We propose an image reconstruction method of digital holography for getting more accurate reconstruction. Digital holography provides both the light amplitude and the phase of a specimen through recording the interferogram. Since the Fresenl diffraction can be efficiently implemented by the Fourier transform, zero padding technique can be applied to obtain more accurate information. In this work, we report the method of frequency domain zero padding (FDZP). Both in computer-simulation and in experiment made with a USAF 1951 resolution chart and target, the FDZD gave the more accurate rconstruction images. Even though, the FDZD asks more processing time, with the help of graphics processing unit (GPU), it can find good applications in digital holography for 3-D profile imaging.
We present the coherent anti-Stokes Raman scattering (CARS) microscopy system that has been implemented by using a photonic crystal polarization maintaining optical fiber. Free space CARS system is hard in alignment and unstable in harsh environment. To overcome this problem the femto-second laser pulses of pump and the Stokes beams were delivered through the optical fiber, so that the system became less complex and robust to the surrounding environment. In order to confirm the feasibility of the fiber-based CARS system, the CARS images of polystyrene beads and zinc oxide (ZnO) are presented.
We present the real-time stroboscopic full-field optical coherence tomography (FF-OCT) system that is based on graphics processing unit (GPU). The basic configuration of the proposed FF-OCT system was the Linnik interferometer. While scanning of a reference mirror in the axial direction, a series of the transverse sectional image was captured with a 2-dimensional CCD camera. To get a depth-resolved 3-D image, the light source of OCT was turned on and off like a stroboscope at the Doppler frequency of the OCT system. The CCD camera used in experiment operated at a rate of 200 frames per second, but the Doppler frequency was ~kHz. To overcome the slow operation of the CCD camera below the Doppler frequency, the light source was operated in the stroboscopic mode. In addition, lock-in detection technique was utilized in order to avoid the dissolution of the coherent signals during the integration time of the CCD camera. Furthermore, the Doppler frequency shift due to nonlinear scanning motion of the reference mirror was monitored by using an auxiliary interferometer and then fed back to the light source driver so that the strobe frequency was always matched with the Doppler frequency of the OCT system. For the real-time 3-D rendering, we used a graphics processing unit.
We propose a dual-channel fiber scanning probe for simultaneous measurement of swept source optical coherence tomography (SS OCT) and fluorescence spectroscopy (FS) signals. For the purpose, SS OCT and FS system were combined by adopting the specially fabricated double cladding fiber (DCF) and wavelength division multiplexer (WDM) coupler, and DCF fiber was directly connected to sample arm of DCF coupler for fiber-based probe. Moreover, for sample scanning, the fiber was driven by piezoelectric bender. Since DCF has dual-channel configuration consists of core and inner cladding, both OCT and FS signals propagate through the two channels at the same time. Therefore, the suggested system enables multifunctional imaging that would make it possible to determine a more specific diagnosis. To demonstrate the feasibility of the probe, a photosensitizer injected in-vivo mice were imaged with scanning speed of 16 Hz and scanning range of 2 mm.
We present a birefringence analysis method based on polarization-sensitive swept-source optical coherence tomography (PS-SS-OCT) for distinguishing pearls. To cope with the round shape of general pearls, a rotation stage was used for the sample scanning. With the system, the birefringence of several cultured pearls including south sea, Akoya, freshwater cultured pearls, and imitation pearls are analyzed and compared. Interestingly, PS-SS-OCT surely shows well developed birefringence patterns of phase retardation and fast axis orientation with the cultured pearls, whereas the pattern does not appear in the imitation pearls. In addition, the intensity image can help to distinguish the cultured pearls. Therefore, PSSS-OCT enables a more accurate interpretation for identifying the cultured pearls from imitation pearls.
We propose full-range spectral domain optical coherence tomography equipped with a fiber-based sample scanner,
which is used for sample scanning and phase shifting for full-range image at the same time. For a fiber-based sample
scanner, since the fiber tip oscillates as a free standing cantilever in general, unintentional phase shift occurs inevitably.
The unintentional phase shift was used for eliminating the bothersome complex conjugate ghost image of OCT. In
addition, fiber was tilted a few degree to give proper phase shift. In this scheme, moreover, image can be obtained
without any physical modification of the scanner. To realize this technique, we constructed the SD-OCT system and
fabricated a magnetically actuated single-body lensed fiber scanner due to advantages of simple design, low operating
voltage, cost-effectiveness and low insertion loss. The scanner was made of lensed fiber loaded with an iron-based bead
and a solenoid which is placed perpendicular to the lensed fiber. When a sinusoidal current is applied into the solenoid,
the lensed fiber oscillated due to magnetic force between the iron-based bead and the solenoid. With the suggested full
range method, we obtained contrast enhanced full-range SD OCT images of pearl and tooth. This simple and effective
method can be applied to any fiber-based scanner and it has great potential as a handheld probe/endoscopic probe in
biomedical imaging field.
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