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Spin-orbit interactions (SOI), describing the transfer of a spin degree of freedom to an orbital angular momentum (OAM), have been widely explored in recent opto-acoustic studies for applications mainly in spintronics and for topological insulators [1]. We report the observation of SOI by Brillouin scattering in an optical nanofiber. Specifically, we describe the transfer of a spin degree of freedom from light incident to the nanofiber to an acoustic vortex with a topological charge of order 2 in the form of OAM. Coupled with the phase matching condition for the energy conservation during Brillouin scattering, it results in a backscattered wave with a spin opposite to the incident wave. This observation allows considering applications of opto-acoustic Brillouin memory based on polarization conversion through a SOI [2]. [ABSTRACT FROM AUTHOR]

Effect of media temperature on the acousto-optic (AO) phase matching condition is examined both theoretically and experimentally by an example of tellurium dioxide crystal with 10.5° cut-angle. It is shown that variation of the AO crystal temperature changes the acoustic wave velocity that is involved into the AO interaction and shifts the AO diffraction phase matching frequency. We introduced the temperature coefficient of AO phase matching frequency shift. The measurements of frequency shift magnitude were carried out at the optical wavelengths from 0.44 µm to 1.52 µm. It is shown that the shift coefficient decreases with the optical wavelength. A method is proposed that makes it possible to calculate the temperature shift coefficients for AO devices in a wide range of optical wavelengths. The coefficients obtained by the proposed method are in good agreement with the experimental data. Ultrasound attenuation is also examined experimentally in the given AO cell in a wide range of acoustic wave frequencies. [ABSTRACT FROM AUTHOR]

The next generation multi-cubic-kilometre water Cherenkov neutrino telescope will be build in the Mediterranean Sea. This telescope, called KM3NeT, is currently entering a first construction phase. The KM3NeT research infrastructure will comprise 690 so-called Detection Units in its final design which will be anchored to the sea bed and held upright by submerged floats. The positions of these Detection Units, several hundred metres in length, and their attached Optical Modules for the detection of Cherenkov light have to be monitored continously to provide the telescope with its desired pointing precision. A standard way to do this is the utilisation of an acoustic positioning system using emitters at fixed positions and receivers distributed along the Detection Units. The KM3NeT neutrino telescope comprises a custom-made acoustic positioning system with newly designed emitters attached to the anchors of the Detection Units and custom-designed receivers attached to the Detection Units. This article describes an approach for a receiver and its performance. The proposed Opto-Acoustical Modules combine the optical sensors for the telescope with the acoustical sensors necessary for the positioning of the module itself. This combination leads to a compact design suited for an easy deployment of the numerous Detection Units. Furthermore, the instrumented volume can be used for scientific analyses such as marine science and acoustic particle detection. [ABSTRACT FROM AUTHOR]

KM3NeT is a future multi-cubic-kilometre water Cherenkov neutrino telescope currently entering a first construction phase. It will be located in the Mediterranean Sea and comprise about 600 vertical structures called detection units. Each of these detection units has a length of several hundred metres and is anchored to the sea bed on one side and held taut by a buoy on the other side. The detection units are thus subject to permanent movement due to sea currents. Modules holding photosensors and additional equipment are equally distributed along the detection units. The relative positions of the photosensors has to be known with an uncertainty below 20 cm in order to achieve the necessary precision for neutrino astronomy. These positions can be determined with an acoustic positioning system: dedicated acoustic emitters located at known positions and acoustic receivers along each detection unit. This article describes the approach to combine an acoustic receiver with the photosensors inside one detection module using a common power supply and data readout. The advantage of this approach lies in a reduction of underwater connectors and module configurations as well as in the compactification of the detection units integrating the auxiliary devices necessary for their successful operation. [ABSTRACT FROM AUTHOR]

Using a combination of the Negative-Positive, the Double Chirped Pulse Amplification techniques with nonlinear XPW temporal filtering in the laser front end allows substantial suppression the ASE level pushing the temporal contrast of amplified 100 TW pulses at 10 Hz operation above 1011. [ABSTRACT FROM AUTHOR]

The paper considers photoacoustic (PA) conversion while irradiating suspensions in extra-small volume probes with laser pulses having small fluence values. Only linear and nonlinear thermooptical laser sound generation regimes were observed. Thus, good repeatability of acoustic signal parameters informative about probe content was achieved. The experiment conducted has shown how one can avoid the decrease of particles detection sensitivity for the thermooptical mode. [ABSTRACT FROM AUTHOR]

We propose a unified theory of acousto-optical diffraction in crystals and wave packet propagation in dispersive media. This formal approach is crucial for precise characterization of light dispersive delay lines performance for femtosecond laser pulses. We found that dispersive phenomena in crystals influence acousto-optical coupling of modes. Modified coupled-wave equations were developed for description of acousto-optical interaction of ultrashort laser pulses. Analysis showed that group delay between the incident and the diffracted pulse results in considerable transformation of pulse envelope and decrease of diffraction efficiency. On the contrary, the influence of phase mismatch on the diffraction efficiency is lower than it is predicted by conventional theory of Bragg diffraction. As a result, the transmission bandwidth for ultrashort wave packets increases several times compared to that for stationary waves and the side lobes of the transmission function disappear. [ABSTRACT FROM AUTHOR]

In this work the mechanical properties of a Photonic Crystal Fiber is achieved using concepts of the rules of mixture of composite materials in order to find the effective area, effective Young’s modulus and the effective density. Results achieved by analytical method are compared to results achieved through a commercial software. Simulation results of acoustic-induced modulation of a Photonic Crystal Fiber Bragg grating obtained using adapted Finite Element and Transfer Matrix Methods is showed. The methodology applied to study the device consists of the achieving of Photonic Crystal Fiber mechanical properties; the strain field in the whole structure is obtained by using the Finite Element Method. Further, the calculated strain field is used on the Transfer Matrix algorithm to obtain the Fiber Bragg Gratings reflected spectrum. The results are compared with conventional Fiber Bragg Gratings Acousto-Optic modulator. Numerical results show that, due to its smaller stiffness, compared to conventional Fiber Bragg Gratings the presence of Photonic Crystal Fiber Bragg Gratings causes an increasing on strain field along the grating when the modulator is excited by particular frequencies. This way, Photonic Crystal Fiber Bragg Gratings can be used in acousto-optic modulators increasing the acousto-optic efficiency and avoiding the need of tapers. [ABSTRACT FROM AUTHOR]

The main objective of this study was to evaluate the feasibility of the optoacoustic (OA) technique for the monitoring of HIFU therapy. Optoacoustic phenomenon is the generation of wideband ultrasonic transients through absorption of laser radiation and subsequent expansion of the heated volume. The excited OA transient can be detected by a wideband piezo-electric transducer and contains information on the distribution of optical properties (absorption and scattering) within the medium. If thermal lesions have different optical properties than the untreated tissue, the lesions will be detectable on the OA waveform. We used boiled and raw porcine liver as phantoms mimicking treated and untreated tissue correspondingly. Optical attenuation, absorption and scattering coefficients of raw and boiled porcine liver were measured by the optoacoustic technique, previously developed by our group [4]. Measured optical absorption in raw liver was at least two times lower than in boiled liver at the laser wavelength of 1064 nm. Then OA technique was employed to detect a lesion produced by a 1.1 MHz focused ultrasound in a liver sample. The lesion was about 2 mm thick located about 1 cm below tissue surface. The feasibility and high promise of the OA approach to lesion detection was demonstrated. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]

Optoacoustic imaging is a promising technique for the detection of subsurface optical inhomogeneities in optically turbid media. A pulsed laser is used to irradiate a sample volume where it is absorbed and causes rapid heating. Ultrasonic waves are launched through the thermoelastic effect and are detected at the sample surface. The detected ultrasonic transients are related to the position dependent absorption coefficient allowing for imaging of the absorbed electromagnetic energy distribution. In this work, the use of optical interferometry for the detection of optoacoustic signals is explored using three detection schemes: a photorefractive crystal based interferometer, a Fabry-Perot sensor head which is coupled directly to the specimen and a Michelson interferometer. Experimental results are presented demonstrating optical detection of optoacoustic transients in both homogeneous absorbing tissue phantoms and optically turbid tissue phantoms. The measured optoacoustic signal profiles are compared to theoretical predictions and the absorption (homogeneous media) coefficients of the phantoms determined. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]

We demonstrate a pulse-shaper capable of independent polarization, phase and amplitude control over each pulse. The set-up is compact and easily switchable between pump-probe and collinear geometries [ABSTRACT FROM AUTHOR]

In this work we implemented an optoacoustic system that uses home-made acoustic transducers having PVDF of 110 μm thickness as piezosensor. The excitation source consisted of a pulsed Nd:YAG at the wavelength of 1064 nm. Soft tissue phantoms of water, gelatin and low-fat milk were used to imitate the optical properties of mammalian tissue. These phantoms were constructed containing an object with enhanced absorption optical properties. These inclusions were used to simulate abnormal tissue within the phantom. With the constructed transducers we were able to detect the inclusions of 1.64 mm thickness using an intensity of about 100 mJ/cm2. The signal coming from the object’s edge starts to be detectable at distances that are dependent of both the object's depth and the scattering properties of the phantom. [ABSTRACT FROM AUTHOR]