Laser-induced plasma-assisted ablation (LIPAA), in which a single conventional pulsed laser of small size is employed (typically 2<sup>nd</sup> harmonic of Nd:YAG laser), enables to process transparent materials like glass with micron order spatial resolution, high speed and low cost. In this process, a laser beam is first directed to a glass substrate placed in vacuum or air. The laser beam passes through the substrate since the wavelength of laser beam must have no absorption by the substrate for the LIPAA process. The transmitted laser beam is absorbed by a solid target (typically metal) located behind the substrate. The target is then ablated, resulting in plasma generation. Due to the interaction of the laser beam and the laser-induced plasma, significant ablation takes place at the rear surface of substrate. This process demonstrates surface microstructuring, crack-free marking, color marking, painting and selective metallization of glass. Based on these achievements, we have developed a prototype of workstation of LIPAA microfabrication system which is now commercially available. The discussion includes mechanism and practical applications in industry of LIPAA process.
Lithium Niobate is an important material in optical communication due to its special characteristics (high electrooptic coefficients and high optical transparency in the near infrared wavelengths). In this paper, we investigated the effects of 775-nm, femtosecond laser radiation on the Lithium Niobate crystal. By focusing the laser beam through a microscope objective, a certain refractive index change may be induced in Lithium Niobate substrate. Based on this effect, channel waveguides and other waveguide structures were fabricated. The output optical fields through them were measured, and the refractive index change of ~6×10<sup>-4</sup> was calculated with the Near-field Method. The properties of these waveguide structures were discussed. We also investigated the waveguides effect induced with different fabrication conditions. The experimental results revealed that different fabrication conditions affect the waveguide effect greatly.
Proc. SPIE. 5063, Fourth International Symposium on Laser Precision Microfabrication
KEYWORDS: Nanostructures, Femtosecond phenomena, Data storage, Fiber lasers, Atomic force microscopy, Near field scanning optical microscopy, Ultrafast lasers, Nanofabrication, Near field optics, Nanoprocess
We have developed the laser nanoprocessing technique by the integration of the ultrafast laser and near-field scanning microscopy (NSOM). The second harmonic femtosecond laser working in the optical near-field with the assistance of NSOM equipment was applied to expose the photosensitive polymer material. The nanopatterns with feature size smaller than the laser wavelength can be fabricated. The optical diffraction limitation is therefore broken through by the near-field nanoprocessing. It was found in our experiment that the nanofabrication feature size depends strongly on the gap between the fiber probe tip and the substrate surface, as well as the laser coupling efficiency. The approach offers the advantages of high precision, speed and selectivity in nanopatterning, and is promising to be used in data storage device manufacture for higher density recording.
A method for surface metallization on transparent substrate with laser induced plasma deposition was described. A laser beam goes through the transparent substrate first and then irradiates on a metal target behind. For laser fluence above ablation threshold for the target, the generated plasma flies forward at a high speed to the substrate and induces metal materials deposition on its rear side surface and even doping into the substrate. The diffusion distribution of metallic particles was measured with Time of Flight Secondary Ion Mass Spectrometer (TOF-SIMS). Electrically conducting films are formed on the substrate with laser beam scanning. The near 1Ω/Square lower resistivity can be formed with precise control of the processing parameters. Laser fluence, pulse repetition rate and scanning speed, distance between the substrate and metal target and overlapping of the metal lines. This technology can be used to form electrodes, resistors, LCD or electronic circuits on the transparent substrates.
Regular and tidy periodic structures hae been directly induced on glasses using a CW CO<sub>2</sub> laser beam with linear polarization. It is experimentally shown that precise periodic structures with the period of several microns can be formed by means of well-set laser parameters. The orientation of the periodic structures formed is the same as that of the laser polarization no matter what the scanning direction is. The occurrence of periodic structures is very sensitive to laser power level and scanning velocity. To obtain appropriate periodic patterns, a combined condition of laser energy and scanning velocity must be satisfied. The period, width and height of the structures are dependent on processing parameters. An interesting phenomenon is that the period decreases with increasing scanning velocity. Permanent relieves with periods, widths and heights varied with the laser parameters are also studied.
KEYWORDS: Femtosecond phenomena, Data storage, Magnetism, Fiber lasers, Atomic force microscopy, Near field scanning optical microscopy, Ultrafast lasers, Optical storage, Pulsed laser operation, Near field optics
We have explored the optical near-field technology for the fabrication of subwavelength-size binary bit by the combination of the femtosecond laser of the second harmonic output with the near-field scanning optical microscopy (NSOM). The photosensitive polymer material was exposed, and the nanopatterns with feature size smaller than the laser wavelenght can be generated. It was found that the feature size depends strongly on the gap between the fiber probe tip and substrate surface. The approach offers the advantages of high precision, speed and selectivity in nanopatterning, and is promising to be used in data storage device manufacture for high density data storage.
It is a high challenge to fabricate glass microstructures in Photonics and LCD industries. Different from direct ablation with ultrafast or short wavelength lasers, laser-induced-plasma-assisted ablation (LIPAA) is one of the potential candidates for transparent substrate microfabrication with conventional visible laser sources. In the processing, laser beam goes through glass substrate first and then irradiates on a solid target behind. For laser fluence above target ablation threshold, plasma generated from target ablation flies forward at a high speed. At a small target-to-substrate distance, there are strong interactions among laser light, target plasma and glass substrate at its rear side surface. With target materials deposition on glass surface or even doping into the substrate, light absorption characteristic at the interaction zone is modified, which causes the glass ablation. LIPAA is used to get color printing of characters, structures and even images on the glass substrate. It is also used to obtain the glass surface metallization for electrodes and circuits fabrication. Potential application of this technique to fabricate functional microstructures, such as micro-Total-Analysis-System (TAS) for DNA analysis and holographic diffuser for IR wireless home networking, is also discussed.
In this paper, we will describe a new method to fabricate optical diffractive gratings on glass surface with direct CW CO2 laser irradiation. A laser beam with linear polarization was focused and scanned on a glass substrate. The interaction of the beam with the material irradiated results in a periodic ridge structure formation on the substrate under a well-controlled laser irradiation dose. Using multi-path scanning method, with a suitable overlap, diffractive grating with large area can be achieved. In this experiment, laser irradiation dose was 50 J/cm2, laser scanning speed was 0.2 mm/s, the diameter of focused beam was 30 ?m, and the grating period was about 8 ?m.