ARF Excitation Research Articles

Optical coherence elastography under homolateral parallel acoustic radiation force excitation for ocular elasticity quantification.

Alteration in the elastic properties of biological tissues may indicate changes in the structure and components. Acoustic radiation force optical coherence elastography (ARF-OCE) can assess the elastic properties of the ocular tissues non-invasively. However, coupling the ultrasound beam and the optical beam remains challenging. In this Letter, we proposed an OCE method incorporating homolateral parallel ARF excitation for measuring the elasticity of the ocular tissues. An acoustic-optic coupling unit was established to reflect the ultrasound beam while transmitting the light beam. The ARF excited the ocular tissue in the direction parallel to the light beam from the same side of the light beam. We demonstrated the method on the agar phantoms, the porcine cornea, and the porcine retina. The results show that the ARF-OCE method can measure the elasticity of the cornea and the retina, resulting in higher detection sensitivity and a more extensive scanning range.

2-D Ultrasonic Array-Based Optical Coherence Elastography.

Acoustic radiation force optical coherence elastography (ARF-OCE) has been successfully implemented to characterize the biomechanical properties of soft tissues, such as the cornea and the retina, with high resolution using single-element ultrasonic transducers for ARF excitation. Most currently proposed OCE techniques, such as air puff and ARF, have less capability to control the spatiotemporal information of the induced region of deformation, resulting in limited accuracy and low temporal resolution of the shear wave elasticity imaging. In this study, we propose a new method called 2-D ultrasonic array-based OCE imaging, which combines the advantages of 3-D dynamic electronic steering of the 2-D ultrasonic array and high-resolution optical coherence tomography (OCT). The 3-D steering capability of the 2-D array was first validated using a hydrophone. Then, the combined 2-D ultrasonic array OCE system was calibrated using a homogenous phantom, followed by an experiment on ex vivo rabbit corneal tissue. The results demonstrate that our newly developed 2-D ultrasonic array-based OCE system has the capability to map tissue biomechanical properties accurately, and therefore, has the potential to be a vital diagnostic tool in ophthalmology.

Luminescence of coesite

Coesite is a polymorph modification of crystalline silicon dioxide with a tetrahedral structure. The luminescence of a single crystal of synthetic coesite was studied under excitation using x-rays, an electron beam, and excimer lasers KrF (248 nm), ArF (193 nm) and F2 (157 nm). Luminescence bands in the regions of 2.5 eV and 4.4 eV appear. The blue band is dependent on temperature and is composed of decay kinetics. Three main decay times are revealed, exhibiting luminescence of a different nature in the same range of the spectrum. One is in the ns range of time with a time constant of about 2 ns. The two other decay times are in the regions of 5 μs and 700 μs. The 5 μs component is also seen under KrF excitation, whereas both the 5 μs and 700 μs components are seen under ArF excitation. The time resolved spectra are mutually similar and they correspond to those under x-ray and e-beam excitation. The UV band is fast with a time constant of less than 1 ns, independent of temperature. Only the 2 ns and 5 μs components are revealed for the blue band under the KrF laser excitation. Blue luminescence thermal quenching takes place for temperatures above 50 K, with good correspondence between the intensities of the thermal dependences under different excitation and that of the decay time constant. The quenching parameters used are 0.05 eV of energy and a frequency factor of 6 · 105 s−1. The UV band is practically independent of temperature in the range 10–290 K. The nature of luminescence is ascribed to the coexistence of a host defect and a self-trapped exciton. The defect is similar to the known oxygen-deficient luminescence center in pure silica glass. The blue luminescence at 700 μs is ascribed to the self-trapped exciton being characteristic of silicon dioxide with a tetrahedral structure.

Photoluminescence excited by ArF and KrF lasers and optical absorption of stishovitemono-crystal

Two photoluminescence bands were found in a stishovite (silicon dioxide) mono-crystalsample under ArF (193 nm) and KrF (248 nm) excitation. The blue band is situated at3.17 ± 0.02 eV in the caseof ArF and at 3 ± 0.2 in the case of KrF. The UV band is at4.55 ± 0.05 eV in the caseof ArF and at 4.5 ± 0.05 eV in the case of KrF. The position of the UV emission band correlates with that excited by x rays. This positionis 4.6 ± 0.05 eV withFWHM 0.8 ± 0.05 eV (Truhins et al 2003 Solid State Commun. 127 415). Theblue band possesses slow decay kinetics with time constant16 ± 2 µs and the UV band isfast on the level of 2 ± 0.5 ns, similarly for both lasers. Thermal quenching of both bands begins forT higher than 150 K. The activation energies are similar for intensity and time constant, and are equal to0.23 ± 0.01 eVand 0.13 ± 0.01 eV for blue and UV bands, respectively, with equal values of frequency factor,2 × 1011 s−1. Optical absorption contains bands at 4.5, 5.5, and 7 eV and a strong band starting from7 eV adjacent to the intrinsic absorption threshold above 8.75 eV. Excitation at 7.86 eV(F2 laser) does not provide luminescence. The nature of the luminescence excited in thetransparency range of stishovite is ascribed to a defect, presumably created byprevious irradiation of the crystal. Similarity of the stishovite luminescence tothat of oxygen-deficient silica glass and also to that induced by irradiation ofα-quartz crystals allows us to conclude similar natures for the defect centers in thesedissimilar materials.

Multiphoton excitation of mercury atoms by photodissociation of HgX2(X=Cl, Br, I)

The multiphoton dissociation of the mercury halides HgX2 (X=Cl, Br, I) to yield highly excited Hg* atoms using ArF and KrF excimer laser excitation is described. The dominant excitation mechanism for the production of Hg* atoms is shown to be via a three-photon sequential excitation path from HgX2(x) through HgX2(b), HgX(B), HgX(virtual) to Hg (73S and 63D).