A force detection technique for single-beam optical traps based on direct measurement of light momentum changes.

Despite the tremendous success of force-measuring optical traps in recent years, the calibration methods most commonly used in the field have been plagued with difficulties and limitations. Force sensing based on direct measurement of light momentum changes stands out among these as an exception. Especially significant is this method's potential for working within living cells, with non-spherical particles or with non-Gaussian beams. However, so far, the technique has only been implemented in counter-propagating dual-beam traps, which are difficult to align and integrate with other microscopy techniques. Here, we show the feasibility of a single-beam gradient-trap system working with a force detection technique based on this same principle.