Extended focus depth for Fourier domain optical coherence microscopy

Laboratoire d'Optique Biomedicale, Ecole Polytechnique Federale de Lausanne, CH-1015 Lausanne, Switzerland.
Optics Letters (Impact Factor: 3.29). 09/2006; 31(16):2450-2. DOI: 10.1364/OL.31.002450
Source: PubMed


We report on a new detection scheme for Fourier domain optical coherence microscopy that exhibits high transverse resolution along an axially extended focal range. Nearly constant transverse resolution of approximately 1.5 microm along a focal range of 200 microm is experimentally verified with a maximum sensitivity of 105 dB. A broad-bandwidth Ti:sapphire laser allowed for an axial resolution of 3 microm in air.

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Available from: Rainer A Leitgeb
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    • "To obtain volumetric data of sufficient axial distance, the sample has to be physically translated and the resulting multiple datasets registered and merged into a single dataset. An alternative solution is to use non-Gaussian beams to achieve extended focus into the tissue (Leitgeb et al., 2006). This latter method has been used to analyze blood flow in adult brain tissue (Bouwens et al., 2014). "
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    • "Ding et al. demonstrated the Bessel beam illumination using an axicon lens to extend DOF in time domain (TD) OCT [2]. Later Leitgeb et al. (2006) implemented it in a FD optical coherence microscopy (OCM) setup [3]. Lee et al. (2008) and Blatter et al. (2011) followed similar approaches to achieve larger extended DOF in a spectrometer based and a swept source (SS) based FD OCT system respectively [4] [5]. Improvement of DOF in OCT is reported with the use of phase masks [6] [7]. "
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    ABSTRACT: In this paper a theoretical model of the full field swept source (FF SS) OCT signal is presented based on the angular spectrum wave propagation approach which accounts for the defocus error with imaging depth. It is shown that using the same theoretical model of the signal, numerical defocus correction methods based on a simple forward model (FM) and inverse scattering (IS), the latter being similar to interferometric synthetic aperture microscopy (ISAM), can be derived. Both FM and IS are compared quantitatively with sub-aperture based digital adaptive optics (DAO). FM has the least numerical complexity, and is the fastest in terms of computational speed among the three. SNR improvement of more than 10 dB is shown for all the three methods over a sample depth of 1.5 mm. For a sample with non-uniform refractive index with depth, FM and IS both improved the depth of focus (DOF) by a factor of 7x for an imaging NA of 0.1. DAO performs the best in case of non-uniform refractive index with respect to DOF improvement by 11x.
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    • "What is needed is a so-called "optical needle" with an almost constant illumination profile over an extended depth range. A so-called Bessel beam (figure 2) [7], generated by an axicon, fulfils these requirements and ensures a uniform narrow illumination profile over an extended depth. "

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