Harnessing polarization spatio-temporal coupling: a new degree of freedom in ultrafast laser material processing

Abstract

Polarization spatio-temporal coupling reveals new degree of freedom in ultrafast laser material processing. Control of modification in fused silica is demonstrated with the use of prism compressors and polarization azimuth of ultrashort pulse laser beam.OCIS codes: (140.3390) Laser material processing; (320.7120) Ultrafast phenomenaThe nanostructuring of transparent media with ultrafast laser pulses has attracted significant interest due to its unique applications. However, little is understood with respect to the physics of light-matter interaction. While most of the formalism for ultrashort pulses expresses the electric field separately in terms of temporal and spatial dependences, one of the major properties of ultrashort pulse generation is spatio-temporal distortions. Studies have shown spatio-temporal induced phenomena with respect to writing direction [1,2] and anisotropic photosensitivity [3] all based around pulse front tilt (PFT) yet they lack the control and understanding of the orientation, direction and quantity of the spatio-temporal distortions. Here we demonstrate the control and characterization of spatio-temporal distortions and PFT with the use of prism compressors in order to control and understand ultrafast phenomena associated with material modification. We also demonstrate anisotropic photosensitivity in fused silica for the first time, to the author's knowledge, which adds an additional level of control with respect to laser material modification. and 10000 pulses when polarization is parallel (0°) and perpendicular (90°) to PFT (Pulse Energy = 1.2 μJ, NA=0.65, PFT = 13.5 fs/mm)A mode-locked regenerative amplified Ytterbium doped Potassium-Gadolinium Tungstate (Yb:KGW) based femtosecond PHAROS laser system (Light Conversion Ltd.) was used in conjunction with a non-collinear optical parametric amplifier (NOPA) to generate femtosecond pulses at 700 nm with 200 kHz repetition rate. A prism compressor in a double pass geometry is used to control the temporal chirp and pulse duration. The laser is then sent to a stage set-up where the laser is focussed into the bulk of fused silica with a 0.65 NA objective lens. A λ/2 waveplate is used to control the polarization orientation with respect to the PFT. The pulses are characterized using a ThorLabs Pulse Characterization FROG Scanning Module; a SHG-based FROG. The ThorLabs based retrieval software measures the trace and reconstructs the electric field to provide the pulse duration and the group delay