The interaction of light and matter leads to many interesting phenomena (such as the rotation of leaves in a Crookes radiometer) and important applications (such as optical tweezers to manipulate microscopic particles). These phenomena and applications involve the momentum transfer process , And observe the law of conservation of momentum. In the process of momentum transfer often involves the discussion of the role of light and light and heat.
Light power comes from the transfer of momentum between a photon and an object. Matter in the process of absorption and scattering of photons, photon momentum transferred to the object, so that the object by the light of the role. Optical tweezers manipulation of microscopic particles that is the role of the use of light.
Light and heat come from the momentum conservation of gas molecules and objects in the light and heat process. For a light-absorbing object in a gaseous environment, the uneven temperature distribution due to uneven light absorption in different parts. Where the temperature is high, gas molecules move at a high velocity and more momentum is transferred back to the object, thereby giving the object a force in the direction of the inverse temperature gradient. The principle of Crookes radiometers is due to this.
Because of the often different environments in which light and light are used (light driven generally in solution, while light and heat are more likely to work in a gaseous environment), few studies have combined these two forces to drive objects. In addition, in general, the light and the thermal energy are mostly shown as the thrust along the light propagation direction. The so-called optical tension force against the light propagation direction has attracted the attention of many researchers in recent years because of its counter-intuitiveness.
Figure 1. Cone optical fiber - micro-nano gold film system of light and thermal simulation results
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The research work is actually the use of the optical power and thermal power in the conical optical fiber due to the different distribution of the competition. From the distal end of the tapered fiber to the tip, its diameter becomes smaller and the evanescent field of the fiber surface also weakens. If the micro-gold piece on the tapered fiber near the tip, the micro-gold sheet in the optical fiber due to the absorption of photons and the light heat will also be weak from strong to form a temperature gradient in the surface of the micro-gold sheet, resulting in a very large light heat. This light and heat can be micro-gold sheet along the direction of light access and pull the opposite direction. When the micro-gold piece is pulled away from the tip, the light power due to scattering will push the gold piece toward the tip of the tapered fiber. The resultant force of light and light is different in different directions of the tapered optical fiber. If the direction of the pointed optical fiber is specified as the positive direction, the resultant force is negative near the tip, that is, the tensile force, and the resultant force away from the tip is positive, that is, For the thrust interval. As a result, a driving system that combines the thermal pull force and the light thrust force is formed, so that the micro gold sheet moves back and forth on the tapered optical fiber.
Figure 2. Micronanoelectronic film in tapered optical drive back and forth on the experimental results
This finding can be used to generate mechanical energy by light and is expected to gain important applications in photomechanical displacement (light-driven motors).
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