Optical tweezer set for launch

17 Jun 2002

A fully automated optical tweezer has been developed and will be installed in the International Space Station in 2005.

A compact optical tweezer will operate in a microgravity environment for the first time when it is installed in the International Space Station (ISS) in 2005. The fully automated system, developed at Northrop Grumman, US, under contract to NASA, will study colloid crystallization (Rev. Sci. Inst 11 4059).

Design of the instrument focused on the special requirements for spaceflight. Andy Resnick, a spokesperson for Northrop Grumman, explained: "The differences between the spaceflight tweezer and tweezers developed for ground based work are driven by three main constraint: size, power consumption, and the need to operate without human intervention. In addition, the need to survive launch into orbit drives the selection of particular materials and mounting methods."

The tweezer setup comprises a continuous-wave diode-pumped Nd:YAG laser; a two-axis acoustic-optic deflector for beam steering; two lenses for beam expansion and imaging; two polarisers to control the beam intensity and trapping strength; and two mirrors to shrink the overall package size.

The Nd:YAG laser will provide 1 W of optical power from a 10 W electrical power supply and was chosen because of its small size and efficient power supply. The overall system is approximately 30 cm x 30 cm x 10 cm.

The researchers have designed the tweezer for a specific set of samples and functions to probe the physics of colloidal crystals. Resnick said: "The samples consist of micron-sized polymethyl methacrylate (PMMA) spheres - a useful analog for atomic systems."

The tweezer will be used to both probe the structure of the particular state of the colloid (rheology and yield stress measurements) and will also be used to manipulate the colloids. "For example a defect could be created by removing a particle or dislocating a row of particles and the effects on the crystal properties can be evaluated," added Resnick.

Resnick told Optics.Org that "partial results will be transmitted back as the experiment proceeds. A lot of data will simply be stored on hard drives and brought back to Earth".

The design is now completed and the main thrust of future work will be a complete characterisation of the tweezer.

The tweezer unit is part of a microscope, termed the light microscope module (LMM), which will be housed in the "fluids combustion facility" within the US portion of the ISS. The module is expected to be in operation for two years.

This work was performed as part of the NASA Microgravity Research Development and Operations Contract.