How to see infrared light. We look at the world through the eyes of a mantis shrimp: the near infrared range How to see infrared

Can we do it? Nope.

We are all used to the fact that flowers are red, black surfaces do not reflect light, Coca-Cola is opaque, nothing can be illuminated with a hot soldering iron like a light bulb, and fruits can be easily distinguished by their color. But let's imagine for a moment that we can see not only the visible range (hee hee), but also the near infrared. Near infrared light is not at all something that can be seen in a thermal imager. It is closer to visible light than to thermal radiation. But it has a number of interesting features - often objects that are completely opaque in the visible range are perfectly translucent in infrared light - an example is in the first photo.
The black surface of the tile is transparent to IR, and with the help of a camera in which the filter is removed from the matrix, you can see part of the board and the heating element.

To begin with, a small digression. What we call visible light is just a narrow band of electromagnetic radiation.
Here, for example, I got this picture from Wikipedia:

We just don't see anything but this small part of the spectrum. And the cameras that people make are initially castrated to achieve the similarity of a photograph and human vision. The camera matrix is able to see the infrared spectrum, but this feature is removed by a special filter (it is called Hot-mirror), otherwise the pictures will look somewhat unusual for the human eye. But if this filter is removed ...

Camera

The test subject was Chinese phone, which was originally intended for review. Unfortunately, it turned out that the radio part of him is cruelly buggy - either he receives calls, or he does not receive calls. Of course, I did not write about him, but the Chinese did not want to either send a replacement or pick up this one. So he stayed with me.
We disassemble the phone:

We take out the camera. Using a soldering iron and a scalpel, carefully separate the focusing mechanism (top) from the matrix.

There should be a thin piece of glass on the matrix, possibly with a greenish or reddish tint. If it's not there, look at the "lens" part. If not there, then most likely everything is bad - it is deposited on the matrix or on one of the lenses, and it will be more problematic to remove it than to find a normal camera.
If it is, we need to remove it as carefully as possible without damaging the matrix. At the same time, it cracked for me, and I had to blow glass fragments from the matrix for a long time.

Unfortunately, I lost my photos, so I'll show a photo of irenica from her blog, who did the same thing, but with a webcam.

That shard of glass in the corner is just the filter. Was filter.

Putting everything back together, taking into account that when the gap between the lens and the matrix changes, the camera will not be able to focus correctly - you will get either a near-sighted or far-sighted camera. It took me three times to assemble and disassemble the camera in order to achieve the correct operation of the autofocus mechanism.

Now you can finally assemble your phone and start exploring this new world!

Paints and substances

Coca-Cola suddenly became translucent. Light from the street penetrates through the bottle, and even objects in the room are visible through the glass.

The cloak went from black to pink! Well, except for the buttons.

The black part of the screwdriver also brightened. But on the phone, this fate befell only the joystick ring, the rest is covered with a different paint, which does not reflect IR. As well as the plastic docking station for the phone in the background.

The pills turned from green to purple.

Both chairs in the office had also gone from gothic black to incomprehensible colors.

The faux leather remained black, while the fabric turned out to be pink.

The backpack (it is in the background of the previous photo) became even worse - almost all of it became lilac.

Like a camera bag. And the cover of the e-book

The stroller went from blue to the expected purple. A retroreflective patch, clearly visible in a conventional camera, is not visible at all in IR.

Red paint, as close to the part of the spectrum we need, reflecting red light, also captures part of the IR. As a result, the red color brightens noticeably.

Moreover, all red paint that I noticed has this property.

fire and temperature

A barely smoldering cigarette looks like a very bright dot in IR. People are standing at the bus stop at night with cigarettes - and their tips illuminate their faces.

The lighter, the light of which in a regular photo is quite comparable to the background lighting in IR mode, blocked the miserable attempts of street lamps. The background is not even visible in the photo - the smart camera worked out the change in brightness by reducing the exposure.

The soldering iron glows like a small light bulb when heated. And in the keep warm mode, it has a soft pink light. And they say that soldering is not for girls!

The burner looks almost the same - well, except that the torch is a little further away (at the end, the temperature drops quite quickly, and at a certain stage it already stops shining in visible light, but still shines in IR).

But if you heat a glass rod with a burner, the glass will begin to glow quite brightly in the IR, and the rod will act as a waveguide (bright tip)

Moreover, the stick will glow for quite a long time even after the heating stops.

And the dryer of the hot air station generally looks like a flashlight with a mesh.

Lamps and light

The letter M at the entrance to the metro burns much brighter - it still uses incandescent lamps. But the sign with the name of the station almost did not change the brightness - it means there are fluorescent lamps.

The yard looks a little strange at night - lilac grass and much lighter. Where the camera in the visible range can no longer cope and is forced to increase the ISO (grain in the upper part), the camera without an IR filter has enough light with a margin.

This photo turned out to be a funny situation - the same tree is illuminated by two lanterns with different lamps - on the left with an NL lamp (orange street lamp), and on the right - LED. The first one in the emission spectrum has IR, and therefore, in the photograph, the foliage below it looks light purple.

And the LED does not have IR, but only visible light (therefore, LED lamps are more energy efficient - energy is not wasted on emitting unnecessary radiation that a person will not see anyway). Therefore, the foliage has to reflect what is.

And if you look at the house in the evening, you will notice that different windows have a different shade - some are bright purple, while others are yellow or white. In those apartments whose windows glow purple (blue arrow), incandescent lamps are still used - a hot spiral shines evenly across the entire spectrum, capturing both the UV and IR range. In the entrances, energy-saving lamps of cold white light (green arrow) are used, and in some apartments - fluorescent warm light (yellow arrow).

Sunrise. Just sunrise.

Sunset. Just a sunset. The intensity of sunlight is not enough for a shadow, but in the infrared range (maybe due to different refraction of light from different wavelengths, or due to the permeability of the atmosphere), shadows are visible perfectly.

Interestingly. In our corridor, one lamp died and the light was barely there, and the second one did not. In infrared light, the opposite is true - a dead lamp shines much brighter than a living one.

Intercom. More precisely, the thing next to it, which has cameras and a backlight that turns on in the dark. It is so bright that it is visible on a conventional camera, but for infrared it is almost a spotlight.

The backlight can also be turned on during the day by covering the light sensor with your finger.

CCTV lighting. The camera itself did not have a backlight, so it was made from shit and sticks. It is not very bright, because it was taken during the day.

Nature

Hairy kiwi and lime green are almost indistinguishable in color.

Green apples have turned yellow, and red apples have turned bright lilac!

White peppers turned yellow. And the usual green cucumbers are some kind of alien fruit.

Bright flowers have become almost monochromatic:

The flower almost does not differ in color from the surrounding grass.

And the bright berries on the bush became very difficult to see in the foliage.

Why berries - even multi-colored foliage has become monophonic.

In short, it will no longer be possible to choose fruits by their color. We'll have to ask the seller, he has a normal vision.

But why is everything pink in the photos?

To answer this question, we have to remember the structure of the camera matrix. I again stole the picture from Wikipedia.

This is a bayer filter - an array of filters painted in three different colors, located above the matrix. The matrix perceives the entire spectrum in the same way, and only filters help to build a full-color picture.
But the infrared spectrum filters pass differently - blue and red more, and green less. The camera thinks that instead of infrared radiation, ordinary light enters the matrix and tries to form a color image. In photographs where the brightness of IR radiation is minimal, ordinary colors still break through - you can notice shades of colors in the photographs. And where the brightness is high, for example, outdoors under the bright sun, the IR hits the matrix in exactly the proportion that the filters let through, and which forms a pink or purple color, clogging all the rest of the color information with its brightness.
If you take pictures with a filter on the lens, the proportion of colors is different. For example, this one:

I found this picture in the ru-infrared.livejournal.com community
There are also a lot of pictures taken in the infrared range. The greenery on them is white because the BB is exposed just on the foliage.

But why do plants turn out so bright?

In fact, this question consists of two - why the greens look bright and why the fruits are bright.
The green is bright because in the infrared part of the spectrum, absorption is minimal (and reflection is maximum, which is what the graph shows):

Chlorophyll is responsible for this. Here is its absorption spectrum:

This is most likely due to the fact that the plant protects itself from high-energy radiation by adjusting the absorption spectra in such a way as to obtain both energy for existence and not be dried out from too generous sun.

And this is the radiation spectrum of the sun (more precisely, that part of the solar spectrum that reaches the earth's surface):

And why does the fruit look so bright?

Fruits in the peel often do not have chlorophyll, but nevertheless - they reflect IR. Responsible for this substance, which is called epicuticular wax - the same white coating on cucumbers and plums. By the way, if you google “white bloom on plums”, then the results will be anything, but not this.
The meaning of this is about the same - it is necessary to preserve the color, which can be critical for survival, and not allow the sun to dry the fruit while still on the tree. Dried prunes on trees are, of course, excellent, but they do not fit into the life plans of the plant a little.

But damn, why a mantis shrimp?

No matter how much I searched for what animals see the infrared range, I came across only mantis shrimp (stomatopods). Here are the paws:

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In a laser, a photon of light, colliding with an excited atom of the medium, stimulates the emission of another photon of the same frequency. Secondary photons, in turn, cause the emission of photons by other excited atoms - as a result, the process of light emission proceeds like an avalanche. But let us try to consider the case when the active medium of the laser is in a subcritical state, i.e., it is too rarefied to support an avalanche-like process. In such a medium, a photon can collide with an unexcited atom, which, having absorbed this photon, goes into an excited state. Another photon, colliding with this excited atom, can now stimulate emission, and two photons will move together, in pairs. In a slightly denser medium and with slightly more intense pumping, this pair of photons can collide with another excited atom, resulting in a photon triplet. In general, about the same number of photons leave the active medium of the laser as entered it, however, the emerging photons form coherent pairs and triplets.

Such "grouped" light has amazing properties. First of all, it is completely unusual for the eye. Thus, red clustered light will bounce off red objects in the usual way. But, since each pair of "red" photons has a total energy equal to the energy of one "blue" photon, such light, due to two-photon absorption, will also excite blue-sensitive receptors. The object will thus appear both red and blue at the same time, perhaps iridescent purple. Most of all, however, Daedalus is occupied by infrared grouped light. All the objects around us emit far infrared radiation in abundance. Therefore, it is enough to place a “photon grouper” by KOSHMAR in front of any object, which collects photons into groups whose total energy lies in the visible region of the spectrum - and here is free lighting for you! True, in grouped IR light, all objects will most likely look creepy, so it would be better if the energy of a group of photons falls in the ultraviolet region. Then, using a conventional phosphor, as in fluorescent lamps, one can excite it due to multiphoton absorption and obtain visible light. This nifty device converts useless infrared background into visible light - like a heat pump pumping heat from cooler to hotter bodies. According to the laws of thermodynamics, these devices can take much more energy (heat and light) from the environment than is necessary to put them into action.

New Scientist, June 26, 1980

From notebook Daedalus

Consider an active medium in which N 1 atoms are in the ground state and N 2 are in an excited state with energy E. In this case, the operating frequency is v = E / h, and if this frequency corresponds to the energy density ПЃv, then the excitation intensity N 1 -> N 2 will be BN 1 ПЃv, where B is the transition probability. Similarly, the stimulated emission intensity is equal to BN 2 ПЃv. Let n photons enter the system. For each of them, the probability of being absorbed during the transition of an atom from state 1 to state 2 is proportional to BN 1 ПЃ; let us denote this probability by KN 1 . Then the number of photons absorbed in the system is equal to nKN 1 for small KN 1 , and n(1 – KN 1) photons pass through the entire medium. The probability that each of these photons stimulates the emission of a photon by an excited atom is equal to KN 2 . Thus, the most probable number of pairs of photons emerging from the medium is n(KN 2)-(1 - KN 1). In other words, we let n photons into the medium and got n (KN 2)G-(1 - KN 1 photon pairs) at the output; thus, the efficiency of our laser for "bunching" photons is 2 / KN 2 (1 - KN 1) This value has a maximum at N 2 = N 1 , i.e. when the pump radiation, which transfers atoms to an excited state due to N 1 -> N 3 -> N 2 transitions, is slightly insufficient to create an inverse population, i.e. i.e. the system is slightly below the threshold for generating laser radiation.When KN 1 = KN 2 = 0.5, the maximum efficiency = 0.5, i.e., it can be expected that approximately half of the total number of photons entering the system will be grouped. groups of not only two, but also three or more photons, but even taking this into account, our scheme looks quite real.

How will photon pairs behave? In physical processes (refraction, scattering, etc.) they should behave exactly like photon-producing ones, but in chemical processes (absorption, etc.) they will most likely exhibit a two-photon absorption tendency, and so each pair will behave like a single photon with twice the frequency. Based on this, it is possible to create street lamps that emit clustered infrared light that easily passes through the fog and at the same time is well perceived by the eye. And how would you feel about the "anti-umbrella" that converts the light of a cloudy day into ultraviolet radiation for tanning? Finally, since the bunched photons are coherent with the photon that originally hit the medium, appropriate glasses will allow direct viewing of the infrared image.

Daedalus receives a letter

Myron L. Walbarsht, Professor of Ophthalmology and Biomedical Engineering, Duke University Medical Center, Durham, Sev. Carolina, USA July 23, 1980

Dear Ariadne!

Your friend Daedalus has considered (p. 448, June 26, 1980) the use of bunched light to excite the blue receptors of the eye through two-photon absorption, and even conceded the possibility of using far infrared radiation to produce visible light. I am enclosing a copy of one of my published papers, "Visual Sensitivity of the Eye to Infrared Radiation" (Journal of the Optical Society of America, 66, 1976, p. 339), which shows that this is indeed possible. I hope that Daedalus will continue his research, but he should be aware that in our days science is moving forward so fast that even a dreamer can fall behind life.

Sincerely, M. Walbarsht

(In the following, grouped light will be shed on the question of priority in the article "".)

Daedalus correctly reasoned that visual receptors can respond to a "coherent pair" of photons with an energy that is half the sensitivity threshold of the receptor. This idea was confirmed by researchers using laser technology. A number of night vision devices are based on a similar principle. - Approx. ed.

I don't know about you, but I've always wondered: what would the world look like if the RGB color channels in the human eye were sensitive to a different wavelength range? Rummaging through the barrels, I found infrared flashlights (850 and 940nm), a set of IR filters (680-1050nm), a black and white digital camera (no filters at all), 3 lenses (4mm, 6mm and 50mm) designed for photography in IR light. Well, let's try to see.

On the topic of IR photography with the removal of the IR filter on Habré, we have already written - this time we will have more opportunities. Also, photos with other wavelengths in RGB channels (most often with the capture of the IR region) can be seen in posts from Mars and about space in general.

These are flashlights with IR diodes: 2 left at 850nm, right - at 940nm. The eye sees a weak glow at 840nm, the right one sees only in complete darkness. For an IR camera, they are dazzling. The eye seems to retain microscopic sensitivity to near IR + LED radiation comes at a lower intensity and at shorter (=more visible) wavelengths. Naturally, with powerful IR LEDs, you need to be careful - with luck, you can quietly get a retinal burn (as well as from IR lasers) - the only thing that saves is that the eye cannot focus the radiation to a point.

Black-and-white 5 megapixel noname USB camera - based on Aptina Mt9p031 sensor. I shook the Chinese for a long time on the topic of black and white cameras - and one seller finally found what I needed. There are no filters in the camera at all - you can see from 350nm to ~1050nm.

Lenses: this one is 4mm, there are also 6 and 50mm lenses. At 4 and 6mm - designed to work in the IR range - without this, for the IR range, without refocusing, the pictures would be out of focus (an example will be below, with a conventional camera and 940nm IR radiation). It turned out that the C mount (and CS mount with a working length that differs by 5mm) - we got from 16mm movie cameras of the beginning of the century. Lenses are still being actively produced - but already for video surveillance systems, including well-known companies like Tamron (a 4mm lens is just from them: 13FM04IR).

Filters: I again found a set of IR filters from 680 to 1050nm from the Chinese. However, the IR transmission test gave unexpected results - it does not look like bandpass filters (as I imagined it), but it seems like a different "density" of color - which changes the minimum wavelength of transmitted light. Filters after 850nm turned out to be very dense, and require long shutter speeds. IR-Cut filter - on the contrary, it only allows visible light to pass through, we will need it when shooting money.

Filters in visible light:

Filters in IR: red and green channels - in the light of a 940nm flashlight, blue - 850nm. IR-Cut filter - reflects IR radiation, so it has such a cheerful color.

Let's start shooting

Panorama in the daytime in IR: red channel - with a filter at 1050nm, green - 850nm, blue - 760nm. We see that the trees reflect the nearest IR especially well. Colored clouds and colored spots on the ground - turned out due to the movement of clouds between frames. Separate frames were combined (if there could be an accidental camera shift) and stitched into 1 color image in CCDStack2 - a program for processing astronomical photographs, where color images are often made from several frames with different filters.

Panorama at night: you can see the difference in color of different light sources: "energy efficient" - blue, visible only in the nearest IR. Incandescent lamps - white, shine in all range.

Bookshelf: Virtually all ordinary objects are virtually colorless in IR. Either black or white. Only some paints have a pronounced "blue" (short-wave IR - 760nm) tint. LCD screen of the game "Just you wait!" - in the IR range does not show anything (although it works on reflection).

Cellular telephone with an AMOLED screen: absolutely nothing is visible on it in IR, as well as a blue indicator LED on the stand. In the background - nothing is visible on the LCD screen either. The blue paint on the metro ticket is IR transparent - and the antenna for the RFID chip inside the ticket is visible.

At 400 degrees, the soldering iron and hair dryer glow quite brightly:

Stars

It is known that the sky is blue due to Rayleigh scattering - accordingly, in the IR range it has a much lower brightness. Is it possible to see the stars in the evening or even during the day against the sky?

Photo of the first star in the evening with a conventional camera:

IR camera without filter:

Another example of the first star against the background of the city:

Money

The first thing that comes to mind for authenticating money is UV radiation. However, banknotes have a lot of special elements that appear in the IR range, including visible to the eye. We have already briefly written about this on Habré - now let's see for ourselves:

1000 rubles with filters 760, 850 and 1050nm: only some elements are printed with ink that absorbs IR radiation:

5000 rubles:

5000 rubles without filters, but with illumination of different wavelengths:
red = 940nm, green - 850nm, blue - 625nm (=red light):

However, the infrared tricks of money do not end there. The banknotes have anti-Stokes marks - when illuminated with 940nm IR light, they glow in the visible range. Photo taken with a conventional camera - as you can see, IR light passes through the built-in IR-Cut filter a little - but because the lens is not optimized for IR - the image is not in focus. Infrared light looks light purple because Bayer RGB filters are transparent to IR.

Now, if we add an IR-Cut filter, we will see only glowing anti-Stokes marks. An element above “5000” glows the brightest, it can be seen even in dim room lighting and backlighting with a 4W 940nm diode / flashlight. There is also a red phosphor in this element - it glows for several seconds after irradiation with white light (or IR->green from the anti-Stokes phosphor of the same label).

The element slightly to the right of “5000” is a phosphor that glows green for some time after irradiation with white light (it does not require IR radiation).

Summary

Money in the IR range turned out to be extremely tricky, and you can check it in the field not only with UV, but also with an IR 940nm flashlight. The results of shooting the sky in IR give rise to hope for amateur astrophotography without traveling far beyond the city limits.

How to see infrared light

New Scientist, June 26, 1980

From the notebook of Daedalus

Consider an active medium in which N 1 atoms are in the ground state and N 2 are in an excited state with energy E. The operating frequency is in this case v = E / h, and if this frequency corresponds to the energy density? v, then the excitation intensity N 1 -> N 2 will be BN 1 ?v, where B is the transition probability. Similarly, the stimulated emission intensity is equal to BN 2 ?v. Let n photons enter the system. For each of them, the probability of being absorbed during the transition of an atom from state 1 to state 2 is proportional to BN 1 ?; let us denote this probability by KN 1 . Then the number of photons absorbed in the system is equal to nKN 1 for small KN 1 , and n(1 – KN 1) photons pass through the entire medium. The probability that each of these photons stimulates the emission of a photon by an excited atom is equal to KN 2 . Thus, the most probable number of pairs of photons emerging from the medium is n(KN 2)?(1 - KN 1). In other words, we let n photons into the medium and got n (KN 2)? (1 - KN 1 photon pairs at the output; thus, the efficiency of our laser for "bunching" photons is 2 / KN 2 (1 - KN 1). This value has a maximum at N 2 = N 1, i.e. when the pump radiation, which transfers atoms to an excited state due to N 1 -> N 3 -> N 2 transitions, is slightly insufficient to create an inverse population, i.e. e the system is slightly below the laser radiation generation threshold. At KN 1 = KN 2 = 0.5, the maximum efficiency = 0.5, i.e., it can be expected that approximately half of the total number of photons entering the system will be grouped. groups of not only two, but also three or more photons, but even taking this into account, our scheme looks quite real.

Daedalus receives a letter

Myron L. Walbarsht, Professor of Ophthalmology and Biomedical Engineering, Duke University Medical Center, Durham, Sev. Carolina, USA July 23, 1980

Dear Ariadne!

Your friend Daedalus has considered (p. 448, June 26, 1980) the use of bunched light to excite the blue receptors of the eye through two-photon absorption, and even conceded the possibility of using far infrared radiation to produce visible light. I am enclosing a copy of one of my published papers, "Visual Sensitivity of the Eye to Infrared Radiation" ( Journal of the Optical Society of America 66, 1976, p. 339), which shows that this is indeed possible. I hope that Daedalus will continue his research, but he should be aware that in our days science is moving forward so fast that even a dreamer can fall behind life.

Sincerely, M. Walbarsht

(Later, grouped light will be shed on the issue of priority in the article "Revisiting Infrared Vision".)

From the book Secrets of the Moon Race author Karash Yury Yuryevich

UN agreements: light at the end of the tunnel or a dead end? "Tunnel" I did not want the reader to get the impression that the 1960s were a time of fruitless hopes, lost illusions and lost

From the book World's Fairs Parade author Mezenin Nikolai Alexandrovich

Paris 1878. "RUSSIAN LIGHT" In France, 1873 - 1879 was generally a period of crisis and decline, which was observed throughout Europe. But Marx, referring to 1878, noted that during this "year, so unfavorable for all other businesses, the railroads prospered; but this

From the CCTV book. CCTV Bible [Digital and network technologies] author Damianovski Vlado

2. Light and television Let there be light. A bit of history Light is one of the main and greatest phenomena of nature, light is not only a necessary condition for life on the planet, but also plays an important role in technical progress and inventions in the field of visual communication:

From the book History of outstanding discoveries and inventions (electrical engineering, electric power industry, radio electronics) author Shneiberg Jan Abramovich

CHAPTER 8 Human genius creates electric light, "similar to the sun" Creation of P.N. Yablochkov of the "electric candle" The creation of sources of electric lighting is one of the fundamental discoveries in the history of mankind. The first to speak

There was an option to buy a cheap VGA resolution digital camera with a viewfinder, but then that would be another thing to carry around.
Recently at the airport, I tried to turn off the TV with people talking loudly with my Universal TV-Be-Gone Controller, but the device didn't work to turn off the TV, so I decided to try and see if it worked or not. I took out my iPhone 4, opened the camera app, pointed the camera at the IR TV-Be-Gone, and pressed the button on the TV-Be-Gone. I did not see the light from the IR LED in the viewfinder of the author's iPhone.
Then it occurred to me to try the FaceTim front camera. I pressed the camera switch button on the iPhone screen and pointed the camera at FaceTime, the TV Be-Gone's still flashing IR light, and finally I could see the light that was coming out of the IR emitter!
The following steps will repeat the steps above and show you how to see infrared light on your standard iPhone 4, and possibly other smartphones and tablets too.

Step 1. Try using the back of the camera to see the light from the infrared LED

On your iPhone, launch the Camera app and point the camera at the TV remote's LEDs remote control.
When you look at iPhone screen, press a few buttons on the remote control.
Even though the remote control probably emits a bright infrared beam, you cannot see it with your eyes because your eyes are not sensitive to light in the infrared frequency (about 940nm for a remote control).
Your iPhone's main camera can't see infrared light because Apple has added a filter to the lens that blocks infrared light so the infrared rays aren't visible on the screen.

Step 2: Now try using the FaceTime front camera to see the light from the infrared LED

Now press the button "switch camera" - the icon in the upper right corner iPhone cameras application so that the screen displays the FaceTime camera view, so that you are likely to see yourself on the screen.
Now point the FaceTime camera at LED your TV remote control and press the button on the remote control.
Your eye cannot see infrared light, but you will now see the infrared light that appears in the viewfinder as a bright white light.
It turns out that the FaceTime camera on the iPhone 4 doesn't have an IR filter! Hooray!