Ablation of metals by ultrashort laser pulses

Nolte, Stefan; Momma, C.; Jacobs, H.; Tünnermann, Andreas; Chichkov, Boris N.; Wellegehausen, B.; Welling, H.

doi:10.1364/josab.14.002716

Cited by 1,056 publications

(600 citation statements)

References 23 publications

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“…It has long been recognized that material removal by ablation strongly depends on the material's properties and the parameters of the laser pulse like fluence, wavelength, and pulse duration. [44][45][46][47][48][49][50][51][52][53][54] The complexity of the ablation process is related to the coupling mechanism of the laser light to the sample as the optical and thermal properties may change considerably upon laser exposure due to heating, formation of excited species, phase transitions, plasma formation, and photochemical reactions. In particular, it has been recognized [44][45][46][47][48][49][50][51][52][53][54] that for ablation of metals short laser pulses have a great advantage because (i) during the laser pulse no free (transparent) plasma can develop; (ii) heat diffusion into the material is negligible.…”

Section: Resultsmentioning

confidence: 99%

Laser-Induced Shape Changes of Colloidal Gold Nanorods Using Femtosecond and Nanosecond Laser Pulses

2000

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Gold nanorods have been found to change their shape after excitation with intense pulsed laser irradiation. The final irradiation products strongly depend on the energy of the laser pulse as well as on its width. We performed a series of measurements in which the excitation power was varied over the range of the output power of an amplified femtosecond laser system producing pulses of 100 fs duration and a nanosecond optical parametric oscillator (OPO) laser system having a pulse width of 7 ns. The shape transformations of the gold nanorods are followed by two techniques: (1) visible absorption spectroscopy by monitoring the changes in the plasmon absorption bands characteristic for gold nanoparticles; (2) transmission electron microscopy (TEM) in order to analyze the final shape and size distribution. While at high laser fluences (∼1 J cm -2 ) the gold nanoparticles fragment, a melting of the nanorods into spherical nanoparticles (nanodots) is observed when the laser energy is lowered. Upon decreasing the energy of the excitation pulse, only partial melting of the nanorods takes place. Shorter but wider nanorods are observed in the final distribution as well as a higher abundance of particles having odd shapes (bent, twisted, φ-shaped, etc.). The threshold for complete melting of the nanorods with femtosecond laser pulses is about 0.01 J cm -2 . Comparing the results obtained using the two different types of excitation sources (femtosecond vs nanosecond laser), it is found that the energy threshold for a complete melting of the nanorods into nanodots is about 2 orders of magnitude higher when using nanosecond laser pulses than with femtosecond laser pulses. This is explained in terms of the successful competitive cooling process of the nanorods when the nanosecond laser pulses are used. For nanosecond pulse excitation, the absorption of the nanorods decreases during the laser pulse because of the bleaching of the longitudinal plasmon band. In addition, the cooling of the lattice occurring on the 100 ps time scale can effectively compete with the rate of absorption in the case of the nanosecond pulse excitation but not for the femtosecond pulse excitation. When the excitation source is a femtosecond laser pulse, the involved processes (absorption of the photons by the electrons (100 fs), heat transfer between the hot electrons and the lattice (<10 ps), melting (30 ps), and heat loss to the surrounding solvent (>100 ps) are clearly separated in time.

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Section: Resultsmentioning

confidence: 99%

Laser-Induced Shape Changes of Colloidal Gold Nanorods Using Femtosecond and Nanosecond Laser Pulses

2000

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“…(ii) Pulse duration is also an important parameter for the generation of nanoparticles. By changing the pulse duration from nanoseconds (ns) to picoseconds (ps) toward femtoseconds (fs), the ablation mechanism changes from melting and thermal evaporation to phase explosion [19,20]. The shorter the pulse duration, the more efficient the ablation process, including a nearly instantaneous evaporation with a minimized heat affected zone [21].…”

Section: Introductionmentioning

confidence: 99%

Influence of processing time on nanoparticle generation during picosecond-pulsed fundamental and second harmonic laser ablation of metals in tetrahydrofuran

et al. 2011

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The influence of fundamental and second harmonic wavelength on ablation efficiency and nanoparticle properties is studied during picosecond laser ablation of silver, zinc, and magnesium in polymer-doped tetrahydrofuran. Laser ablation in stationary liquid involves simultaneously the fabrication of nanoparticles by ablation of the target material and fragmentation of dispersed nanoparticles by post irradiation. The ratio in which the laser pulse energy contributes to these processes depends on laser wavelength and colloidal properties. For plasmon absorbers (silver), using the second harmonic wavelength leads to a decrease of the nanoparticle productivity over process time along with exponential decrease in particle diameter, while using the fundamental wavelength results in a constant ablation rate and linear decrease in particle diameter. For colloids made of materials without plasmon absorption (zinc, magnesium), laser scattering is the colloidal property that limits nanoparticle productivity by Mie-scattering of dispersed nanoparticle clusters.A. Schwenke · P. Wagener · S. Barcikowski ( ) Laser Zentrum Hannover e.V.,

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“…Laser-induced material removal involves the following steps: absorption of the laser energy by the material, redistribution of the absorbed energy within the target material, and the ablation of material by evaporation and/or melt ejection [7,9,24]. When a laser beam is deposited into the material surface, the free electrons are heated to a very high temperature by absorbing the laser energy.…”

Section: Discussionmentioning

confidence: 99%

“…For the ultrafast laser pulse with a high power intensity (~10 13 J/cm 2 in our experiments), the electrons are driven to a very high temperature (far above the vaporization temperature) while the lattice remains unheated during the pulse. If the laser fluence is not far above the ablation threshold, studies in other materials systems have demonstrated that the heat diffusion into the surrounding material is negligible, with the absence of melted material [24]. Therefore, theoretically, high precision machining of aero-engine materials should be possible with femtosecond laser pulses.…”

Section: Discussionmentioning

confidence: 99%

Femtosecond Laser Micromachining of Single-Crystal Superalloys

Feng

Picard

Liu

et al. 2004

Superalloys 2004 (Tenth International Symposium)

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Investigations on femtosecond laser micromachining of single crystal superalloys with and without plasma-sprayed thermal barrier coatings were conducted under laser fluences ranging from 0.1 J/cm 2 up to 160 J/cm 2 . Micromachining was carried out in air using a titanium:sapphire laser system ( = 780 nm) operating at a repetition rate of 1 kHz and delivering individual pulses of ~150 fs duration. The ablation threshold of the single crystal superalloy was determined as 203 ± 20 mJ/cm 2 . Laser-induced damage was examined by means of scanning electron microscopy and transmission electron microscopy. These studies indicate a complete absence of any melting, recast layers, heat-affected zones or microcracks in the vicinity of the machining area. The only form of damage observed in the single crystal superalloy machined near or above the ablation threshold was a laser-induced plastically deformed layer with a maximum extent of ~5 m. Machining through ceramic thermal barrier coatings on a superalloy produced no delamination along the superalloy/coating interfaces or cracks within the TBC or bond coat. The residual roughness of the machined surface was in the sub-micron range. The present study suggests that femtosecond laser micromachining is a very promising technique for production of finescale features in multi-layer material systems for aerospace and power generation components.

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Ablation of metals by ultrashort laser pulses

Cited by 1,056 publications

References 23 publications

Laser-Induced Shape Changes of Colloidal Gold Nanorods Using Femtosecond and Nanosecond Laser Pulses

Laser-Induced Shape Changes of Colloidal Gold Nanorods Using Femtosecond and Nanosecond Laser Pulses

Influence of processing time on nanoparticle generation during picosecond-pulsed fundamental and second harmonic laser ablation of metals in tetrahydrofuran

Femtosecond Laser Micromachining of Single-Crystal Superalloys

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