Emission spectrum recorded during Si wafer micromachining. The data was recorded with femtosecond laser pulses. The overall emission spectrum can be decomposed into a sharp LIBS signal from atomic Si at 390.55 nm and a broader feature corresponding to the SSHG centered at 400 nm. The rest of the broad emission corresponds to a broadband PE. The inset shows the experimental setup used for this experiment. The sample was mounted on a motorized translational stage, L1, L2, and L3 are 300, 600, and 50 mm lenses, respectively, BS is a dichroic beamsplitter which transmits 800 nm and reflects from 300 to 650 nm.
Focus distance dependence. (a) Intensity for different spectral emissions [PE (◼), SSHG (●), and Si-LIBS (▲)], as a function of distance from the focus recorded with 0.2 mJ/pulse. (b) Total photoemission intensity as a function of distance from the focus recorded for different pulse energies; (◼), (○), and (▲). Data was obtained by moving the objective toward the sample; positive values imply the laser focuses inside the sample.
Femtosecond LIBS dependence on linear chirp recorded for Si atomic emission line at 390.552 nm using MIIPS box pulse shaper with the laser intensity of . Inset shows the chirp dependence data for very large chirp values obtained by moving the compressor grating.
Si-LIBS (◼) and SHG (◻) signal dependence on sinusoidal phase modulation with femtosecond laser pulses. The corresponding phase functions as a function of are shown in the upper insets with wavelength in -axis (770–830 nm).
Si-LIBS and SSHG spectra obtained by applying sinusoidal modulation are plotted as 2D maps with femtosecond laser pulses. Panel (a) shows a typical MIIPS trace obtained with a SHG crystal, and panel (b) shows all the emission components observed under micromachining conditions, including the broad plasma, the SSHG features which are similar to those in panel (a) and the Si atomic emission.
Effect of phase modulation on the morphology of micromachined features obtained on Si (100) wafer (scale ) with femtosecond laser pulses. Images shown here are obtained with TL pulses (35fs) and highly chirped pulses (, equivalent to 1ps). Other conditions including power and focus are the same for both experiments. Notice the extensive melting associated with the hole made with chirped pulses.
The LIBS power threshold dependence on the bandwidth of the laser pulse (full-width at half maximum). Each data point is an average of 5 experimental measurements.
Temporal profile of the pulses with sinusoidal phase function when (a) and (b). Left column: spectral power (dashed line) and phase (solid line); right column: calculated time profile of the intensity.
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