Laser Zentrum Hannover e.V.
Laser Zentrum Hannover
Address:
Hollerithallee 8, Hannover 30419, Germany
Phone:
49- 511-27 880
Fax:
49-511-278 8100
E-mail:
info@lzh.de
Website:
www.lzh.de
Company Profile:
The LZH has been active in research, development, consulting and training in all fields of lasertechnology.
The LZH has been active in research, development, consulting and training in all fields of lasertechnology.
The Hanover Laser Center is dedicated to research, development, consulting and training in all fields of laser technology.
2. Laser Zentrum Hannover eV (Germany) research direction: two-photon polymerization - a new micromachining method
Two-photon photosensitive material polymerization three-dimensional micromachining is a very effective microfabrication technology, which can produce 100nm or better manufacturing resolution! In two-photon photosensitive material polymerization three-dimensional micromachining requires near-infrared femtosecond oscillators (around 800 nm) and a computer-controlled three-dimensional positioning system. In order to take advantage of the high resolution inherent in two-photon polymerization, high-resolution, high-precision positioning systems, such as piezoelectric device-controlled manipulators and scanning mirrors, are required. However, the piezoelectric devices have a range of movement of only a few hundred micrometers in each direction. Accordingly, although an optical scanning system can realize beam movement, it must deflect the written beam through the outer edge of the focusing device, a process that can easily distort the image of the outer portion of the beam, resulting in energy loss.
3-D Microstructure Fabrication System
To overcome these limitations, the Laser Zentrum Hannover eV has developed a self-contained, mobile 3-D fabrication system at the micron and nanometer scales. The system integrates a femtosecond laser, a scanning galvanometer for fast small-area inscription and a motorized linear positioning system (Aerotech). The femtosecond laser is a SESAM mode-locked, titanium-jeweled femtosecond laser from High Q, Austria, with an average power of 200 mW, a wavelength of 800 nm, a pulse width of less than 100 fs, and a repetition frequency of 73 MHz. The positioning system has three axes with a travel of 10 cm each, and the 3-D system also has a rotary axis that can process curved cylindrical structures. The 3D femtosecond microstructure fabrication system has been commercialized!
For two-photon polymerization micromachining, there is an X-Y two-dimensional scanning galvanometer that utilizes an oil immersion with a high numerical aperture to deflect the beam and focus the femtosecond laser onto a photosensitive material or resin (shown in Figure 3). The scanning galvanometer is mounted on a large travel X-Y positioning system. A CCD camera is mounted on the device to facilitate real-time monitoring. The sample is placed on a two-dimensional translation stage.
Using the scanning galvanometer and the translation stage to move the girdle in three dimensions, complex three-dimensional structures can be formed inside the resin. The accuracy of this scanning galvanometer-based writing is 100 nm, while the accuracy of the positioning system is higher than 400 nm.
Negative and positive photoresists are two types of photosensitive materials that can be processed by two-photon polymerization. With negative photoresists, two-photon exposure results in cross-linking of the polymerized chains, allowing for the removal of unexposed areas. When positive photoresists are used, the exposure causes breakage of the chains, creating small units that can be dissolved and removed. Most of the pore structure can be achieved by removing small fragments from the sample, and in this respect, positive photoresists are somewhat more efficient.
Negative lithography materials can be categorized as either solid or liquid. Solid-state negative photoresists are epoxy-based cation-activated materials, as shown in Figure 4. The cation-activated system (e.g., the commercially available SU8 photoresist) produces an acid when it interacts with the light beam. In this case, the polymerization occurs not during laser radiation, but during baking after exposure. This is a very important property of cationic reactive photoresists because the difference in refractive coefficients between exposed and non-exposed regions is so small as to be negligible. This makes it possible to combine direct laser writing with holographic exposure technology.
Liquid materials, with the exception of organochemical ceramics, are basically acrylated, and the polymerization reactions that occur during the action of the beam are triggered by photoinitiators. This allows the state of the reaction to be monitored in real time.
Photonics applications
Because of these optical properties, those polymer photosensitive materials can be used in the fabrication of micro-optical elements and devices, such as micro-prism arrays, diffractive optics, and so on
More sub-wavelength sizes of miniaturized optical elements require newer technologies. The use of metal-indicated surface plasmonic gene polarization as an information carrier in a so-called "optical circuit" is one such means. (See "Expression of plasmonic nanophotons", Photonics Spectra, 2006, Issue 1). Surface plasmonic gene polarization is an electromagnetically excited proliferation between or among metals and insulators. He carries certain information, such as bending or splitting, on the insulator surface along the metal waveguide, or on the metal surface along the insulator. These microstructures obtained by two-photon polymerization have been successfully realized on gold surfaces.
Two-photon polymerization is rapidly developing and has been successfully applied to the micromachining of three-dimensional photonic crystals and templates for photonic crystals. In particular, it allows the presence of any defects on the substrate, which is essential for practical applications. Photonic crystals are periodic structures with spatially alternating insulating constants.
In such microstructures optical accretion at specific optical frequencies (energy gap bands) is excluded. If the insulating constants change periodically in all directions, the microstructure is a three-dimensional photonic crystal. Depending on this topological relationship and the corresponding insulating constants, the optical properties of the photonic crystal can be set. Since Eli Yablonoviteh and Sajeev John introduced the concept of three-dimensional photonic crystals in 1987, photonics has been a continuing research interest today, although fabricating fully three-dimensional gap-band photonic crystals in the visible range is still a challenge!
Recognizing all-photonic gap-band photonic crystals requires the microstructure of three-dimensional high refractive index materials. The most attractive approach is to penetrate a fabricated stencil with a high refractive index material and then remove the stencil. It is even more difficult to make the stencil using the most negative photoresist, because the microstructure is very stable in those materials and does not dissolve easily. Figure 7 shows an example of a photonic crystal stencil made with SU8, where the polymer is weak and soluble with positive photoresists. This is a good place to make a three-dimensional template. The image above shows a scanning electron microscope image of a photonic crystal stencil made with S1813 photoresist.
Another way to make photonic crystals is to use a hybrid inorganic/organic photosensitive material that contains a high percentage of inorganic/organic material, as shown in Figure 7. With this approach, it is possible to bypass the replica template step and create three-dimensional inorganic microstructures! By appropriate thermal treatment of inorganic/organic multimaterials, it is possible to remove the organic components and leave the inorganic components directly from the laser-produced three-dimensional microstructures. In this way, two-photon polymerization (or more broadly, two-photon activation processing) and thermal post-processing techniques can be used for 3D photonic crystal microstructure fabrication.
Two-photon polymerization technology has promising applications in the biological field, including tissue engineering, drug delivery, medical injection, and medical sensing. In tissue engineering, it is possible to generate three-dimensional microstructured surgical tables that require dexterous manipulation of the active tissues in the body that are bound to the body tissues, which is a challenging task! Combined with suitable materials, two-photon polymerization can precisely manipulate this three-dimensional microsurgical table, which can simulate and generate cellular microenvironments, as shown in Figure 8. What's more, this high-resolution technique allows for the control of cellular organization throughout the microsurgical table, and even cell-to-cell interactions. A further benefit is that the intensity of the near-infrared laser two-photon polymerization used is not harmful to the cells, and therefore can also be applied to manipulate and package the cells.
Ormocer is the most interesting material for biomedical applications. Polymer biocompatibility has recently been studied and the results have shown that cells adsorb well to this material and have a growth rate comparable to that of biologically active materials.
Microneedles
Two-photon polymerization can also be applied to the manufacture of complex drug injection devices such as microneedles. Microneedle technology can overcome many of the drawbacks associated with traditional injection methods, such as painless injections and avoiding muscle damage at the injection site.
Additionally, the flexibility of two-photon polymers has led to a complete overhaul of the needle design, the structural properties of which are shown in Figure 9. The microneedle tip injection technique is still in the process of further research.
3. Status of Laser Industry Development
The fastest growing laser industry in the European region is Germany, especially in laser material processing is in the world's leading position.
In 1986, Germany put forward the 1987-1992 "laser research and laser technology" funding priorities of the BMFT funding program, the actual investment in the five-year period of 262 million marks, funding priorities and funding allocations: 36% of the lasers and components, application technology and system integration 48.9%, 12.2% of the laser measurement and analysis of lasers and other 2.3%; that is, about 72% of the funding for the development of laser industry
In Europe, the fastest development of the laser industry is Germany, especially in the world's leading edge of laser material processing. In other words, about 72% of the funding goes to the subject of laser material processing (light sources, components, systems and methods).
Six research institutes of the research groups (FHG, MPG, GFE), nine large laser centers, 30 research groups in university institutes, and about 900 researchers participated in the project. The more famous institutes and centers established during this period are: Fraunhofer Institute for Laser Technology, Berlin Institute for Solid-State Laser Research, Hanover Laser Center, Stuttgart Center for Applied Beam Research and so on.
According to the 1994 statistics of the German Mechanical Engineering Association (DMA), the total number of light sources (CO2 and YAG lasers) used for material processing was 1,364, with an output value of 165 million marks, an increase of 13% over 1993; the number of laser devices increased by 39%. 39%. Particularly the low-power lasers used in marking and dentistry, i.e. YAG lasers, showed a disproportionate growth rate. As a result, the number of lasers used in process technology in Germany is higher than at any time in the past. German companies (mainly Rofin-sinar Laser, Trumpf Laser Technologies, Haas Solid State Lasers, Lambda Physik, etc.) lead the world market with almost 40% of the light sources used for material processing. At the same time, contracts were signed for 1,544 lasers worth DM 177 million.
The turnover of laser systems also increased considerably in 1994, with the production of 860 systems worth DM 235 million, an increase of 51% in the number of units and 17% in sales. At the same time, 937 systems worth DM 249 million were contracted (58% growth in the number of units and 18% growth in the value of production), which is close to the production volume forecast for 1995. In terms of laser light sources, CO2 accounted for 42% and Nd:YAG for 35%; in terms of laser systems, CO2 laser processing systems accounted for 56% and YAG laser processing systems for 40%, with the CO2 laser processing system being supplied by Trumpf and the Rofin-Sinar laser processing system being supplied by Rofin-Sinar in cooperation with the Griesheimer GmbH, which has resulted in the Lascontur series of laser processing machines. The Lascontur range of laser processing machines has been formed. The growth in the export sector shows that German companies are competitive internationally and that the German laser industry is still on the rise.
After the completion of the 1987-1992 BMFT "laser research and laser technology" funding program, Germany in 1993 proposed a new "laser 2000" funding program.
The strategic objectives are:
* To create the scientific and technological basis for laser technology in the 21st century.
* Support innovation in laser technology to maintain and enhance international competitiveness in the production of lasers and their industrial applications.
* Remove scientific and technological barriers to laser applications. Future Priorities in Laser Research and Laser Technology:
* Fundamentals of Next-Generation Lasers Key topics include:
- High-power diode lasers
- Diode-pumped solid-state lasers
- New mechanisms for high-power gas lasers.
* Precision Processing The key topics are:
- Evaluation of laser methods
- Laser-induced production methods
- Ultraviolet laser photonics
* Fundamentals of pioneering new fields of application
- Optical measurement and detection methods for lasers
- Nonlinear optics - Laser bio-dynamics and microprocessing (covering the Non-linear optics - Laser biodynamics and microprocessing (in the molecular and atomic range)
- Laser optical measurement and inspection of products and environmental technologies
* Laser medicine The main topics of focus are:
- New laser solutions for medical technology
- Optical tomography
Funding program start and end date: 1993-1997 Funding: DM 275 million Germany's efforts to promote laser processing technology have not only led to the establishment of nine laser centers, but also to the development of a new laser technology. Germany in order to promote the laser processing technology, in addition to the establishment of nine national laser centers, but also a large number of laser processing stations; at the same time, in large, medium and small enterprises to actively establish laser processing production lines, such as: Volkswagen automobile factory gear laser processing production line; Mercedes-Benz automobile factory *** there are 18 plants, of which eight plants are installed in the laser processing production line; Thyssen steel company's sedan floor laser welding production line; Siemens company set up a laser processing production line; the car floor laser welding production line; the company set up a laser processing production line. Thyssen Steel laser welding production line; Siemens established a wire wrapped lead laser spot welding production line, contactor core, armature laser welding production line, integrated circuit laser fine-tuning production line and semiconductor wafer laser gross and annealing production line and so on. In the "laser 2000" in particular, 94-95, 5 million marks a year (25 projects), to the approval of laser processing technology projects in small and medium-sized factories funded 200,000 marks each project.
This is the official website of the Laser Center Hannover, Germany, which can be found at http://www.laser-zentrum-hannover.de/de/index.php
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