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Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy (ATOM)

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Published on: June 28, 2017

Near-field time-reversal amplification.

Stephane G Conti¹, Philippe Roux, William A Kuperman

¹Marine Physical Laboratory, SIO-UCSD, 9500 Gilman Drive, La Jolla, California 92093-0238, USA. sconti@ucsd.edu

The Journal of the Acoustical Society of America

|June 8, 2007

Summary

This study introduces near-field time reversal (NTR) to achieve subwavelength focusing without knowing the original source. The method amplifies weak near-field signals, enabling high-resolution focusing for acoustic waves.

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Area of Science:

Acoustics
Wave physics
Optics

Background:

Classical time-reversal mirrors are limited by diffraction to wavelength-order spatial resolution.
Previous subwavelength focusing techniques require full source knowledge or near-field evanescent waves.

Purpose of the Study:

To demonstrate subwavelength focusing without prior knowledge of the probe source.
To introduce and validate the near-field time reversal (NTR) procedure for enhanced spatial resolution.

Main Methods:

Recording the field at a distance from the probe source.
Amplifying low-amplitude near-field data using analytical continuation of the spatial spectrum.
Performing near-field time reversal (NTR) using recorded field phase information.

Main Results:

Achieved subwavelength focusing without a priori source information.
Successfully amplified weak near-field data for improved spatial resolution.
Demonstrated a spatial resolution of lambda/20 with audible acoustic wavefields.

Conclusions:

Near-field time reversal (NTR) overcomes the diffraction limit for spatial resolution.
NTR enables subwavelength focusing using only the phase of the recorded field.
The technique is experimentally validated for acoustic waves in air.