We proposed a novel THz generation technique beyond the limitation of the input optical pulse width, based on phase modulation via cascaded chi((2)) process. When intense THz electric field generated by optical rectification lies in electro-optic (EO) crystal, emitted THz field gives phase modulation to the optical excitation pulse. The phase modulation causes excitation pulse narrowing and consequently gives rise to the enhancement of conversion efficiency and THz wave bandwidth broadening. We experimentally realize this generation technique with high chi((2)) EO crystal LiNbO(3) and with subpicosecond pulse from Yb-doped fiber laser. It opens new concept of THz technologies.

We introduce an alternative approach of pulsed laser deposition (PLD) using groups of closely time spaced (20 ns) femtosecond laser pulses, namely burst-mode fs-PLD. This approach enables a broad and continuous tunability over the material morphologies ranging from nanoparticle aggregates to epitaxial thin films with completely droplet-free and atomically smooth surfaces. The tunability of materials is realized by simply tuning laser parameters. An unusual phenomenon of laser-matter interaction is revealed in terms of the breakdown of nanoparticles, the enhancement of plasma ionization, and the decrease of ablation threshold during the burst-mode fs-ablation. A TiO2 film, a wide band gap semiconductor, was deposited with as low as 50 nJ of pulse energy. This approach and the phenomenon are applicable to many other materials.

In this paper we study the influence of the processing wavelength on process efficiency and quality at picosecond microdrilling in steel. Possible optical setups for utilizing the second harmonic will be presented, and the influence of wavelength on the drilling rate will be discussed. The potential of helical drilling with the second harmonic in 1 mm thick CrNi-steel will be investigated with regard to process efficiency and hole quality. An analysis will be given of the role of particle-ignited atmospheric plasma and the relation between isophote contour and hole morphology. Our study reveals that a substantial enhancement of both precision and productivity can be achieved by using frequency-doubled instead of infrared radiation. It is shown that plasma ablation and melt production can be minimized by drilling with the second harmonic.

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IMRA's ultrashort pulse fiber laser products continue to evolve to expand the application scope. The latest prototype FCPA produces pulses with less than 500-fs pulse duration at a 50-kHz repetition rate. At the fundamental wavelength of 1045 nm, the pulse energy is greater than 10 µJ. The increase in pulse energy over the standard FCPA µJewel permits greater flexibility in the focusing conditions applicable for micromachining, enabling a wider variety of laser-machined structures and profiles. This paper describes the latest micromachining application areas being studied with this new laser.