What is laser
Laser is known as one of the four great inventions of the 20th century:
Laser is not the light existing in nature, but the light invented by human beings based on quantum theory. What distinguishes laser from natural light is the characteristics of laser and the process of laser generation
Laser is called “the fastest knife, the brightest light and the most accurate ruler”:
Compared with natural light, laser has the characteristics of high intensity, good monochromaticity, good coherence and good directivity.
Laser is the product of atomic stimulated radiation:
Excited by the energy of the pump source, the atom can transition to a high-energy state.
At this time, when it encounters an external photon with a specific frequency, it will release an identical photon. The two photons will make more atoms transition and produce the same photon.
This process is called stimulated radiation, and the generated light is called “laser”.
The frequency, phase, propagation direction and polarization state of photons emitted by stimulated radiation and foreign photons are exactly the same, so the laser has the characteristics of high intensity, good monochromaticity, good coherence and good directivity.
Schematic diagram of atomic energy level transition
Schematic diagram of stimulated radiation process
Features of laser
- Good directivity
- Good monochromaticity
- High strength
- High coherence
- Commercial use began in the 1970s and is now in the stage of rapid development:
- Einstein first proposed stimulated radiation in 1917;
- In 1960, the world’s first ruby solid state laser appeared;
- 1970s laser has entered the commercial era.
- After the exploration of the interaction mechanism between laser beam and matter, the application field of laser is also expanding. After the 1990s, the industrial application has entered a high-speed development stage.
Development history of laser technology
Two applications of laser
The characteristics of high intensity, good monochromaticity, good coherence and good directivity determine the two application scenarios of laser:
Laser has the outstanding advantage of high energy density, which has important applications in material processing, weapons, medical treatment and other fields.
The laser has good monochromaticity and directivity. It is suitable for information transmission (optical communication) and distance measurement (optical measurement). Compared with traditional electric communication, optical communication has the advantages of large capacity, long distance, good confidentiality and light weight.
Laser processing equipment
Laser processing is representative of precision processing technology. The main driving force for growth comes from the substitution of traditional processing methods:
Compared with other processing methods, laser processing has the advantages of high efficiency, high precision, low energy consumption, small material deformation and easy control.
These advantages are closely related to the two characteristics of “non-contact processing” and “high energy density” of laser processing:
Non contact machining:
The laser is completely completed by the heat generated by the interaction between the laser and the material.
There is no contact between the processing tool and the material in the whole process, so that the processed material is not affected by the force, and the residual stress is relatively small.
Because the diameter of the beam can be controlled to be very small, the accuracy is also high;
High energy density:
The power density of laser processing can reach more than 107w/cm2, thousands or even tens of thousands of times that of flame, arc and other processing methods;
Higher power density means that the laser can process a very small area on the processing object without affecting the materials around the micro area, so the processing accuracy and processing efficiency are higher.
- High efficiency
- Low energy consumption
- Small deformation
- Easy to control
Laser: the core unit of laser equipment
Laser is the component used to generate laser and the core component of laser equipment:
- The value of laser is 20% – 40% of the total value of complete set of laser processing equipment, or even higher;
- Pumping, stimulated radiation and other processes take place in the laser;
- A typical laser is composed of laser working material (emitting energy), pump source (lifting energy), optical resonator (propagating energy), etc.
Basic structure diagram of laser
Types of laser
There are many classification methods for lasers, among which four are the most commonly used:
It can be divided into gas laser, solid laser, liquid (dye) laser, semiconductor laser, excimer laser, etc;
Taking gas as the working material, the common ones are CO2 laser, He-Ne laser, argon-ion laser, He-Cd laser, copper vapor laser, various excimer lasers, etc., especially CO2 laser is most used in industry.
Metal ions that can produce stimulated emission are doped into the crystal and used as working materials. Commonly used crystals include ruby, corundum, aluminum garnet (commonly known as YAG), calcium tungstate, calcium fluoride, yttrium aluminate and lanthanum beryllate, among which YAG is the most commonly used crystal at present.
The working substance used is a solution formed by dissolving some organic dyes in liquids such as ethanol, methanol or water.
Also known as laser diode, the working materials used are semiconductor materials, such as gallium arsenide (GaAs), cadmium sulfide (CDS), indium phosphide (INP), zinc sulfide (ZnS), etc.
The working material used is glass fiber doped with rare earth elements.
Fiber laser is a laser that uses fiber as working medium.
Fiber laser has excellent performance and is known as the “3rd generation laser”:
(1) Because the fiber has the characteristics of small volume, winding, low volume area ratio and high photoelectric conversion rate, the fiber laser has the advantages of miniaturization and intensification, good heat dissipation and high photoelectric conversion rate;
(2) At the same time, the laser output by the fiber laser can be directly derived from the fiber, so the fiber laser has high processing adaptability and can adapt to the processing application in any space;
(3) In structure, the fiber laser has no optical lens in the resonant cavity, so it has the advantages of no adjustment, no maintenance and high stability.
(4) In addition, the beam quality of fiber laser is also excellent.
|Types of laser||Typical type||Laser wavelength||Maximum output power||Energy conversion efficiency||Features|
|Gas laser||CO2 laser||About 10.6um infrared||1-20kw||8%～10%||Good monochromaticity and high energy conversion efficiency|
|Liquid laser||6G dye laser||UV to IR||–||5%～20%||The output wavelength is continuously adjustable, the energy conversion power is high, easy to prepare and cheap|
|Solid state lasers||YAG / ruby laser||Visible to near infrared||0.5-5kw||0.5%～1%||Low output power, low energy conversion rate and good monochromaticity.|
|Semiconductor lasers||GaAs diode laser||100nm―1.65um||0.5-20kw, two-dimensional array can reach 350kW||20% – 40%, laboratory 70%||High energy conversion power, small volume, light weight, simple structure, long service life and poor monochromaticity.|
|Fiber laser||Pulsed / CW fiber laser||1.46um―1.65um||0.5-20kw||30%-40%||Miniaturization, intensification, high conversion efficiency, high energy output, high beam quality, no optical collimation and less maintenance.|
Energy output waveform (working mode):
It can be divided into the continuous laser, pulse laser and quasi-continuous laser. Pulse laser can be further divided into millisecond laser, microsecond laser, nanosecond mechanism, picosecond laser, femtosecond laser, attosecond laser, etc;
Continuously output stable energy waveform during working time, with high power, and can process materials with large volume and high melting point, such as metal plates;
According to the pulse width, pulse lasers can be further divided into millisecond lasers, microsecond lasers, nanosecond mechanisms, picosecond lasers, femtosecond lasers and attosecond lasers;
Femtosecond lasers and attosecond lasers are called ultrafast lasers.
The power of pulse laser is much lower than that of continuous laser, but the machining accuracy is higher than that of continuous laser. Generally, the narrower the pulse width is, the higher the machining accuracy is;
Quasi CW laser:
Between continuous laser and pulse laser, high-energy laser can be output repeatedly in a certain period.
|Classification method||Laser category||Features|
|Classification by working mode||CW laser||The excitation of the working material and the corresponding laser output can be carried out continuously in a long time range|
|Pulsed laser||It refers to a laser with a single laser pulse width of less than 0.25 seconds and working only once at a certain interval. It has a large output peak power and is suitable for laser marking, cutting and ranging.|
|Classification by pulse width||Millisecond (MS) laser||10-3S|
|Microsecond (US) laser||10-6S|
|Nanosecond (NS) laser||10-9S|
|Picosecond (PS) laser||10-12S|
|Femtosecond (FS) laser||10-15S|
Output wavelength (color):
It can be divided into X-ray laser, ultraviolet laser, infrared laser, visible laser, etc;
It can be divided into low power laser (< 100W), medium power laser (100w-1500w) and high power laser (> 1500W).
Classification of lasers
Major laser suppliers include: Coherent, IPG, nLight, Newport, Trump, Rofin (acquired by Coherent), DILAS, SPI(acquired by Trumpf), mitsubishi, Kawasaki, MAX, JPT, Raycus, FEIBO, GUOKE, ANPIN, HFB.