Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Counter-propagating dual-trap optical tweezers based on linear momentum
  conservation   We present a dual-trap optical tweezers setup which directly measures forces
using linear momentum conservation. The setup uses a counter-propagating
geometry, which allows momentum measurement on each beam separately. The
experimental advantages of this setup include low drift due to all-optical
manipulation, and a robust calibration (independent of the features of the
trapped object or buffer medium) due to the force measurement method. Although
this design does not attain the high-resolution of some co-propagating setups,
we show that it can be used to perform different single molecule measurements:
fluctuation-based molecular stiffness characterization at different forces and
hopping experiments on molecular hairpins. Remarkably, in our setup it is
possible to manipulate very short tethers (such as molecular hairpins with
short handles) down to the limit where beads are almost in contact. The setup
is used to illustrate a novel method for measuring the stiffness of optical
traps and tethers on the basis of equilibrium force fluctuations, i.e. without
the need of measuring the force vs molecular extension curve. This method is of
general interest for dual trap optical tweezers setups and can be extended to
setups which do not directly measure forces.

1
The categories of this paper are: cs
2
The categories of this paper are: math
24
The categories of this paper are: dg-ga
16
The categories of this paper are: stat
19
The categories of this paper are: eess
26
The categories of this paper are: bayes-an
28
The categories of this paper are: alg-geom
18
The categories of this paper are: econ
21
The categories of this paper are: adap-org
13
The categories of this paper are: quant-ph
23
The categories of this paper are: solv-int
33
The categories of this paper are: plasm-ph
27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
11
The categories of this paper are: hep-lat
14
The categories of this paper are: math-ph