term paper of physics (2)

7/31/2019 Term Paper of Physics (2)

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Optical tweezersIntroduction:

Optical tweezers is a new type of optical micro-manipulation and micro-

fabrication system. Different from conventional mechanical system, the opticaltweezers can tweeze, manipulate and fabricate small work pieces such as

biological cells, organelles and other micro-particles by light. It is a remote micro-

process without any mechanical touch.

The principle of optical tweezers is: when a laser beam is tightly focused to

act on the micro-particle, the photon can transfer its momentum to the particle

which thus achieves the weak force, and the composition of forces added to the

micro-particle in the converged optical field points to the center of the optical field.

Therefore, no matter where the micro-particle is in the optical field, the gradient

force in this field can firmly trap it within the optical field, i.e., the focus spot ofthe laser beam. When the laser beam moves, it brings the movement of the micro-

particle simultaneously and makes the precise control on the micro-particle

possible. Because it uses laser beam to realize the non-mechanical-touch capture,

no mechanical damage occur on the micro-particle. Also because all the

mechanical parts of the optical tweezers are far away from the captured object, it is

a remote-control operation, no mechanical parts affect the particles surroundings.

Therefore the optical tweezers is especially applicable to the research on the live

bio-particles. The trap of optical tweezers over micro-particles is not rigid but

flexible like a spring, which can real-time measure the interaction forces among the

micro-particles during the operation process. Thus the optical tweezers can also actas a force probe during this process or a force sensor. All these characteristics not

only make the optical tweezers as a mechanical hand able to control micro-

particles but also an ideal means of investigating static and dynamic mechanics of

micro-particles.

Description of the product:Our optical tweezers product incorporates laser technology, digital technology

and micro-imaging system. Infrared laser (808nm) or red laser (650nm) is focusedon the micro-object and traps it. The micro-manipulation process can be monitored

and recorded into a PC computer via micro-imaging system and CCD camera. The

laser beam can be focused to a spot with minimal diameter of 1 m. The size ofordinary biological cells is about few micrometer, so this system can satisfy the

requirement of most biological and physical experiments.


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Video 1: the demonstration of trapping and moving PMMA beads.

Video 2: the demonstration of trapping and moving yeast cell.


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In colloid physics, it can be applied to study the interaction among small

particles.

In nanotechnology research, optical tweezers can be used to drive micro-

mechanic components and measure mechanical parameters of micro-system.

This system can be used as not only an optical tweezers but also a platform for

investigation of interactions between laser and small particles. By extending its

functions, it can be used for studying the material particle variation process with

different wavelength and different pulse duration of the laser.

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Education field:At present time, the laser experiments for physics graduate and undergraduate

students are almost based on the electromagnetic effect and thermal effect of the

laser. The college physics books have pointed out long before that the photon has

momentum. The optical tweezers is produced just on this mechanical effect oflight. The optical tweezers experiment can impel students to further understand the

inherent essence of light.

By doing the optical tweezers experiment, students can comprehend the

construction and principles of the optical microscope, the working principle of

CCD, the influence of the different luminance sources on the microscopic

resolution, the concept of diffraction limitation, the relationship among individual

conjugate areas in optical microscope. All these trainings will enrich students

theoretical and practical knowledge in optics.

Optical tweezers is a new tool for investigation of life science with

optoelectronic technology. Many biological and physical phenomena are involvedin the experiment. This optical-mechanical-electrical integrated system can

extensively broaden the students knowledge and lay a solid foundation for theirfuture development.

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