Effects of modulation phase of ultrasound-modulated light on the ultrasound-modulated optical image in turbid media

In this paper, our investigations suggest that the modulation phase of ultrasound-modulated light escaping from the different locations in the ultrasonic field is different. In turbid media, the modulation phase causes the ultrasound-modulated light intensity collected outside the media to fluctuate. However, the ultrasound-modulated optical technology uses the ultrasound-modulated light signals to image. Consequently, the modulation phase affects the quality of ultrasound-modulated optical imaging.     

Relative contributions of porosity and mineralized matrix properties to the bulk axial ultrasonic wave velocity in human cortical bone

Velocity of ultrasound waves has proved to be a useful indicator of bone biomechanical competence. A detailed understanding of the dependence of ultrasound parameters such as velocity on bone characteristics is a key to the development of bone quantitative ultrasound (QUS). The objective of this study is to investigate the relative contributions of porosity and mineralized matrix properties to the bulk compressional wave velocity (BCV) along the long bone axis. Cross-sectional slabs from the diaphysis of four human femurs were included in the study. Seven regions of interest (ROIs) were selected in each slab. BCV was measured in through-transmission at 5 MHz. Impedance of the mineralized matrix (Z_m) and porosity (Por) were obtained from 50 MHz scanning acoustic microscopy. Por and Z_m had comparable effects on BCV along the bone axis (R = −0.57 and R = 0.72, respectively).     

Acoustic Radiation Force Impulse-Imaging for the evaluation of the thyroid gland: a limited patient feasibility study

Purpose

Real-time tissue elastography, a qualitative elastography method, has shown promising results in the diagnostic work up of thyroid nodules. However, to our knowledge no study has evaluated a quantitative elastography method in the thyroid gland. The present study is a feasibility study evaluating Acoustic Radiation Force Impulse-Imaging, a novel quantitative elastography method in the thyroid gland.

Methods

ARFI-imaging involves the mechanical excitation of tissue using short-duration acoustic pulses to generate localized displacements in tissue. The displacements induce a lateral shear-wave propagation which is tracked using multiple laterally positioned ultrasound “tracking“ beams. Inclusion criteria were: thyroid nodules ?1 cm, non-functioning or hypo-functioning on radionuclide scanning, and cytological/histological assessment of thyroid nodule as reference method. All patients received conventional ultrasound, and examination of the thyroid gland including Power Doppler Ultrasound using a 9 MHz linear transducer, in addition real-time elastography (RTE) was performed at 9 MHz frequency and ARFI-imaging was performed at 4 MHz using Siemens (ACUSON S2000) B-mode-ARFI combination transducer.

Results

Sixty nodules in 55 patients were analyzed. Three nodules were papillary carcinoma. The stiffer the tissue the faster the shear wave propagates. The results obtained indicated that the shear wave velocity in thyroid lobes ranged between 0.5 and 4.9 m/s. The median velocity of ARFI-imaging in the healthy nodule-free thyroid gland, as well as in benign and malignant thyroid nodules was 1.98 m/s (range: 1.20-3.63 m/s), 2.02 m/s (range: 0.92-3.97 m/s), and 4.30 m/s (range: 2.40-4.50 m/s), respectively. While no significant difference in median velocity was found between healthy thyroid tissue and benign thyroid nodules, a significant difference was found between malignant thyroid nodules on the one hand and healthy thyroid tissue (p = 0.018) or benign thyroid nodules (p = 0.014) on the other hand. Specificity of ARFI-imaging for the differentiation of benign and malignant thyroid nodules was comparable with RTE (91-95%).

Conclusions

ARFI can be performed in the thyroid tissue with reliable results.     

Scattering matrices of Lamb waves at irregular surface and void defects

Time-harmonic solution of Lamb wave scattering in a plane-strain waveguide with irregular thickness is investigated based on stair-step discretization and stepwise mode matching. The transfer relations of the transmission matrices and reflection matrices are derived in both directions of the waveguide. With these, an explicit expression of the scattering matrix is derived. When the scattering region of an inner irregular defect is geometrically divided into several parts composed of sub-waveguides with variable thicknesses and void regions with vertical free edges corresponding to the plate surfaces, the scattering matrix of the whole region could then be derived by modal matching along the artificial boundaries, as explicit functions of all the scattering matrices of the sub-waveguides and reflection matrices of the free edges. The effectiveness of the formulation is examined by numerical examples; the calculated scattering coefficients are in good accordance with those obtained from numerical simulation models.     

Continuous-wave Yb-doped Sc2SiO5 thin-disk laser

We present in this Letter experimental results of a Yb:Sc(2)SiO(5) (Yb:SSO) thin-disk laser. To our knowledge, this is the first lasing demonstration of this crystal in thin-disk configuration reported on to date. Preliminary tests regarding the characterization and the laser operation are presented. Two different resonator configurations, a simple linear multimode cavity, and a fundamental-mode folded resonator providing a double pass in the laser crystal were set up. The gain and the small signal gain of the available Yb:SSO sample were calculated using the experimental results of the multimode resonator. The operation in a fundamental-mode resonator with the double pass in the laser crystal led to 9.4 W of output power with an optical efficiency of 25.4%.     

High average power 2 μm generation using an intracavity PPMgLN optical parametric oscillator

An intracavity quasi-phase-matched optical parametric oscillator (OPO) has been developed for the purpose of generating radiation with high average power and high repetition rate in the 2 μm regime. The device is a degenerate OPO based on a 3 mm thick MgO-doped periodically poled LiNbO(3) (PPMgLN) crystal, which is pumped in turn within the cavity by a diode side-pumped, Q-switched 1 μm Nd:YAG laser operating at 10 kHz. Up to 20 W broadband 2 μm radiation can be generated with a compact configuration under the crystal temperature of 115 °C. The beam profile is close to circularly symmetric with M(2) ~ 10.     

Coherence-polarization mixing in resonance gratings

We show, using rigorous diffraction theory, that resonance gratings can be used to transfer partial spatial correlation to partial polarization even if the incident light beam is fully polarized. The phenomenon is based on the fact that either of the two orthogonal polarization components can be coupled into the leaky waveguide mode, leading to a strong phase delay, while the other one is reflected without being coupled into the grating. Numerical demonstrations are based on a Gaussian Schell-model beam and a grating analysis performed by rigorous Fourier modal method.     

Design for broadband high-efficiency grating couplers

In this Letter, we propose general optimization methods to design broadband high-efficiency grating couplers for planar waveguides. We attribute the coupling bandwidth to the mismatch of effective indices between the diffracted beam and the actual grating structure around the operation wavelength for fiber to waveguide excitation. The coupling bandwidth formula is deduced. A simple parameter-separate optimization procedure is proposed for general layered grating couplers for high coupling efficiency. Using our principle, we optimized a grating coupler for a horizontal slot waveguide operating at wavelength 1.55 μm for TM polarization. The grating coupler has 1 dB bandwidth of 60 nm and coupling efficiency of 65% with incident light from single-mode optical fiber (SMF) at 8°.     

Relevance of continuously self-imaging gratings for noise robust imagery

We have designed miniaturized, simple, and robust cameras composed of a single diffractive optical element (DOE) that generates a continuously self-imaging (CSI) beam. Two different DOEs are explored: the J₀ Bessel transmittance, characterized by a continuous optical transfer function (OTF) and the CSI grating (CSIG), characterized by a sparse OTF. In this Letter, we will analyze the properties of both DOEs in terms of radiometric performances. We will demonstrate that the noise robustness is enhanced for a CSIG, thanks to the sparsity of its OTF. A camera using this DOE has been made and experimental images are presented to illustrate the noise robustness.     

Diode-pumped mode-locked femtosecond Tm:CLNGG disordered crystal laser

A diode-end-pumped passively mode-locked femtosecond Tm-doped calcium lithium niobium gallium garnet (Tm:CLNGG) disordered crystal laser was demonstrated for the first time to our knowledge. With a 790 nm laser diode pumping, stable CW mode-locking operation was obtained by using a semiconductor saturable absorber mirror. The disordered crystal laser generated mode-locked pulses as short as 479 fs, with an average output power of 288 mW, and repetition rate of 99 MHz in 2 μm spectral region.