Lukas Urech

Designed polymers for laser-based microthrusters: correlation of thrust with material, plasma, and shockwave properties (Plenary Paper)

The micro laser plasma thruster (μLPT) is a micropropulsion device, designed for the steering and propelling of small satellites (10 to 100 kg). A diode laser is focused on a two-layer polymer tape, where it forms a plasma. The thrust produced by this plasma is used to control the satellite motion. Three different polymers (GAP, PVN and PVC) doped with carbon and/or IR-dye were investigated for their performance as fuel polymer. The different dopants for GAP seem to have only little influence in the ablation properties. The most pronounced differences are observed in the fragment ejection detected in the shadowgraphy measurements and the crater appearance. For all carbon doped polymers, the ablation spots have a similar rough morphology. The shadowgraphy measurements of PVN reveal, that the shockwave and particle plume propagates faster as in the case of the other polymers. The particle plumes showed a very different expansion behavior for all polymers, whereas the plasma temperature and electron density measurements showed no significant difference. Only PVC displayed a slower almost linear drop of the plasma temperature over time. The thrust measurements showed the best results for GAP.

Giant Momentum Coupling Coefficients from Nanoscale Laser-initiated Exothermic Compounds

*† ‡ § ** †† ‡‡ We report here on results obtained with laser-initiated micro-propellants, such as PVN, PVC, GAP, NC, and mixtures of these. All samples were doped with a laser absorbing component. In some cases, this was carbon nanopearls with 10nm mean diameter, while, in others, it was a carbon-based ink with ∝m-size particles. We also report results of performance tests for absorbers tuned to the 935-nm laser wavelength.

Incubation behaviour in triazenepolymer thin films upon near-infrared femtosecond laser pulse irradiation

The effects of laser radiation induced by a sequence of ultrashort (130 fs), near- infrared (800 nm) Ti:sapphire laser pulses in ~1 µm thick triazenepolymer films on glass substrates have been investigated by means of in-situ real-time reflectivity measurements featuring a ps-resolution streak camera and a ns-resolution photodiode set-up. The polymer films show incubation effects when each laser pulse in the sequence has a fluence below the single-pulse damage threshold. Non-damage conditions are maintained for several incubation pulses such that the reflectivity of the film shows a rapid decrease of up to 30% within 1 ns but subsequently recovers to its initial value on a ms timescale. Additional pulses lead to a permanent film damage. The critical number of laser pulses needed to generate a permanent damage of the film has been studied as a function of the laser fluence. Once damage is created, further laser pulses cause a partial removal of the film material from the glass substrate. Scanning force microscopy has been used to characterise ex-situ the irradiated surface areas. Based on these complementary measurements possible incubation mechanisms are discussed.

Designed polymers for laser-based microthrusters: correlation of thurst with material, plasma, and stockwave properties

The micro laser plasma thruster (μLPT) is a micropropulsion device, designed for the steering and propelling of small satellites (10 to 100 kg). A diode laser is focused on a two-layer polymer tape, where it forms a plasma. The thrust produced by this plasma is used to control the satellite motion. Three different polymers (GAP, PVN and PVC) doped with carbon and/or IR-dye were investigated for their performance as fuel polymer. The different dopants for GAP seem to have only little influence in the ablation properties. The most pronounced differences are observed in the fragment ejection detected in the shadowgraphy measurements and the crater appearance. For all carbon doped polymers, the ablation spots have a similar rough morphology. The shadowgraphy measurements of PVN reveal, that the shockwave and particle plume propagates faster as in the case of the other polymers. The particle plumes showed a very different expansion behavior for all polymers, whereas the plasma temperature and electron density measurements showed no significant difference. Only PVC displayed a slower almost linear drop of the plasma temperature over time. The thrust measurements showed the best results for GAP.