Laser is another great invention after nuclear energy, computer and semiconductor since the 20th century. It is called "the fastest knife", "the most accurate ruler" and "the brightest light". The light excited by atoms is named "laser".
The highest intensity of focused laser reaches the order of 10 22 W/cm2. In addition, this super-strong light field is extremely fast in time domain. In the far ultraviolet (XUV) band, the ultrafast time scale of laser pulses has broken through femtosecond (fs, 10- 15 seconds) and entered a new category of attosecond (as, 10- 18 seconds).
Light is the energy absorbed by electrons in atoms, jumping from low energy level to high energy level, and then falling back from high energy level to low energy level. When falling back, the released energy is released in the form of photons. Laser is a queue of photons that are lured (excited). The photons in this photon queue have the same optical characteristics and the same pace.
For example, ordinary light sources, such as light bulbs, emit different photons and will run in all directions, which is very uneven. But the photons in the laser are all bent in one place, which makes them invincible and powerful.
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It is called the brightest light because the laser beam can diverge in one direction in parallel, with almost no attenuation and very high brightness. At its brightest, it is even 654.38+000 billion times brighter than the sun.
In addition, laser is very good at ranging, and the measured distance is very accurate, so it is also called the most accurate ruler.
Laser has many characteristics: first, laser is monochromatic, or single frequency. Some lasers can produce lasers with different frequencies at the same time, but these lasers are isolated from each other and used separately.
Secondly, the laser is coherent light. The characteristic of coherent light is that all its light waves are synchronous, and the whole beam of light is like a "wave train". Thirdly, laser is highly concentrated, that is, it needs a long distance to disperse or converge.
Laser velocimetry is to measure the moving distance of the measured object twice at a specific time interval, so as to obtain the moving speed of the measured object. Therefore, laser velocimetry has the following characteristics:
1. Because the laser beam is basically a ray, the estimated speed range is far from the effective range of radar speed measurement, and it can be measured beyond 1000M;
2, the speed measurement accuracy is high, and the error is
3. In view of the principle of laser velocimetry, the laser beam must be aimed at the reflection point perpendicular to the plane of the laser beam. However, because the measured vehicle is too far away and in motion, or the plane of the car body is not large, the success rate of laser velocimetry is low and difficult, especially for the police on duty, which is very intense and easy to fatigue;
4. In view of the principle of laser velocimeter, laser velocimeter can not be used in motion, but only in static state; Therefore, the laser velocimeter cannot be called "mobile electronic police". When used in a static state, the driver can easily find that there is detection, so the expected purpose can not be achieved;
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