Hanover laser center
Hannover laser center, Germany
Address:
No.8 Hollerie Street, Hanover, Germany, 304 19.
Telephone:
49-5 1 1-27 880
Fax:
49-5 1 1-278 8 100
E-mail:
info@lzh.de
Website:
www.lzh.de
Company profile:
LZH actively participates in research, development, consultation and training in all fields of laser technology.
Hanover Laser Center has been devoted to research, development, consultation and laser technology training in the field of laser technology.
2. The research direction of Hanover eV Laser Center: two-photon polymerization-a new micromachining method.
Three-dimensional micromachining of two-photon photosensitive materials polymerization is a very effective micromachining technology, which can produce 100nm or even better manufacturing resolution! Three-dimensional micromachining of two-photon photosensitive materials requires a near-infrared femtosecond oscillator (about 800nm) and a computer-controlled three-dimensional positioning system. In order to give full play to the inherent high resolution of two-photon polymerization, high-resolution and high-precision positioning systems are needed, such as operating table controlled by piezoelectric devices and scanning galvanometer. However, the piezoelectric device only has a moving range of several hundred microns in each direction. Therefore, although the optical scanning system can move the beam, it must deflect the writing beam through the outer edge of the focusing device, and this process can easily distort the image of the outer edge of the beam, resulting in energy loss.
Three-dimensional microstructure manufacturing system
In order to overcome the above limitations, the Laser Zentrum Hannover eV in Germany has developed an independent and movable three-dimensional manufacturing system in micro and nano scales. The system integrates a femtosecond laser, a scanning galvanometer for rapid small-area engraving and an electrokinetic linear positioning system (Aerotech). Femtosecond laser is a SESAM mode-locked Ti: sapphire femtosecond laser from Austria's High Q company, with an average power of 200mW, a wavelength of 800nm, a pulse width of less than 100fs and a repetition rate of 73MHz. The positioning system has three axes, and the stroke of each axis is 10cm. The 3D system also has a rotating shaft, which can process curved cylindrical structures. 3D femtosecond microstructure manufacturing system has been commercialized!
Two-photon polymerization micromachining has an X-Y two-dimensional scanning galvanometer, which deflects the light beam by oil immersion with high numerical aperture and focuses the femtosecond laser on the photosensitive material or resin (as shown in Figure 3). The scanning galvanometer is installed on the long-stroke X-Y positioning system. The equipment is equipped with CCD camera for real-time monitoring. The sample is placed on a two-dimensional translation stage.
By moving the beam waist in three dimensions with a scanning galvanometer and a translation table, a complex three-dimensional structure can be formed inside the resin. The writing accuracy based on scanning galvanometer is 100nm, while the accuracy of positioning system is higher than 400nm.
Negative photoresist and positive photoresist are two kinds of photosensitive materials that can be processed by two-photon polymerization. When negative photoresist is used, two-photon exposure will lead to cross-linking of polymer chains, so that unexposed areas can be removed. When using positive photoresist, exposure will cause chain breakage and produce small units that can be dissolved and removed. Most of the pore structure can be achieved by removing a small amount of debris from the sample. In this respect, positive photoresist is more effective.
Negative lithography materials can be divided into solid and liquid. As shown in fig. 4, the solid negative photoresist is an epoxy-based cationic activation material. Cationic activation system (such as commercial SU8 photoresist) interacts with light beam to generate acid. In this case, polymerization does not occur during laser irradiation, but during baking after exposure. This is a very important characteristic of cationic active photoresist, because the difference of refractive index between exposed area and unexposed area is very small, even negligible. This makes it possible to combine direct laser writing with holographic exposure technology.
Except for organic ceramics, liquid materials are basically propylene-based, and the polymerization reaction in the process of beam action is initiated by photoinitiator. In this way, the progress of the reaction can be monitored in real time.
Photonics application
Because of these optical properties, these polymer photosensitive materials can be used to manufacture micro-optical elements and devices, such as micro-prism arrays and diffractive optical elements.
The miniaturization of sub-wavelength optical elements requires newer technology. In the so-called "optical path", it is one of the means to change species by using surface plasmon gene polarization represented by metal as information carrier. (See "Nanophoton Indicator Cytoplasmic Gene", Photon Spectrum, 2006, 1+0). Surface plasmon polarization is the electromagnetic excitation diffusion between metal and insulator. He is on the surface of the insulator along the metal waveguide. These microstructures obtained by two-photon polymerization have been successfully realized on the gold surface.
Two-photon polymerization technology has developed rapidly and has been successfully applied to the micromachining of three-dimensional photonic crystals and photonic crystal templates. In particular, it allows any defects on the base layer, which is very important for practical application. Photonic crystals are periodic structures with alternating insulation constants in space.
In this microstructure, optical proliferation at a specific optical frequency (band gap) is excluded. If the insulation constant changes periodically in all directions, the microstructure is a three-dimensional photonic crystal. According to this topological relationship and the corresponding insulation constant relationship, the optical characteristics of photonic crystals can be set. Since Eli Yablonoviteh and Sajeev John put forward the concept of three-dimensional photonic crystals in 1987, photons have become a continuous research hotspot. However, it is still a challenge to make full three-dimensional photonic crystals in the visible range!
All-photonic bandgap photonic crystals need to know the microstructure of three-dimensional high refractive index materials. The most attractive method is to infiltrate the template with high refractive index material and then take it out. It is more difficult to make templates with the most negative photoresist, because this microstructure is very stable and difficult to dissolve in those materials. Fig. 7 is an example of a photonic crystal template made of SU8. In the case of using positive photoresist, this polymer material is weakly soluble and is a good place to make three-dimensional templates. The above picture is a scanning electron microscope image of a photonic crystal template made of S 18 13 photoresist.
Another way to make photonic crystals is to use a large proportion of inorganic/organic mixed photosensitive materials, as shown in Figure 7. In this way, three-dimensional inorganic microstructure can be made without copying the template! By proper heat treatment of inorganic/organic multicomponent materials, organic components can be directly removed from the three-dimensional microstructure made by laser, leaving inorganic components. In this way, two-photon polymerization technology (or more broadly, two-photon activation treatment) and thermal post-treatment technology can be used to make three-dimensional photonic crystal microstructure.
Two-photon polymerization technology has broad application prospects in the biological field, including tissue engineering, drug introduction, drug injection and medical sensing. In tissue engineering, we can make a three-dimensional microstructure operating table, and the micro-operating table needs to skillfully control the active tissue combined with the body tissue, which is a challenging job! Combined with suitable materials, two-photon polymerization can accurately control the three-dimensional micro-operating table and simulate the generation of cell microenvironment, as shown in Figure 8. More importantly, this high-resolution technology can control the cell tissue and even the interaction between cells in the whole micro-operating table. Another advantage is that the high-intensity near-infrared laser two-photon polymerization technology is harmless to cells, so it can also be used to control and package cells.
Ormocer is the most interesting material in biomedical applications. Recently, the biocompatibility of polymer has been studied. The results show that cells have good adsorption to this material and the growth rate is equivalent to that of bioactive materials.
Microneedle
Two-photon polymerization can also be used to manufacture complex drug injection equipment, such as microneedles and other devices. Micro-needle technology can overcome many shortcomings related to traditional injection methods, such as painless injection and avoiding physical injury at the injection site.
Moreover, the flexibility of the two-photon polymer completely changes the design of the needle, and its structural characteristics are shown in Figure 9. Microneedle injection technology is still in the process of further research.
3. Development status of laser industry
In Europe, Germany's laser industry is developing fastest, especially in the world's leading position in laser material processing.
1986, Germany put forward the BMFT funding plan of 1987- 1992 "Laser research and laser technology". During these five years, the actual investment was 262 million marks, and the key points and allocation of funds were: laser and components 36%, applied technology and system integration 48.9%, laser measurement and laser analysis 65,438. In other words, about 72% of the funds are used for laser material processing (light source, components, systems and methods).
The research group (FHG, MPG, GFE) consists of 6 research institutes, 9 large laser centers, and research groups of 30 university research institutes, with about 900 researchers participating. The famous research institutions and centers in this period are: Flawn Hof Laser Technology Institute, Berlin Solid-State Laser Institute, Hanover Laser Center, Stuttgart Beam Application Research Center, etc.
According to the statistics of German Machinery Manufacturing Association-Laser Materials Processing Alliance 1994, materials processing produced a total of 364 sets of light sources (CO2 and YAG lasers)/KLOC-0, with an output value of 165 million marks, which is higher than 1993/0/3%; The number of laser equipment has increased by 39%. In particular, YAG laser, a low-power laser used in marking and dentistry, has a disproportionate growth rate. Therefore, the laser used in processing technology in Germany is higher than ever before. German companies (mainly Rofin-sinar laser company, Trumpf laser technology company, Haas solid-state laser company, Lambda Physik company, etc.). ) accounts for almost 40% of the world market and is in a leading position. At the same time, we also signed an order contract for 1544 laser with a value of1770,000 marks.
The turnover of 1994 laser system has also increased significantly, and 860 systems have been produced, valued at DM 235 million, with a growth rate of 5 1% and a sales growth rate of 17%. At the same time, 937 system contracts worth DM 249 million were signed (the number of units increased by 58% and the output value increased by 18%), which was close to the predicted output 1995. As for the laser source, CO2 accounts for 42% and Nd:YAG accounts for 35%. In terms of laser system, CO2 laser processing system accounts for 56%, YAG laser processing system accounts for 40%, CO2 laser processing system is self-operated by Trumpf company, and Rofin-Sinar company cooperates with Grisham company to form Lascontur series laser processing machine. The growth of exports shows that German enterprises have strong competitiveness in the world, and the German laser industry is still on the rise.
After completing the funding plan of 1987- 1992 BMFT "Laser research and laser technology", Germany put forward a new funding plan of "Laser 2000" in 1993.
The strategic objectives are:
* Create the scientific and technological foundation in the field of laser technology in 2 1 century.
Support laser technology innovation, and maintain and strengthen the international competitiveness of laser production and laser industrial application.
* Eliminate scientific and technological barriers to laser applications. The future focus of laser research and laser technology;
* The basic key themes of the new generation laser are:
High power diode laser
diode pump solid state laser
New mechanism of high power gas laser.
* The key themes of precision machining are:
Evaluation of laser method
Laser induced production method
Ultraviolet laser photon technology
* Open the foundation for new application fields.
Laser optical measurement and detection method
Nonlinear optics, laser biodynamics and microprocessing (involving molecular and atomic range)
Laser optical measurement and detection of products and environmental protection technology
* The key theme of laser medicine is:
New laser scheme in medical technology
Optical tomography
Start and end time of funding plan: 1993- 1997 Funding amount: DM 275 million. In order to popularize laser processing technology, Germany has established a large number of laser processing stations in addition to nine national laser centers. At the same time, actively establish laser processing production lines in large, medium and small enterprises, such as the gear laser processing production line in Volkswagen factory; Mercedes-Benz Automobile Factory has 18 workshops, 8 of which are equipped with laser processing production lines; Thyssen steel company's laser tailor-welded production line for automobile floor; Siemens has established laser spot welding production lines for winding leads, laser welding production lines for contactor cores and armatures, laser trimming production lines for integrated circuits and laser texturing and annealing production lines for semiconductor silicon wafers. In "Laser 2000", it is specifically proposed that in 1994-95, 5 million marks (25 projects) will be provided every year, and 200,000 marks will be subsidized for each project for small and medium-sized factories that have approved laser processing technology projects.
This is the official website of Hanover Laser Center, Germany. You can click to view: http://www.laser-zentrum-hannover.de/de/index.php.