Characterisation of Diamond-Like Carbon (DLC) laser targets by Raman spectroscopy

• Published in: Journal of physics. Conference series 2016-04, Vol.713 (1), p.12007
• Main Authors: Haddock, D., Parker, T, Spindloe, C, Tolley, M
• Format: Article
• Language: English
• Subjects: Argon plasma; Bonding strength; Carbon; Diamond-like carbon films; Flow velocity; Foils; Gas flow; High power lasers; Laser targets; Lasers; Methane; Physics; Plasma enhanced chemical vapor deposition; Raman spectroscopy; Sodium chloride; Spectrum analysis; Substrates; Thickness
• ISSN: 1742-6588; 1742-6596
• DOI: 10.1088/1742-6596/713/1/012007

The search for target materials suitable for High Power Laser Experiments at ultralow thicknesses (below ten nanometres) is ongoing. Diamond-Like Carbon is investigated as an answer for a low-Z material that can survive target chamber pump-down and laser prepulse. DLC was produced using Plasma-Enhanced Chemical Vapour Deposition, using with varying gas flow mixtures of argon and methane. The methane plasma deposits amorphous carbon onto the substrate and the argon plasma re-sputters the weakly bonded carbon leaving a high proportion of diamond-like bonding. Bonding natures were probed using Raman spectroscopy; analysis of the resulting spectrum showed that flow rates of 40sccm 60sccm methane to argon produced DLC films with a diamond-like (sp3) content of ∼20%. Increasing the methane gas flow decreased this value to less than 5%. DLC foils were processed into laser targets by method of float off; using a sodium chloride release layer and lowering into water, this was then lifted onto an array of apertures allowing for laser irradiation of the material with no backing. DLC with 20% sp3 content showed superior yield when compared to other materials such as metals and some plastics of the same thickness, with ∼70% of the target positions surviving the float off procedure at