Characteristics, application and market prospect of ultrafast laser
2021-08-02
In fact, nanosecond, picosecond and femtosecond are time units, 1ns = 10-9s, 1ps = 10-12s, 1FS = 10-15s. This time unit represents the pulse width of a laser pulse. In short, a pulsed laser is output in such a short time. Because its output single pulse time is very, very short, such a laser is called ultrafast laser. When the laser energy is concentrated in such a short time, huge single pulse energy and extremely high peak power will be obtained. During material processing, the phenomenon of material melting and continuous evaporation (thermal effect) caused by long pulse width and low-intensity laser will be avoided to a great extent, and the processing quality can be greatly improved.
In industry, lasers are usually divided into four categories: continuous wave (CW), quasi continuous (QCW), short pulse (Q-switched) and ultra short pulse (mode locked). Represented by multimode CW fiber laser, CW occupies most of the current industrial market. It is widely used in cutting, welding, cladding and other fields. It has the characteristics of high photoelectric conversion rate and fast processing speed. Quasi continuous wave, also known as long pulse, can produce MS ~ μ S-order pulse with a duty cycle of 10%, which makes the peak power of pulsed light more than ten times higher than that of continuous light, which is very favorable for drilling, heat treatment and other applications. Short pulse refers to ns pulse, which is widely used in laser marking, drilling, medical treatment, laser ranging, second harmonic generation, military and other fields. Ultrashort pulse is what we call ultrafast laser, including pulse laser of PS and FS.
When the laser acts on the material with the pulse time of picosecond and femtosecond, the machining effect will change significantly. Femtosecond laser can focus on a spatial area smaller than the diameter of hair, making the intensity of electromagnetic field several times higher than the force of atoms to check the electrons around them, so as to realize many extreme physical conditions that do not exist on the earth and cannot be obtained by other methods. With the rapid increase of pulse energy, high power density laser pulse can easily peel off the outer electrons, make the electrons break away from the bondage of atoms and form plasma. Because the interaction time between laser and material is very short, the plasma has been ablated from the material surface before it has time to transfer energy to the surrounding materials, which will not bring thermal impact to the surrounding materials. Therefore, ultrafast laser processing is also known as "cold processing". At the same time, ultrafast laser can process almost all materials, including metals, semiconductors, diamonds, sapphires, ceramics, polymers, composites and resins, photoresist materials, thin films, ITO films, glass, solar cells, etc.
With the advantages of cold processing, short pulse and ultrashort pulse lasers have entered the precision processing fields such as micro nano processing, fine laser medical treatment, precision drilling, precision cutting and so on. Because the ultrashort pulse can inject the processing energy into a small action area very quickly, the instantaneous high energy density deposition changes the electron absorption and movement mode, avoids the influence of laser linear absorption, energy transfer and diffusion, and fundamentally changes the interaction mechanism between laser and matter. Therefore, it has also become the focus of nonlinear optics, laser spectroscopy, biomedicine, strong field optics Condensed matter physics is a powerful research tool in scientific research fields.
Compared with femtosecond laser, picosecond laser does not need to broaden and compress pulses for amplification. Therefore, the design of picosecond laser is relatively simple, more cost-effective, more reliable, and is competent for high-precision, stress-free micro machining on the market. However, ultra fast and ultra strong are the two major trends of laser development. Femtosecond laser also has greater advantages in medical treatment and scientific research. It is possible to develop the next generation of ultrafast laser faster than femtosecond laser in the future.
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