A frequency doubled femtosecond Ti: sapphire laser at a wavelength of 400 nm, a pulse width of 160 fs, and a repetition rate of 1 kHz was used with a computer controlled galvo head to write periodical structures in Si <100>. Laser pulses of ∼130 nJ were focused using an objective lens of 0.65 NA. Laser parameters were optimized for efficient submicron ablation, yielding 700 nm wide by 600 nm deep lines. 1-D and 2-D periodical structures of 5 and 5x5 micron periods, respectively, were fabricated and examined using optical and atomic force microscopy. The quality of the 1-D and 2-D structures was highly depended on the light polarization orientation with respect to micromachining direction. With optimized fs laser parameters, high quality 1-D and 2-D periodical structures were obtained, which would have applications in optical devices.

ZnO based semiconductors have emerged as promising materials for energetic photon detection. Aimed to improve photon detection efficiency, we have successfully grown ZnO nanowires based on vapor- liquid-solid approach. In this paper, we examine the influence of oxygen partial pressure on the quality ZnO nanowires. Optical properties of the nanowires grown under different oxygen environment were characterized, and we found that low oxygen partial pressure can result in large concentration of defect states, as reflected by increased visible emission and an elevated threshold for stimulated emission.

Our recent progress in the direct-write femtosecond laser material processing technologies, nanostructuring, and fabrication of photonic devices is reviewed. Special attention is given to the sub-wavelength microstructuring of metals and two-photon polymerization (2PP) technique. Formation of microbumps and nanojets on thin metal films under single pulse laser irradiation is discussed. Microstructuring of different photosensitive materials by 2PP technique is demonstrated. Numerous applications of this technology for the fabrication of 3d structures, waveguides, photonic crystals, etc. are studied.

Laser cutting and welding are well established industrial applications. To maintain productivity and to guarantee product quality the industry tries to introduce monitoring and control systems. The long term goal is the autonomous laser machine. Signal assessment is advancing by monitoring and simulation of the dynamical processes. Applying the advanced results about diagnosis and modelling broadens the potentials to cope with productivity and quality features in drilling, trepanning and fine cutting.

As result, in cutting two mechanisms for the formation of adherent dross are revealed theoretically, identified by the monitoring system and can be avoided by modulation of the laser beam power. In welding, the dynamic model predicts the formation of pores sets in or is suspended depending on modulation frequency for the laser power. In drilling the mechanisms governing the maximum depth of the drilled hole – still showing efficient melt removal – are identified experimentally and can be related to the processing parameters theoretically

Femtosecond laser irradiation has various noticeable effects on fused silica. It can locally increase the index of refraction or modify the material chemical selectivity. Regions that have been exposed to the laser are etched several times faster than unexposed regions. Various observations reported in the literature seem to show that these effects are possibly related to a combination of structural changes and the presence of internal stress. However, a detailed analysis of the contribution of both effects is still lacking.

In this paper, we present systematic SEM-based investigations performed on fused silica (a-SiO2). Line-patterns were first scanned on the substrate using a femtosecond laser and then etched in a low-concentration HF solution. The effects of various laser parameters like power and scanning speed are analyzed and we show further evidence of an interface between two different etching regimes.

The results on laser shot peening and its characterization for Inconel 600 are presented. Using an X-ray diffraction technique we show that the residual compressive stresses can be successfully induced in Inconel 600 with parameters of laser peening, which are close to that of 316L stainless steel. The on-line monitoring system involving the acoustic pulse measurements is described for quality control of laser shot peening process. We found that sample scanning during laser processing results in a system of column-like microstructure, which is tilted in direction of scanning. The features of optical properties of tilted microstructure are described. We revealed that the base material injected into the confining water due to laser ablation is transformed to spherical nanoparticles with diameter of 60 nm.

Multiphoton absorption has become a powerful technique for the creation of three-dimensional micro- and nanostructures. Here we review some of our recent progress towards creating functional microdevices with multiphoton absorption. Specific thrusts of our research include development of new resins for multiphoton absorption polymerization, design of novel schemes for metal deposition, and post-fabrication ablation of polymeric structures.

The microscopic origin of unconventional superconductivity1 is one of the most fascinating questions2–3 in condensed matter physics. In recent years, important questions have been raised about the nature of the normal (metallic, non-superconducting) state above the superconducting critical transition temperature (Tc). In fact, it is now generally agreed4,5 that a better understanding of the nature of the normal state is crucial to our understanding of the microscopic origin of the superconducting state.

Pulsed laser deposition (PLD) has been applied to fabricate thin films of a variety of materials. However, formation of micron-sized particulates during conventional nanosecond laser-based deposition process makes it unsuitable for growing high quality nanoscale materials. Owing to a nonequilibrium non-thermal ablation mechanism and characterized by their short pulse duration compared to thermal diffusion time (tens of picoseconds), ultrafast laser pulses are able to produce particulate-free precursor vapor for nanoscale material deposition. In this article, the foundation of non-thermal ultrafast laser ablation will be examined by both experimental and theoretical investigations. Ultrafast laser-induced high-density electron ejection and subsequent build -up of a strong electric field above the target material were observed. Mass spectrometry and electron microscopy measurements confirmed the particulate-free nature of ultrafast laser ablation. Using ultrafast laser-based particulate-free PLD approach, high quality ZnO nanowires were grown on sapphire and silicon substrates. The optical properties of ZnO nanowires, including the external and internal quantum efficiency of nanowire nanolasers, were experimentally determined. In addition, a nanowire UV photodiode based on p−Si/n−ZnO nanowires was successfully fabricated. This first nanowire photodiode device shows good photocurrent characteristics when operated under reverse bias.

Diode laser pumped solid-state lasers such as rod, disk or slab lasers are on the way to govern as new systems developed in the last years the applications of laser radiation for various applications in innovative technologies. The laser radiation is used either as a tool for materials processing or as a source for radiation generation beside of applications in life science, environment, medicine, analytics, and others. The state-of-the-art of diode laser pumped solid state lasers is described highlighting beam quality, efficiency, mean time between failure, and compactness in order to discuss new laser radiation governed processes aimed for rapid manufacturing by rapid prototyping via selective laser melting, surface cleaning, surface polishing, and generation of EUV radiation.

A new THz/IR/UV photon source at Jefferson Lab is the first of a new generation of light sources based on a Energy-Recovered, (superconducting) Linac (ERL). The machine has a 160 MeV electron beam and an average current of 10 mA in 75 MHz repetition rate hundred femtosecond bunches.

These electron bunches pass through a magnetic chicane and therefore emit synchrotron radiation. For wavelengths longer than the electron bunch the electrons radiate coherently a broadband THz ∼ half cycle pulse whose average brightness is > 5 orders of magnitude higher than synchrotron IR sources. Previous measurements showed 20 W of average power extracted[1]. The new facility offers simultaneous synchrotron light from the visible through the FIR along with broadband THz production of 100 fs pulses with >200 W of average power (see G. P. Williams, this conference).

The FELs also provide record-breaking laser power [2]: up to 10 kW of average power in the IR from 1 to 14 microns in 400 fs pulses at up to 74.85 MHz repetition rates and soon will produce similar pulses of 300–1000 nm light at up to 3 kW of average power from the UV FEL. These ultrashort pulses are ideal for maximizing the interaction with material surfaces. The optical beams are Gaussian with nearly perfect beam quality. See www.jlab.org/FEL for details of the operating characteristics; a wide variety of pulse train configurations are feasible from 10 microseconds long at high repetition rates to continuous operation.

The THz and IR system has been commissioned. The UV system is to follow in 2005. The light is transported to user laboratories for basic and applied research. Additional lasers synchronized to the FEL are also available. Past activities have included production of carbon nanotubes, studies of vibrational relaxation of interstitial hydrogen in silicon, pulsed laser vapor deposition, nitriding of metals, and energy flow in proteins. This paper will present the status of the system and discuss some of the opportunities provided by this unique light source for modifying and studying materials.

We describe a > 100 Watt broadband THz source that takes advantage of the relativistic enhancement of the radiation from accelerating electrons according to the formula assigned the name of Sir Joseph Larmor[1, 2]. This is in contrast to the typical 1 milliwatt sources available in a laboratory. Specifically, for relativistic electrons the emission is enhanced by the fourth power of the increase in mass. Thus for 100 MeV electrons, for which the mass increases by a factor of ∼ 200, the enhancement is > 109. The experiments use a new generation of light source called an energy recovery linac (ERL) [3], in which bunches of electrons circulate once, but in which their energy is recovered. In such a machine the electron bunches can be very much shorter than those, say, in storage rings or synchrotrons.

The Jefferson Lab facility operates in new limits of emission from relativistic particles involving both multiparticle coherence and near-field emission in which the velocity (Coulomb) term in the classical electrodynamical theory becomes as important as the acceleration term (synchrotron radiation).

The sub-picosecond pulses of light offer unique capabilities in 2 specific areas, namely time-resolved dynamics, and imaging. High resolution THz spectroscopy has recently revealed sharp vibrational modes for many materials including malignant tissue, proteins, DNA, pharmaceuticals and explosive materials. Energetically the THz range embraces superconducting bandgaps, and regions of intense interest in the understanding of systems in which correlated motions of electrons are important, such as colossal magneto-resistive and high-Tc materials. The very high power levels of the new source will allow non-linear effects to be observed as well as the creation of novel states of materials, including electric-field driven localization[4]. We will give examples of existing work in these areas and present opportunities afforded by the new source.

An overview of research results related to the femtosecond laser ablation-based method for nanofabri-cation in aqueous solutions is presented. The method makes possible the production of stable biofunctionalized gold nanoparticle colloids with extremely small size (down to 2–2.5 nm) and size dispersion (down to 1–1.5 nm). The colloids are of importance for biosensing applications.

Laser micro-machining is finding many applications in materials processing and manufacturing. Various laser techniques are being used to fabricate micro-electronics, optics, and medical components. This paper will mainly deal with the fundamental issues involved in laser-matter interaction. Our studies are focused on laser induced thermal and thermomechanical phenomena and phase change mechanisms that determine the materials removal process during laser micro-machining. It is shown that during nanosecond laser machining, explosive phase change could occur, during which the liquid is superheated to close to the thermodynamic critical point, followed by an explosive, homogeneous phase transformation. On the other hand, it is observed in the experiment that the time needed for nucleation during laser induced phase explosion is on the order of one nanosecond. Thus, when a laser with a pulsewidth of the order of picosecond or less is used, it is likely that the material can be heated above the critical point, and another type of phase change, spinodal decomposition is possible. Molecular dynamics studies showed that with the use of a femtosecond laser pulse, it is possible to superheat the material to above the critical point, and spinodal decomposition is the dominant mechanism for materials removal.

Nanometer-scale surface topology modification has been demonstrated using NSOM (near-field scanning optical microscope) delivered femto-second pulses. The ablation laser has a pulse width of 150 femto-second and wavelength of 387-nm. The laser pulses are coupled into the free end of a multimode optical fiber that a nanometer-size NSOM probe was fabricated on the other end with small orifice. The transmitted laser pulses from the probe orifice illuminates and machines the substrate surface when the probe is in near-field range of the substrate surface. The produced feature on Silicon surface is as least 200-nm deep with hole diameter around 200-nm. Near-field coupling of the laser has the potential to achieve ablation of feature size less than diffraction limit. Using NSOM delivery method also allows us to take advantage of nanometer metrology in precision surface ablation or other type of preformed surface modification. The ability of monitoring surface topology of substrate in real time enables us to accomplish the in-situ surface processing. We have demonstrated the technique of drilling 200-nm air holes on a pre-formed 600-nm wide wave guide. This method can be used to fabricate one-dimensional photonic crystal on a waveguide in ambient environment. The experiment design and performance evaluation will be discussed.

Size distribution of gold nanoparticles in aqueous solution during pulsed laser irradiation (Nd:YAG laser, wavelength of 355 nm, pulse width 30 ps) is observed by transmission electron microscope (TEM). Interestingly, we observed that a single peak distribution of gold nanoparticles sizes (initially centered around 25 nm) is gradually turned into a two-peaks one upon laser radiation. Initial particles reduced their sizes and smaller particles were formed, resulting in the bimodal size distribution. In these bimodal size distributions, two peaks are observed, one is at 6 nm, and another is at 24 nm.

In a-Si:H solar cells, light trapping has been sought as a method to enhance absorption and improve the efficiencies of these devices. Here we present results for surface texturing of 2μm thick a-Si:H films by 800 nm wavelength femtosecond laser. The texture led to a significant enhancement in optical absorption (80%) in visible through near IR (60%). The textured surface was examined by a scanning electron microscope (SEM) and atomic force microscope (AFM). The results indicated the formation of dense spikes with height of 65–75 nm. The samples were completely black after femtosecond laser treatment.

Femtosecond laser is a perfect laser source for materials processing when high accuracy and small structure size are required. Due to the ultra short interaction time and the high peak power, the process is generally characterized by the absence of heat diffusion and, consequently molten layers. Various induced structures have been observed inside glasses after the femtosecond laser irradiation. Here, we report the refractive index change, space-selective valence state manipulation of active ions, nano-grating and precipitation control of nanoparticles by a femtosecond laser in glasses. The mechanisms of the observed phenomena were also discussed.

Reactive multilayer films of Co and Al were irradiated using femtosecond and nanosecond pulse-length lasers. While no ignition of a self-propagation reaction occurred during the laser machining studies, we observe considerable differences in the morphology and extent of damage induced by femtosecond and nanosecond lasers. Using scanning electron microscopy, we show that single metal layers can be removed at the micron scale with negligible damage to the underlying layers using femtosecond pulse-length lasers.

Using femtosecond laser machining, we have fabricated photonic bandgap materials that influence propagation of phonon-polaritons in ferroelectric crystals. Broadband polaritons were generated with impulsive stimulated Raman scattering (ISRS) using an ultrashort laser pulse, and the spatial and temporal evolution of the polaritons were imaged as they propagated through the fabricated structures with polariton real-space imaging. These techniques offer a new approach to optical materials design.