Showing papers by "Oscar E. Martínez published in 1997"
TL;DR: In this paper, a real-time detection of pulsed laser surface melting was performed by analyzing the photoacoustic signals produced on the samples and comparing the amplitudes of the transversal and longitudinal waves allowed them to identify the fluence thresholds for surface melting.
Abstract: Real time detection of pulsed laser surface melting was performed by analyzing the photoacoustic signals produced on the samples. Comparison between the amplitudes of the transversal and longitudinal waves allowed us to identify the fluence thresholds for surface melting. The method was tested with AISI 304 stainless steel samples and the results obtained were checked against direct metallographic analysis.
15 citations
TL;DR: It is demonstrated that, by changing the altitude and the azimuth incident angles on the gratings of the conventional grating-pair compressor used in chirped-pulse amplification, an extra degree of freedom is added, which results in a continuous adjustment of second-, third-, and fourth-order dispersions.
Abstract: We demonstrate that, by changing the altitude and the azimuth incident angles on the gratings of the conventional grating-pair compressor used in chirped-pulse amplification, an extra degree of freedom is added. This results in a continuous adjustment of second-, third-, and fourth-order dispersions, which allows one to compensate for those dispersions that originated in the expansor or in the amplifier medium as a result of material dispersion or self-phase modulation, even with small out-of-plane tilts of the expansor and compressor. Analytical calculations of the high-order dispersions introduced by this compressor and examples for a pulse with a central wavelength at 800 nm are presented.
12 citations
TL;DR: In this article, the authors show that the thermal contribution is proportional to the average tunneling current and that this can be used to distinguish it from other contributions, such as thermal expansion of the sample or tip in a laser-assisted scanning tunneling microscope (STM) junction.
Abstract: Thermal expansion of the sample or tip in a laser-assisted scanning tunneling microscope (STM) junction can obstruct the study of other phenomena related with STM–light interactions, when photoinduced currents are analyzed. In this article, we show that the thermal contribution is proportional to the average tunneling current and that this can be used to distinguish it from other contributions. Simultaneous tunneling current–voltage and photoinduced current–voltage curves are recorded for highly oriented pyrolitic graphite and gold samples with a Pt tip. We have done the measurements for two different polarizations of the incident beam. We show that the I–V curves can be used to discriminate between different mechanisms that appear, producing photoinduced currents.
12 citations
TL;DR: In this paper, the reproducibility of electron beam pulses generated by a high power, cold cathode glow discharge is greatly improved by adding a small continuous keep-alive discharge current.
Abstract: We have demonstrated that the reproducibility of electron beam pulses generated by a high power, cold cathode glow discharge is greatly improved by adding a small continuous keep-alive discharge current. A current of the order of 200 μA was found to limit the shot to shot current variation to within 1.5%. This stabilization in turn reduces by an order of magnitude the fluctuations of the energy density deposited on the target, demonstrating a reliable energy source for surface treatment.
12 citations
TL;DR: In this paper, a simple semi-empirical model of the electron beam generated by a pulsed cold cathode electron gun was developed, which describes analytically the observed self-focusing of the discharge and predicts the dynamical variation of the focal distance, in good agreement with experiments.
Abstract: A simple semiempirical model of the electron beam generated by a pulsed cold cathode electron gun has been developed. The model describes analytically the observed self-focusing of the discharge and predicts the dynamical variation of the focal distance, in good agreement with experiments. This effect plays a major role in the determination of the effective duration of the energy pulse. The model was used to conduct simple calculations of energy thresholds for melting of solid materials, giving helpful insight on ranges of operation of this kind of electron gun for its application to material processing. A comparison with available experimental data for Mg/sub 70/Zn/sub 30/ samples is given.
7 citations
5 citations
TL;DR: In this article, a compact pulse stretcher is introduced that uses standard curved gratings and provides positive group-delay dispersion and adequately matches the standard grating pair compressor, which makes it useful in chirped-pulse amplification systems.
Abstract: We recently introduced a new compact pulse stretcher [Opt. Lett.22, 811 (1997)] that uses standard curved gratings and has several advantages over other systems. It provides positive group-delay dispersion and adequately matches the standard grating pair compressor, which makes it useful in chirped-pulse amplification systems. We analyze the conditions that the different parameters of the stretcher must satisfy to be afocal as well as the problem of chromatic aberrations.
3 citations
TL;DR: A compact pulse stretcher using curved diffraction gratings is presented, which introduces positive group-delay dispersion and can operate in conjunction with a standard grating-pair compressor in chirped-pulse amplification systems.
Abstract: A compact pulse stretcher using curved diffraction gratings is presented. It introduces positive group-delay dispersion and can operate in conjunction with a standard grating-pair compressor in chirped-pulse amplification systems. It presents several advantages over other systems proposed: It has no degrees of freedom and so is not highly sensitive to alignment errors, it is easy to align, it has a compact and robust design, and it uses standard optics. The frequency-dependent delay, dispersions up to third order, and the design parameters of the stretcher–compressor system that will yield good matching are analyzed. Examples of design specifications for a 40-fs pulse with a central wavelength of λ=800 nm are given.
3 citations