To calculate the result, the four detector outputs are processed by an operation circuit. This creates the potential field to be measured. A second He-Ne laser beam is used for the 3D measurement. Through contact with the microparticle, some of the light from the evanescent wave is coupled out and scattered, where it can be imaged by the microscope and detected by the quadrant photodiode. In the new system, the trapping light comes from both above and a second evanescent wave below.
Thermal energy causes the particle to be constantly moving.
To compensate for this, many measurements are taken over a period of time, and the resulting data is used to calculate a 3D probability function. Other contributions to the particle's position, such as temperature and gravity, can also be pulled out in order to produce curves that show the effect of radiation pressure alone. To demonstrate that the evanescent wave does indeed make a difference to the particle position, researchers also included a shutter so that it could be selectively turned on and off. A shutter in the system allows the potential experienced by the particle to be measured with the new evanescent wave both off and on. The team was also able to measure the scattering force caused by the light, demonstrating how it decreased with light intensity.