IFTA calculation of frequency patterns for acousto optical laser beam shaping

Abstract

Since high-power ultrashort pulsed (usp) laser sources are commercially available, customers are facing the issue of delivering high power appropriately onto their work piece. This results in an inefficient usage of the provided laser power. Current technologies allow either for fast deflection or spatial adaption of the laser beam. To access a fast temporal and spatial distribution of the laser power the use of the acousto optic (AO) effect was proposed and experimentally confirmed. While the usage of AO beam deflection is well known for decades, the application as a beam shaper is subject of current research. This technology is capable to operate at several MHz. Therefore, two orthogonal AO deflectors (AOD) are placed in the Fourier plane of a lens. If a proper acoustic signal is applied synchronized to the laser pulses, each pulse is affected by a quasistatic arbitrary grating. The desired intensity distribution can now be observed in the image plane of the lens. The AO deflectors are driven by a two-channel arbitrary waveform generator followed by an amplifier stage. In this paper we present an algorithm based on an Iterative Fourier Transform Algorithm (IFTA) to calculate the acoustic field from an input intensity distribution. The intensity distribution is projected in x- and y-direction to convert into two separated 1D-profiles. Via the IFTA the necessary phase delays for both directions are calculated. Then the corresponding acoustic signals are computed and hardware restrictions like the modulation bandwidths of the AOD and the signal generators are consider for the iterative optimization. Also the amplifiers amplitude response characteristics are taken into account. The resulting 2D intensity distribution is simulated by convolution of both signals. We present results of intensity distributions by AO beam shaping. The practical restrictions of achievable beam profiles of an AO beam shaping device are discussed. Finally we show micro structures generated by such a device.Since high-power ultrashort pulsed (usp) laser sources are commercially available, customers are facing the issue of delivering high power appropriately onto their work piece. This results in an inefficient usage of the provided laser power. Current technologies allow either for fast deflection or spatial adaption of the laser beam. To access a fast temporal and spatial distribution of the laser power the use of the acousto optic (AO) effect was proposed and experimentally confirmed. While the usage of AO beam deflection is well known for decades, the application as a beam shaper is subject of current research. This technology is capable to operate at several MHz. Therefore, two orthogonal AO deflectors (AOD) are placed in the Fourier plane of a lens. If a proper acoustic signal is applied synchronized to the laser pulses, each pulse is affected by a quasistatic arbitrary grating. The desired intensity distribution can now be observed in the image plane of the lens. The AO deflectors are driven by a two-c...