Simultaneous spatio-temporal focusing describes the technique of spectrally dispersing an ultrashort pulse to increase it’s duration, before recombining all the spectral components to reform the short pulse at the focus of a lens. This has several advantages for optical applications using ultrashort pulses, enabling a focus with large lateral extent but displaying much greater axial confinement than with conventional focussing. Meanwhile non-linear propagation inside samples is also minimised. We extend the technique to generate multiple SSTF focal spots via holography. In contrast to previous implementations, a phase hologram is placed in the ultrafast beam while it is spatially chirped. Thus, we show that it is possible to create multiple focal spots formed by SSTF arranged in three dimensions. Demonstrations are given for ultrashort pulse laser machining on the surface and inside glass. Furthermore, due to the strong pulse front tilt exhibited by an SSTF spot, we show how multiple spots can be stitched together in space and time to generate extended intensity distributions. Spatially overlapped regions can be overlapped in time using the property of pulse front tilt such that holographic arrays of SSTF spots can be created with apparently no spatial separation.
Patrick S. Salter, Bangshan Sun, Clemens Roider, Alexander Jesacher, Johannes Strauß, Johannes Heberle, Michael Schmidt, and Martin J. Booth, "Parallelized SSTF-overlapping foci in space and time (Conference Presentation)," Proc. SPIE 10549, Complex Light and Optical Forces XII, 105490O (Presented at SPIE OPTO: January 31, 2018; Published: 14 March 2018); https://doi.org/10.1117/12.2291482.5751529326001.
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Study of self-shadowing effect as a simple means to realize nanostructured thin films and layers with special attentions to birefringent obliquely deposited thin films and photo-luminescent porous silicon