Open Access
Add to BibSonomy
Abstract
Laser propulsion of a graphene sponge shows tremendous potential in propellant-free flight, photoresponsive actuators and micro opto-electro mechanical systems. However, the mechanism is still in dispute and the propulsion force hasn’t been accurately measured, seriously hindering its development. This work develops a quantitative method to measure the propulsion force. It is found that the characteristics of the force agree qualitatively with the Knudsen force due to laser-induced thermal nonequilibrium in rarefied gas, which might be another possible mechanism of laser propulsion of a graphene sponge. Also, this kind of laser propulsion is highly efficient, stable and sustainable.
© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Light-matter interactions [1–5] lead to various optical actuating techniques that can be used for photonic propulsion and photoresponsive actuators. The reported photonic propulsion solutions mainly include light pressure [6–8], light-induced ablation [9–11] and optical gradient force [12–14]. Meanwhile, the photoresponsive actuators can be realized by photothermal [15–19], photochemical [20], photomechanical [21], and photoelectronic actuating schemes [22]. Although there are diversiform application scenarios, the core issue of optical actuating techniques is the conversion of light-to-work. In order to realize stable, repeatable and precise actuating force output with high energy efficiency, advanced optical actuating schemes and mechanisms are always desired.
Recently, direct laser propulsion of graphene sponge (LPGS) [23] attracts widespread attention from the fields of photonics [24–26], materials [27,28] and space exploration, where the light-driven propulsion force was estimated to be several orders of magnitude higher than that of traditional light pressure. Due to the propellant-free advantage of LPGS, graphene is regarded as a promising material to build the next generation of light-driven spacecrafts for space exploration [29]. Meanwhile, the LPGS is also regarded as a new photoelectronic actuating scheme for light-to-work conversion, which can be used to fabricate photoresponsive actuator and micro opto-electro mechanical system [30–32]. However, in order to realize the above applications, the mechanism of LPGS should be experimentally confirmed and the laser propulsion force should be quantitatively measured.
At present, the mechanism of LPGS is still a controversial issue. Zhang et al. firstly proposed a possible mechanism of laser-induced electron emission to explain their experimental result [23]. But several scholars and groups concerned about the sustainability of LPGS according to the electron emission mechanism [33]. More seriously, Wu et al. [34] challenged this mechanism and put forward an alternative theoretical view that the laser propulsion is possibly originated from the interaction between the temperature-heterogeneous graphene sponge and rarefied gas in the vacuum chamber. However, up to now, no experiments have been performed to confirm the mechanism of LPGS. Moreover, the propulsion force hasn’t been accurately measured, and people still have no answer if this kind of laser propulsion is sustainable. These unresolved issues seriously hinder the development and practical use of LPGS.
In this work, a graphene-sponge gravity pendulum driven by laser was designed, and the optical lever method was used to quantitatively measure the laser propulsion force. The propulsion force induced by a mW-level laser beam exceeds 4.3 µN with a high energetic efficiency of 62.6 mN/kW. Besides, our experiments have proved that this kind of propellant-free laser propulsion is stable and sustainable.
2. Experimental setup
2.1 Laser propulsion of a graphene sponge in a glass tube at low pressure
Cm-level graphene sponge blocks with density of ∼ 18 mg/cm3 were supplied by a commercial corporation XFNANO. Graphene sponge fragments were taken off a block and then put into a half-open glass tube (Fig. 1(a)). Argon at low pressure was pumped into the half-open glass tube, and meanwhile the glass tube was sealed with a flame gun. The final pressure of Argon inside the sealed glass tube was between 1 Pa and 10 Pa.
Fig. 1. Laser propulsion of graphene sponge in a closed glass tube at low pressure. (a) The photograph of the glass tube (the inset is the graphene sponge fragments). (b) The experimental facility. (c) The photograph of graphene sponge before laser propulsion. (d) The photograph of graphene sponge under laser irradiation. (e) The photograph of graphene sponge after laser propulsion.
2.2 Preparation of the reflecting mirror
A 0.17 mm thick glass substrate was cleaned by acetone, alcohol, deionized water, respectively, and then dried by N2. Afterwards, the gold nanofilm was deposited onto the glass substrate using an ion sputter. The deposition time was 100 s and the deposition current was 6.2 mA and the deposition air pressure was 6.8 Pa.
3. Results and discussion
3.1 Laser propulsion of a graphene sponge in a glass tube at low pressure
Firstly, we perform a simple and fundamental experiment of the LPGS. In order to avoid the possible laser ablation effect, a mW-level continuous laser with wavelength of 488 nm was adopted. The maximum laser power output is less than 100 mW, and the diameter of laser spot is about 1 mm. As shown in Fig. 1(a), (a) small number of graphene sponge fragments (total mass < 1 mg) taken off a block are put into a glass tube that is filled with argon at low pressure between 1 Pa to 10 Pa. As shown in Fig. 1(b), (a) simple experimental facility of laser propulsion was built, and the laser beam propagation direction was from left to right. Herein the output laser power is set to 70 mW and a manually controlled shutter is used to switch the laser beam. Before laser irradiation, the graphene sponge is stably located in the left side of glass tube with no internal flow of gas (Fig. 1(c)). After laser irradiation for less than 1 s (Fig. 1(d)), the graphene sponge moves forward clearly along the laser beam propagation direction (Fig. 1(e)). The dynamic process is further displayed in the Visualization 1.
According to the above experiment, it can be confirmed that a propulsion force has been produced under laser irradiation in the glass tube at low pressure, which agrees with Zhang’s results on the whole [23]. However, in addition to the possible mechanism of laser-induced electron emission proposed by Zhang, the LPGS might be also originated from the Knudsen force because rarefied gas still remains in the vacuumed chamber or glass tube. Under laser irradiation, the front side of graphene sponge absorbs more photon energy and therefore has higher temperature than the back side. In this case, the molecules that reflected on the hot side of graphene sponge have higher momentums than those reflected on the cold side, thus causing a force that acts from hot to cold, which is generally called Knudsen force (or radiometric force) [35]. These two mechanisms are highly different. Firstly, for the mechanism of Knudsen force, the propulsion force firstly increases then decreases when the air pressure increases, which shows a bell-shape curve [36]. In free molecular or nearly free molecular flows (i.e. at relatively low air pressure), the momentum transfer between the object surface and the gas molecule is the most efficient, thus the Knudsen force is positively correlated with the air pressure. With further increasement of the air pressure, molecular collisions increase and thus the thermal nonequilibrium in gas becomes less significant, and the Knudsen force gradually weakens [37]. Secondly, for the mechanism of laser-induced electron emission, when the air pressure increases, the airflow resistance increases and thus the propulsion force decreases. According to the above analysis, precise measurements of the laser propulsion force at different air pressures are needed for the confirmation of the reasonable mechanism.
3.2 Experimental design for the quantitative measurement of laser propulsion force
In order to avoid the possible laser ablation and irreversible damage of the graphene sponge, the experimental laser power we used was extremely low (< 100 mW) thus producing small propulsion force. Herein, a graphene-sponge gravity pendulum driven by a weak laser beam was designed, and the reflection-based optical lever method was used to accurately measure the small propulsion force. The conceptual diagram of the experimental facility is described in Fig. 2. As shown in Fig. 2(a), a graphene-sponge gravity pendulum with measurable mass is placed inside a vacuum chamber, and the left propulsion laser beam (488 nm) can travel through a shutter and shine onto the front side of the graphene sponge. A small reflecting mirror (marked in green) is linked to the back of the gravity pendulum, which reflects the detection laser beam (355 nm) onto a receiving screen. Once the left propulsion laser irradiates the graphene sponge, the propulsion appears and causes a tiny deflection angle θ. Then, a significant displacement of the reflected laser spot on the receiving screen can be easily observed and manually measured. In other words, the tiny deflection angle is amplified by the “optical lever”. On the basis of geometry knowledge, the deflection angle θ can be calculated by the formula $\tan \theta = \frac{{\varDelta h}}{D}$. If the mechanical equilibrium of the graphene-sponge gravity pendulum is realized during laser propulsion, the deflection angle θ is stable. Figure 2(b) shows a simplified force equilibrium analysis of the graphene-sponge gravity pendulum, where T is the tension on the swinging arm and G is the total gravity of the graphene-sponge pendulum. In this case, the laser propulsion force ${F_{laser}}$ is decided by the following equation:
Fig. 2. Conceptual diagram of the laser propulsion and force measurement system. (a) The schematic diagram of the experimental facility. (b) Simplified force equilibrium analysis of the graphene-sponge gravity pendulum.
3.3 Experimental measurement and mechanism analysis of the laser propulsion force
A home-made experimental facility was built to realize the design shown in Fig. 2. In the experiments, an ion sputter was simply modified and provided a vacuum chamber and the vacuum-pumping system (Supplement 1, Fig. S1). As shown in Fig. 3(a), the swinging arm of the pendulum is made of a 0.06 mm thick conductive copper foil tape, which is freely placed on a conductive grounded cross bar. A small number of graphene sponge fragments (the total area is 5 mm × 5 mm, and the total mass is less than 1 mg) is sticked on the bottom of the copper swinging arm. The mass of copper swinging arm is far greater than that of graphene sponge, which is conducive to construct a stable swing system and reduce the measurement error. The propulsion laser beam (488 nm) can travel through the transparent vacuum chamber and shine onto the graphene sponge (Fig. 3(b)). A gold nanofilm supported on a glass (See Experimental setup) as a reflecting mirror is sticked on the back of the copper swinging arm (Fig. 3(c)), which reflects the detection laser beam (355 nm) onto the receiving screen (inset of Fig. 3(c)). The total mass of the graphene-sponge gravity pendulum is 0.123 g (Supplement 1, Fig. S2), which consists of the graphene sponge fragments, the copper swinging arm and the reflecting mirror. The spatial distance between the graphene sponge and the receiving screen in experiments (i.e. D in Fig. 2(a)) is 4 m.
Fig. 3. Experimental facility and results of laser propulsion with different air pressures and laser powers. (a) The photograph of graphene-sponge gravity pendulum. (b) The photograph of graphene-sponge gravity pendulum under laser irradiation. (c) The photograph of the reflecting mirror and the inset shows the reflected light spot on the receiving screen. (d) The laser propulsion force as a function of air pressure. (e) The laser propulsion force as a function of laser power.
The adjustable range of the air pressure in the vacuum chamber and the laser power received by the graphene sponge are 3 ∼ 40 Pa and 0 ∼ 70 mW, respectively. Under different air pressures and laser powers, $\varDelta h$ was collected (Supplement 1, Fig. S3) and the corresponding ${F_{laser}}$ was calculated according to Eq. (1). As shown in Fig. 3(d) (and Supplement 1, Fig. S4), with the increasement of air pressure from 3 Pa to 20 Pa, the laser propulsion force firstly increases then decreases regardless of laser power, which indicates a typical and stable bell-shape characteristic of Knudsen force in rarefied gas [19]. Additionally, according to the previous studies, Knudsen force is closely related to Knudsen number (Kn = λ/L) and reaches the maximum when Kn is about 0.1, where λ is the mean free path of gas molecules and L is the length of an object in the gaseous environment [20]. In our experiment, the length of graphene sponge (L) on the gravity pendulum is about 5 mm and the laser propulsion force reaches the maximum at 5 Pa (the corresponding mean free path of gas molecules λ is 1.38 mm). Therefore, Kn for the maximum propulsion force in our experiment is calculated to be 0.276, which is consistent with the previous research (Kn = 0.1). Last but not least, under the assumption of nearly free molecular flow, the Knudsen force at the air pressure of 3 Pa is roughly estimated to be in the range from 3 µN to 5.8 µN (See supporting information), which matches well with our experimental result (2.1 µN) for the laser power of 70 mW (Fig. 3(d)).
As shown in Fig. 3(d), for air pressure of 5 Pa and laser power of 70 mW, the measured laser propulsion force is 4.3 µN. The corresponding energetic efficiency is as high as 62.6 mN/kW that is orders of magnitude higher than the light pressure propulsion. As shown in Fig. 3(e), increasing laser power appropriately leads to higher Th and therefore higher ${F_{laser}}$, which provides an external and convenient way to precisely control the ${F_{laser}}$. Besides, for an ultra-low laser power of 7 mW (the corresponding laser power density is 8.9×103 W/m2), the laser propulsion force is still remarkable, indicating an ultra-low demand of energy supply.
3.4 Stability and sustainability of the laser propulsion
The long-term sustainability is also important for the practical use of LPGS in propellant-free flight and photoresponsive actuator. Herein, the same experimental facility (Figs. 3(a), 3(b) and 3(c)) was used to investigate the long-term laser propulsion force. Real-time video surveillance was implemented to record the coordinate positions of the reflected light spot on the receiving screen (inset of Fig. 3(c)). Figure 4 shows the calculated real-time laser propulsion force every 15 s in the tests. As shown in Fig. 4(a), the laser propulsion forces are stable from 75 s to 345 s for the laser power of 30 mW (Visualization 2 and Visualization 3). As shown in Fig. 4(b), the laser propulsion forces are stable from 75 s to 330 s for the laser power of 50 mW (Visualization 4 and Visualization 5). Therefore, for a fixed air pressure and laser power, the laser propulsion force is stable and sustainable, where the tiny irregular changes of the force are mainly result from the vibration noise of the mechanical vacuum-pumping system. It should be noted that, the sustainability tests here are just simple validations using the home-made system. In principle, we believe that the continuous working time of this kind of laser propulsion can be much longer than 250 s after an optimized engineering design.
Fig. 4. The measured laser propulsion force as a function of time. (a) The air pressure is 5 Pa and the laser power is 30 mW. (b) The air pressure is 5 Pa and the laser power is 50 mW.
4. Conclusions
In this work, a graphene-sponge gravity pendulum driven by laser was designed, and the optical lever method was used to quantitatively measure the optical actuating force in LPGS. The measured force displayed the following features: high energetic efficiency of propulsion (62.6 mN/kW); ultra-low demand of the laser power (< 7 mW); repeatable and sustainable propulsion; bell-shape characteristic of the force-pressure curve. This work has developed a quantitative method to study and design the LPGS, and developed another possible mechanism of laser-induced Knudsen force to explain the LPGS. The high energetic efficiency and considerable propulsion force make it a potential technology for applications in propellant-free flight, photoresponsive actuator, sensing and micro opto-electro mechanical systems.
Funding
Key Technology Research and Development Program of Shandong (2018GGX101008); National Natural Science Foundation of China (11874232).
Disclosures
The authors declare no conflicts of interest.
See Supplement 1 for supporting content.
References
1. L. Wang, X. Chi, L. Sun, and Q. Liu, “Carbon nanotube bridges fabricated by laser comb,” Nanoscale 11(20), 9851–9855 (2019). [CrossRef]
2. L. Wang, X. Wang, X. Wang, and Q. Liu, “Laser drilling sub-10 nm holes on an island-shaped indium thin film,” Appl. Surf. Sci. 527, 146771 (2020). [CrossRef]
3. R. Zhang, Q. Zhao, X. Wang, J. Li, and W. Y. Tam, “Circular Phase-Dichroism of Chiral Metasurface Using Birefringent,” Nano Lett. 20(4), 2681–2687 (2020). [CrossRef]
4. T. Jiang, M. Xiao, W.-J. Chen, L. Yang, Y. Fang, W. Y. Tam, and C. T. Chan, “Experimental demonstration of angular momentum-dependent topological transport using a transmission line network,” Nat. Commun. 10(1), 434 (2019). [CrossRef]
5. M. Muñoz-Castro, N. Walter, J. K. Prüßing, W. Pernice, and H. Bracht, “Self-Holding Optical Actuator Based on a Mixed Ionic−Electronic Conductor Material,” ACS Photonics 6(5), 1182–1190 (2019). [CrossRef]
6. A. Lee, P. Zhang, Y. Xu, and S. Jung, “Radiation pressure-induced nonlinearity in a micro-droplet,” Opt. Express 28(9), 12675–12687 (2020). [CrossRef]
7. F. Pan, K. Cui, G. Bai, X. Feng, F. Liu, W. Zhang, and Y. Huang, “Radiation-Pressure-Antidamping Enhanced Optomechanical Spring Sensing,” ACS Photonics 5(10), 4164–4169 (2018). [CrossRef]
8. W.-T. Chiu, D. R. Mortensen, M. J. Lipp, G. Resta, C. J. Jia, B. Moritz, T. P. Devereaux, S. Y. Savrasov, G. T. Seidler, and R. T. Scalettar, “Pressure Effects on the 4f Electronic Structure of Light Lanthanides,” Phys. Rev. Lett. 122(6), 066401 (2019). [CrossRef]
9. D. J. Förster, S. Faas, R. Webera, and T. Graf, “Thrust enhancement and propellant conservation for laser propulsion using ultra-short double pulses,” Appl. Surf. Sci. 510, 145391 (2020). [CrossRef]
10. H. Yu, X. Wu, Y. Yuan, H. Li, and J. Yang, “Confined geometry and laser energy affect laser plasma propulsion,” Opt. Express 27(7), 9763–9772 (2019). [CrossRef]
11. L. Jiao, B. S. Truscott, H. Liu, M. N. R. Ashfold, and H. Ma, “Imaging spectroscopy of polymer ablation plasmas for laser propulsion applications,” J. Appl. Phys. 121(1), 013303 (2017). [CrossRef]
12. O. Ilic and H. A. Atwater, “Self-stabilizing photonic levitation and propulsion of nanostructured macroscopic objects,” Nat. Photonics 13(4), 289–295 (2019). [CrossRef]
13. X. Xu, L. Shi, L. Ren, and X. Zhang, “Optical gradient forces in PT-symmetric coupled-waveguide structures,” Opt. Express 26(8), 10220–10229 (2018). [CrossRef]
14. H. Zheng, X. Li, Y. Jiang, J. Ng, Z. Lin, and H. Chen, “General formulations for computing the optical gradient and scattering forces on a spherical chiral particle immersed in generic monochromatic optical fields,” Phys. Rev. A 101(5), 053830 (2020). [CrossRef]
15. Y. Zhou, J. Tan, D. Chong, X. Wan, and J. Zhang, “Rapid Near-Infrared Light Responsive Shape Memory Polymer Hybrids and Novel Chiral Actuators Based on Photothermal W18O49 Nanowires,” Adv. Funct. Mater. 29(33), 1901202 (2019). [CrossRef]
16. W. Wang, C. Xiang, D. Sun, M. Li, K. Yan, and D. Wang, “Photothermal and Moisture Actuator Made with Graphene Oxide and Sodium Alginate for Remotely Controllable and Programmable Intelligent Devices,” ACS Appl. Mater. Interfaces 11(24), 21926–21934 (2019). [CrossRef]
17. Y. Yang, Y. Tan, X. Wang, W. An, S. Xu, W. Liao, and Y. Wang, “Photothermal Nanocomposite Hydrogel Actuator with Electric-FieldInduced Gradient and Oriented Structure,” ACS Appl. Mater. Interfaces 10(9), 7688–7692 (2018). [CrossRef]
18. Y. Hagiwara, T. Taniguchi, T. Asahiac, and H. Koshima, “Crystal actuator based on a thermal phase transition and photothermal effect,” J. Mater. Chem. C 8(14), 4876–4884 (2020). [CrossRef]
19. D. Hua, X. Zhang, Z. Ji, C. Yan, B. Yu, Y. Li, X. Wang, and F. Zhou, “3D printing of shape changing composites for constructing flexible paper-based photothermal bilayer actuators,” J. Mater. Chem. C 6(8), 2123–2131 (2018). [CrossRef]
20. Y. Yu, T. Maeda, J. Mamiya, and T. Ikeda, “Photomechanical Effects of Ferroelectric Liquid-Crystalline Elastomers Containing Azobenzene Chromophores,” Angew. Chem., Int. Ed. 46(6), 881–883 (2007). [CrossRef]
21. A. Casner and J.-P. Delville, “Giant Deformations of a Liquid-Liquid Interface Induced by the Optical Radiation Pressure,” Phys. Rev. Lett. 87(5), 054503 (2001). [CrossRef]
22. Y. Hu, Z. Li, T. Lan, and W. Chen, “Photoactuators for Direct Optical-to-Mechanical Energy Conversion: From Nanocomponent Assembly to Macroscopic Deformation,” Adv. Mater. 28(47), 10548–10556 (2016). [CrossRef]
23. T. Zhang, H. Chang, Y. Wu, P. Xiao, N. Yi, Y. Lu, Y. Ma, Y. Huang, K. Zhao, X.-Q. Yan, Z.-B. Liu, J.-G. Tian, and Y. Chen, “Macroscopic and direct light propulsion of bulk graphene material,” Nat. Photonics 9(7), 471–476 (2015). [CrossRef]
24. M. H. Rahaman and B. A. Kemp, “Negative force on free carriers in positive index nanoparticles,” APL Photonics 2(10), 101301 (2017). [CrossRef]
25. W. Strek, R. Tomala, M. Lukaszewicz, B. Cichy, Y. Gerasymchuk, P. Gluchowski, L. Marciniak, A. Bednarkiewicz, and D. Hreniak, “Laser induced white lighting of graphene foam,” Sci. Rep. 7(1), 41281 (2017). [CrossRef]
26. L. Jiao, R. Chen, X. Zhu, Q. Liao, H. Wang, L. An, J. Zhu, X. He, and H. Feng, “Highly Flexible and Ultraprecise Manipulation of Light-Levitated Femtoliter/ Picoliter Droplets,” J. Phys. Chem. Lett. 10(5), 1068–1077 (2019). [CrossRef]
27. M. Chen, G. Li, W. Li, D. Stekovic, B. Arkook, M. E. Itkis, A. Pekker, E. Bekyarova, and R. C. Haddon, “Large-Scale Cellulose-Assisted Transfer of Graphene Toward Industrial Applications,” Carbon 110, 286–291 (2016). [CrossRef]
28. F. Guo, Y. Jiang, Z. Xu, Y. Xiao, B. Fang, Y. Liu, W. Gao, P. Zhao, H. Wang, and C. Gao, “Highly stretchable carbon aerogels,” Nat. Commun. 9(1), 881 (2018). [CrossRef]
29. I. Levchenko, K. Bazaka, S. Mazouffre, and S. Xu, “Prospects and physical mechanisms for photonic space propulsion,” Nat. Photonics 12(11), 649–657 (2018). [CrossRef]
30. Y. Wu, J. Zhu, and L. Huang, “A review of three-dimensional graphene-based materials: Synthesis and applications to energy conversion/storage and environment,” Carbon 143, 610–640 (2019). [CrossRef]
31. M. Yang, Z. Yuan, J. Liu, Z. Fang, L. Fang, D. Yu, and Q. Li, “Photoresponsive Actuators Built from Carbon-Based Soft Materials,” Adv. Opt. Mater. 7(16), 1900069 (2019). [CrossRef]
32. Y. Hu, J. Liu, L. Chang, L. Yang, A. Xu, K. Qi, P. Lu, G. Wu, W. Chen, and Y. Wu, “Electrically and Sunlight-Driven Actuator with Versatile Biomimetic Motions Based on Rolled Carbon Nanotube Bilayer Composite,” Adv. Funct. Mater. 27(44), 1704388 (2017). [CrossRef]
33. N. Gabor, “Lift off for graphene,” Nat. Photonics 9(7), 419–420 (2015). [CrossRef]
34. L. Wu, Y. Zhang, Y. Lei, and J. M. Reese, “Do thermal effects cause the propulsion of bulk graphene material,” Nat. Photonics 10(3), 139 (2016). [CrossRef]
35. Y. Li, A. M. Abazari, M. B. Gerdroodbary, T. D. Manh, N. D. Nam, P. Valipour, R. Moradi, and H. Babazadeh, “Three-dimensional DSMC simulation of thermal Knudsen force in micro gas actuator for mass analysis of gas mixture,” Measurement 160, 107848 (2020). [CrossRef]
36. A. Ketsdever, N. Gimelshein, S. Gimelshein, and N. Selden, “Radiometric phenomena: From the 19th to the 21st century,” Vacuum 86(11), 1644–1662 (2012). [CrossRef]
37. S. F. Gimelshein, N. E. Gimelshein, A. D. Ketsdever, and N. P. Selden, “Analysis and Applications of Radiometeric Forces in Rarefied Gas Flows,” AIP Conf. Proc. 1333, 693–700 (2011). [CrossRef]
