A. Borowiec

Subwavelength ripple formation on the surfaces of compound semiconductors irradiated with femtosecond laser pulses

High-spatial-frequency periodic structures on the surfaces of InP, GaP, and GaAs have been observed after multiple-pulse femtosecond laser irradiation at wavelengths in the transparency regions of the respective solids. The periods of the structures are substantially shorter than the wavelengths of the incident laser fields in the bulk materials. In contrast, high-frequency structures were not observed for laser photon energies above the band gaps of the target materials.

Subsurface modifications in indium phosphide induced by single and multiple femtosecond laser pulses: A study on the formation of periodic ripples

We use cross-sectional transmission electron microscopy to study the damage induced below the surface of indium phosphide (InP) samples by single and multiple femtosecond laser pulses with a photon energy lower than the InP band gap. Single-pulse irradiation creates a ∼100 nm deep crater with a resolidified surface layer consisting of quasiamorphous indium phosphide. The resolidified layer has a thickness of ∼60 nm at the center and extends laterally beyond the edge of the crater rim. Exposure to multiple femtosecond pulses of 2050 nm center wavelength results in the formation of laser-induced periodic surface structures (LIPSS) with two different periods, one (∼1730 nm) less than but close to the laser wavelength and one (∼470 nm) four times smaller. Segregation beneath both types of ripples leads to the formation of In-rich particles embedded in the resolidified surface layer. Extended defects are detected only below the center of the multiple-pulse crater and their distribution appears to be correlated...

Imaging the strain fields resulting from laser micromachining of semiconductors

The residual strain fields resulting from laser micromachining of grooves in indium phosphide with femtosecond and nanosecond light pulses are analyzed using a spatially resolved degree-of-polarization photoluminescence technique. Significant differences in the geometry of the strain patterns are observed in grooves machined by femtosecond and nanosecond pulses. For the specific conditions investigated, the sign of the degree of polarization signal is opposite in the two cases indicating that areas under tension in femtosecond machined samples are under compression in nanosecond machined samples and visa versa. The experimental data are compared with results from a finite element model.

Electron and atomic force microscopy studies of femtosecond laser machining of Si, GaAs and InP

Summary form only given. The application of femtosecond light pulses to materials processing has recently become a topic of great interest. Femtosecond laser ablation dynamics has been extensively studied by techniques including time-of-flight and has also been treated theoretically. However, although numerous experimental studies have demonstrated excellent spatial control in femtosecond laser machining, relatively few investigations have explored details of the near-surface changes in crystallographic structure and the localized changes in target composition. In this study we characterize laser-machined semiconductor samples, employing a combination of scanning (SEM) and transmission (TEM) electron microscopies as well as atomic force microscopy (AFM).

10-fs pulses from two-stage capillary-prism compressor

Summary form only given. The use of femtosecond laser pulses has advanced the understanding of atomic, molecular and solid-state dynamics. This progress has created the need for even shorter pulses and prompted the further development of femtosecond lasers and pulse compressors. An elegant way of reducing the pulse width was first demonstrated by Nisoli et al. (1996), who used a hollow core fiber-prism compressor to shorten high-energy 140-fs pulses to 10 fs (assuming sech/sup 2/ pulse shape). In this compressor the laser pulses are first spectrally broadened by self-phase modulation in a hollow core fiber waveguide filled with noble gasses at high pressure. Subsequently, a portion of the broadened spectrum is carefully selected and compressed by a pair of prisms. In a later version Nisoli et al. implemented chirped mirrors in the compressor in order to correct for high-order dispersion effects and were thus able to compress 20-fs pulses down to sub 5 fs. We present a two-stage capillary-prism compressor capable of producing 30-fs pulses from the first stage and 1O-fs pulses from the second compressor stage.

Imaging the strain fields resulting from femtosecond laser micromachining of semiconductors

Summary form only given. Laser-based processing with femtosecond light pulses has attracted considerable attention due to the qualitatively different light-matter interactions. The ultrashort light pulses facilitate removal of target material with minimal thermal effects. Many future applications depend on an understanding of the details of the machined materials, in terms of lateral damage, residual strain and localized changes in optical, mechanical and electronic materials properties. In this work we characterize laser-machined semiconductor samples, utilizing the degree-of-polarization photoluminescence technique supported by scanning and transmission electron microscopy.