In-system optimization of a hologram for high-stability parallel laser processing.

A method for optimizing a computer-generated hologram (CGH) for high-stability laser processing is proposed. The CGH is optimized during laser processing; therefore, unpredicted dynamic changes in the laser processing system, in addition to its static imperfections, are automatically compensated for by exploiting the rewritable capability of the spatial light modulator. Consequently, the short-term and long-term stability are improved, which will contribute to the realization of high-speed, high-precision laser processing. A CGH that generated 36 parallel beams was continuously optimized, and the maximum uniformity reached 0.98, which is higher than reported in previous research. To the best of our knowledge, this is the first demonstration of gradual improvement of parallel laser processing with in-process optimization of the CGH. Furthermore, it was also demonstrated that the performance of the laser processing system against unexpected disturbances was improved.

Sparse-exposure technique in holographic two-photon polymerization.

Holographic two-photon polymerization is based on a high-speed, low-loss parallel laser irradiation technique inside photosensitive materials using a computer-generated hologram displayed on a liquid crystal spatial light modulator. We demonstrated a sparse exposure technique combining parallel exposure and scanning exposure to improve the fabrication throughput and to achieve simultaneous fabrication of linear structures with different widths. We also demonstrated fabrication of space-variant structures by changing a CGH, as well as parallel fabrication of voxel structures with single femtosecond laser pulse irradiation.

Holographic femtosecond laser processing using optimal-rotation-angle method with compensation of spatial frequency response of liquid crystal spatial light modulator.

Holographic femtosecond laser processing performs high-speed parallel processing using a computer-generated hologram (CGH) displayed on a liquid crystal spatial light modulator. A critical issue is to precisely control the intensities of the diffraction peaks of the CGH. We propose a method of compensating for the spatial frequency response in the design of CGH using the optimal-rotation-angle method. By applying the proposed method, the uniformity of the diffraction peaks was improved. We demonstrate holographic femtosecond laser processing with two-dimensional and three-dimensional parallelism.