Optics Express: Qingdao University of Science and Technology's research on macroscopic laser traction in thin gas

It is reported that the research of researchers from Qingdao University of Science and Technology on macroscopic laser pulling based on the Knudsen force in rarefied gas was published in Optics Express with the title of "Macroscopic laser pulling based on the Knudsen force in rarefied gas".

In the past decade, the optical traction of micro and nano objects has been fully proved. However, the optical traction of macroscopic objects is challenging. In this paper, the laser traction of macroscopic objects in a thin gas is introduced. The macro scale graphene aerogel/silica bilayer is placed in the thin gas; The silicon dioxide layer is irradiated by a laser beam; The graphene aerogel/silica bilayer was pulled by a macro scale laser in thin gas. The pull force greater than three orders of magnitude than the radiation pressure is further measured by using the gravity pendulum device. This work extends the scope of optical traction from micro to macro, and provides an effective technical approach for macro optical operation.

Researchers have designed a macrostructure consisting of the front layer of cross-linked graphene (CLG) and the back layer of silica. When a Gaussian laser beam irradiates the rear layer in a rarefied gas environment (5 Pa), a macroscopic laser pull will be generated due to the effect of photothermal Knudsen force. The phenomenon of laser traction is qualitatively described with a light torsion pendulum device, and the laser traction force is measured with a gravity pendulum device.

Light torsion pendulum and macroscopic laser traction mechanism and torsion pendulum experimental device

Figure 1: Macroscopic laser traction mechanism and torsion pendulum experimental device. (A) The mechanism of macroscopic laser driving bulk CLG materials based on Knudsen force. (B) Based on the macroscopic laser traction mechanism of Knudsen force, the yellow layer is a low thermal conductivity optical transparent material. (C) Schematic diagram of torsion pendulum device, CLG-silica sample is fixed at the end of swing arm. (D) Twisted front photo, insert shows cylindrical CLG material. (E) Twist back photo. (F and G) The entire torsion device in the vacuum chamber.

The real experimental device of the gravity pendulum is shown in Figure 2 (A-C). Swing arm size is 50mm × 5 mm × 0.18 mm. The diameter of copper wire is only 0.06 mm, which is conducive to reducing friction resistance.

Figure 2. The experimental device and results of measuring laser tension with a gravity pendulum. (A-C) Size and material details of gravity pendulum device. (D) Photo of gravity pendulum without laser traction. The detection light with a wavelength of 360 nm is irradiated on the Au nano-film reflector on the back of the gravity pendulum. The upper right image shows the corresponding reflection detection (360 nm) laser spot on the optical screen. (E) Photos of laser traction gravity pendulum with wavelength of 488 nm. The upper right illustration shows the reflection detection (360 nm) laser spot on the optical screen.

The reflectivity and transmissivity of CLG materials are measured with a spectrometer (Ocean Optics USB4000) and an optical microscope (Olympus, BX51). The laser power described in this paper is measured by an optical power meter (Thorlabs PM100A).

Macroscopic laser traction experiment with different laser wavelength and different laser power
The macro laser traction experiment was carried out in a vacuum chamber (Fig. 1 (G)), and the internal air pressure was 5 Pa. As shown in Figure 3 (A), without laser irradiation, it will not swing. Subsequently, a continuous Gaussian laser beam with a wavelength of 532 nm is irradiated on the silicon dioxide layer on the back of the CLG-silicon dioxide sample from right to left (as shown by the green arrow in Figure 3 (B)). The laser power irradiated on the material is 60 mW, and the light is not focused. In this case, it is observed that the torsion pendulum rotates counterclockwise and the macro CLG-silica sample is pulled towards the light source (Fig. 3 (B) and (C)).

Figure 3: Macroscopic laser traction with different laser wavelengths. (A-C) Dynamic laser pull with 532 nm wavelength. (B-F) Twisted pendulum dynamic laser pull with wavelength of 488 nm. (G-I) Dynamic laser pull with 360 nm wavelength. The arrows B, E and H indicate the laser moving direction. The black dotted lines in C, F and I indicate that there is no initial position of the laser pulling torsion pendulum.

In addition, the relationship between the laser power and the rotation angle of the torsion pendulum is qualitatively studied by using a laser beam with a wavelength of 488 nm. As shown in Figure 4 (A-F), when the power of laser irradiation on the material increases from 17 mW to 85 mW, the maximum rotation angle of the torsion pendulum increases from 1 ° to 8.3 °. The experimental results show that there is a positive correlation between the laser incident energy and the tension amplitude. This is because after the laser energy is enhanced, the thermal movement of gas molecules increases the temperature difference between the front and rear sides, resulting in greater recoil.

Figure 4: Macroscopic laser traction with different laser power. (A-F) The maximum rotation angle of the torsion pendulum when the tensile laser power (irradiated on the material) is 0 mW, 17 mW, 34 mW, 51 mW, 68 mW and 85 mW respectively. The laser wavelength is 488 nm. The black dotted line in B-F indicates the initial position of the twist when there is no laser pull.

Measurement of laser tension

Figure 5: Measuring principle of laser tension. (A) Schematic diagram of gravity pendulum experimental device. (B) The mechanical balance analysis of the laser traction gravity pendulum regards the gravity pendulum as a rigid body rotating around the 0 axis.

In Optics Express, Wang Lei, a member of the research team of Qingdao University of Science and Technology of China, and his colleagues proved that the macro-graphene-silica composite they designed can be used for laser traction in a thin gas environment. The pressure in this environment is much lower than the atmospheric pressure. Wang Lei said: "Our technology provides a non-contact long-distance traction method, which may be useful for various scientific experiments." "The rarefied gas environment we use to demonstrate this technology is similar to the environment found on Mars. Therefore, it may one day operate vehicles or aircraft on Mars."

Article source:
Lei Wang et al, Macroscopic laser pulling based on the Knudsen force in rarefied gas, Optics Express (2022). DOI: 10.1364/OE.480019
Journal information: Optics Express
https://doi.org/10.1364/OE.480019
https://phys.org/news/2023-01-optical-tractor-macroscopic.html