Diwu Yang

3D-visual laser-diode-based photoacoustic imaging

We present a 3D-visual laser-diode-based photoacoustic imaging (LD-PAI) system with a pulsed semiconductor laser source, which has the properties of being inexpensive, portable, and durable. The laser source was operated at a wavelength of 905 nm with a repetition rate of 0.8 KHz. The energy density on the sample surface is about 2.35 mJ/cm(2) with a pulse energy as low as 5.6 μJ. By raster-scanning, preliminary 3D volumetric renderings of the knotted and helical blood vessel phantoms have been visualized integrally with an axial resolution of 1.1 mm and a lateral resolution of 0.5 mm, and typical 2D photoacoustic image slices with different thickness and orientation were produced with clarity for detailed comparison and analysis in 3D diagnostic visualization. In addition, the pulsed laser source was integrated with the optical lens group and the 3D adjustable rotational stage, with the result that the compact volume of the total radiation source is only 10 × 3 × 3 cm(3). Our goal is to significantly reduce the costs and sizes of the deep 3D-visual PAI system for future producibility.

Cost-efficient laser-diode-induced optical-resolution photoacoustic microscopy for two-dimensional/three-dimensional biomedical imaging

Abstract. Solid-state laser systems, such as traditional Nd:YAG-based lasers, are commonly used for noninvasive biomedical photoacoustics with nanosecond pulse duration and millijoule pulse energy. However, such lasers are both bulky and expensive for use as a handy tool for clinical applications. As an alternative, a semiconductor light source has the advantages of being compact, inexpensive, and robust. In addition, the main drawback of low peak output power may make it exactly suitable for the imaging modalities, which require relatively low pulse energies, such as acoustic- and optical-resolution photoacoustic microscopy (AR/OR-PAM). We propose a cost-efficient OR-PAM for two-dimensional/three-dimensional (2-D/3-D) biological imaging based on a pulsed near-infrared laser diode. By raster scanning, typical 2-D photoacoustic images were obtained at different scales, and 3-D surface renderings were clearly reconstructed with a marching cubes algorithm. This initial study would promote the production of portable OR-PAM technology for clinical and biomedical applications.

Optical transmission through compound gold surface relief slit arrays

The optical transmissions through compound gold surface relief slit arrays were investigated theoretically by using the finite difference time domain method. The differences of transmission, reflection, and absorption spectra of the bare slit and the surface relief grating are discussed. The transmission spectra influenced by different dielectric constants of medium in the two slits and different slits widths. When the two slits fill different dielectrics, the presence of the medium induces a red-shift of the plasmon resonances. Along with the dielectric constant in one slit increasing, there appear obvious dips in the transmission spectra. Based on the magnetic and electric field distributions, Fabry-Pérot-like resonance and phase resonance mechanisms have been suggested for the physical origins of these observations.

Design of a portable noninvasive photoacoustic glucose monitoring system integrated laser diode excitation with annular array detection

A near-infrared photoacoustic glucose monitoring system, which is integrated dual-wavelength pulsed laser diode excitation with eight-element planar annular array detection technique, is designed and fabricated during this study. It has the characteristics of nonivasive, inexpensive, portable, accurate location, and high signal-to-noise ratio. In the system, the exciting source is based on two laser diodes with wavelengths of 905 nm and 1550 nm, respectively, with optical pulse energy of 20 μJ and 6 μJ. The laser beam is optically focused and jointly projected to a confocal point with a diameter of 0.7 mm approximately. A 7.5 MHz 8-element annular array transducer with a hollow structure is machined to capture photoacoustic signal in backward mode. The captured signals excitated from blood glucose are processed with a synthetic focusing algorithm to obtain high signal-to-noise ratio and accurate location over a range of axial detection depth. The custom-made transducer with equal area elements is coaxially collimated with the laser source to improve the photoacoustic excite/receive efficiency. In the paper, we introduce the photoacoustic theory, receive/process technique, and design method of the portable noninvasive photoacoustic glucose monitoring system, which can potentially be developed as a powerful diagnosis and treatment tool for diabetes mellitus.

Noninvasive photoacoustic detecting intraocular foreign bodies with an annular transducer array

We present a fast photoacoustic imaging system based on an annular transducer array for detection of intraocular foreign bodies. An eight-channel data acquisition system is applied to capture the photoacoustic signals using multiplexing and the total time of data acquisition and transferring is within 3 s. A limited-view filtered back projection algorithm is used to reconstruct the photoacoustic images. Experimental models of intraocular metal and glass foreign bodies were constructed on ex vivo pigs eyes and clear photoacoustic images of intraocular foreign bodies were obtained. Experimental results demonstrate the photoacoustic imaging system holds the potential for in clinic detecting the intraocular foreign bodies.

Optical transmission through metallic split-ring resonator with inner cross dimer array

We investigate numerically the optical properties through gold split-ring resonator (SRR) with inner cross dimer array by using the finite difference time domain (FDTD) method. The dependence of the geometrical parameters on the optical properties of SRR with inner cross dimer array is studied. The study covers the change of transmission spectra with the metallic cross arm length, width of air slits, width of SRRs and environmental dielectric constants. The spatial distributions of the electric and magnetic fields are also discussed to further understand more basic physical mechanisms behind some dip and peak.

Thermal Transport of Flexural and In-Plane Phonons Modulated by Bended Graphene Nanoribbons

Ballistic thermal transport properties are investigated comparatively for out-of-plane phonon modes FPMs and in-plane phonon modes IPMs in bended graphene nanoribbons GNRs. Results show that the phonon modes transports can be modulated separately by the phonon dispersion mismatch between armchair and zigzag GNRs in considered system. The contribution of FPMs to total thermal conductance is larger than 50% in low temperature for perfect GNRs. But it becomes less than 20% in the bended GNRs. Furthermore, this contribution can be modulated by changing the structural parameters of the bended GNRs. The result is useful for the design of thermal or thermoelectric nanodevices in future.

Tunable plasmon resonance in Ag-Au split-ring resonator with inner metallic cross heterogeneous dimer array

The plasmon resonance behavior in Ag-Au split-ring resonator (SRR) heterogeneous dimer array has been investigated numerically by using the finite difference time domain (FDTD) method. The resonance dips were tuned with the metallic SRR dimer arrays constituted by different metals. For the Ag-Au heterogeneous SRRs dimer array, with the arms of metallic cross lengths increasing, the resonance dips in the visible region red shifted but the locations of resonance modes in the near-infrared region kept immovability. On the contrary, the locations of resonance dips in the visible region kept immovability but the resonance modes in the near-infrared region red shifted obviously with the air cuts widths decreasing. The whole resonance dips exhibited a red-shift as the environmental dielectric constants increase. The electric and magnetic field distributions of certain resonance wavelengths were also investigated.