THE FRACTIONAL BISPECTRUM NOISE REDUCTION TECHNIQUE AND APPLICATIONS IN INTERFEROMETRY

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Babaie, J. (2019). THE FRACTIONAL BISPECTRUM NOISE REDUCTION TECHNIQUE AND APPLICATIONS IN INTERFEROMETRY. Unc Charlotte Electronic Theses And Dissertations.
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Abstract

In the field of optical metrology, there are many existing techniques for measurement of the surface profile or film thickness of a sample of interest. However, many of these common techniques break down when there exists a high level of noise in the output optical signal due to the nature of certain types of samples. Sources of noise that can suppress the signal information can come from highly rough surfaces and turbulence within the medium if there is necessity for light to transmit through. This dissertation presents the results of a research effort to develop a technique to suppress the noise content in order to distinguish the signal. In particular, a noise-reduction technique, Fractional BiSpectrum, was developed for the purpose of properly identifying signal frequencies within the measurement data when these frequencies have a known relationship with each other. It is also shown how this technique can be implemented within common interferometry setups such as those measuring the thickness of films with turbid material as well as the surface profile and/or roughness of a sample and still make the proper measurement, i.e. identify the proper temporal or spatial frequency within a noisy signal. It is demonstrated that using this noise-reduction technique enables to produce a confident measurement – i.e. enhance SNR greater than 3dB. In some of the demonstrated cases, enhancement will lead to the detection of the correct measurement parameter – i.e. thickness or height value - where the existing techniques fail.

Details
Author

Babaie, Jonathan

Title

THE FRACTIONAL BISPECTRUM NOISE REDUCTION TECHNIQUE AND APPLICATIONS IN INTERFEROMETRY

Physical Description

1 online resource (167 pages) : PDF

Date

2019

Degree Granting Institution

University of North Carolina at Charlotte

Abstract

In the field of optical metrology, there are many existing techniques for measurement of the surface profile or film thickness of a sample of interest. However, many of these common techniques break down when there exists a high level of noise in the output optical signal due to the nature of certain types of samples. Sources of noise that can suppress the signal information can come from highly rough surfaces and turbulence within the medium if there is necessity for light to transmit through. This dissertation presents the results of a research effort to develop a technique to suppress the noise content in order to distinguish the signal. In particular, a noise-reduction technique, Fractional BiSpectrum, was developed for the purpose of properly identifying signal frequencies within the measurement data when these frequencies have a known relationship with each other. It is also shown how this technique can be implemented within common interferometry setups such as those measuring the thickness of films with turbid material as well as the surface profile and/or roughness of a sample and still make the proper measurement, i.e. identify the proper temporal or spatial frequency within a noisy signal. It is demonstrated that using this noise-reduction technique enables to produce a confident measurement – i.e. enhance SNR greater than 3dB. In some of the demonstrated cases, enhancement will lead to the detection of the correct measurement parameter – i.e. thickness or height value - where the existing techniques fail.

Genre

doctoral dissertations

Subjects--Topics

Optics

Degree

Ph.D.

Keywords

Bispectrum
Coating
Film Thickness
Laser Interferometry
Optical Metrology
Speckle Pattern

Subject Area

Optical Science & Engineering

Advisor(s)

Farahi, Faramarz

Committee Members

Farahi, Faramarz
Davies Allen, Angela
Smith, Stuart
Tabarraei, Alireza

Degree Note

Thesis (Ph.D.)--University of North Carolina at Charlotte, 2019.

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Rights Holder Information

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Identifier

Babaie_uncc_0694D_12247

Permalink

http://hdl.handle.net/20.500.13093/etd:2111