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When people go in for eye cancer treatment, they sometimes get something called "linac photon treatment." It's a linear accelerator that makes a beam of electrons, which slams into a block of tungsten. That produces gamma rays through bremsstrahlung. In medicine the term "gamma ray" is reserved...

Sounds like the kind of lasers they sell on AliExpress. They even have 20,000mW for $13.95.

Sellers of 594nm lasers usually describe the color as amber, which is subjectively beyond golden yellow, but not quite orange. Contrary to popular belief, most of us see color the same most of the time. Even through our eyes and viewing conditions differ, we have excellent color-correction...

A basic laser is usually something that emits light, then two mirrors so that the light can bounce back and forth. The mirrors have to be perfectly flat and perfectly aligned. A central spot in one of the mirrors is only half silvered and lets some of the light out. The light-emitting material...

The Wikipedia keeps getting stricter, not more lenient. If you want to write an article about a company, you first need to demonstrate its notability with reliable secondary sources. I tried doing that for 2 minutes on Google Books and didn't have much luck. Then I searched on CNI (Changchun New...

Yellowstone's mantle plume became disconnected from the underlying heat source hundreds of thousands of years ago. That's why the plume is so cold. The upper part has nearly solidified. That means we're safe for at least a few hundred thousand years. Geologists are also not sure if it will ever...

Thanks for the heads up on the 980. My barber's been telling me I have a hole in the back of my head, and I kept thinking he was joking. After your post I asked a friend to have a look. Sure enough, you can see light through the hole. When I close my left eye it goes dark. Also, I don't have a...

If you shine it on brushed metal (not totally safe since it's still specular reflection, but maybe somewhat safer) you can see the cyan. At these wavelengths, the red and green cones are more sensitive than the rods, so the 490 is being seen scotopically. It is apparently a second harmonic...

Cats have better hearing than humans. Earthquakes produce various sorts of waves, p-waves, s-waves, etc. By the time you feel it, some of those other waves have already gone by.

A laser is like a knife. Most people use knifes as eating utensils, or to spread butter. We also use them to chop vegetables, cut meat, etc. Surgeons use special knives called scalpels to cut people open. Some people even make a living as professional knife-throwers. If you enjoy collecting...

Cats can see infrared about as well as humans can, but no better. If you can't see it, the cat can't see it. Cat's have way better night vision than humans. That makes people think they can see infrared. UPDATE: Just thought of something: mice or bugs in the walls.

I'm just going to give you the data and let you work out the math yourself. At 650nm the sensitivity of the human eye is 0.107 of maximum. Peak sensitivity of 1.000 is at 555nm. At 532nm (common green laser pointer) it's 0.862. For 405nm there are conflicting figures. CIE 1931 says 0.00064 while...

I took one your photos and adjusted the white balance. No settings or adjustments, just clicked on "white balance." Eyeballs, like digital cameras and computer monitors, are like unbinned diodes: no two are alike, and you never know what you're going to get. Your right eye doesn't see color...

According to CIE 1931 (and 1978) the human eye is about 8 times as sensitive to 530 nm as to a 650. A 50 mW 532 should therefore look about as bright as 400 mW 650 nm red. FastTech has 50mW greenies for $8.52. It's advertized as 5mW but is really 50-60. Get the "stars" model in the "stylish...

I agree that viewing angle makes a huge difference. When trying to see a hard-to-see beam, it's a question of how small you can make it in your field of view. Looking down the beam really helps. On the other hand, if you want to see how far it's going, something like 90 degrees would be ideal...

It depends on the distance. In my home town, roughly square-shaped and 7 miles on a side, we have four hills that are more than 900 feet high, 13 more that are over 500 feet high, and a whole bunch in the 200-500 foot range. From the top of one these hills, the bottom could be anywhere from 2 or...

I think the only way to answer that question is with two people: one shining the laser up, and someone else standing on a high hill or small mountain some distance away looking horizontally towards the beam. When your eyes are close to the source of the beam, the perspective lines make it...

It's normal to lose interest in hobbies. I have dozens of hobby interests that come and go. Most of them form clusters of related hobbies. For example, light, color, and vision is a cluster that includes interest in lasers, diodes, fine arts, graphic design. In each hobby I learn something that...

First, the site looks like shlock. That should tell you something. Second, lasers in the near-infrared range are indeed "cold" in that the dot doesn't concentrate on your skin, but penetrates quite a bit, thus spreading out the heat. Not to mention the dots tend to be pretty big. I have a...

A few weeks ago there was an article in paper about new EU rules on laser pointers, restricting them to <1mW. The World Health Organization (WHO) has been pushing this for years. I was worried the US would go that route. Laser Pointer Safety - Statistics, laws, and general laser pointer news...