Researchers at Osaka University have developed a technique to improve the precision of laser beam and wavefront shaping achieved by conventional methods at no additional cost by optimizing the virtual phase network . The results of their research have been published in Scientific reports.
A high-quality, flat-beam beam is sought in various fields, such as uniform laser treatment and medicine, as well as ultra-high intensity laser applications for accelerators and nuclear fusion. The shape of the beam is essential for achieving the capabilities and potential effects of the laser. However, since the shape of the beam and the wavefront vary with the laser, the shaping of the beam is essential to produce the desired shapes to meet various needs.
Static and adaptive beamforming methods have been developed for various applications. With the diffractive optical element (DOE) as the static method, the inclination and flatness of the edges are weak and the wavefront deforms after shaping. (Figure 1 (a)) In addition, the computer-generated hologram (CGH) as a typical adaptive method presents the same difficulties.
In parallel, an adaptive beamforming technique using a Spatial Light Modulator (SLM) coded phase grating with Spatiofrequency filtering in the Fourier plane in a 4f system has been developed. (Figure 2 (a)) This conventional method generates a square flat beam by spatially controlling the efficiency of diffraction without distorting the wavefront. However, since the extracted and residual components overlap in the Fourier plane, it was necessary to cut the high spatial frequency (HSF) component of the extracted component, thus limiting the flatness and stiffness of the edges of the shape of the resulting beam. (Figure 1 (b))
In this study, the group has developed a high precision, universal beamforming technique that can be used for different lasers from ultraviolet to near infrared.
This method spatially separates the residual and extracted components in the Fourier plane using a virtual diagonal phase network (Figure 2 (b)) and eliminates the overlap by making the grating vector, kg, non-parallel to the normal vectors, kx or ky, of the desired beam profile, which are parallel to each other in the conventional scheme.
By effectively using only the extracted components containing HSF components, high resolution beam shaping has been achieved. This made it possible to obtain a very uniform flat beam of any shape, without ripples, by eliminating the edge of the profiled beam at a height of 20 μm, which is less than 20% of that obtained with a classic vertical phase network.
Corresponding author, Yoshiki Nakata, said: "Our method, which optimizes beam shaping by improving resolution and accuracy, will contribute to a broad field, including basic research, manufacturing, and manufacturing. In conventional beam shaping systems, shaping accuracy can be greatly improved at no additional cost simply by modifying the SPF and phase grating encoded on an SLM. "
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More information:
Yoshiki Nakata et al. Using the High Spatial Frequency Component in Adaptive Beam Shaping Using a Virtual Diagonal Phase Network, Scientific reports (2019). DOI: 10.1038 / s41598-019-40829-7
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University of Osaka
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The quality of laser beam shaping can be improved at no additional cost (April 24, 2019)
recovered on April 24, 2019
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