Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Diffraction effects in length measurements by laser interferometry   High-accuracy dimensional measurements by laser interferometers require
corrections because of diffraction, which makes the effective fringe-period
different from the wavelength of a plane (or spherical) wave $\lambda_0$. By
using a combined X-ray and optical interferometer as a tool to investigate
diffraction across a laser beam, we observed wavelength variations as large as
$10^{-8}\lambda_0$. We show that they originate from the wavefront evolution
under paraxial propagation in the presence of wavefront- and intensity-profile
perturbations.

23
The categories of this paper are: solv-int
9
The categories of this paper are: nlin
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
21
The categories of this paper are: adap-org
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
19
The categories of this paper are: eess
1
The categories of this paper are: cs
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph