The classifications categorise lasers according to their ability to produce damage in exposed people, from class I (no hazard during normal use) to class IV, for example of 2000 watt CO2 laser (be able to cut thick steel).
Class I laser is a low output power device. It is inherently safe and can avoid all electrostatic hazards. It wouldn’t cause any damage to human body or skin under any condition. There is no need of other auxiliary safety equipment when using Class I laser. Here are several application areas of CLASS I laser: Laser printer, CD player, CD-ROM device, geological survey equipment and laboratory equipment.
Class II laser is also a low-power device (power< 1 milliwatt). However, this laser will cause eye damage if the person deliberately stares into the beam for an extended period (longer than 15mins). The users should avoid looking into Class II laser beam, and should not point the beam into anyone’s eyes. In addition, to view the Class II laser through the telescope should be avoided as well. In fact, if Class II laser is pointed into your eyes, you should immediately head to one side or close your eyes instantly, preventing any laser damage. Some application examples of Class II laser are Classroom Demonstration, Laser Pointer, Collimation Equipment, and Distance Measuring Equipment.
Class IIIa laser is a continuous laser wave belonging to the medium power device (1-5 milliwatts). Its usage is similar to Class II laser, for example, laser pointer and laser scanner. Looking straight into Class IIIa laser is dangerous. Please do not stare at Class IIIa laser beam under any circumstances. Please do not align Class IIIa laser pointer with anyone’s eyes. Looking through the telescope at Class IIIa laser is forbidden. The user has to pay attention to these precautions.
Class IIIb laser is a medium power device (5-500 milliwatts or 10 j/cm2). The use of Class IIIb includes spectrum instrument, stereoscopic photography and laser light for entertainment. Looking straight in Class IIIb is very dangerous, and the scattering of the laser also could cause damage to the eyes. Do not directly look into Class IIIb laser and also do not use telescope equipment to watch laser beam. Anyone who works in laser area must wear protective clothing and eye-patch under any circumstances. Before operating Class IIIb laser device, it’s necessary to read through its safety manual.
Class IV laser is a high power device (greater than 500 milliwatts or 10 j/cm2). The applications of Class IV laser, for example, are laser surgery, investigation, incision, weldment and fibre mechanical process. Likewise, Class IV laser and its scattering could have damage to eyes and skins. It is highly dangerous, being able to result in a fire. Anyone in the radiation scope of Class IV laser must wear protective clothing and eye-patch. Any reflector should be away from Class IV laser, as a great number of people’s eyes were burnt due to the reflection by reflectors. Please do not expose hands and/or skins anytime within the radiation scope of Class IV laser. Before using Class IV laser device, you have to read through its safety manual.
Hope this information could help you to avoid the damage by laser!
Base on time of flight: R=CT/2.
When PRR=33,000Hz, the time interval between two continuous laser pulses is
△T = 1/PRR = 1/33,000 = 3.03 μS.
The main advantage of full waveform digitisation LiDAR is shown as the following:
With traditional multi-echo technique (analog technology) in vegetation covered area, the first echo contains about 85% of the total reflected signals, the second echo is between 8% and 10%, the third echo occurs 3-5%, and the fourth echo barely returns.
While the first echo return comes more often from canopy top surface and the upper of the trees, only some third echoes could penetrate trees and shrubs to the ground (or some second echoes, if with a low vegetation coverage). Therefore, for high vegetation coverage area, such as Hong Kong, Nan Jing, Shen Zhen, etc., the traditional LiDAR with analog technique is powerless. Inversely, full waveform digitisation LiDAR could receive echoes more than 10 times (or even 40 times), thus only a few percent transmissivity is still able to obtain the topographic map of a high vegetation coverage area.
It takes times for the optical internal transmission and reception. This time could be converted into the distance, and the value will depend on the design of different devices.
The stronger the target reflectivity is, the further the equipment can collect. In the nature, the general reflectivity is about 20% to 40%.
The reflectivity of 90% can only be achieved by laboratory objectives, such as prism, target, etc., or vacuum objective that more than 90% of it is in a vacuum.
When the scan speed and the pulse frequency are certain, the further the distance is, the lower the point density is, and then the precision decreases.
Therefore, to ensure a long measurement distance, the point frequency should be set up lower, lowering the point density, decreasing the precision.