Nd：YAG lasers are optically pumped lasers using flashtube or laser diodes，when Nd:YAG crystals being used as gain medium,the typical output wavelength is 1064nm in the infrared.Wavelength of 1064nm is easily absorbed by metal surface and has high power density,enabling to produce narrower kerf.Because of these features,Nd:YAG crystals are widespread used in manufacturing.
Theotry
The main components of device are:
Gain medium - Nd YAG
Nd:YAG crystals can absorb wavelength of 730nm—760nm and 790nm—820nm, Neodymium ions in glasses act as a laser gain medium.When Nd is being pumped into excitation,after a particular atomic transition it typically emitting 1064nm light. The highest output power can be 1000W in continuous mode,and the highest average power of output can be 400W, when pulse width is 10ns the energy can be 1GW/cm2 after being focused. Nd:YAG crystals being gain medium can make lasers have shorter output wavelength and provide more precise laser marking because of narrower kerf .
Q-switching
For pulsed mode there should add a Q-switching to improve the output power of lasers and compress width of laser pulse. The emitted light of Nd:YAG lasers is 1064nm which is within spectral region of V:YAG crystals,so V:YAG crystals are appropriate for Nd:YAG lasers. Cr4+:YAG is a crystal that is used for passive Q-switching in lasers, and it is also an new laser material. It is applied in the range of 900-1200 nm and 1350-1600 nm.
Reflective mirror——mirror with high-reflective film,which can reduce transmittance and allow light reflect many times in resonant cavity,so power of light will be improved.Mirror with paratially reflective film makes laser light output.
Pump source——Provide energy for gain medium of laser,the energy is absorbed in the medium so that producing excited states.Population inversion will be achieved when the number of particles in one excited state exceeds the number of particles in the ground state or a less-excited state.LD and flash lamp are usually applied in Nd:YAG lasers as pump source.
Feature
- Being easily absorbed by metal surface
- High power density
- Good welding quality
Application
- Laser drilling
Nd:YAG crystals work as gain medium help lasers emit laser light with wavelength of 1064nm which is easily absorbed by metal surface with highly centered in time and space.Power density of laser light can reach by focusing system which enables laser light to drilling in various kinds of materials.Nd:YAG crystals have properties that are beneficial to manufacturing such as low threshold,good thermal conductivity. is easily absorbed by metal surface.Special optical system helps laser light hit the specified manufacturing point,make the laser light beams focused so that there are enough energy to drilling.
- Laser marking
A methods to leave marks on an object.The point where the laser touches the surface should be on the focal plane of the laser’s optical system.This point is typically small, Nd:YAG crystals work as gain medium help lasers emit laser light with wavelength of 1064nm,this wavelength enables produce light spot with a very small radius which is appropriate for laser marking.In order to get laser light with high peak power and narrow pulse width,usually using Cr:YAG crystals as Q-switch.Cr4+：YAG crystal is a kind of saturable absorber which enables absorb more energy within wavelength of 9μm~1.2μm,among these wavelengths,wavelength of 1.06μm is a main absorption band which is caused by energy level transition.
- Laser welding
Nd:YAG lasers are the most practical lasers in manufacturing because of high power density.The typical pulse frequency of Nd:YAG lasers reaches 0.05~50kHZ,average power reaches 20~50W. Nd:YAG lasers can weld various kinds of materials with thickness in the range of several nanometers to a few millimeters.
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