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Imaging of trace species distributions by degenerate four-wave mixing: diffraction effects, spatial resolution, and image referencing

Imaging of trace species distributions by degenerate four-wave mixing: diffraction effects, spatial resolution, and image referencing
Imaging of trace species distributions by degenerate four-wave mixing: diffraction effects, spatial resolution, and image referencing
We describe the theory of imaging by degenerate four-wave mixing (DFWM) using a standard diffraction theory of imaging by coherent light. We demonstrate that, even with the phase-conjugating geometry, no aberration correction can be achieved by DFWM imaging. We demonstrate the coherent nature of DFWM image formation using spatially modulated signals generated in flame OH in the phase-conjugating geometry. The intensity distribution in the Fourier plane of a telecentric lens system is shown to be the spatial Fourier transform of the object distribution characteristic of coherent imaging. The brightness of the DFWM signals exceeds that of similar laser-induced fluorescence signals that can be discriminated by restricting the aperture of the imaging system while still allowing a spatial resolution of approximately 70 µm. DFWM imaging with the forward-folded boxcars geometry is demonstrated and used in a simple referencing scheme to compensate for structure on the images imposed by nonuniformity of the laser beams employed. Images formed in NO are used to illustrate that structure on a scale of less than 100 µm arising from beam inhomogeneity can be removed by this referencing technique.
0003-6935
5959-5968
Ewart, P.
ff22a0d8-2e47-46cf-a721-64b5f68da6a3
Smith, Peter G.R.
8979668a-8b7a-4838-9a74-1a7cfc6665f6
Williams, Richard B.
c46c705e-6678-4591-8ea0-d25049264d63
Ewart, P.
ff22a0d8-2e47-46cf-a721-64b5f68da6a3
Smith, Peter G.R.
8979668a-8b7a-4838-9a74-1a7cfc6665f6
Williams, Richard B.
c46c705e-6678-4591-8ea0-d25049264d63

Ewart, P., Smith, Peter G.R. and Williams, Richard B. (1997) Imaging of trace species distributions by degenerate four-wave mixing: diffraction effects, spatial resolution, and image referencing. Applied Optics, 36 (24), 5959-5968. (doi:10.1364/AO.36.005959).

Record type: Article

Abstract

We describe the theory of imaging by degenerate four-wave mixing (DFWM) using a standard diffraction theory of imaging by coherent light. We demonstrate that, even with the phase-conjugating geometry, no aberration correction can be achieved by DFWM imaging. We demonstrate the coherent nature of DFWM image formation using spatially modulated signals generated in flame OH in the phase-conjugating geometry. The intensity distribution in the Fourier plane of a telecentric lens system is shown to be the spatial Fourier transform of the object distribution characteristic of coherent imaging. The brightness of the DFWM signals exceeds that of similar laser-induced fluorescence signals that can be discriminated by restricting the aperture of the imaging system while still allowing a spatial resolution of approximately 70 µm. DFWM imaging with the forward-folded boxcars geometry is demonstrated and used in a simple referencing scheme to compensate for structure on the images imposed by nonuniformity of the laser beams employed. Images formed in NO are used to illustrate that structure on a scale of less than 100 µm arising from beam inhomogeneity can be removed by this referencing technique.

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Published date: 1997

Identifiers

Local EPrints ID: 440851
URI: http://eprints.soton.ac.uk/id/eprint/440851
ISSN: 0003-6935
PURE UUID: 403cfd53-be06-4a8d-a664-aad9b73d85d2
ORCID for Peter G.R. Smith: ORCID iD orcid.org/0000-0003-0319-718X

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Date deposited: 20 May 2020 16:31
Last modified: 17 Mar 2024 02:42

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Contributors

Author: P. Ewart
Author: Richard B. Williams

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