Be careful photographing self-driving cars

It appears that the lasers used by self-driving cars can damage digital camera sensors. So, should you be inclined to photograph such new technology be careful. See this article which gives a real world example. Forewarned is forearmed, article is here.

It appears that the lasers used by self-driving cars can damage digital camera sensors. So, should you be inclined to photograph such new technology be careful. See this article which gives a real world example. Forewarned is forearmed, article is here.

And it doesn't damage people eyes?

And it doesn't damage people eyes?

 

If some idiot designer uses lasers of the wrong wavelength, definitely. It could also happen if a laser of a retina-safe wavelength malfunctions and puts out too much power.

If some idiot designer uses lasers of the wrong wavelength, definitely. It could also happen if a laser of a retina-safe wavelength malfunctions and puts out too much power.

Well I can't see a laser that can damage the camera but not eyes. So if it can damage eyes then shouldn't be illegal?

According to the article, the laser is specifically designed NOT to damage human eyes. Apparently it operates at a wavelength that while safe to eyes can damage digital camera sensors.

Well I can't see a laser that can damage the camera but not eyes.

 

It's not so simple, as I found out in the 1980s when I was at UCLA doing research on human speech. I proposed to use LEDs for some measurements, and had to get approval from a committee on research on human subjects. A member of the committee, unfortunately, confused LEDs with lasers, something which would be much less likely nowadays. He made me jump through a few hoops before I could have my proposal approved.

 

Bebu you might want to look at this, which gives a short description of the situation with laser pointers. They present similar concerns.

There's also the subject of person-to-person differences. When I go to a meeting at which someone is using a laser pointer, I try to avoid looking at the screen when the laser is on it, but I always leave the meeting with painful eyes. I appear to be over-sensitive to that flavor of light. :-(

 

BTW, Hector, until a few years ago I had to shepherd 3-4 projects a year through our own IRBs (Institutional Review Boards, for those lucky enough not to be familiar with them.) At one point I spent quite a while explaining (to physicians at that) why blowing into a tube ("spirometry") didn't present any untoward dangers to patients' health. :-)

In my day job, the most powerful I regularly interact with is your garden variety HeNe gas discharge laser. With that said, we have some significantly more powerful ones kicking around work, and I'm reminded of a sign I saw posted somewhere a while back:

 

"Warning: Do not stare directly into Laser with remaining eye"

What about the laser beam reflecting off of something directly to the camera sensor? Is that a valid concern?

what about the laser beam affecting the eyes of critters? particularly dogs and cats!

According to the trade magazine, Laser Focus World at, https://www.laserfocusworld.com/articles/print/volume-54/issue-12/world-news/automotive-lidar-lidar-for-self-driving-cars-comes-in-many-competing-forms.html

 

 

"905 VS. 1550 NM

One big question is what wavelength to use. So far, the leading lidar sources have been 905 nm diode lasers, which are inexpensive, readily available, and easily detected by silicon photodiodes. However, power levels used in open areas are limited by eye-safety standards because 905 nm light penetrates to the retina, which in practice restricts lidar range to tens of meters. Top lidar pulse powers can be 10X higher for 1550 nm, which does not reach the retina, says Umar Piracha, a senior researcher for IMEC (Kissimmee, FL). The longer wavelength also produces more photons per unit power, and less sunlight reaches the ground at 1550 nm than at 905 nm. Piracha says that strong cases exist for both wavelengths, but Davis expects 1550 nm to win ultimately."

 

So, the lasers used in self-driving cars can achieve eye safety by using either an invisible lower power near-infrared wavelength that penetrates the retina, or by using a higher power laser operating at a longer. but still invisible, infrared wavelength, that does not penetrate the retina. I tend to think that the higher power longer wavelength would be the more damaging to camera sensors. And, if you are using a camera converted to infrared photography, watch out!

IF, I owned a body converted to infrared capabilities, this would give me pause. It's not like these vehicles broadcast their presence, making it hard to guard one's gear against the odd beam of the longer wave length when you are quite unaware of it.

Pretty much any common optical material, whether optical glass or various types of plastic, is opaque to 1550nm(~6000cm-1) light. Even calcium fluoride(Fluorite) is opaque at that long of a wavelength-you need to move into salt optics like KBr or more likely things like zinc selenide to transmit that.

 

I wouldn't worry about a 1550nm laser affecting anything...even common IR converted cameras and IR-sensitive film are only really sensitive to near-IR. I haven't measured the cut-off of my one IR converted camera, which is CCD based(Nikon D80), but Kodak HIE only went down to 950nm and current IR films cut that by about 100nm.

Ben - Thanks for the clarification. I was going to look up the transmission properties of optical glass but hadn't gotten around to it. I now recall that a long time ago I was looking for an optical material for a window that transmitted near infrared for a laser, and settled on sapphire. But, that is not a common nor inexpensive optical material.

Ben - Thanks for the clarification. I was going to look up the transmission properties of optical glass but hadn't gotten around to it. I now recall that a long time ago I was looking for an optical material for a window that transmitted near infrared for a laser, and settled on sapphire. But, that is not a common nor inexpensive optical material.

 

I work with mid-IR at work all the time(~400-4000cm-1, or 2500-25000nm), although the only laser is a 632.8nm(red) HeNe and the IR comes from a ceramic wafer heated to incandescence. Most of our focusing optics are front-surface gold mirrors, although a few key parts-most notably the beamsplitter that makes all of the "magic" happen-is made of KBr. The whole purpose of my IR set-ups are to see at what wavelengths a particular chemical/sample absorbs(different types of bonds have different "signature" absorbances). Depending on what we're doing, we either use transmission where the sample is held between salt plates-I've used NaCl, KBr, and AgCl all depending on the nature of the sample-or something called attenuated total reflectence using internal reflections in a diamond/zinc selenide crystal.

 

My point in all of that is that standard optical glass doesn't help you any.

 

Also, even though we use KBr and the like in the lab, you REALLY don't want to use it out in "real world" applications. All of mine are continuously purged with dry air(which also gets run through a CO2 scrubber). Back in the fall, I pulled out one that had been in storage for 2-3 years, and found the beamsplitter fogged to the point where it was unusable. By contrast, I have one from the mid-90s that has been in continuous use, and the optics in it are still perfect.

If you really want to photograph a self-driving car, you could use an infrared cut-off filter, which are designed to block infrared wavelengths while passing visible light. Edmund Optics, for example, sells them.

FWIW, which is not a lot, I was able to find a radar/laser speed sensor device for my new car, which does not react to its own or others radar/laser avoidance systems.

 

So apparently there is some ability to differentiate different systems?

 

Being close to the armpit of the nation, we don't seem to have many intentionally self-driving cars here.