Laser beam shaping, i.e., modulation of the phase, mode and amplitude of a laser beam, is an important technology that enables many practical laser applications. Specific laser beam modes, such as Airy beam, Bessel beam and Laguerre-Gaussian (LG) beam, enable critical applications in optical manipulation, biomedical imaging, laser fusion and material processing etc. Accordingly, various beam shaping techniques have been proposed and developed. The most effective and common laser beam shaper is designed with a spatial light modulator (SLM). For example, a liquid crystal (LC)-based SLM achieves arbitrary beam shaping with good efficiency and resolution for both continuous-wave (CW) and pulsed lasers. Alternatively, beam shapers can be designed with a deformable mirror (DM) device, which can generate arbitrary phase or amplitude profiles. Although the aforementioned methods are effective and commercially available, they are limited by the shaping rate and resolution, i.e., the LC-SLM can only operate at 100 s Hz and a typical DM device has less than 10,000 pixels.
A digital micromirror device (DMD) can be considered as a programmable binary mask, consisting of several million micromirrors. Each micromirror is an independent pixel with two stable angular positions, i.e., ±12°. Recently, the DMD has been reported to shape continuous wave (CW) lasers. The DMD is a promising device for next-generation laser beam shapers for the following reasons: (1) broad wavelength range, i.e., from ultraviolet (˜320 nm) to far infrared (2500 nm) with appropriate coatings; (2) high pattern rate, up to 32.5 kHz; (3) high damage threshold; and (4) insensitivity to polarization. Despite these advantages, applications of DMD in beam shaping methods have been limited to CW lasers to date due to the complexity involved in compensating the dispersion in pulsed lasers.
As ultrafast lasers such as femtosecond lasers are essential to a myriad of scientific and industrial applications, e.g., two-photon excited (TPE) microscopy, second-harmonic generation, laser filamentation, micro machining and light bullet generation, new high-speed and high resolution femtosecond beam shaping technologies may facilitate a multitude of new scientific studies and applications. The extension of DMD technologies to ultrafast lasers can thus advance the performance limit of conventional beam shaping methods.
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