Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Optical gradient force nano-imaging and -spectroscopy   Nanoscale forces play an important role in different scanning probe
microscopies, most notably atomic force microscopy (AFM). In contrast, in
scanning near-field optical microscopy (SNOM) a light-induced coupled local
optical polarization between tip and sample is typically detected by scattering
to the far field. Measurements of the optical gradient force associated with
that optical near-field excitation would offer a novel optical scanning probe
modality. Here we provide a generalized theory of optical gradient force
nano-imaging and -spectroscopy. We quantify magnitude and distance dependence
of the optical gradient force and its spectral response. We show that the
optical gradient force is dispersive for single particle electronic and
vibrational resonances, distinct from recent claims of its experimental
observation. In contrast, the force can be absorptive for collective
resonances. We provide a guidance for its measurements and distinction from
competing processes such as thermal expansion.

27
The categories of this paper are: comp-gas
31
The categories of this paper are: ao-sci
0
The categories of this paper are: hep-ph
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
30
The categories of this paper are: q-alg
8
The categories of this paper are: hep-ex
28
The categories of this paper are: alg-geom
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
18
The categories of this paper are: econ
16
The categories of this paper are: stat
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th