jackery's blog

There are many different types of high power laser pointer. According to the color classification, there are green, red, blue, purple, etc. The more common ones are green and red laser pointers; there are also different colors of laser pointers classified by wavelength; secondly, they are classified according to power. High-power laser pointers also have low-power laser pointers because the eyes can follow the laser beam along the entire length of the laser beam. On the other hand, many red laser pointers have no visible beam unless they are very powerful. When the laser is in contact with the solid, the human eye can only reliably pick up the red dot.

Some manufacturers are now selling bundled diode blue laser pointer with a measuring power of more than 1,500 MW. However, since the claimed power of the "laser pointer" product also includes IR power (only in DPSS technology), there is still a beam (the reason is described below), and the comparison based on the strictly visible blue component from the DPSS-type laser is still problematic. And the information is often unavailable. Due to the use of high-order harmonic neodymium and the low frequency doubling conversion efficiency, in the optimized DPSS module, the ratio of IR power converted to 473 nm blue laser is usually 10-13%, which is about the typical value of green laser Half (20-30%).

Blue lasers can also be made directly with InGaN semiconductors, which can produce blue light without doubling the frequency. 450 nm (447 nm plus/minus 5 nm) blue laser diodes are still available on the open market. Some blue diodes can provide very high output; like Nichia NDB7K75 diodes, continuously output more than 5 watts of energy when overloaded. These devices are brighter than 405 nm violet laser diodes at the same power because the longer wavelength is closer to the maximum sensitivity of the human eye. The mass production of laser diodes used in commercial equipment such as laser projectors is driven by price.

Some of the laser light emitted by the Laser pointer can be seen with the beam, and the beam will follow wherever it is irradiated, while some cannot be seen. Do you know why?

What is the Tyndall effect?

If the laser is not directed at you in a vacuum, you will not be able to see it. However, the air we breathe together is not a vacuum. Among them are dust, suspended particles and so on. The bright "passage" of the laser light is formed by the scattering of light by these particles. We call it the "Dyndall Effect". Light is when the electrons in the atom absorb energy, transition from a low energy level to a high energy level, and then fall back from a high energy level to a low energy level. The energy released during the fall is released in the form of photons. Light travels in a straight line. An example is usually mentioned. When the floor is sweeping in the classroom, there is sunlight through the bed glass, and we can see that the sunlight is straight. The sunlight shining on the dust is diffusely reflected, so we can see the propagation path of the sunlight from all directions. In the same way, although the laser is a parallel beam, it will be reflected in all directions by the air and dust during the process of spreading in the air, so it can be seen from all directions. If it is in a vacuum, it can only be seen by facing the laser against the direction of laser propagation.

Visible Green laser pointer beam in astronomical applications

The main purpose of using lasers in astronomical observatories is to combat atmospheric interference, especially the interference of tropospheric air close to the ground, in order to obtain clearer astronomical images. The earth is surrounded by a thick atmosphere, which not only reduces the brightness of the stars, but also interferes with the shape of the stars. This interference is very powerful, even visible to the naked eye, and it is precisely it that produces the "flash and flash". Astronomical phenomenon.

After years of exploration, astronomers have explored an adaptive optics system that can automatically counteract the interference caused by the atmosphere, but this system requires a sufficiently bright guide star as a basis for correction, but the sky usually lacks Such a star, so some people thought of using a laser to artificially create a bright star. For example, sodium laser guide star.