Programmable focal spot shaping of amplified femtosecond laser pulses

Abstract

We describe the programmable spatial beam shaping of 100-kHz, 4-microJ amplified femtosecond pulses in a focal plane by wave-front modulation. Phase distributions are determined by a numerical iterative procedure. A nonpixelated optically addressed liquid-crystal light valve is used as a programmable wave-front tailoring device. Top-hat, doughnut, square, and triangle shapes of 20-microm size are obtained in a focal plane. Their suitability for femtosecond laser machining is demonstrated.

On focused fields with maximum electric field components and images of electric dipoles

“…The focused wavefront can be tailored by setting a proper amplitude, phase and polarization distributions in the pupil of the focusing lens [10,11]. Nowadays it is possible to realize almost any complex transmission function in the pupil plane, using for example liquid crystal-based devices [12][13][14][15].…”

Field in Focus with a Maximum Longitudinal Electric Component

“…The optimum pupil field is found to be radially polarized; however, the amplitude is not of doughnut type but increases monotonically with distance to the optical axis in a way that depends on the numerical aperture. This pupil field is easy to realize using, for example, liquid crystal-based devices [13][14][15][16]. The full-width-athalf-maximum of the squared amplitude of the maximum longitudinal component is, depending on the numerical aperture, 15% to 30% less than that of the classical Airy spot.…”

Advances in Femtosecond Micromachining and Inscription of Micro and Nano Photonic Devices

“…The pulses typically have a low M 2 factor (ISO Standard 11146, 2005); more details on this are covered in section 4. This allows the pulses to be shaped easily through a number of techniques (N. Sanner et al, 2005). However, complex pulse shaping is not typically applied in most systems.…”