With the availability of off-the-shelf commercial ultrafast lasers, a small revolution in materials research is underway, as it is now possible to use these tools without being an expert in the development of the tools themselves. Lasers with short-duration optical pulses—in the sub-picosecond (less than one-trillionth of a second) range—are finding a variety of applications, from basic research on fast processes in materials to new methods for microfabrication by direct writing. A huge range of pulse energies are being used in these applications, from less than 1 nJ (a billionth of a joule) to many joules.

We discuss recent experimental and theoretical results on ultrafast materials dynamics. Intense, femtosecond lasers can deposit energy in a time that is short compared with relaxation processes and can generate extremely large carrier densities that drive bond softening, nonthermal melting, and ablation. In particular, we present optical experiments on electronic softening of coherent phonons in bismuth and x-ray experiments on ultrafast disordering in indium antimonide that probe the bonding of the lattice under successively higher carrier concentrations. We review a number of molecular dynamics simulations and their assumptions, which address nonthermal melting. Large-scale molecular dynamics simulations elucidate the role of void formation in laser ablation.

Ultrafast lasers have long been used to study the dynamics of fast optical, electronic, and chemical processes in materials. These tools can also be used in a variety of optical pump and probe spectroscopies to generate and detect acoustic signals with frequencies on the order of 100 GHz, and to generate and detect thermal waves with penetration depths on the scale of nanometers. The short wavelengths of these probes make them ideal for the study of the mechanical and thermal properties of thin films, their interfaces, and nanostructures. We describe the picosecond-laser acoustics technique and demonstrate how it can be used to extract the elastic constants and the adhesion of thin films and probe the normal modes of vibration of nanostructures. The thermal properties of thin films are also accessible through time-domain thermoreflectance. Since the mechanical and thermal properties can be obtained quickly on micrometer-scale regions of a sample, spatial mapping of the properties is also possible.

The materials science community is poised to take advantage of new technologies that add unprecedented time resolution to already existing spatial-resolution capabilities. In the same way that chemists and biologists are using ultrafast optical, photon, and particle techniques to reveal transition pathways, materials scientists can expect to use variations of these methods to probe the most fundamental aspects of complex transient phenomena in materials. The combination of high-spatial-resolution imaging with high time resolution is critical because it enables the observation of specific phenomena that are important to developing fundamental understanding. Such a capability is also important because it enables experiments that are on the same time and length scales as recent high-performance computer simulations. This article describes several new techniques that have great potential for broader application in materials science, including electron, x-ray, and γ-ray imaging.

When a femtosecond laser pulse is focused inside a transparent material, the optical intensity in the focal volume can become high enough to induce permanent structural modifications such as a refractive index change or the formation of a small vacancy. Thus, one can micromachine structures inside the bulk of a transparent material in three dimensions. We review the mechanisms of and techniques for bulk modification of transparent materials using femtosecond laser pulses and discuss the fabrication of photonic and other structures in transparent materials, including waveguides, couplers, gratings, diffractive lenses, optical data storage, and microfluidic channels.

In this article, we present summaries of the evolution of surface morphology resulting from the irradiation of single-crystal silicon with femtosecond laser pulses. In the first section, we discuss the development of micrometer-sized cones on a silicon surface irradiated with hundreds of femtosecond laser pulses in the presence of sulfur hexafluoride and other gases. We propose a general formation mechanism for the surface spikes. In the second section, we discuss the formation of blisters or bubbles at the interface between a thermal silicon oxide and a silicon surface after irradiation with one or more femtosecond laser pulses. We discuss the physical mechanism for blister formation and its potential use as channels in microfluidic devices.

The use of ultrafast laser pulses is having an impact on materials processing in profound ways. “Machining” with femtosecond pulses affords considerable advantages over nanosecond pulses, such as subdiffraction-limited material ablation, where ablated spot dimensions are below that achievable when longer pulses are focused to the minimum spot size dictated by optical physics. These properties have been exploited to address what had become a critical problem in the semiconductor industry, the repair of patterned photomasks. We will describe how the fundamentals of femtosecond laser ablation have been implemented in a machine designed to repair photomasks. We will also describe experiments designed to deposit Cr metal onto fused-silica substrates using 100-fs, 400-nm light pulses at atmospheric pressure. Multiphoton dissociation of Cr(CO)6 adsorbed on fused-silica substrates initiates Cr deposition. The mechanisms for deposition on both transparent (fused silica) and absorbing (Cr metal) substrates are discussed. Finally, we describe experiments that were carried out to extend the photomask repair process to shorter wavelengths (below 200 nm) using light generated by frequency-mixing of ultrashort, 30-fs pulses in an Ar-filled capillary.