Erich Goetzinger

Measurement and imaging of birefringence and optic axis orientation by phase resolved polarization sensitive optical coherence tomography.

We present an improved method of polarization sensitive optical coherence tomography that enables measurement and imaging of backscattered intensity, birefringence, and fast optic axis orientation simultaneously with only one single A-scan per transverse measurement location. While intensity and birefringence data are obtained in a conventional way, the optic axis orientation is determined from the phase difference recorded in two orthogonal polarization channels. We report on accuracy and precision of the method by measuring birefringence and optic axis orientation of well defined polarization states in a technical object and present maps of birefringence and, what we believe for the first time, of optic axis orientation in biological tissue.

Transversal phase resolved polarization sensitive optical coherence tomography

We present a novel optical coherence tomography (OCT) method to measure backscattered intensity and birefringence properties (retardation and fast axis orientation) and apply it to imaging of human ocular tissue. The method is based on a Mach Zehnder interferometer, on transversal scanning, and on a polarization sensitive two-channel detection. A highly stable carrier frequency is generated by acousto-optic modulators (AOMs). This allows a phase sensitive demodulation by the lock-in technique. Since the recording of individual interference fringes is avoided by this method the amount of data to be recorded and processed is considerably reduced. We demonstrate this method on human cornea and anterior chamber angle and present, to the best of our knowledge, the first OCT images of retardation and fast axis orientation of the anterior chamber angle region in vivo.

Three dimensional polarization sensitive OCT of human skin in vivo

We present three dimensional images of backscattered intensity, and to the best of our knowledge, the first 3D-images of retardation and fast axis orientation of human skin in vivo. The images were recorded with a phase resolved, polarization sensitive optical coherence tomography (OCT) system which is based on a fast transversal scanning of the sample. The three dimensional data sets were obtained by recording several en face images at different depths within the sample. Intensity and retardation images are combined to a 4 dimensional animation to enhance the visualization of the three dimensional data set. The three dimensional information enables a more accurate interpretation of the structural and birefringence information as compared to 2 dimensional B-scans. Birefringence properties of different skin regions are presented and discussed.

Transversal ultrahigh-resolution polarizationsensitive optical coherence tomography for strain mapping in materials.

Optical coherence tomography (OCT) and its extension, polarization-sensitive (PS-)OCT, are techniques for contactless and nondestructive imaging of internal structures. In this work, we apply PS-OCT for material characterization. We use a transversal scanning, ultra-high resolution (UHR-)PS-OCT setup providing cross-sectional as well as inplane information about the internal microstructure, the birefringence and the orientation of the optical axis within the material. We perform structural analysis and strain-mapping for different samples: we show the necessity of UHR imaging for a highly strained elastomer sample, and we discuss the effect of large birefringence on the PS-OCT images. Furthermore, we investigate high-aspect ratio photoresist moulds for the production of microelectromechanical parts (MEMS), demonstrating that transversal UHR-PSOCT is a promising tool for non-destructive strain-mapping.

Ultrahigh-resolution polarization-sensitive optical coherence tomography

We present, to the best of our knowledge, the first ultrahigh resolution, polarization sensitive OCT images of human tissue in vivo. The system is based on a Mach Zehnder interferometer and a transversal scanning of the sample. A broadband superluminescent diode with a center wavelength of 897nm and a bandwidth (FWHM) of 155nm was used. The depth resolution of the system was measured with ~ 4 micrometer in air. The actual scanning speed of 1000 transversal lines per second enables the acquisition of an image (B-scan) consisting of 1600(x) x 1000(z) pixels in 1 second. The whole signal is recorded by a polarization sensitive detection unit at the interferometer exit which enables a phase resolved measurement. From the recorded data we were able to obtain backscattered intensity, retardation and cumulative fast axis orientation of the sample. Images of these parameters obtained from a technical sample and from a human cornea in vivo are presented.

Three dimensional polarization sensitive optical coherence tomography of normal and pathologic human cornea

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of optical coherence tomography (OCT). We used phase resolved PS-OCT to measure and image three dimensional birefringent properties of pathologic and non pathologic human corneas and compare the results. Knowing the retardation and optic axis distribution might be useful information for early detection of different corneal diseases.

Polarization-sensitive optical coherence tomography: a comparison of methods

Polarization sensitive optical coherence tomography (PS-OCT) is a functional extension of optical coherence tomography (OCT) which reveals the birefringent properties of a biological sample. Several reports on PS-OCT have demonstrated its ability to measure and image birefringence distribution in different tissues. We compare different methods, based on the use of one or more input polarization state. The image quality for single input state methods is better than if two input states are used, however, the latter methods are preferable if fiber interferometers are used or if measurements are to be performed trough superficial birefringent layers. The different image quality is probably due to a speckle effect.

Ultra-high resolution optical coherence tomography for material characterization and quality control

Optical coherence tomography (OCT), so far mainly used in the biomedical field, has a high potential as non-destructive and contactless technique for material characterization and analysis. For these applications, OCT systems with ultra-high resolution in the micrometer range and capable of high imaging speeds are required. In this work, we combine ultra-high resolution imaging using a femtosecond Ti:sapphire laser as light source with the concepts of transversal OCT. Based on acquisition by heterodyne detection via acousto-optic modulators (AOMs), and by using an xy-galvano scanner unit we are able to obtain en-face scans with sizes as large as 3 x 3 mm2 within a few seconds. The ultra-high resolution of our OCT system of 2.95 μm axially and 4 μm laterally, both in air, is shown to be essential for imaging of different compounds and fibre materials. We demonstrate the benefits of en-face scanning OCT for various applications in material investigation where in-plane information is of interest which can hardly be obtained by cross-sectional OCT.

Speckle statistics in optical coherence tomography and speckle reduction by frequency compounding

In this paper we are investigating the possibility of a frequency compounding method for speckle reduction in optical coherence tomography. The method is based on incoherent summation of the magnitudes of two independent interferometric signals, which were recorded at two different center wavelengths simultaneously. We derive the corresponding speckle statistics for amplitude based OCT signals recorded with single and dual frequency sources and compare the theoretical results with measurements obtained in a uniformly scattering sample. Finally we demonstrate our method by comparing images of human skin recorded in vivo with and without frequency compounding. The compounding method results in an increased contrast and improved image quality without loss of resolution.

Retinal pigment epithelium pathologies investigated with phase resolved polarization sensitive optical coherence tomography

A polarization sensitive optical coherence tomography (PS-OCT) instrument was used to investigate the retinal pigment epithelium (RPE). The instrument uses the polarization properties of light to record backscattered intensity, retardation and fast axis orientation simultaneously and needs only one measurement per sample location to retrieve these parameters. The polarization state of light backscattered from within the RPE was found to be random. This can be observed in PS-OCT images by random retardation and axis orientation values within the RPE layer. In diseased eyes where the normal retinal structure is corrupted (e.g. RPE atrophy, RPE detachment) the localization of the RPE within OCT images which do not provide polarization information (standard OCT) is rather difficult. Since the RPE is the only structure within the retina to cause this polarization scrambling, PS-OCT can be used for contrast enhancement and enables the exact localization of the RPE in these pathologies. Therefore it is possible to determine if the RPE is still preserved in regions of interest. Furthermore, in patients with RPE atrophy an enhanced penetration depth into the choroid and even into the sclera was observed. Because of birefringence introduced by the sclera the border between choroid and sclera could easily be determined.