Those infrared contact lenses

I think it's about time I wrote about this story, as it has made the newspapers, including a good piece in the Guardian.

Basically, this follows on from something I have noted before, back in March 2019, whereby Chinese and American researchers extended the range of rodent vision by injecting nanoparticles into their eyes. Now, a team including some of the original researchers have put the nanoparticles into contact lenses which can achieve a similar effect in humans, who can report on their experience better than the mice.

I think it's important to note that the nanoparticles absorb photons with wavelengths in the range 800 to 1600 nm (a little more than the range of IR film or digital sensors) and emit it in the range 400 to 700 (visible light), mostly around 550 and 650. So this is not thermal imaging and it won't enable you to see in the dark (without suitable IR illumination). Also, because the partlcles absorb and then emit, two things happen. One is that the upconversion takes some energy, so the intensity will be reduced. The other is that this doesn't appear likely to give you a sharp image but whether the result looks like the old HIE halation or is basically foggy isn't clear. My guess is the latter. So you could detect an IR source but it wouldn't look like an IR photograph. However, the team say that using their material in glasses makes things sharper, so I may be misunderstanding the process.

Another bonus, which the news coverage picked up on, is that the IR passes easily through thin skin, such as your eyelids, so you can see the results even with your eyes closed.

Different input wavelengths can be shifted to different output wavelengths. This isn't like colour infrared film but is actually more interesting and nuanced, with the examples reported by the Guardian being 980nm shifted to blue, 808nm to green and 1532nm to red.

I look forward to finding out more.

[Original paper: www.cell.com/cell/abstract/S0092-8674(25)00454-4]

Injections can give you near-infrared vision

Scientists in China and the USA have developed a technique to extend the range of vision by injecting nanoparticles behind the retina (so without any external technology). These particles bind to the photoreceptors in the eye and can convert low energy (near-infrared) photons to a higher energy (green). This has been demonstrated to allow mice to add near-infrared to their range of visible 'colours' with no side-effects.

I first came across this in New Scientist: Mice given ‘night vision’ by injecting nanoparticles into their eyes ... but the full paper is also available online via Cell.com.

One interesting thing about this is that a transfer of energy also occurs in photosynthesis, between types of chlorophyl, and in sensitising film to accept longer-wavelengths.

[Ma et al., Mammalian Near-Infrared Image Vision through Injectable and Self-Powered Retinal Nanoanten- nae, Cell (2019), https://doi.org/10.1016/j.cell.2019.01.038]

More on visual sensitivity to IR

Following on from the experiment to extend human vision into the near infrared (part of my previous post) I found related papers in the Journal of the Optical Society of America and Acta Physica Polonica.

The first from OSA:

Visual sensitivity of the eye to infrared laser radiation
David H.Sliney, Robert T Wangemann, James K Franks (all U.S. Army Environmental Hygiene Agency, Aberdeen Proving Ground, Maryland) and Myron L Wolbarsht (Duke University Eye Center, Durham, North Carolina)

JOSA, Vol 66, Issue 4, pp. 339-341 (1976)

You can find the paper online (membership/paywall) on the Optics Infobase

The abstract reads:

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.

Similarly, but more recent and with open access is ...

Perception of the Laser Radiation for the Near Infrared Range
D. Kecika, J. Kasprzaka, (both Department and Ophthalmology Clinic, I Medicine Faculty, Medical University of Warsaw) and A. Zając (Institute of Optoelectronics, Military University of Technology, Warsaw)

ACTA PHYSICA POLONICA A, Vol 120, No 4, pp 686-687

This paper is available as a PDF.

This abstract reads:

During the diagnostic research done by means of optical devices equipped with radiation sources from the near infrared range the phenomena indicating the perception possibility of this range by a human eye were observed. In this contribution the initial results of the research of this phenomenon were presented. Sources of radiation applied in laser polarimeters (785 nm) and devices designed for optical coherent tomography (820, 850 nm) were taken into particular consideration. Perception tests with the use of a laser diode generating at the wavelength of 940 nm were also carried out. It was stated that the radiation from the range examined can be recorded by a human eye giving a colour sensation — in practice independently of the wavelength of the radiation beam falling into a retina.

I suspect this kind of experiment with lasers falls into the don't try this at home category but it demonstrates that the usual limits quoted for human visual sensitivity are not necessarily the only ones.

There's some interesting notes about this also in the Wikipedia entry on light.

The final word may have to go to a paper I found in the Proceedings of the National Academy of Sciences of the United States of America (PNAS vol 111 no 50) with (sorry) too many authors to list (let's just say Palczewska et al) and with the title Human infrared vision is triggered by two-photon chromophore isomerization. Almost totally out of my area of expertise but if you have the knowledge then you can access the paper (paywall) via this link. I'll leave it to the report's authors to have the final word ... quoted from their '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.

More snippets

Apologies for not posting yet this year ... but here are a few items to make up for it.

Towards the end of last year I came across a claim that a special diet could extend human vision into the edge of the near infrared.

Petapixel carried an explanation of the research project and also a rebuttal by a neuroscientist. The original crowd-funded experiment page is on experiment.com and the group carrying out the research is called Science for the Masses. Since last August the web seems to have gone quiet on the project.

A slight increase in deep red sensitivity would be useful for astronomers wanting to view the universe at the wavelength of hydrogen-alpha: 656.28 nm. Canon produced a camera modified to give similar better response a few years back and Nikon have now also done so, although theirs is a high-resolution full-frame camera. It's the D810A. The older Canon still had some infrared filtering in place so it couldn't be used for infrared photography, but it is unclear whether this is the case with the Nikon. The press release is unclear although DP Review suggests that there is still filtering.

For those of you interested in the BBC's natural history infrared shooting, there is a training film on line where Colin Jackson explains his technique. However, this his team moved on to using modified Canon DSLR cameras rather than 'pure' video cameras so the film is a little out of date.

Finally, a thermal imaging video showing cloud formations across the earth, shot from space at a wavelength of 6.5 µm. (This is worth expanding for a better view.)