DHA - Instrumentation Construction and development of the DHAThe DHA [1] is a Holographic Optical Tweezers system, which relies on the field gradient produced by a tightly focused laser beam to generate a force that draws dielectric particles into the region of highest light intensity. A spatial light modulator enables the incoming laser beam to be diffracted into a series of outgoing laser beams, each of which can produce one optical trap. The DHA can be seen in Figure 1, and an abbreviated optics layout is shown in Figure 2. Mirrors between shelves have been omitted, as have alignment mirrors. The system has also been designed with laser safety in mind, and the laser can only be accessed by opening specific panels.
Figure 1. The DHA workstation, including microscope with camera and image splitter, user interface, hologram generator and microscope xyz stage control. |
Figure 2. The schematic of the DHA workstation. |
An 18W laser is used to pump a Ti:sapphire ring laser which can be tuned to operate between
700-900 nm, and typically operates at 800 nm to minimise damage to biological cells. A LabVIEW
interface has been developed to allow mouse control of individual traps, and a series of other
interfaces are available, such as entering pre-programmed coordinates, webcam position monitoring
and joystick control.
The mouse software allows for group functions, so that a series of points can be manipulated as a
single solid. A series of particles can be translated, rotated and scaled in 3D. This is shown
in Figure 3.
Figure 3. Manipulation of yeast cells (Saccharomyces cerevisiae) using an arrangement of traps controlled using the software toolkit. |
The position of the particles can also be monitored using a high-speed CCD, and the forces applied
to individual cells can be recorded at 500Hz.
A fundamental aspect of the research is the construction and continuing development of the DHA.
Full details of the current state of the equipment can be found on the
overview page. A number of algorithms are being
developed to improve the control of groups of optical traps, and interfaces for recent equipment
additions are being added.
Further details about the instrument can be seen in [1].
Adding power Some nanotools may require some form of external power to be applied to the device in able to function. Methods to introduce different types of power into the sample cells are investigated. The effects of various electrical and magnetic fields on trapped particles are investigated.
References[1] G. Gibson et al., Holographic assembly workstation for optical manipulation. Journal of Optics A: Pure and Applied Optics 10(4), 044009 (2008).
DHA linksThe links below provide information on other areas of the DHA project.