viewing one directly or even shining on brushed metal - DON'T!

OTOH I metered it with an IR filter and the Ophir doesn't even pick it up. Some IR does escape (the camera can see it) but it's cerainly far less than 1mW. My meter can detect a 1mW laser just fine.

After I made absolutely sure it was <1mW I tried to look into it... and there it was. A shiny blueish green light. Not quite cyan to my eyes, more like what I expected from 500nm or so. Bright like when you look straight into a high-power LED. I can't be sure it's monochromatic, but it doesn't spread much on a grating and is surely narrow-band enough not to be LED emission.

DON'T TRY THIS AT HOME UNLESS YOU'VE METERED THE LASER WITH THE EXACT SAME IR FILTER YOU'RE USING, AND YOU KNOW FOR SURE YOUR METER PICKS <1mW!!!!!

Thanks for the heads up on the 980. My barber's been telling me I have a hole in the back of my head, and I kept thinking he was joking. After your post I asked a friend to have a look. Sure enough, you can see light through the hole. When I close my left eye it goes dark. Also, I don't have a left pupil anymore.

 

[Insomniac]

Tried the colour test and managed to get a zero! Surprising, given that some tiles still looked out of place to me, but I couldn't get them in any position that looked 'perfect'.

I'd be interested to see if it was a fluke or not, but can't be buggered trying again.

 

[Atomicrox]

Yep, figured as much when you said you could see the dot across the room. I've got a true 5mW 780nm and I can see the spot across the room on a white wall only when the room is dark/dim. I've tested <1mW 848nm and I could just barely see it when looking head on into the aperture.

I can't see the 980nm dot at all, but I can see the second line on a wall if I'm very close to it (not across the room) and the room is absolutely dark.

I also have one of those 780nm (doing around 3mW) and I can see the dot across the room if it's poorly lit. I can also see 808nm dots without any issue.

Never had anything between 808 and 980. Would be nice to get some more lasers and find out what my cut-off WL is.