laser sensor principle and application Overview

Light and laser lasers were among the most significant scientific and technological achievements of the 1960s. Its rapid development has been widely used in defense, production, medical and non-electrical measurement. Unlike ordinary light, lasers need to be produced by lasers. The working substance of the laser, under normal conditions, most of the atoms are in a stable low energy level E1. Under the action of external light of appropriate frequency, the atomic absorption photon energy at the low energy level is excited and transitions to the high energy level E2. The photon energy E=E2-E1=hv, where h is the Planck constant and v is the photon frequency. Conversely, under the induction of light of frequency v, atoms at level E2 will transition to a lower energy level to release energy and emit light, called stimulated radiation. The laser firstly makes the atom of the working substance abnormally at a high energy level (ie, the population number is reversed), so that the stimulated radiation process is dominant, so that the induced light of the frequency v is enhanced and can pass through the parallel mirror. The formation of avalanche-type amplification produces strong stimulated radiation, referred to as laser.

The laser has three important characteristics:

1 high directionality (ie high directionality, low light velocity divergence angle), the laser beam extends over a few kilometers, but only a few centimeters;

2 high monochromaticity, the frequency width of the laser is 10 times smaller than ordinary light;

3 high brightness, using laser beam convergence can produce temperatures up to several million degrees.

Lasers can be divided into four types according to the working substance:

1 Solid-state laser: Its working substance is solid. Commonly used are ruby lasers, ytterbium-doped yttrium aluminum garnet lasers (ie, YAG lasers), and neodymium glass lasers. Their structure is roughly the same, characterized by small and sturdy, high power, and the neodymium glass laser is the device with the highest pulse output power, which has reached tens of megawatts.

2 gas laser: its working substance is gas. Various gas atoms, ions, metal vapors, and gas molecular lasers are available. Commonly used are carbon dioxide lasers, helium neon lasers and carbon monoxide lasers, which are shaped like ordinary discharge tubes and are characterized by stable output, good monochromaticity and long life, but low power and low conversion efficiency.

3 liquid laser: It can be divided into chelate laser, inorganic liquid laser and organic dye laser. The most important one is organic dye laser. Its biggest feature is that the wavelength is continuously adjustable.

4 semiconductor laser: It is a younger type of laser, of which the more mature is a gallium arsenide laser. It is characterized by high efficiency, small size, light weight and simple structure. It is suitable for carrying on airplanes, warships, tanks and infantry. It can be made into a range finder and a sight. However, the output power is small, the orientation is poor, and the ambient temperature is greatly affected.

Laser sensor application

Non-contact long-distance measurement can be achieved by using the high directivity, high monochromaticity and high brightness of the laser. Laser sensors are often used for measuring physical quantities such as length, distance, vibration, speed, and azimuth. They can also be used for flaw detection and monitoring of atmospheric pollutants.

Laser length measurement: Precision measurement length is one of the key technologies in the precision machinery manufacturing industry and optical processing industry. Modern length measurement is mostly carried out by using the interference phenomenon of light waves, and the accuracy mainly depends on the monochromaticity of light. The laser is the ideal light source, which is 100,000 times purer than the best single-color light source (氪-86 lamp). Therefore, the laser length measuring range is large and the precision is high. It is known from the optical principle that the relationship between the maximum measurable length L of the monochromatic light and the wavelength λ and the line width δ is L = λ / δ. With a 氪-86 lamp, the maximum length can be measured to be 38.5 cm. For longer objects, segmentation measurement is required to reduce the accuracy. If a helium gas laser is used, it can measure up to several tens of kilometers. It is generally measured within a few meters and has an accuracy of 0.1 micron.