School of Electrical and Electronic Engineering

Supervisor:A.Prof Yuan Xiaocong,Larry, A.Prof Tang Dingyuan

Project Members:Mr. Lee Woei Ming, Mr. Yap Way Lin

Division of Microelectronic / Photonics

Look around you and try to pick up an object around you without using any kind of physical tools. Now try to rotate it.

Find it impossible?

Perhaps only a Jedi Knight or a tractor beam from Borg ship in Star Trek(Fig.1) can accomplish such a feat. Such feat is no longer a fiction realized in the world of entertainment…

Fantasy has come True ….right here in NTU. While the fictional tractor beam can entrap a gigantic spaceship, our version can manipulate micro-particles.

Our team has opened up a new and exciting research prospect in developing optical tools to control DNA and manufacture Nano-robot in Singapore. The future development of laser-based biological research and applications should be very bright indeed

Figure.1- A Scene from Star Trek-The Next Generation featuring a Tractor Beam

In our project, we have written a new program that can successfully generated a wide variety of Computer Generated Hologram(CGH) with dislocations. Subsequently, fabricating the CGH onto 35mm slides which is easily available. Once the fabrication is done, a He-Ne laser beam of 632.8nm is directed onto the hologram to produce the “Tractor Beam” which look like an American-doughnut (Fig.3)

This process force the laser profile to change from Gaussian profile to Laguerre-Gauss (LG) profile. By altering the profile of the beam, we have created a new version of optical tweezers. It offers a whole new dimension of laser manipulation. This novel optical trap can trap as well as rotate any micro-particle regardless of its intrinsic property.

Only recently, the year 2001, that a group of Scottish scientists have been able to rotate micro-particles using the same technology as us (Fig.2).

Figure 2 Rotation of microscopic particles using optical laser tweezers

Figure.3-Doughnut shaped

(LG) beam at 1st and -1st order

School of Electrical and Electronic

Engineering

Commercial Optical tweezers(Trapping only) system from Cell Robotics Inc & Arryx Inc

NTU-Succeed in creating array of LG beam for Micro-particle trapping and rotation

1999

1980

193

6

R.A.Beth - Measured Optical angular momentum

Arthur Ashkin – Succeeded Single Beam Trapping only

1995

University of Queens land & University of St.Andrews – Using LG beam to trap and Rotation of particles

200

2

World’s 1st Optical trapping And Rotation tools from Singapore ?

2005

?

Supervisor:A.Prof Yuan Xiaocong,Larry, A.Prof Tang Dingyuan

Project Members:Mr. Lee Woei Ming, Mr. Yap Way Lin

Phase singularities(Fig.4) singularities carry angular momentum due to the associated helical wave-front (Fig.5) structure, which is able to transfer energy to the particles and thus trap setting them into rotation. This rotation will act as a trap. Hence, by trapping the particles it performs a task like a pair of optical tweezers.

Along the center of the laser beam, the phase of a wave is not defined as it changes at phase of 2π. As it propagates, it will create a singularity. This singularity will cause the central intensity of the laser beam is zero. This creates the dark circular spot in the center of the laser beam, which is also known as the Laguerre-Gauss (LG) modes. In most conventional methods, diffractive optics are used to form the Laguerre-Gauss (LG) modes, which is tedious and costly. In our project, CGH was used which is much cheaper and easier to set-up

Figure.4 – Phase Singularity

Figure.5 - Helical Wave-front

Existing Optical Tweezers New Optical Tweezers

•Trapping of micro-particles •Trapping and Rotating micro-particles in 3D

•Costly (cost of optics) •Cheaper (Hologram)

•Tedious to set-up (optics alignment) •Less tedious to set-up (versatile CGH)

•Restriction by reflective and absorptive property of the particles

•Not restricted by the reflective and absorptive property of the particles