Abstract
A complex modulation algorithm for focusing beam shaping with a phase-only spatial light modulator is designed. This method modulates the amplitude and phase of a collimated beam synchronously, and the modulated beam passing through an objective lens will generate a shaped focusing beam. The characteristic of the complex modulation was studied, while the Mixed-Region Amplitude Freedom (MRAF) method was selected as a comparative reference in this research. In the theoretical simulation, the complex modulation shows excellent performance with a roughness of 0.32% RMS and 0.54% MAX. Otherwise, to further verify this complex modulation algorithm, an experiment was implemented to generate a square-shaped focusing flattop beam. The complex modulation generated a flattop beam with a roughness of 3.1% RMS and 6.1% MAX, better than the MRAF method. This result also proves that this complex modulation has better robustness.
Highlights
There are numerous research studies on the collimated beam shaping with the SLM,7–9 a collimated flattop beam passing through a focal lens will not generate a flattop focusing beam
The Mixed-Region Amplitude Freedom (MRAF) algorithm has an iterative Fourier transform and is a variant of the GS algorithm where the constraint applied to the image plane is split into two regions: a signal region that contains the target intensity pattern information and a noise region that utilizes the remainder of the area to restore the high frequency
The simulation results of the comparison of MRAF and complex modulation algorithms are shown in Fig. 2.23 The first row shows the results of the MRAF algorithm of the desired 60 pixel square pattern
Summary
The high-precision machining of sensitive materials requires good uniformity of the focusing beam in laser processing. The beam shaping method is a suitable way of generating a flattop beam with different shapes in laser processing. The SLM (Spatial Light Modulator) can transform the shape conveniently and quickly as the electrical input signal is changed, which is used in the beam shaping research. there are numerous research studies on the collimated beam shaping with the SLM, a collimated flattop beam passing through a focal lens will not generate a flattop focusing beam. Because the modulated collimated beam will generate a shaped focusing beam through an F-theta lens, this modulation in the optical pupil can fit the galvanometer and reduce the machining system size, unlike the object imaging (geometric masks) method, which requires a very long object distance to obtain a small focal spot.. There are no reports on the optical pupil function realized by the complex modulation, especially in the application of generating a focusing flattop beam. For this purpose, we present a new complex. Scitation.org/journal/adv modulation algorithm that intends to encode the full complex pupil field using a phase-only SLM to generate a shaped focusing flattop beam by combining phase retrieval, which was applied to evaluate wavefront aberrations in the Hubble telescope.. Scitation.org/journal/adv modulation algorithm that intends to encode the full complex pupil field using a phase-only SLM to generate a shaped focusing flattop beam by combining phase retrieval, which was applied to evaluate wavefront aberrations in the Hubble telescope. A comparison with the MRAF algorithm, previously adapted to laser micro-machining, is presented to benchmark the algorithm
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