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Low-order harmonic generation in metal ablation plasmas in nanosecond and picosecond laser regimes
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10.1063/1.3686740
/content/aip/journal/jap/111/4/10.1063/1.3686740
http://aip.metastore.ingenta.com/content/aip/journal/jap/111/4/10.1063/1.3686740

Figures

Image of FIG. 1.
FIG. 1.

Spectra of emissions detected (a) upon ablation of a copper target with 6 ns, 1064 nm pulses of 11 mJ, and in the presence (b) of the fundamental driving beam of the same wavelength propagating at 0.6 mm from the target with a delay of 250 ns. The energy of the driving beam was 560 mJ. The lines corresponding to third harmonic (TH) and the second order of the fifth harmonic (2FH) and of the atomic copper lines are indicated.

Image of FIG. 2.
FIG. 2.

Normalized intensity of the third harmonic (355 nm) of the ns driving laser as function of the ablation pulse energy for (a) Mn, (b) Cu, and (c) Ag. The conditions were the following: driving laser energy 560 mJ, distance to target 0.6 mm, delay 250 ns. Both ablation and driving laser pulses have durations within ns range.

Image of FIG. 3.
FIG. 3.

(Color online) Log-log plot of the signals corresponding to the TH (open squares) and of the second order of the FH (2FH, solid circles) of the ns driving laser detected at a distance of 0.6 mm from the target as function of the laser pulse energy, for ns, 1064 nm ablation of metal targets. The conditions were (a) Mn, ablation pulse energy 5 mJ, delay 250 ns; (b) Cu ablation pulse energy 10 mJ, delay 250 ns; and (c) Ag ablation pulse energy 12 mJ, delay 300 ns. The units in the vertical axes allow the comparison of the relative intensity of the same harmonic for the three metals. As indicated, the slopes are compatible with a third and fifth order non-linear processes.

Image of FIG. 4.
FIG. 4.

(Color online) Normalized harmonic signals of the third (open squares) and fifth (solid circles) orders of the IR ns driving laser in metal ablation plasmas induced by a 6 ns, 1064 nm ablation laser with pulse energy of 5, 10, and 12 mJ for (a) Mn, (b) Cu and (c) Ag respectively, as a function of the delay between the ablation event and the arrival of the ns driving laser, and at a distance of 0.6 mm from the surface of the target. The driving laser power was 560 mJ. A z-scan plot for copper, where the TH and FH are measured as a function of the position of the IR focus (z) with respect to the center of the ablation plasma in the direction of propagation, is represented (d) for a delay of 250 ns. Experimental points are shown together with Gaussian fits with the widths (FWHM) indicated in the graph.

Image of FIG. 5.
FIG. 5.

Third harmonic (a) of the IR ps driving laser in copper ablation plasma induced by a 38 ps, 1064 nm ablation laser with pulse energy of 10 mJ as a function of the delay between the ablation event and the arrival of the ns driving laser, and at a distance of 0.2 mm from the surface of the target. The driving laser power was 4.5 × 1013 W/cm2. Z-scan plot (b) for copper, where the TH is measured as a function of the position of the IR focus (z) with respect to the center of the ablation plasma in the direction of propagation, for a delay of 25 ns. The experimental points are shown together with the gaussian fit yielding the indicated width (FWHM).

Image of FIG. 6.
FIG. 6.

(Color online) Normalized intensity of the TH signal at 355 nm as the position of the fundamental IR beam is displaced from the surface of the metal target (x distance) with ablation and driving lasers with pulses of (a) ns and (b) ps duration. For each distance probed, the delay between the ablation beam at 1064 nm and the fundamental beam was set at the value corresponding to the optimum signal. The solid lines are visual guides while the dotted lines represent a x −2 decay.

Tables

Generic image for table
Table I.

Position in ns of the temporal maximum of TH and FH in 1064 nm ablation plasmas of metals in ns and ps domains.

Generic image for table
Table II.

Full-width-half maximum of harmonic emissions (in mm) as a function of the position of IR driving laser focus with respect to centre of ablation plasma in the direction of laser propagation (z-scan). The distance of the propagation direction of the driving laser to the target is 0.6 mm for ns pulses and 0. 2 mm for ps pulses. Estimated error is 5%.

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/content/aip/journal/jap/111/4/10.1063/1.3686740
2012-02-23
2014-04-16
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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Low-order harmonic generation in metal ablation plasmas in nanosecond and picosecond laser regimes
http://aip.metastore.ingenta.com/content/aip/journal/jap/111/4/10.1063/1.3686740
10.1063/1.3686740
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