Influence Of Laser Pulse Shape Research Articles

Influence of laser pulse shape and cleanliness on two-photon microscopy

Nonlinear microscopy, including two-photon microscopy, requires pulsed lasers as light source. Typically, when choosing the appropriate pulsed laser for two-photon microscopy, the pulse repetition rate, pulse width, total power output, and output beam diameter are among the critical parameters which are often emphasised. Here, we demonstrate that the pulse shape, often overlooked, can have significant impact on the two-photon microscopy excitation efficiency and the effective signal brightness. We provide metrics to ease practical selection of pulsed laser sources for two-photon microscopy.

Effect of the Laser Processing Parameters on the Selective Laser Melting of TiC–Fe-Based Cermets

The influence of laser pulse shaping on the formation of TiC-Fe-based cermets with different laser process parameters is investigated. The impact of pulse shaping and laser melting peak power on the microstructural development and mechanical properties of SLM-built parts is addressed. This research focuses primarily on the process parameters required to produce crack-free components and includes investigations of mechanical properties such as microhardness and fracture toughness. To acquire optimal process parameters, samples were manufactured using pulse shaping technology with varying laser melting peak power and exposure time. The influence of laser melting peak power and pulse shape on microstructure development and phases was analyzed using a scanning electron microscope and X-ray diffraction.

The influence of laser pulse shape and separation distance on dissimilar welding of Al and Cu films

Pulsed Nd:YAG laser welding of Aluminum-Copper (Al-Cu) electrical connections has been investigated, focusing attention on the definition of optimal process parameters to achieve low thickness joints by varying the laser pulse shape and separation distance. Heterogeneous joints comprising Al and Cu are often required in electrical applications due to the inherent characteristics of these materials. Nevertheless, welding of dissimilar metals such as Al and Cu involves many challenges due to the high reflectivity and poor weldability between the materials, which produce brittle microstructural compounds that lead to a reduction in mechanical and electrical properties. Metallurgical, mechanical, electrical and thermal analyses have been performed on Al-Cu lap joints to evaluate the effect of different pulse separation distances and shapes on the resulting weld seam. Process optimization achieved welded joints with a low penetrating depth and maximum tensile loads of over 110 kgf. Preliminary experiments were carried out to establish a process parameter feasibility window. A first set investigated variations in pulse energy and distance for square pulses, while a second set saw variation of the pulse energy, pulse distance and pulse shape. It was found that an optimal pulse distance for a specific parameter set exists, while a pulse shape that includes material preheating produces better results in terms of mechanical strength and electrical resistance than a pulse with high initial peak power.

Influence of laser-pulse shape and surface recombination on the photon generation rate in experiments on the dynamical casimir effect

We study the influence of laser-pulse shape and surface recombination on the photon generation rate in the so-called MIR experiment on the dynamical Casimir effect. Numerical calculations show that the surface recombination can be neglected at low (helium) temperatures and its influence on the photon recombination rate is rather small at higher (nitrogen) temperatures. It appears that long (tens of picoseconds) laser pulses could be preferable for semiconductors with very small (less than 10 ps) bulk recombination times. Moreover, for a given energy of laser pulses (exceeding some critical value), it is possible to find a pulse duration such that the photon generation rate becomes almost independent of the recombination time in a rather wide range of values (about 25 ps). These results can facilitate the performance of the experiment.

Influence of laser pulse shape on dry laser cleaning

The influence of laser pulse shape and pulse duration on dry laser cleaning is investigated by means of combined experimental and theoretical approaches. Possibilities to enhance damage-free particle removal efficiency by adjusting the temporal parameters of laser irradiations are discussed. The numerical description predicts that the removal of sub-micron particles by excimer lasers occurs in the ‘quasi-static’ inertia force regime. Experiments are based on an electro-optic gating system capable of switching off either leading or trailing edges of an excimer laser pulse. It is demonstrated that the inertia force corresponding to the pulse trailing front may play a role in laser cleaning but not as the dominant mechanism. Both the surface temperature and the expansion dynamics of materials are calculated in order to examine their role in dry laser cleaning. This study helps to determine the dominant mechanism responsible for particle removal by nanosecond laser pulses.

Influence of laser pulse shape both on temperature profile and hardened layer depth

This paper presents a mathematical modelling and numerical calculations of heat conduction problems where laser generated heat is assumed as a surface heat source. Also the effect of a laser time structure on a hardened layer depth is examined. Temperature profiles for different laser pulse shapes are determined from the solution of a linear one-dimensional heat conduction equation for semi-infinite medium and discussed in terms of the parameters evolution such as dimensionless: temperature, heat flux, hardening depth, laser impulse duration and increasing time of triangular pulse shape.

Laser pulse shape influence on optically induced dynamic processes

In this paper, the influence of laser pulse shape on laser drilling process and on optoacoustic effect is studied. Results for two laser applications: laser drilling in aluminium and laser drilling in hard dental tissue are presented. Observed changes in the interaction processes are compared to the optoacoustic (OA) signals. Results confirm that laser pulse shape might have a significant influence on the interaction processes and can be used to increase machining efficiencies. With laser pulse shape, one can effectively induce desired dynamics of the melted material. However, if the process is cumulative in its nature like in the case of drilling in dentin, then the laser pulse shape is less important. Optoacoustic signals are found to depend on the laser pulse shape. However, usually used signal parameters for on line monitoring are not linearly correlated with the drilling efficiency. At least more complex signal analysis is needed. Presented method of signal analysis enables determination of the onset time of changes in the interaction mechanism and determination of energy threshold in the case of hard dental tissue drilling.

Influence of the shape of the exciting laser pulse on fluorescence saturation in the quantitative analysis of dissolved trace organic substances

Theoretical investigations of the influence of the exciting laser pulse shape on fluorescence saturation in the quantitative analysis of a single-component fluorescing solution, when the Raman signal of the solvent is usedas a reference, are carried out. A quantity α is introduced, responsible for the influence of laser pulse shape on the precision of the analysis. The dependences of α on the exciting radiation photon flux density I m in the range I m = 10 22 − 10 28 photons/cm 2⋯s and on the duration of the exciting pulses τ p in the range τ p = 0.6 − 60 ns are computed for different pulse shapes in the case of rhodamine 6G dissolved in water. Conditions when α is, in practice, independent of τ p and of the pulse shape are found. A general analytical expression is found for α, which produces errors not greater than several percent when compared to the computed values of α. An experimental verification of the theoretical results in the case of a rectangular-shaped pulse in the spatial domain and a Gaussian-shaped pulse in the temporal domain is realized.