Industrial current situation of the development of high power semiconductor laser
High power and high beam quality is in laser material processing are two basic requirements.In order to increase the output power of high power semiconductor laser, a dozen or dozens of single pipe can be integrated laser chip encapsulation, forming laser article, article would multiple stacking can form laser two-dimensional fold, fold laser array of optical power can achieve kilowatt is even higher.But with the increase of semiconductor laser article number, the beam quality will drop.In addition, the particularity of semiconductor laser structure shaft beam quality is not consistent: fast, slow fast axis beam quality close to the diffraction limit, and the slow axis of the beam quality is poor, this makes the semiconductor laser is limited by a lot of in industrial application.In order to realize high quality, wide range of laser processing, laser must meet the high power and high beam quality at the same time.Now, therefore, developed countries will be the research and development of new high power, high beam quality of high power semiconductor laser as an important research direction, in order to meet the demands for higher laser power density of laser material processing applications.
The key technology of high power semiconductor laser including semiconductor laser chip epitaxial growth technology, semiconductor laser chip package and collimating optics, laser laser beam shaping technology and integration technology.
1. The semiconductor laser chip epitaxial growth technology
The development of high power semiconductor laser research design is closely related with its denotation chip structure.In recent years, the United States, Germany and other countries to invest in this aspect, and made major progress, is a world leader.And the first of all, the strain of quantum well structure, increase the photoelectric performance of high power semiconductor laser, reduces the threshold current density of the device, and expand the coverage of the emission wavelength of GaAs based materials is.Second, adopting aluminum active area to improve the transverse optical laser chip disaster damage optical power density, so as to improve the power output of the device, and increase the service life of the device.Moreover, a big wide waveguide optical cavity structure increased the size of the beam near field pattern, reduced the output optical power density, thereby increasing the output power, and extend the device lifetime.At present, the commercialization of the semiconductor laser chip of electro-optical conversion efficiency has reached 60%, electro-optic conversion efficiency in the laboratory for more than 70%, is expected in the near future, semiconductor laser chip of electro-optical conversion efficiency can reach above 85%.
2. The semiconductor laser chip package and optical collimation
Laser chip cooling and encapsulation is an important link in manufacturing high power semiconductor laser, because of the high power semiconductor laser output power is high, the light emitting area is small, its work when the heat generated by the density is high, the chip package structure and technology put forward higher requirements.At present, the international use copper heat sink, more active cooling way, brazing technology to realize the encapsulation of high power semiconductor laser array, depending on the encapsulation structure, and can be divided into the microchannel heat sink package and conduction heat sink encapsulation.
The special structure of the semiconductor laser causes the fast axis direction of the beam divergence Angle is very large, nearly 40 °, and the slow axis of divergence Angle is only about 10 °.In order to make the long distance transmission in order to facilitate the follow-up optical laser processing, the need for beam collimation.Due to the small size of semiconductor laser light emitting unit, at present, the international common collimating method is the collimating lens.Among them, the fast axis collimating lens is usually large numerical aperture micro-column aspherics, slow axis collimating lens is corresponding to each light emitting unit micro cylindrical lens.After fast axis collimation, fast axis direction divergence Angle can reach 8 mrad, slow axis direction divergence Angle can reach 30 mrad.
3. The semiconductor laser beam shaping technology
International common product of optical parameters is used to describe the beam quality of semiconductor laser, optical parameters of the product is defined as a direction on the spot radius and the direction of the product of the far field divergence half Angle.Optical parameters of the product determines the size of the laser beam quality, product of optical parameters, the smaller the beam quality, the better.Because of the particularity of the semiconductor laser structure fast and slow axis of beam quality, the difference is bigger, uniform distribution of light beam in order to get the space, the need for semiconductor laser beam shaping, in the light of the fast and slow axis parameters product homogenization.Many international adopt the method of beam splitting rearrangement for beam shaping, namely slow axis of the beam segmentation first, and then rotate rearrangement, reduce the slow axis of light spot size, increase the spot size fast axis direction, thus realize the fast and slow axis light homogenization parameters of the product.Has been reported the fast and slow axis of optical parameters of product homogenization of beam shaping methods mainly include: optical fiber beam shaping method, reflection, refraction plastic plastic, folding reflection shaping method, etc.
4. The semiconductor laser integration technology
Use of multiple beam space coupling, coupling of polarization, wavelength, the coupling beam and beam shaping technology, the increase of semiconductor laser output power at the same time with high beam quality of laser beam.At present, many companies and research institutes abroad with the method of combining a variety of coupling techniques, have realized the kilowatt power output.German company Laserline commercialization of direct output of semiconductor laser, the output power can be up to 10 kw, spot size 0.6 mm * 3 mm, beam quality 60 x 300 mm mrad, power density of 550 kw/cm2;The company's optical fiber coupled laser diode output reaches the end of the optical fiber continuous 10 kw output power, fiber diameter 1 mm, numerical aperture NA = 0.2, beam quality 100 mm mrad, power density of 1 mw/cm2.
