M. Lenzner

Sub-10-fs mirror-dispersion-controlled Ti:sapphire laser

We demonstrate the generation of nearly bandwidth-limited 8-fs optical pulses near 0.8 microm from a self-mode-locked Ti:sapphire laser oscillator, using chirped dielectric mirrors for dispersion control. The mode-locking performance is described, and limitations are discussed.

Generation of 0.1-TW 5-fs optical pulses at a 1-kHz repetition rate

A compact all-solid-state femtosecond Ti:sapphire oscillator¿amplifier system using no grating-based pulse stretcher produces 20-fs, 1.5-mJ pulses at a 1-kHz repetition rate. The pulses are subsequently compressed in a hollow-fiber chirped-mirror compressor. The system delivers bandwidth-limited 5-fs, 0.5-mJ pulses at 780 nm in a diffraction-limited beam.

Laser ablation of dielectrics with pulse durations between 20 fs and 3 ps

Laser‐induced ablation has been extended down to a pulse duration of 20 fs generated by a Ti sapphire laser system at a wavelength of 780 nm. Barium aluminum borosilicate glass with an extremely high glass transformation temperature (∼600 °C) served as target material. The most significant observation was a substantial decrease of the ablation threshold fluence at pulse durations below 100 fs. All results indicate a dominant role of multiphoton absorption in addition to collisional ionization in this time domain.

Sub-20-fs, kilohertz-repetition-rate Ti:sapphire amplifier

A simple four-pass Ti:sapphire amplifier is seeded by sub-10-fs pulses generated from a mirror-dispersion-controlled Ti:sapphire laser. Pulses of 17-18-fs duration with energies up to 50 and 100 microJ have been produced at repetition rates of 2 and 1 kHz, respectively. Because of the absence of a pulse stretcher, this performance is achieved from an extremely compact system.

Photoablation with sub-10 fs laser pulses

Ablation experiments in several glasses with single and multishot irradiation by laser pulses in the 10-fs pulse duration domain are presented; physical and technological implications are discussed. We demonstrate that these short pulses offer the potential for lateral and vertical machining precision of the order of 100 nm.

Laser micromachining of barium aluminium borosilicate glass with pulse durations between 20 fs and 3 ps

Laser-micromachining of high-tech glass has been extended down to a pulse duration of 20 fs generated by a Ti sapphire laser system at a wavelength of 780 nm. A systematic electronmicroscopic study shows that, below 100 fs, an extreme precision and a substantial decrease of the ablation threshold fluence with respect to pulse laser processing with pulses in the picosecond and nanosecond range could be achieved. The technical relevance of this novel microtechnology is discussed. The morphology of the ablated areas is not determined by thermal processes, i.e. the heat affected zone. It is controlled by non-linear optical coupling effects. Multi-photon absorption becomes highly efficient below laser pulse durations of 100 fs so that light penetration is minimized and ablation cavities become smooth. At longer pulse durations, a higher light penetration due to a lower number of non-linearly absorbed photons allows mechanical relaxation processes in the glass material leading to roughening.

Amplitude and chirp characterization of high-power laser pulses in the 5-fs regime.

Frequency-resolved optical gating (FROG) based on second-harmonic generation has been demonstrated to be capable of high-fidelity measurement of the electric-field envelope and of the temporal evolution of the instantaneous carrier frequency of 0.1-TW 5-fs pulses without the need for any correction for systematic experimental errors. At a 1-kHz repetition rate, pulse energies of a few microjoules are sufficient for reliable FROG characterization of pulses with durations down to the single-cycle regime. The results obtained reveal that carefully designed hollow-fiber chirped-mirror compressors are able to deliver high-power sub-10-fs pulses with a smooth Gaussianlike leading edge that has an intensity contrast of approximately 10(-2) .

Structuring of dielectric and metallic materials with ultrashort laser pulses between 20 fs and 3 ps

Laser-micromachining of barium aluminum borosilicate glass, fused silica and stainless steel has been extended down to a pulse duration of 20 fs generated by a Ti:sapphire laser system at a wavelength of 0.8 micrometer. A systematic study shows that, below 100 fs, an enhanced precision and a substantial decrease of the ablation threshold fluence in comparison to pulse laser processing with pulses in the picosecond and nanosecond range could be achieved. The physical mechanism and the technical relevance of this novel microtechnology is discussed.

Compact, high-throughput expansion-compression scheme for chirped pulse amplification in the 10 fs range☆

Abstract A novel pulse stretching-compression system suitable for kHz-rate chirped-pulse amplification of ≈10 fs pulses in Ti:sapphire systems is demonstrated. The material dispersion of the system components used for pulse selection and isolation broadens the wide-band seed pulses by a factor of ≈300, allowing amplification up to the submillijoule energy range. The compressor consists of a pair of prisms and newly-developed chirped multilayer dielectric mirrors for compensating high order dispersion. Using this simple scheme a recompression of unamplified pulses down to 15 fs with a throughput as high as 80% is demonstrated.

Femtosecond-pulse laser machining of semiconducting materials

Summary form only given. Machining investigations of crystalline silicon have been performed with laser pulses at a wavelength of 780 nm in the range between 5 fs and 400 fs. Applying 100 pulses per spot, surface damage thresholds were determined by the measurement of the damage diameter. In this pulse duration regime, the threshold fluences were nearly constant. Single-pulse investigations with 5 fs pulses yielded a value of about 0.15 J cm/sup -2/ identical to the multi-pulse experiment. This is in contradiction to the behaviour of dielectrics where incubation effects alter the optical properties down to the 5 fs pulse regime. Employing laser pulses with a duration of 130 fs at a wavelength of 800 nm, single-pulse ablation thresholds of 0.23 J cm/sup -2/ and 0.16 J cm/sup -2/ were determined for Si and InP in air, respectively. The threshold fluence was calculated from the linear relation between the square of the diameters versus the logarithm of the laser fluences.