high power picosecond laser is widely applied in material micro processing, led line cutting, solar energy photovoltaic and scientific research at its high peak power rate, narrow pulse width（10-12s）, adopting picosecond laser processing material with precision processing, small thermal effect, no burrs on processing edge. compared with femtosecond laser（10-15s）. picosecond laser has many advantages, as it is no need to expand or compress the pulse if strengthening the power rate. picosecond laser possesses simple structure so it is highly cost-effective with reliable function. at the same time, the pulse width of picosecond laser is short enough to cope with very precise and micro fabrication.
at present, the demand for picosecond lasers in domestic market is very large, yearly over 800 sets and most of them depend on imports which are expensive and inconvenient for maintenance. several domestic manufactures providing picosecond lasers are limited by stability and have low market share.
the mono-pulse energy of industrial grade high power picosecond lasers needs to reach the level of micro code or even sub mj, while the frequency of lock-mode seed laser is above mhz, and the mono-pulse energy seed is usually nj. in order to obtain high mono-pulse energy, the seed frequency can be reduced by the pulse selection technique, and then the high mono-pulse energy output can be achieved through high gain amplifier. the working theory of picosecond is as the below figure. the structure mainly includes three parts: seed laser, pulse unit and amplifier. mhz high frequency seed optical pulse is selected khz laser pulse by acousto-optic or electro optic modulator, then the pulse achieves high mono pulse energy output by single or multi grade amplifier.
fiber amplifier has the advantages of high
output, high gain amplifier（>109）, stable and single structure, relatively low production cost. the defect is affected by
the nonlinearity of the optical fiber and cannot get high single pulse energy
output, usually less than 10uj.
picosecond seed source technology
seed source technology is the core technology of picosecond laser. the function of the seed source directly determines the stability and reliability of the picosecond laser. the most difficult to control and failure is the seed laser. how to delay the life time of the saturable absorber mirror is the key to the seed source technology.
seed laser can be divided into two categories: solid seed for semiconductor pump technology and fiber seed for fiber technology. the solid seed has the defects of complex structure, large volume, high cost and poor stability. the saturable absorber mirror used for the lock-mode bears high power and heat. the life of the solid seed is usually less than 1500 hours. in order to meet the service life of 10000 hours, it is necessary for the saturable absorber mirror to change point frequently. in contrast, the power and heat of the optical fiber seed source are much lower, and the service life is much longer. even if the saturable absorber mirror is not changed, its life can reach more than 10000 hours.
in addition, the fiber seed source has the advantages of simple structure, low cost, stable performance, basic maintenance and so on. so it has become the first choice of the major laser suppliers.
picosecond amplifier technology
in order to obtain large single pulse energy output, seed pulse needs to be amplified by high gain amplifier. the difficulty of picosecond amplifiers lies in how to control the beam quality of the amplified laser and how to avoid the damage of the devices in the amplifier due to the high peak power. there are three kinds of high gain amplifiers: optical fiber amplifier, regenerative amplifier and multipath traveling wave amplifier. the following table compares the advantages and disadvantages of the three amplifiers from several dimensions.
the advantage of the regenerative amplifier is that the gain of the amplifier is high and the >200uj single pulse energy output is easily obtained. the defect is that the structure of the magnifying cavity is complicated and the pulse timing is very strict. at the same time, it needs to join the electro-optic cavity emptying function. it is difficult to make, high cost, and not easy to control the stability.
the advantage of the multipath traveling wave amplifier is that the structure is simple, stable, reliable, low cost, high power output and high single pulse energy output easily. the defect is that the gain of single stage amplification is small and can reach 103-104. but it can gain the gain by increasing the enlargement series. most of the laser manufacturers are used at present. this kind of amplifier.
the advantage of the regenerative amplifier is that the gain of the amplifier is high and the >200uj single pulse energy output is easily obtained. the defect is that the structure of the magnifying cavity is complicated and the pulse timing is very strict. at the same time, it needs to join the electro-optic cavity emptying function. it is difficult to make, high cost, and not easy to control the stability.
the advantage of the multipath traveling wave amplifier is that the structure is simple, stable, reliable, low cost, high power output and high single pulse energy output easily. the defect is that the gain of single stage amplification is small and can reach 103-104. but it can gain the gain by increasing the enlargement series. most of the laser manufacturers are used at present. this kind of amplifier.
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fiber amplifier |
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boost gain |
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stability control |
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advanced control technology
besides the seed source and amplifier technology, the key technologies of picosecond laser include pump source drive and temperature control, pulse selection, pulse synchronization, data recording, power regulation and monitoring.
pump source driving and temperature control technology determine the power and wavelength stability of pump light, which directly affects the stability of output laser pulse. the pulse selection technology requires the modulator to have <10ns rise and fall time, and the pulse synchronization problem should be considered to avoid the pulse being cut off. data recording technology can understand all the data changes in the laser operation and track the usage state of the laser. power regulation and monitoring technology can adjust and monitor the output power of laser in real time, so it is essential in laser processing.
picosecond laser- bellin laser
since belline launched the first picosecond laser in 2013, more than 500 picosecond lasers have been used in industrial processing. at the beginning of 2017, a new generation of amber series of picosecond laser products was introduced. the product uses picosecond fiber seed source and multipath traveling wave amplifier to achieve high peak power picosecond laser output. the product covers picosecond infrared power 1-50w, picosecond green light power 1-25w. the width of the picosecond pulse is <15ps, and the beam quality is m^2<1.3. amber series lasers are equipped with advanced control system, laser integrated remote diagnosis, data recording, power regulation and monitoring functions to ensure the long and stable operation of laser, and meet the 24/7 application of industrial customers.
figure 1：50w picosecond laser amber ir-50 500h duper power curve
figure 2: 50w picosecond laser amber ir-50 beam quality test
