Jump to content
UltravioletPhotography

Humans can see Infrared?


Damon

Recommended Posts

Any science textbook will tell you we can’t see infrared light. Like X-rays and radio waves, infrared light waves are outside the visual spectrum.

But an international team of researchers co-led by scientists at Washington University School of Medicine in St. Louis has found that under certain conditions, the retina can sense infrared light after all.

 

Perhaps they need to research earlier publications, not such a new discovery perhaps.

 

A scientific paper from 38 years ago!

Sliney, David H.; Wangemann, Robert T.; Franks, James K.; Wolbarsht, Myron L. (1976). "Visual sensitivity of the eye to infrared laser radiation". Journal of the Optical Society of America 66 (4): 339–341. "The foveal sensitivity to several near-infrared laser wavelengths was measured. It was found that the eye could respond to radiation at wavelengths at least as far as 1064 nm. A continuous 1064 nm laser source appeared red, but a 1060 nm pulsed laser source appeared green, which suggests the presence of second harmonic generation in the retina."

Link to comment

Yes, the mechanism seems sometimes to involve two-photon excitation (green perception) and sometimes single-photon (red perception.) I also called attention to something similar in an earlier post:

 

http://www.ultraviol...__fromsearch__1

 

From a safety standpoint, I would use something like those goggles with utmost caution. For the IR to produce a visible retinal image, it must be quite bright. It cannot be emphasized enough that the eye's protective responses to excess brightness (discomfort, blinking, and iris constriction) are completely inoperative with infrared. One can do oneself a lot of damage without even realizing anything is amiss. Normal light is not intense enough to give the green two-photon effect.

Link to comment

Thanks guys.

Figures it not a new finding. It always seems when a new thing is discovered, you look around hard enough and lo and behold someone has already done it. Although perhaps this go around the technology may help them get more out of the "new" discovery. Maybe not.

 

OlDoinyo--I should have paid attention to your post--sorry!

Yeah I am steering away from those homemade goggles. Thanks for that information.

 

That's what I get for trying to be smart.

 

-D

Link to comment
But we cannot really see-see IR, just 2-photon-see IR.

so hmmmmm.......

 

""A continuous 1064 nm laser source appeared red, but a 1060 nm pulsed laser source appeared green, which suggests the presence of second harmonic generation in the retina"

 

We can see IR under certain conditions and this includes IR laser light. As reported, a CONTINUOUS 1064nm laser appears red, but a PULSED 1060nm laser appears green. Only the latter case is due to the 2 photon process.

 

I personally have seen the red response when using a continuous 985nm diode laser during Raman spectroscopy. I have not seen a green response but I also can't ever remember using a pulsed IR laser.

Link to comment

The article requires subscription but here is what is freely available from PNAS.org.

***********************************************************************************************************************

Human infrared vision is triggered by two-photon chromophore isomerization.

Significance

This study resolves a long-standing question about the ability of humans to perceive near infrared radiation (IR) and identifies a mechanism driving human IR vision. A few previous reports and our expanded psychophysical studies here reveal that humans can detect IR at wavelengths longer than 1,000 nm and perceive it as visible light, a finding that has not received a satisfactory physical explanation. We show that IR light activates photoreceptors through a nonlinear optical process. IR light also caused photoisomerization of purified pigments and a model chromophore compound. These observations are consistent with our quantum mechanical model for the energetics of two-photon activation of rhodopsin. Thus, humans can perceive IR light via two-photon isomerization of visual pigment chromophores.

Abstract

Vision relies on photoactivation of visual pigments in rod and cone photoreceptor cells of the retina. The human eye structure and the absorption spectra of pigments limit our visual perception of light. Our visual perception is most responsive to stimulating light in the 400- to 720-nm (visible) range. First, we demonstrate by psychophysical experiments that humans can perceive infrared laser emission as visible light. Moreover, we show that mammalian photoreceptors can be directly activated by near infrared light with a sensitivity that paradoxically increases at wavelengths above 900 nm, and display quadratic dependence on laser power, indicating a nonlinear optical process. Biochemical experiments with rhodopsin, cone visual pigments, and a chromophore model compound 11-cis-retinyl-propylamine Schiff base demonstrate the direct isomerization of visual chromophore by a two-photon chromophore isomerization. Indeed, quantum mechanics modeling indicates the feasibility of this mechanism. Together, these findings clearly show that human visual perception of near infrared light occurs by two-photon isomerization of visual pigments.

 

A pdf of supplementary information, methods and figures, is also free to download.

**********************************************************************************************************************

 

This new paper has not claimed to "discover human IV vision" but rather has worked out the photoreceptor mechanism.

 

Also for the record, Sliney (1976) is cited.

 

"If I have seen further than others, it is by standing upon the shoulders of giants." - Isaac Newton

Link to comment
I suspect that the pulsed 1060-nm laser had a peak beam intensity several orders of magnitude greater than the CW 1064-nm laser, thus enabling the two-photon mechanism; presumably, the pulses were short enough that damaging levels of irradiation did not occur at the retina. The two-photon mechanism cannot explain what was observed with the CW laser, and possibly not anything seen in ambient light through goggles, because the irradiation intensity is (thankfully) insufficient for that.
Link to comment
The Palczewska PNAS paper, which I have access to, states "Some authors of the present paper perceived low energy IR laser radiation of 1,060 nm as a pale greenish light" which is not entirely consistent with in Sliney's 1976 abstract above. I do not have a copy of David's paper, so I have not read it yet. However I am not certain if second harmonic generation (aka frequency doubling) and two-photon visual chromophore isomerization are necessarily mutually exclusive pathways.
Link to comment

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
×
×
  • Create New...