We recently reported on an Optical Coherence Microscopy technique, whose innovation intrinsically builds on a recently reported - 2 microm invariant lateral resolution by design throughout a 2 mm cubic full-field of view - liquid-lens-based dynamic focusing optical probe [Murali et al., Optics Letters 34, 145-147, 2009]. We shall report in this paper on the image acquisition enabled by this optical probe when combined with an automatic data fusion method developed and described here to produce an in-focus high resolution image throughout the imaging depth of the sample. An African frog tadpole (Xenopus laevis) was imaged with the novel probe and the Gabor-based fusion technique, demonstrating subcellular resolution in a 0.5 mm (lateral) x 0.5 mm (axial) without the need, for the first time, for x-y translation stages, depth scanning, high-cost adaptive optics, or manual intervention. In vivo images of human skin are also presented.

Endoscopic imaging in tubular structures, such as the tracheobronchial tree, could benefit from imaging optics with an extended depth of focus (DOF) to accommodate the varying sizes of tubular structures across patients and along the tree within the same patient. Yet the extended DOF needs to be accomplished without sacrificing resolution while maintaining sufficient sensitivity and speed of imaging. In this Letter, we report on the measured resolution and sensitivity achieved with a custom-made micro-optic axicon lens designed to theoretically achieve an 8 mm DOF. A measured invariant resolution of approximately 8 microm is demonstrated across a 4 mm measured DOF using the micro-optic axicon while achieving an invariant sensitivity of approximately 80 dB with a 25 mW input power. Double-pass Bessel beam spectral-domain optical coherence tomography with an axicon micro-optic lens (i.e., <1 mm in diameter) is, for the first time to our knowledge, demonstrated in a biological sample demonstrating invariant resolution and signal-to-noise ratio across a 4 mm measured DOF, which is compared to Gaussian beam imaging.

We analyze the three most common profiles of scanning functions for galvanometer-based scanners (GSs): the sawtooth, triangular and sinusoidal functions. They are determined experimentally with regard to the scan parameters of the input signal (i.e., frequency and amplitude). We study the differences of the output function of the GS measured as the positional error of the oscillatory mirror from the ideal function given by the input signal of the device. The limits in achieving the different types of scanning functions in terms of duty cycle and linearity are determined experimentally for the possible range of scan parameters. Of particular importance are the preservation of an imposed duty cycle and profile for the sawtooth function, the quantification of the linearity for the sinusoidal function, and the effective duty cycle for the triangular, as well as for the other functions. The range of scan amplitudes for which the stability of the oscillatory regime of the galvo mirror is stable for different frequencies is also highlighted. While the use of the device in certain scanning regimes is studied, certain rules of thumb are deduced to make the best out of the galvoscanner. Finally, the three types of scanning functions are tested with a Fourier domain optical coherence tomography (FD OCT) setup and the conclusions of the study are demonstrated in an imaging application by correlating the determined limits of the scanning regimes with the requirements of OCT.

An optical coherence tomography (OCT) for high axial resolution corneal imaging is presented. The system uses 375 nm bandwidth (625 to 1000 nm) from a broadband supercontinuum light source. The system was developed in free space to minimize image quality degradation due to dispersion. A custom-designed spectrometer based on a Czerny Turner configuration was implemented to achieve an imaging depth of 1 mm. Experimentally measured axial resolution was 1.1 μm in corneal tissue and had a good agreement with the theoretically calculated resolution from the envelope of the spectral interference fringes. In vivo imaging was carried out and thin corneal layers such as the tear film and the Bowman’s layer were quantified in normal, keratoconus, and contact lens wearing eyes, indicating the system’s suitability for several ophthalmic applications.

We report an optical design for a low-cost optics, broadband, astigmatism-corrected practical spectrometer. An off-the-shelf cylindrical lens is used to remove astigmatism over the full bandwidth. Results show that better than 0.1 nm spectral resolution and more than 50% throughput were achieved over a bandwidth of 400 nm centered at 800 nm.

The optical aberrations induced by imaging through skin can be predicted using formulas for Seidel aberrations of a plane-parallel plate. Knowledge of these aberrations helps to guide the choice of numerical aperture (NA) of the optics we can use in an implementation of Gabor domain optical coherence microscopy (GD-OCM), where the focus is the only aberration adjustment made through depth. On this basis, a custom-designed, liquid-lens enabled dynamic focusing optical coherence microscope operating at 0.2 NA is analyzed and validated experimentally. As part of the analysis, we show that the full width at half-maximum metric, as a characteristic descriptor for the point spread function, while commonly used, is not a useful metric for quantifying resolution in non-diffraction-limited systems. Modulation transfer function (MTF) measurements quantify that the liquid lens performance is as predicted by design, even when accounting for the effect of gravity. MTF measurements in a skinlike scattering medium also quantify the performance of the microscope in its potential applications. To guide the fusion of images across the various focus positions of the microscope, as required in GD-OCM, we present depth of focus measurements that can be used to determine the effective number of focusing zones required for a given goal resolution. Subcellular resolution in an onion sample, and high-definition in vivo imaging in human skin are demonstrated with the custom-designed and built microscope.

Abstract. We investigate morphological differences in three-dimensional (3-D) images with cellular resolution between nonmelanoma skin cancer and normal skin using Gabor domain optical coherence microscopy. As a result, we show for the first time cellular optical coherence images of 3-D features differentiating cancerous skin from normal skin. In addition, in vivo volumetric images of normal skin from different anatomic locations are shown and compared.

Most of full-range techniques for Frequency Domain Optical Coherence Tomography (FD-OCT) reported to date utilize the phase relation between consecutive axial lines to reconstruct a complex interference signal and hence may exhibit degradation in either mirror image suppression performance or detectable velocity dynamic range or both when monitoring a moving sample such as flow activity. We have previously reported a technique of mirror image removal by simultaneous detection of the quadrature components of a complex spectral interference called a Dual-Detection Frequency Domain OCT (DD-FD-OCT) [Opt. Lett. 35, 1058-1060 (2010)]. The technique enables full range imaging without any loss of acquisition speed and is intrinsically less sensitive to phase errors generated by involuntary movements of the subject. In this paper, we demonstrate the application of the DD-FD-OCT to a phase-resolved Doppler imaging without degradation in either mirror image suppression performance or detectable velocity dynamic range that were observed in other full-range Doppler methods. In order to accommodate for Doppler imaging, we have developed a fiber-based DD-FD-OCT that more efficiently utilizes the source power compared with the previous free-space DD-FD-OCT. In addition, the velocity sensitivity of the phase-resolved DD-FD-OCT was investigated, and the relation between the measured Doppler phase shift and set flow velocity of a flow phantom was verified. Finally, we demonstrate the Doppler imaging using the DD-FD-OCT in a biological sample.