Visualization of the spatiotemporal dynamics of propagation is fundamental to understanding dynamic processes ranging from action potentials to electromagnetic pulses, the two ultrafast processes in biology and physics, respectively. Here, we demonstrate differentially enhanced compressed ultrafast photography to directly visualize propagations of passive current flows at approximately 100 m/s along internodes from Xenopus laevis sciatic nerves and of electromagnetic pulses at approximately 5×107 m/s through lithium niobate. The spatiotemporal dynamics of both propagation processes are consistent with the results from computational models, demonstrating that our method can span these two extreme timescales while maintaining high phase sensitivity.
Development work was conducted on ferroelectric materials that are widely used for optical modulation, light generation, optical filtering, and nanophotonic devices. Ferroelectric crystals with periodic variations in the second-order nonlinearity have been applied in laser frequency conversion, generation of entangled photons, and optical solitary wave devices. Here, we show electrical and optical characteristics of a ferroelectric crystal 0.25Pb(In1/2Nb1/2)O3–0.42Pb(Mg1/3Nb2/3)O3–0.33PbTiO3 (short as PIMNT). The coercive field of PIMNT crystal with different orientation ranges from 4.9 to 5.8 kV / mm. Optical transmission and refractive indices of the crystal are investigated after being poled along different directions. The dispersion curves were fitted with Cauchy dispersion equations. The optical transmission of [011]-poled PIMNT single crystal is more than 65% above 0.5 μm, which is much higher than that of [001] and [111] directions. Orientation dependence of transition energies is presented in detail. Direct band gap, indirect band gap, and phonon energy can be adjusted with different orientations. The coercive field of PIMNT crystal is much lower than that of LiNbO3 crystal (21 kV / mm). These results show that PIMNT single crystal is a promising candidate material in nanophotonics.
As piezoelectric materials, optical properties of xPb(In1/2Nb1/2)O3–(1-x-y)Pb(Mg1/3Nb2/3)O3–yPbTiO3 single crystals were not perfectly known. Here refractive indices and optical transmission of 0.25Pb(In1/2Nb1/2)O3–0.42Pb(Mg1/3Nb2/3)O3– 0.33PbTiO3 (PIMNT) single crystal are investigated after poled along different directions. Cauchy dispersion equations of the refractive indices were obtained by least square fitting, which can be used to calculate the refractive indices in the low absorption wavelength range. After poled along [011] direction, the optical transmission of PIMNT single crystal is more than 65% above 0.5 μm, which is much higher than that of [001] and [111] directions. Energy band gap was obtained from absorption coefficient.
We present a spatial frequency domain multiplexing method for extending the imaging depth range of a SDOCT system
without any expensive device. This method uses two reference arms with different round-trip optical delay to probe
different depth regions within the sample. Two galvo scanners with different pivot-offset distances in the reference arms
are used for spatial frequency modulation and multiplexing. While simultaneously driving the galvo scanners in the
reference arms and the sample arm, the spatial spectrum of the acquired two-dimensional OCT spectral interferogram
corresponding to the shallow and deep depth of the sample will be shifted to the different frequency bands in the spatial
frequency domain. After data filtering, image reconstruction and fusion the spatial frequency multiplexing SDOCT
system can provide an approximately 1.9 fold increase in the effective ranging depth compared with that of a
conventional single-reference-arm full-range SDOCT system.
A high speed swept source optical coherence tomography (SS-OCT) system capable of full-range imaging is presented. Wave-number carrier frequency is introduced into the spectral interference signal by a transmissive dispersive optical delay line (TDODL). High carrier frequency in the spectral interference signal corresponding to an equivalent distance-shift is exploited to obtain full-range OCT imaging. Theoretical development is conducted with the instantaneous coherence function introduced for a complete description of a spectral interference signal. Performance advantage of the TDODL-based method over the conventional approach where only one side (positive or negative path length difference) is used for imaging to avoid overlaying mirror artifacts is confirmed by the measured envelopes of spectral interference signal. Feasibility of the proposed method for full-range imaging is validated in a custom-built SS-OCT system by in vivo imaging of a biological sample.
A portable choroidal laser Doppler flowmeter (LDF) with enhanced sensitivity based on a scattering plate is developed. The portable LDF is weighted 2 kg operated at center wavelength of 780 nm, leading to a better penetration into the eye fundus in contrast to the previous LDF operated at center wavelength of 670 nm. Enhancement of number of detected photons that undergo Doppler scattering and improved measured speed of choroidal blood flow are achieved with the use of a scattering plate positioned in front of the eye. The mechanism of detection and sensitivity enhancement is theoretically analyzed. Evaluation of system performance is done by in vivo measurements on ten volunteers. The results demonstrate that an increased percentage of backscattering light at high Doppler shift frequency is collected due to utilization of the scattering plate. However, this kind of light detection influences spatial resolution of the system and decreases the total signal measured. The proposed method for detection and sensitivity enhancement might be useful in a case where the perception of very slight alternation of blood flow is pursued and the spatial resolution is not as critical as that in a choroidal vascular bed.
A high-speed linear wavelength-swept laser source working at center wavelength of 1309 nm is demonstrated.
Wavelength tuning is performed using a compact polygon filter in Littrow telescope-less configuration. The repetition
frequency of the wavelength-swept laser source is up to 50 kHz with the polygon scanned at a speed of 694 rotations per
second. The turning range is 130 nm and full width at half maximum (FWHM) is 61 nm. The average output power can
reach to 7 mW. The developed swept laser source can be implemented in optical frequency domain imaging, optical
reflectometry, and other test or measurement applications.
Wavelength-encoded imaging uses wavelength division multiplexing to produce cross-sectional images without
mechanical scanning, and could be of a great interest in endoscope applications. In this paper, a scheme for
wavelength-encoded imaging using time-encoded Frequency-domain optical coherence tomography (swept-source
optical coherence tomography, SS-OCT) is presented. This approach implements swept broadband source with
narrow instantaneous spectral width and low dispersion diffraction grating to simultaneously produce depth-lateral
imaging of the sample. Compared to previous spectral-domain wavelength-encoded endoscope, the proposed
method enables high-speed and high dynamic range detection. System design such as image resolvable points,
imaging resolution as well as theoretical analysis of the interference signal pattern are developed.
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