Ultrafast laser filamentation in ethanol for nanomaterials synthesis
Ultrafast laser filamentation occurs when laser light propagating in nondiffracting regime, at high laser intensity for distance greater than Rayleigh length in transparent media. An extended high intensity core with clamped intensity, supercontinuum and plasma is generated during laser filamentatio...
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| Format: | Thesis |
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2022
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| Summary: | Ultrafast laser filamentation occurs when laser light propagating in nondiffracting regime, at high laser intensity for distance greater than Rayleigh length in transparent media. An extended high intensity core with clamped intensity, supercontinuum and plasma is generated during laser filamentation. In this work, the characteristics of laser filamentation in ethanol is studied, and the possibilities of nanomaterials synthesis from the generated plasma is explored. In the first part of the work, the dependence of ultrafast laser filamentation on the incident laser energy is studied via measurement of energy loss, side view imaging, forward emission, time integrated optical emission spectroscopy and transmitted beam profiles. The results show that laser filamentation starts at ~110 times of critical power of self-focusing (Pcr). As the laser energy increases (310 Pcr), stronger and multiple filamentation occurred and emission peaks are detected. Finally, at even higher laser energy (750 Pcr), ethanol is vaporised. The characteristics of laser filamentation is discussed and nanomaterials synthesis is performed at the laser energy where multiple filamentation occur below the vaporisation threshold. Nanodiamonds are obtained, as characterised by absorbance measurement, photoluminescence, XPS and HR-TEM. In the second part, the role of laser repetition rate in ultrafast laser filamentation in ethanol is studied; to determine its effect on laser filamentation, and to increase the yield for nanomaterials synthesis. The results indicate that laser repetition rate influence the laser filamentation process through thermal process. At fixed laser energy of 90 µJ (110 times Pcr), laser filamentation occurs only at the repetition rate of <1 kHz. No filamentation is obtained above 1 kHz. Laser filamentation is inhibited due to thermal defocusing. At 400 µJ, laser filamentation is observed for all repetition rates where heat convection occurs and increase the interaction rate. In addition, improved fluid flow in ethanol helps in laser filamentation nanomaterials synthesis. |
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