Laser-Induced Decomposition and Ablation Dynamics Studied by Nanosecond Interferometry. 2. A Reactive Nitrocellulose Film

Abstract

Laser-induced decomposition and accompanying ablation dynamics of a reactive nitrocellulose film doped with a Cu-phthalocyanine derivative as a light absorber was investigated by applying a nanosecond interferometric technique. While nitrocellulose does not absorb XeF 351 nm excimer laser pulse, the film is heated instantaneously via rapid photothermal conversion in the doped Cu-phthalocyanine derivative. Below the ablation threshold, the irradiated film expanded transiently with no permanent etching; namely, thermal expansion and contraction processes were directly followed in the ns time region. Above the ablation threshold the expansion of the film was started during the excimer laser pulse, and then explosive decomposition was initiated, continuing in a few hundreds ns after the excitation. Generation of shock wave and ejection of gaseous plume were also observed by nanosecond photographic technique. The shock wave emerged at 100−200 ns after excitation and later than the typical shock wave formation time reported in general. The slow formation is consistent with the slow initiation of the decomposition, suggesting a specific ablation process of the nitrocellulose film. Temperature elevation caused by the excimer laser irradiation results in an exothermic decomposition of nitrocellulose, leading to a further temperature rise of the film. Consequently self-acceleration of the reaction is enhanced and an explosive self-sustaining decomposition is induced after reaching the explosive decomposition condition. Ablation rate was determined to be 0.63 m/s which is slower than that of detonation but faster than that of combustion.

Time-resolved techniques as probes for the laser ablation process

“…This method focuses on the structuring of the remaining polymer and is therefore used mostly in the lower fluence range (at fluences above 1 J cm À2 , the ablation rates are in most cases, quite high, making the data evaluation very difficult). Previous studies using this technique have shown that some polymers exhibit a pronounced swelling and a delayed material removal [12,13], whereas other polymers revealed structuring without swelling [14][15][16][17].…”

“…Ns-shadowgraphy can be used to image the material, which is ejected after laser irradiation [13,18,19]. This method can be used from fluences close to the threshold up to the fluence which creates plasma.…”

Low-cost photomask fabrication using laser ablation

“…Then the mass loss slows down between 100°C and 150°C. The quick mass loss from 150°C and the exothermic peak at 169°C come from autocombustion of the nitrocellulose component of the lacquer (Furutani et al, 1998). Less volatile components leave above 250-300°C.…”

“…M a n u s c r i p t 11 Therefore the used consumer lacquer is more UV absorbing that pure nitrocellulose. Probably other components added to its formulation act as sensitizer dyes (Furutani et al, 1998) -see the appendix for the qualitative composition of the consumer lacquer. Fig.…”

Nanosecond surface interferometry measurements on designed and commercial polymers

“…A variation of this technique has been used in previous studies to observe the ablation process of different polymers. In some cases surface swelling prior to material removal was observed [18,19], while in other cases the material removal started and ended with the laser pulse [19][20][21]. Pronounced surface swelling has been used as an indication for a photothermal process, where thermal expansion is observed prior to ablation.…”