What is the longest wavelength of laser light you have seen?

I forgot to post here when I finished my 685nm laser.
I'm convinced it is slightly more crimson (i.e. less orange) than regular 650/660nm lasers. The difference is very small, though. Only barely noticeable and only on the right surfaces...
Brightness wise, 30mW looks very similar to 3.5mW of regular red.

Now we need something slightly abov 700nm to compare.

I found out the highest wavelength that anyone can safely see and still see the color. It's about 1140nm.

Assuming your eyes are photopically (color vision) dark-adapted, that the laser shining in your eye has a 3 mm beam, and that it's shining in your eye for 1 second, if it was 850 nm it would need 8 nanowatts of output measured at the pupil for the average person to see it and see pure saturated color.

At 905 nm you would need 100 nanowatts. At 1064 nm you would need 69 microwatts. At 1152 nm you would need 3 to 4 mW. The only problem is, 2.5 mW is the maximum safe limit, so you can't safely see 1152. However, since the power needed rises by about 1.5 orders of magnitude for every 50 nm, going down to about 1140 nm should do the trick.

How did you find that out?

zyxwv99 said:

I found out the highest wavelength that anyone can safely see and still see the color. It's about 1140nm.

Assuming your eyes are photopically (color vision) dark-adapted, that the laser shining in your eye has a 3 mm beam, and that it's shining in your eye for 1 second, if it was 850 nm it would need 8 nanowatts of output measured at the pupil for the average person to see it and see pure saturated color.

At 905 nm you would need 100 nanowatts. At 1064 nm you would need 69 microwatts. At 1152 nm you would need 3 to 4 mW. The only problem is, 2.5 mW is the maximum safe limit, so you can't safely see 1152. However, since the power needed rises by about 1.5 orders of magnitude for every 50 nm, going down to about 1140 nm should do the trick.

Click to expand...

Interesting.

So what power would be needed to "see" CO2 ?? 10000 nm ??
Of course just kidding - this IR wound not reach retina - eye is not transparent to this termal IR ....

My source for this:

Visual sensitivity of the eye to infrared laser radiation
David H. Sliney, Robert T. Wangemann, James K. Franks, and Myron L. Wolbarsht
JOSA, Vol. 66, Issue 4, pp. 339-341 (1976)
Optics InfoBase: Journal of the Optical Society of America - Visual sensitivity of the eye to infrared laser radiation
Optics InfoBase: Journal of the Optical Society of America - Table of Contents

You can read it online if you're willing to pay money. I just went to the library and special ordered it. They had it in a warehouse across the street so it only took one day. For 30 cents I got a photocopy of the three-page article.

It reviews all the previous major studies. Turns out the earlier ones were not taken seriously because of inadequate precautions to guarantee what wavelengths people were really seeing. In this study they went to extreme lengths. On the 1064nm laser, they used 4 filters, each with 5 nm bandwidth and 0.1% transmission outside the bandwidth. Then they ran tests and cross-checks.

Now I'm trying to look up archives of laser eye accidents to find out the highest wavelength anyone has ever seen even with eye injury. I'm guessing it's about 1250 nm for long duration, maybe 1342 for a femtosecond pulse.

As for seeing 10600 nm, the problem is not the opacity of the eye, since with enough power the light would still get through. The real problem would be your brain instantly turning into a ball of steam. The ensuing explosion would send bits of skull, scalp and hair flying all over the place. What was left of your head would instantly burst into flames.

Which wouldn't be so bad had you actually seen the light, only here's the problem: all this would happen before your eye had a chance to send a signal to your brain.

I'd +1 you but the forum won't let me.

When installing and tuning pulsed OPOs my eye response falls off sharply at 856 nm at the long end and about 410 at the short end. I'm the company LSO and I have the needed goggles and Joule meters to do this safely. We actually do the math for this. Viewing near UV is on my serious no-no list.

Our products tune about 214 to 2100 nm, unless you order the longer wavelength extenders, and then the IR goes out to 11 microns. . We throttle things back sharply, put on goggles to block the 1064 fundamental, 532, and 355. Then when training customers we can carefully play " Guess that Line" in the visible.

At the short end, with 7 nanosecond pulses, its hard to find things that don't fluoresce to determine the short end.

Steve

Confirmed that I can see the dot of a 9mW 850nm laser on the wall - across the room in the dark, ~40cm away in a room with lights on (paying a lot of attention, it's easy to miss and hard to focus on).

It's faint and looks "dull red", duller than anything I've seen up to 808nm.

Now my upper limit has been limited (no pun intended) to the 850-980nm range, at least for safe viewing of the dot.

Edit: anyone knows a cheap source for lasers in that range?

Wow, I haven't even participated in this.

Well...the longest I have seen would have to be my 654nm LaserGlow pointer....ya.....um....:wtf:

Edit: Actually, Freshman year in HS I was working on a project and saw a 808nm I believe or 1064nm 10 Watt laser etching a piece of wood

-Alex

The a 808nm laser, what are you actually seeing with the red dot? It doesn't appear to be that difficult to see to me, a normal red, although not much intensity. My assumption has been that the red dot isn't 808nm but some other product from the laser, was that a wrong assumption?

808nm looks like 650nm to me, but far less bright and "duller". I can see it easily as well.

If the dot is full of tiny bright and dark "speckles" (interference pattern) you're seeing the actual laser and not some LED emission (don't look at the dot of the 10W laser on your sig, you'll hurt your eyes!).

I built a 500mW 808nm laser some time ago and noticed right off that when it was focused I could see a small faint dot of red collimated light. However, when I use my IR camera to focus the beam, it is a huge bright beam. My conclusion was that the 808nm laser diode output a small amount of higher frequency light along with the infrared light that I could not actually see. With an IR camera the 500mW beam is green ( a function of how the camera works ) but is much brighter than the vestigial red dot that I could see with my own eyes.

Why? Cameras are great at seeing 808nm light too. However it'll show up different colours between cameras and depending on settings such as white balance.

If the laser is burning then yes, you will see the incandescent material, but the dim red dot IS the 808nm light.

That red dot that I can see is of a small diameter. Very small. It is also very dim, which could be explained by the eye's inferior visual acuity at that wavelength. However, since the 500mW beam is so easily seen with an IR camera and is much brighter and by extension, of greater diameter, is there an abstract you can site to give more weight to your argument?

Do you see the interference speckles on the dot? If you do then it's coherent (laser emission, not residual LED emission).
Then you can use a diffraction grating in front of your camera to see if there is only one line. Then you'll be sure you're seeing the 808nm.

As Things said I bet you are.