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The fluence dependence of the laser ablation of selected polymers was studied within the range from 1-150 J/cm 2 . A TEA CO 2 laser operating at 10.6 µm with 300 ns main pulse length and up to 20 J pulse energy was used to ablate prepared polymer samples with single pulses of laser energy. Measurements of parameters such as the ablated mass per spo...
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... model is one of the least complex and has a simple dependence on τ m , so that using the threshold fluences derived above for the C m , the parameter estimate will be very close. A typical plot of η i vs. fluence is shown in Figure 2. Following the Fresnel equations, the theoretical normal incidence τ m for a polymer with a smooth surface and index of refraction within 1.2-1.6 is approximately 0.95-0.99. ...
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Results are presented from study of the effi ciency (ablated mass per unit energy, mechanical recoil momentum per unit energy) of laser ablation for a light-curable polymer. A substantial difference is seen between the thresholds and indicated criteria for laser ablation effi ciency in the liquid and cured phases. The highest energy effi ciency for...
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... In Fig. 5, the solid line shows the optimum laser energy density for a ¼ 0 measured in experiment. The dashed dotted line and dashed line show the optimum laser energy density for the incidence angle of 0 calculated from the equation of Sinko 24 and Phipps, 17 respectively. The optimal fluence expression of Phipps's is obtained by maximizing the vaporization model. ...
... 17 The optimal fluence expression of Sinko's is obtained by the laser fluence dependent ablation model. 24 Both the optimal fluence prediction expression could be used for the impulse coupling at low fluence with the laser wavelength from UV to IR and the pulse duration from ns to ms FIG. 5. The relative impulse coupling coefficient of (a) steel, (b) aluminum, and (c) iron at the laser incidence angles of 0 and 45 . ...
A calibrated pendulum measuring device and a dimensionless analysis method were used to measure the impulse coupling coefficient at different laser intensities with aluminum, steel, and iron targets. The experiment was performed with a pulsed laser with the wavelength of 1.06 μm and the pulse duration of 7 ns. The experimental measurements of the variation of the impulse coupling coefficient versus the laser energy density agree with the theoretical prediction, and the optimum laser energy density correlated with the maximum impulse coupling coefficient corresponding to the theoretical predictions. The impulse coupling coefficients with laser incidence angles of 0 ° and 45 ° are compared for understanding of the effects of the ablation plume on the impulse coupling effect, and the experimental result shows that the impulse coupling effect grows as the incidence angle changes from 0 ° to 45 °. Furthermore, the transmittance of the incident laser through the ablation plume in front of the target is deduced from the impulse measurements, and the effect of the ablation plume on the impulse coupling at high laser intensity is discussed. In order to investigate the weak impulse coupling effect, which is difficult to obtain from the experiments, the impulse coupling coefficient at low laser energy density was calculated by the finite element simulation.
... The GAP subdetonation impulse bit also shows a 74% improvement over the solid propellant baseline case, and the detonation cases yield a 222% improvement over the solid propellant impulse bit, and a corresponding 86% improvement over the subdetonation cases. Investigations of the effect of laser fluence in ablative laser propulsion [3,17] have shown that as the fluence increases past some threshold fluence value, the coupling coefficient tends to decrease and the specific impulse increases. The sensitivity of the coupling coefficient to the fluence decreases as the fluence increases. ...
... The full detonation simulation resulted in a much lower specific impulse (approximately half of the subdetonation specific impulses) which is due to a much larger mass ejection. The relationship between mass and fluence was explored for other materials in [17]; the lower-fluence region (between 0.1 to 1:0 MJ=m 2 ) seems to decrease in similar fashion as the coupling coefficient, but above 1:0 MJ=m 2 , the mass ejections rise again and level off. Our simulations indicate a similar decrease in the lowerfluence region for the subdetonation cases of GAP. ...
Interest in development of micro-and nanosatellites has led to the design of the microlaser ablation plasma thruster. Previous work succeeded in constructing a working computational model of the microthruster's operation via MACH2, a two-dimensional magnetohydrodynamic code; however, this model was limited to simulating only nonenergetic solid propellant ablation in the microthruster. Recent experimental investigations have demonstrated that use of an exothermic (energetic) propellant can significantly improve performance of the microthruster and allow for higher-thrust modes of operation. The present work details new simulations of exothermic glycidyl azide subdetonation and full detonation processes; the results indicate a successful capability to match the detonation characteristics of the glycidyl azide and its ablative behavior. Particularly, the threshold for the onset of detonation in the fuel is explored and matches within approximately 14% of theoretical calculations of threshold pressure. This demonstrates the possibility to explore the selection of fuel for the microlaser ablation plasma thruster via computational investigations. Glycidyl azide polymer subdetonation simulations indicate a 74% improvement in impulse bit over the previous nonenergetic propellant. A confined ablation setup is also explored for detonation, which demonstrates a vast improvement to performance while suppressing the propagation of shocks.
... where f m mirrors the ablation mechanism (photochemical, or better: following Beer's law, and photothermal) and f v reÀects the model for the exhaust velocity (Index A: [16], Index B: [17]) yielding 4 major model combinations, denoted as 1, 5, 6, and 10 in [15], with ...
We report on an international cooperation between Nagoya University (NU), Japan and DLR Stuttgart, Germany on scaling issues in laser ablative propulsion. Lessons learned from
collaborative work in the laboratory will be summarized with respect to the comparability of experimental methods and corresponding standardization issues. With the background of previous experimental research at the University of Alabama in Huntsville (UAH), experimental work with CO2 lasers in a moderate (NU) and high (DLR) pulse energy range on laser ablation of POM is presented. Profilometry results of target surfaces are compared with fluence distributions from beam
propagation modeling. Ablation from flat targets is reported with respect to energy and area scaling and compared with results from ablative propulsion employing parabolic nozzles.
... The distribution of electron concentration in a sur face plasma formation under laser stimulation of (CH 2 O) n target is given in Fig. 9; according to these data, the velocity of motion of vapor front 75 ns after Linear coefficients of absorption of (C 2 F 4 ) n target: (1, 5) femtosecond ablation, (5) [11,18]; (2) micro nanosecond abla tion [20][21][22][23][24][25][26][27]; (3) spectrophotometrically determined [7] spectral dependence of the coefficient of absorption; (4) IR spectropho tometry [28]; hollow symbols correspond to measurements in vacuum. 3 km/s. ...
A description is made of the experimental-diagnostic module with femtosecond terawatt laser complex (τ0.5 ∼ 45–70 fs, λ = 266, 400, and 800 nm) and of the pioneering procedure of combined ultrahighspeed interferometry and interference
microscopy (Michelson and Mach-Zehnder schemes) of the processes of interaction between ultrashort laser pulses and condensed
media in vacuum. Results are given for the first time of the investigation of spectral-energy thresholds and rates of laser
ablation of a number of solidstate media using elements of the polymer series (C2F4)
n
, (CH2O)
n
in the UV-NIR wavelength range of laser radiation in atmospheric conditions and in vacuum p ∼ 10−2 Pa.
... An increase in both I sp and C m could be somewhat unexpected, since these two parameters are intrinsically related to each other in an inverse fashion, but because the nozzle improved the overall ablation efficiency (at least, strictly in a mathematical sense), more specific impulse and coupling coefficient were accessible to the micro-thruster. This demonstration of increasing available ablation efficiency, and hence increasing both coupling coefficient and specific impulse, was observed experimentally as well [34]. The nozzle tests performed indicate that coupling coefficient and specific impulse increase with increasing nozzle half-angle, and that a longer nozzle (around 210µm in length) is more appropriate for creating larger thrusts than a smaller (90µm) nozzle. ...
... These simulations have not identified the optimal design. However, the typical nozzle trends demonstrated experimentally [34] and to be expected [11] have been shown to be the same for subkilogram laser micropropulsion for some nozzle designs, which indicates that the coupling coefficient can be greatly improved for solid passive propellants. Previous experimental work [35] has already been performed for the physical fabrication of nozzles on this scale, and these simulations provide work that may be used in future experiments to verify nozzle designs sufficient for substantial performance improvement of the micro-thruster operation. ...
Keeping in view the weightage of electric propulsion over chemical propulsion, materials from metals to polymers and liquid (water) have been tested as propellants in ablative laser propulsion. This emerging propulsion technique can be widely used for aerospace applications like debris removal in the range of cm, pointing micro and nano satellites, laser micro thrusters for spacecraft attitude, and orbit control. Laser propulsion can become a less expensive alternative to chemical propulsion. In this review, we compile the work done in ablative laser propulsion and different modes of propulsion along with the efficiency of different propellants. We summarize the optimized propulsive parameters with solid propellants and liquid propellants along with the efficiencies and theories of laser thrusters with optimized specific impulses. The article provides precise developments done in the field of ablative laser propulsion and deep insights into the analysis done between the different propellants used recently in ablative laser propulsion.
Conventional propellant materials, such as polymers and single metal elements, have long been investigated for their potential in pulsed laser micropropulsion (LMP) technology. However, achieving superior LMP efficiency through physical mixing of these materials remains a significant challenge. In this study, we present a paradigm shift by introducing porous crystalline polymers, known as Metal‐Organic Frameworks (MOFs), as novel propellants in pulsed LMP. MOFs are composed of metal cations and organic ligands that form ordered structures through coordination, eliminating the problem of local hot zones arising from uneven physical mixing encountered in LMP. In direct comparison to conventional polymers and single element targets, MOFs exhibit substantially higher LMP efficiency. By precisely tailoring the metal atom fraction within MOFs, an extraordinary ultrahigh efficiency of 51.15% is achieved in pulsed LMP, surpassing the performance of similar materials previously reported in the literature. This pioneering application of MOFs not only revolutionizes the field of laser micropropulsion but also opens up new frontiers for MOF utilization in various energy applications.
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More and more researchers have been showing great interest in laser propulsion for its outstanding merits, such as high specific impulse, low cost, etc. Laser propulsion research programs and their development history abroad have been introduced briefly. The latest progress of laser propulsion researches is summarized. Degree of maturation of related technologies is analyzed, such as laser, transmission control system, thermodynamic protection of nozzle, etc. The development trend of laser propulsion is discussed. The application prospect of laser propulsion is presented. The key problems that should be urgently sloved are pointed out such as the indepth study on operation mechanism of laser propulsion.
In the case of low laser energy density, the vaporization process dominates the impulse production compared with other physical processes. One dimensional theoretical model was employed to describe the relationship among energy density and momentum coupling coefficients, specific impulse and the internal efficiency. Theoretical results show that there is an optimum energy density with maximum momentum coupling coefficient. The specific impulse increases with the increase of energy density. For a constant value of transmissivity, the internal efficiency approaches a constant as energy density increases. These theoretical analytical results can be helpful for further experimental works.
Polyoxymethylene (POM) has been widely studied as a promising laser propulsion propellant when paired to CO2 laser radiation. POM is a good test case for studying ablation properties of polymer materials, and within limits, for study of general trends in laser ablation-induced impulse. Mechanisms such as vaporization, combustion, and plasma are evaluated and a description is made of the link between the fluence of the beam and the resulting temperature of the target. For characterization of propulsion parameters, almost all previous studies of POM considered limited ranges of ambient pressure and incident fluence. As a result, despite many studies, there is no general understanding of POM ablation that takes into account pressure, spot area, fluence, and effects from confinement and combustion. This paper reviews and synthesizes CO2 laser ablation propulsion work using POM targets in order to make preliminary steps to address this deficiency. Previously published data is compared in terms of ablated mass as well as propulsion parameters such as momentum coupling coefficient (Cm) and specific impulse (Isp), within a range of fluences from about 1×104-5×106 J/m2, ambient pressures from 10-2-105 Pa, and laser spot areas from 10 -6-10-3 m2.
