Effect Of Laser Pulse Width Research Articles

Bubble Dynamics Induced by Pulsed-Laser Evaporation of Ink as a Method to Develop Novel Print Heads

The bubble dynamics induced by direct laser heating is experimentally analyzed as a first step to assess the technical feasibility of laser-based ink jet technology. To understand the interaction between laser light and ink, the absorption spectrum is measured for various ink colors and concentrations. The hydrodynamics of laser-generated bubbles is examined by laser flash photography. When an Ar ion laser pulse (wavelength 488nm) with an output power up to 600 mW is incident on the ink solution through a transparent window, a hemispherical bubble with a diameter up to ∼ 100 μm can be formed with a lifetime in the range ∼O(10 μs) depending on the laser power and the focal-spot size. A parametric study has been performed to reveal the effect of laser pulse width, output power, ink concentration, and color on the bubble dynamics. The results show that the bubble generated by a laser pulse is largely similar to that produced by a thin film heater. Consequently, the present work demonstrates the feasibility of developing a laser-actuated droplet generation mechanism for applications in ink jet print heads. Furthermore, the results of this work indicate that the droplet generation frequency is likely to be further increased by optimizing the process parameters.

Effect of Holmium:YAG Laser Pulse Width on Lithotripsy Retropulsion in Vitro

The effect of laser pulse width on calculus retropulsion during ureteroscopic lithotripsy is poorly defined because of the limited availability of variable pulse-width lasers. We used an adjustable pulse-width Ho:YAG laser to test the effect of pulse width on in vitro phantom-stone retropulsion and fragmentation efficiency. An Odyssey 30 Ho:YAG laser (Convergent Laser Technologies, Oakland, CA) with adjustable pulse width (350 or 700 microsec) was used to treat spherical 10-mm plaster calculi in a model ureter (N = 40) and calix (N = 16) utilizing 200- and 400-microm fibers (10 Hz, 1.0 J). Calculi were placed in a waterfilled clear polymer tube, and laser energy was applied continuously in near contact until the stone had moved 8 cm. The time (seconds) and energy (joules) needed to cause the stone to traverse this distance was recorded. Stones were also placed in a stainless-steel mesh calix model in which retropulsion was limited. Laser energy was applied for 5 minutes at each pulse width. A laser-energy meter (Molectron Detector Inc, Portland OR) was used to quantify fiber transmission efficiency after 1 minute of continuous lithotripsy for each fiber at each pulse width. Retropulsion was greater for stones treated at 350 microsec, indicated by a shorter time to traverse the model ureter. For the 200-microrm fiber at 350 microrsec, the average time was 11.5 seconds v 20.3 seconds at 700 microsec (P < 0.001). The average total energy delivered was 114.9 J at 350 microsec v 199.8 J at 700 microsec (P < 0.001). For the 400-microm fiber at 350 microsec, the average time was 5.8 seconds v 11.9 seconds at 700 microsec (P < 0.001). The average total energy was 57.1 J at 350 microsec v 127.3 J at 700 microsec (P < 0.001). In the caliceal model, at 350 and 700 microsec with the 200- and 400-microm fibers, mass loss was 34.9% and 33.4% (P = 0.8) and 14.6% and 21.6% (P = 0.04), respectively. The reduction in energy transmission at 350 microsec and 700 microsec with the 200- microm fiber after 60 seconds of continuous lasing was 8.82% v 9%, respectively (P = 0.95). For the 400-microm fiber, the transmission loss was 18.4% at 350 microsec v 4.4% at 700 microsec (P = 0.0002). When treating ureteral calculi, retropulsion can be reduced by using a longer pulse width without compromising fragmentation efficiency. For caliceal calculi, the longer pulse width in combination with a 400-microm fiber provides more effective stone fragmentation.

Effect of laser pulsewidth on the generation of multi-color laser emission by stimulated Raman scattering and four-wave Raman mixing in a KGd(WO 4) 2 crystal

Picosecond and femtosecond lasers having different pulsewidths were employed for the generation of multi-color laser emission via stimulated Raman scattering and four-wave Raman mixing using a KGd(WO 4) 2 crystal. Seven emission lines, consisting of high-order Stokes and anti-Stokes emissions, were observed at a laser pulsewidth of 20 ps and a pulse energy of 70 μJ.

The effect of laser pulse width on multiple-layer 316L steel clad microstructure and surface finish

Multiple layer laser cladding is a flexible rapid prototyping and tooling process that allows a fully dense wall or surface to be fabricated from the consolidation of a metal powder. The microstructure and resultant physical properties of the material are determined by process parameters, one of which is the pulse width of the laser used. In this work, a CO 2 laser, operating at different pulse widths and in continuous mode is used to assess this effect. Microstructural characterisation of multiple layers of consolidated 316L steel is carried out and the dimensions, surface roughness and hardness of the built samples compared with the generating pulse widths.

Effects of laser pulsewidth on higher-order harmonic generation in the barrier-suppression-ionization intensity regime

We studied the highest harmonic photon energies of high-order harmonic generation (HHG) for He, Ne, Ar, Kr, Xe, and N2. This research employed 65-fs and 150-fs Ti:sapphire laser pulses, of which the peak intensities in a vacuum are higher than the barrier-suppression-ionization (BSI) intensities. We fitted two analytical formulae to the experimental results of HHG. One formula, which was obtained by fitting an analytical formula to the results by a quantum mechanical simulation of HHG, expresses the highest interaction intensity by a function of the BSI intensity and the Keldysh γ-parameter. The other formula is derived by introducing the saturation intensity of HHG, which was proposed by Chang et al. [Phys. Rev. Lett. 79, 2967 (1997)]. We discuss the highest interaction intensity for the condition when the peak laser intensities are higher than the BSI intensities.

Short pulsed laser machining: How short is short enough?

Machined feature quality is examined, and the effects of laser pulse width (and thus peak power or intensity) are investigated for the following four laser systems: (1) a millisecond-class, free-running Nd:YAG; (2) a 100-nanosecond-class, Q-switched Nd:YAG laser; (3) a 100-picosecond-class, mode locked Nd:YAG laser; and (4) a 100-femtosecond-class, Ti:sapphire chirped pulse amplification laser. The effect of shorter laser wavelength is also examined by using the second harmonic wavelength of the Nd:YAG laser in the Q-switched and the mode locked pulse formats. Hole drilling and cutting of superalloy, ceramic, and composite materials are studied. The machined feature quality is improved as the pulse width becomes shorter and the peak intensity becomes higher. The shorter wavelength provides another significant improvement. Finally, an attempt is made to view these quality improvements in the context of process throughput and cost of ownership.

Phase transformation kinetics—the role of laser power and pulse width in the phase change cycling of Te alloys

The effect of laser pulse width and amplitude on the kinetics of laser-induced phase transformations of thin films of Te alloys has been mapped. This map, called a phase transformation kinetics diagram, shows distinct regions of crystallization and amorphization and allows important material parameters to be determined. The observed regions were correlated with results from temperature modeling. The minimum crystallization time was measured to be 50 ns for pure Te and increases to 550 ns for Te80Sn20 and 80 μs for Te90Ge10. A boundary, determined by the critical quench rate, separates the region of melt followed by amorphous quench, from melt followed by crystallization. Three methods of reversible cycling are demonstrated.

The effects of laser pulsewidth and molecular lifetime on the experimental determination of one-photon and two-photon excitation spectra

We demonstrate that it is important to know both the observed fluorescence lifetime (τ) and the excitation pulsewidth ( \Gamma ) in order to determine the effect of changes in \Gamma on the measurement of one- and two-photon excitation spectra. If \Gamma/\tau is greater than 3, it is sufficient to measure I_{F}/I_{L}^{n} or I_{F}/N_{L}^{n} for n -photon excitation spectra ( n = 1 and 2), where I F is the peak fluorescence intensity, I L is the peak intensity of the excitation pulse, and N L is the total number of photons per pulse. When \Gamma/\tau is less than 3, however, the pulsewidth dependence of I_{F}/I_{L}^{n} or I_{F}/N_{L}^{n} should be treated by using the pulse-width correction functions defined in this paper. A simple method to estimate observed fluorescence lifetimes is also described where one needs only to measure \Gamma and the time interval between the peak intensity of an excitation pulse with a Gaussian or near Gaussian temporal profile and the peak fluorescence intensity. Tables of correction factors are provided which can be used to generate accurate values of these functions for arbitrary ratios of \Gamma/\tau using interpolation techniques. The treatment of the effect of non-Gaussian excitation pulses on the measurement of one- and two-photon excitation spectra is discussed.