###### Abstract
Various materials can be used as propellants for LAPPTs such as metals, oxides, carbon, and polymers, owing to the high energy density deposition of the laser [22; 23; 24]. Even though polymeric propellants are considered a promising option due to their relatively  
Figure 1: Schematics of PPT, (**a**) coaxial PPT and (**b**) laser-assisted (LA) PPT. low conductivity and high specific heat [25], most of them have a white or transparent appearance, resulting in lower laser absorption coefficients that limit their performance in an LAPPT [26; 27]. Recently, there has been growing interest in researching modified composite propellants fabricated by incorporating additives that have diverse properties for better application in LAPPTs. In 2018, [PERSON] et al. [28] investigated the effect of additives such as aluminum, silicon, copper oxide, and aluminum oxide on the characteristics of the plasma plume of a modified PTFE propellant. They explained that doping a PTFE with aluminum boosted the deposition of thermal energy inside the propellant and improved the ablated mass bit of the propellant accordingly. In 2020, [PERSON] et al. [29] investigated the impact of aluminum content, laser fluence, and environmental pressure on the ablated plume dynamics of an Al/PTFE propellant. It was found that the laser energy absorption of the propellant tended to change from volume absorption to surface absorption with the addition of Al powder. In 2021, [PERSON] et al. [30] experimentally analyzed the discharge characteristics and thrust performance of chemical propellants composited with ammonium nitrate (AN), 5-amino tetraazole, carbon powder, and PTFE as well as the effect of the proportion of PTFE on thrust performance. They proved that the chemical propellants achieved a higher thrust performance than PTFE. In 2022, [PERSON] et al. systematically investigated the influence of different polymer propellant additives (alloys, oxides, salts, carbon) on LAPPT performance. They revealed that the alloy additives improved the impulse bit; the salt additives promoted the stability of the discharge process; and the oxides produced higher specific impulse and thrust efficiency [2; 31]. [PERSON] et al. also found that the carbon-composited propellants had a higher specific impulse, momentum coupling coefficient, discharge success rate, and thrust efficiency compared to the other samples [32]. While these studies suggested that composite propellants impregnated with various optical-favored dopants enhanced the performance of LAPPTs, the principle by which they influenced the characteristics of the plume remains uncertain. In this study, we conducted a comparative analysis of plume characteristics generated by modified composite propellants filled with nano-carbon powder, graphite, and graphene under laser irradiation. First, we fabricated composite propellant samples filled with different carbon dopants under identical conditions. Next, we employed a high-speed camera to capture dynamic plume behavior resulting from the laser ablation of these composite propellant samples. Then, we used an image processing method to extract feature parameters of the dynamic plumes, which were then subjected to analysis to determine the preferred dopant. Furthermore, we investigated the dependence of plume characteristics on the doping ratio.